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Old 10-28-2018, 07:20 PM   #1
SRT8-X
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'69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHING

I'll start with the basics; I have a 1969 C10 that has been going through a frame-off / nut and bolt restoration for several years. Below this introduction, please find the specs for the engine and drivetrain. I apologize in advance but my summary and narrative will be lengthy as I want to provide as much information and detail in hopes that someone has an idea of what may help.

Engine:

1965 Chevy 327 CID
Stock internals
Stock double hump “462 fuelie heads”
NEW Edelbrock Performer EPS Intake
NEW Edelbrock Performer 14063 600 CFM carb with electric choke
NEW Edelbrock Perfromer RPM 1721 Fuel Pump (reads 4.5-5.5 PSI on gauge)
NEW Edelbrock billet fuel filter and fuel line
NEW AC Delco GF61P in line fuel filter & steel fuel lines from tank
NEW Hamburgers 3225 1” aluminum spacer
NEW Performance Distributors / DUI HEI vacuum advance distributor with 50k volt coil and high dwell Dyna-Module, advance from timed side of the carb
NEW Performance Distributors / DUI C9051BK Live Wires under header 8mm wires with heat shield
NEW Autolite AP86 Platinum Plugs
NEW Ceramic Coated Shorty Headers
NEW 2-1/2” stainless exhaust with Flowmaster 40-series mufflers turned down at rear axle
NEW Billet Specialties breather with integrated PCV valve
Original GM in cab tank with sender
NEW Derale 16927 4000 CFM dual 13” puller cooling fans and shroud
NEW Full Painless wiring chassis wiring harness, electric fan harnesses fans on 195 / off 175
NEW 180 degree thermostat
NEW Lokar throttle cable conversion and kick-down cable
NEW Optima battery and true 0 gauge oxygen free copper cables
All gaskets are FelPro

Transmission / Drivetrain:

Mildly built TH350 trans with stock stall converter, B&M Trick Shift fluid
NEW Derale 14200 3-1/4” deep pan with cooling tubes
NEW Derale 13900 650 CFM Transmission cooler mounted under passenger side of cab
NEW B&M modulator with steel modulator vacuum line sourced from T-fitting at rear of intake
NEW aftermarket CPP Power Steering
NEW aftermarket Wilwood Master Cylinder / CPP Booster Power Brakes
3:73 stock rear differential with one-piece driveshaft, NEW Moser 30-spline axles and Bendix drum brakes

The problem is once the truck is warmed up, it begins to stumble or surge off idle, often misfiring from off idle to about 2500 RPM making it frustrating cruising around town. It runs OK cold but not great. Once it reaches 2500-3000 RPM, the misfire clears and it runs great. The kick-down works great and the truck is a blast 3000 RPM and up. However, off the line, even if taking off slowly with minimal throttle or flooring it, the truck does not go as it should, sputtering and popping, hesitating, etc. It has never been bad enough where it stalls though. WOT from standstill does not do much more than limited throttle off the line. Cruising and WOT is different however as it's further up the RPM range resulting in good performance. As noted, it runs great cool, idles great both cool and hot. It also does have an intermittent small miss at idle at times as well known by a vibration and a vacuum gauge. There is not enough power to take off well much less to spin the tires off the line or power-brake (under load).

The engine has not had any internal work or inspection since installing a few years ago even though we've only put about 400 miles on the truck since getting her roadworthy. The engine oil is clean and has Royal Purple 10W30 oil installed, K&N screw on filter and a touch of Marvel Mystery Oil. It does have a small transmission leak at the front seal / pump but shifts fine and does not show any signs of internal damage. The truck has an “under load” intermittent vibration at 40 MPH + that goes away if put in neutral leading me to believe there could be a converter balancing issue. We run 93 octane pump gas with Lucas ethanol treatment and Marvel Mystery oil at every fill up. I started using the Mystery Oil at the suggestion of a buddy who believed we may have a valve sticking. There is some valve train noise at times but it’s not significant beyond anything I’ve heard with other SBC engines.

Other than the new parts, I’ve tried tuning the carb for rich / lean settings, tried several variations of metering rods and springs, several choke settings, several idle settings, all (3) accelerator pump rod settings. I have not replaced or checked the accelerator pump itself or the floats in the carb, as it was new in the box prior to install. Vacuum registers about 20” Hg at ide but does have a -1-2” fluctuation at idle sporadically. The engine timing is set at 16į initial at idle and 36į total timing @ 3200 RPM. This has been verified several times and reset, adjusted, reset, etc. I have put heat insulation boots on the two rear plug wires due to their proximity to the header tubes and noticing an arc on cylinder #7 even with the live wires. The new live wires have white residue from resting on the headers but they are supposed to be rated to 1200 degrees. I have not seen any arcs here under darkness but some plug wires are very tight against portions of the headers due to the run being short on this custom set. Compression seems good based on feel but I have not tested each cylinder. I have not pulled the valve covers to set the lash but have physically observed the rockers and springs.

No parts, other work or tuning have made a significant change for better or worse. I’ve done all the work on the truck myself with the exception of the upholstery on door panels and dash pad so I’m opposed to trusting a local shop or others to try diagnosing this situation and don’t have an open checkbook to do so. My father was my mentor, this truck was his daily driver for nearly a decade in the 90’s and I’ve built it as a tribute to him after his passing in 2016. I’d really like to complete this and have a solid running truck as it’s been meticulously built otherwise. Please help if you can and if you have any ideas. Thanks in advance for your time if you’re able to reply with any suggestions or comments.
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1969 C10 Stepside (current project)
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2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
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Old 10-28-2018, 08:08 PM   #2
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Nice to see a beautiful truck...great job!

Performance Distributors / DUI HEI vacuum advance distributor ?

Did you have the distributor advance curve tailored to the truck, gearing etc?
Sounds like its a bit slow to bring in the advance....

Misfire under load could also be a plug lead arcing across to a ground...maybe to a header pipe....in Park try looking under the hood in the dark and blipping the throttle....darkness makes the spark more visible...

I would be looking more at the distributor first...including the module...

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Old 10-28-2018, 08:11 PM   #3
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

If you have the initial timing correct, the first thing I would suspect is that the carb is jetted too lean. I had a 1406 on my 305 CI in my Skylark, and with headers you will have to feed it a little more fuel. I think that I went 4 numbers richer on the jets but don't remember what I did with the metering rods. You will need to buy the kit. It isn't that expensive, and should give you what you need.

Mine would stumble off idle, but if I went heavier into the throttle, the accelerator pump would cover the lean condition just enough to start laying rubber. Does yours cover the stumble if you stab the throttle harder? Or does it just backfire?
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Old 10-28-2018, 08:23 PM   #4
SRT8-X
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Quote:
Originally Posted by AussieinNC View Post
Nice to see a beautiful truck...great job!

Performance Distributors / DUI HEI vacuum advance distributor ?

Did you have the distributor advance curve tailored to the truck, gearing etc?
Sounds like its a bit slow to bring in the advance....

Misfire under load could also be a plug lead arcing across to a ground...maybe to a header pipe....in Park try looking under the hood in the dark and blipping the throttle....darkness makes the spark more visible...

I would be looking more at the distributor first...including the module...


Thanks for the comments and I appreciate your response. I canít say enough about the forum and how itís allowed me to silently research but this has gone too far. The distributor was calibrated to 24 degrees at 3000 RPM per the build specs and for street applications. I set full timing at 36 not accounting for this spec. Do I need to offset the timing for this spec or is 36 degrees 36 degrees regardless. It does idle on or ďdieselĒ sometimes too.
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Old 10-28-2018, 08:25 PM   #5
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Originally Posted by SRT8-X View Post
Thanks for the comments and I appreciate your response. I canít say enough about the forum and how itís allowed me to silently research but this has gone too far. The distributor was calibrated to 24 degrees at 3000 RPM per the build specs and for street applications. I set full timing at 36 not accounting for this spec. Do I need to offset the timing for this spec or is 36 degrees 36 degrees regardless. It does idle on or ďdieselĒ sometimes too. Iíve tried looking at the wires under dark but will try again with some help and get an underneath view since theyíre so tight.
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Old 10-28-2018, 08:28 PM   #6
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Originally Posted by Steeveedee View Post
If you have the initial timing correct, the first thing I would suspect is that the carb is jetted too lean. I had a 1406 on my 305 CI in my Skylark, and with headers you will have to feed it a little more fuel. I think that I went 4 numbers richer on the jets but don't remember what I did with the metering rods. You will need to buy the kit. It isn't that expensive, and should give you what you need.

Mine would stumble off idle, but if I went heavier into the throttle, the accelerator pump would cover the lean condition just enough to start laying rubber. Does yours cover the stumble if you stab the throttle harder? Or does it just backfire?
Thanks, I have a kit but itís for the older Carter AFB series and it seems all the part numbers changed on the jets and rods. Iíll grab a new Edelbrock kit and try to focus on the jets too if the timing situation isnít the issue.

Mine stumbles off the line regardless of throte input. The only variable is that it does not run nearly as bad when cool. When cruising 30 MPH plus, it will downshift and run great when I stick it.
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Old 10-28-2018, 09:12 PM   #7
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Have you done a compression test? How do the spark plugs look?
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Old 10-28-2018, 09:18 PM   #8
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Before and after changing the plugs, they tend to be brownish and dry at the electrode however there is some oil on the threads. I have not done a compression test with a gauge but the compression while bumping over with the finger was significant.
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1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-28-2018, 10:07 PM   #9
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

First, have you verified top dead center with your balancer/zero timing mark?

Your timing sounds right on; 36 total is perfect. All in at 3200 rpm isn't bad. 2800-3000 may be a little better, but nothing of concern. You said the distributor is "calibrated to 24 degrees at 3000 RPM per the build specs and for street applications". Does that mean the mechanical advance is 24 degrees? How many degrees does the vacuum advance provide?

Do you still have the manual for the carb? You need it to setup the carb up right and calibrate it. You're gonna have to open your carb and set the float levels. They're always off out the box due to shipping and whatever. Since you have 20" vacuum, your step up springs should be the plain silver ones that come in the cal kit. Silver is the strongest/stiffest set.

What cam and specs? Fuel pump install ok? Any degraded or twisted fuel lines? Sounds like you have enough fuel pressure. Hmmmm.....
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Old 10-28-2018, 11:51 PM   #10
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

[QUOTE=68 P.O.S.;8373603]First, have you verified top dead center with your balancer/zero timing mark?

Thanks for the reply. Yes, TDC was verified with the #1 screw in tool and was previously done with the compression as well.

Your timing sounds right on; 36 total is perfect. All in at 3200 rpm isn't bad. 2800-3000 may be a little better, but nothing of concern. You said the distributor is "calibrated to 24 degrees at 3000 RPM per the build specs and for street applications". Does that mean the mechanical advance is 24 degrees? How many degrees does the vacuum advance provide?

I’m going to call Performance Distributor tomorrow to ask about this and if it changes anything. I’m assuming the 24 degrees is all mechanical as they instruct purchasers to set timing with the vacuum advance disconnected which I followed. I have not timed with the advance connected but I can do this to verify what the vacuum advance is adding.

Do you still have the manual for the carb? You need it to setup the carb up right and calibrate it. You're gonna have to open your carb and set the float levels. They're always off out the box due to shipping and whatever. Since you have 20" vacuum, your step up springs should be the plain silver ones that come in the cal kit. Silver is the strongest/stiffest set.

Yes, I have the manual. I’ll definitely take a look at the floats and set them as well as trying the plain silver step up springs.

What cam and specs? Fuel pump install ok? Any degraded or twisted fuel lines? Sounds like you have enough fuel pressure.

Funny thing is the fuel pressure was consistent 5.5 psi when installing the fuel pump but now reads 4.5 or so a month later. This install went smooth but I did notice an oil leak at the pump base I need to take care of. The fuel lines are all new and I used all high end aluminum fittings along with the Edelbrock braided hose hit to the metal filter and carb fuel line.

Does the fact that this only occurs consistently when hot make a difference with some of these suggestions? Thanks again for the responses. These are helpful.
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2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
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Old 10-29-2018, 12:14 AM   #11
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Might want to get rid of those autolite plugs and install some AC Delcos. I have heard of folks having issues with autolites
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Old 10-29-2018, 12:19 AM   #12
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Your timing numbers don’t add up.
24 in the mechanical with a total of 36 gives you 12 initial not 16.
Is the esp intake an air gap type?
What cam?

Try a dry fuel pressure gauge. Oil filled ones don’t like heat.
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Old 10-29-2018, 08:04 AM   #13
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

It sounds like once the carb transitions off the idle and primary circuit that it clears up. I too would be looking at jetting up and 4 sizes seems to be a good start.

Before that, try adding two full turns on the mixture screws to richen up the idle mixture and see if that doesnít improve things.

I assume that all of these issues are at a steady throttle application and not when you are ďpunching itĒ? Sudden application of throttle and response issues are usually because of insufficient accelerator pump shot. But Edelbrocks are not as affected usually because of the secondary air door that keeps from giving too much air that the accelerator pump canít make up for it.

Great looking truck BTW.
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Old 10-29-2018, 09:57 AM   #14
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Arrow Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Try putting your timing light on each plug wire and running the the engine up to the rpm with misfire and see if the light flashes indicate a misfire. Does the flashing show smooth movement as the timing advances and retards on each cylinder?. This should help you decide if the problem is fuel or ignition. My first thought was that you have a bad ground inside the distributor at low RMP (advance) and once the advance mechanism moves the plate enough the ground is restored and the engine runs as it should. Have you tried disconnecting the vacuum line to the vacuum advance and running it?
I would concentrate on the ignition side before diving into the carburetion side. It would be easier to swap the distributor with a simple point style to prove the ignition is good or bad than swapping carbs. The fact that the problem gets better with RPM leads me to believe that you don't have a cap or plug wire problem.
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Old 10-29-2018, 10:18 AM   #15
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Smile Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Ok I'll weigh in with a possibility....you might not be getting full needed voltage to the HEI/coil (equivalent) at lower/idle speeds, noting that you list an HEI unit as the distributor.
If you aren't....then the engine will run like it misses at lower speeds and can be hard to start.
Anything above 2500-2800 rpm starts to smooth things out as the alternator puts out more voltage to compensate for the low end, low speed voltage deficiency.

You can test this by running a 'hot' 12 volt wire direct from the battery to your hei or coil....then start up the truck and see how it runs.
This will essentially bypass any original wiring that might be deficient or failing to provide the voltage lower down.

All good
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Old 10-29-2018, 11:05 AM   #16
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

I think itís a lost cause and you should give up so I can take that sweet truck off your hands

Yes, your distributor should have 24 degreesÖ.was just trying to verify. Keep your total timing at 36, it should run very well there. Yes, you can plug your vac advance into the manifold vac port on the carb to see how much advance it provides. It should have no more than 10-15 degrees in it and be plugged in to manifold vac for it to work right. Another possibility, did you add the HEI and are you using the original power wire? The stock power wire has a resistor in it and wonít give the HEI the full 12 volts it needs. You can de-pin the wire from the harness and replace it with an un-resisted power wire.

Glad you kept the manual; it has lots of helpful info. Get the 1487 calibration kit, and together with the manual, youíll have everything you need to set it up correctly.

Geezer is correct on the pressure gauge. The heat under the hood doesnít agree with the liquid filled gauges and makes them read incorrectly. Maybe your Delco inline filter is making the fuel pump work a bit harder, reducing pressure? Heís also correct on your timing numbers too. I let that go since your total timing of 36 is more important than the initial.

I agree with HO455, make sure your ignition system is good to go, then move on to the carb. Test the distributor to make sure you didnít get a bad unit. It happens.
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Old 10-29-2018, 11:24 AM   #17
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by Fbks_Cruiser View Post
Might want to get rid of those autolite plugs and install some AC Delcos. I have heard of folks having issues with autolites
Thanks, I may go that route as well, I've heard the Gen I small blocks can be partial to AC Delco for some reason. Please note I ran regular Autolites originally and just switched to the platinum Autolites trying to rid this issue. Just another note, they are gapped at 0.50" +/- per Performance Distributors instruction due to the high voltage coil.
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1969 C10 Stepside (current project)
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2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-29-2018, 11:28 AM   #18
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by geezer#99 View Post
Your timing numbers donít add up.
24 in the mechanical with a total of 36 gives you 12 initial not 16.
Is the esp intake an air gap type?
What cam?

Try a dry fuel pressure gauge. Oil filled ones donít like heat.
Thanks for the reply. I did not account for the calibration in the distributor in setting the timing. I found TDC, verified, set initial to 16į at idle (950 - 1000 RPM) at the zero mark on the timing tab, then set total timing to 36į at 3200 RPM. I will be calling Performance Distributors to verify this but their instructions for setting timing comply with the method I used, not referencing the calibration specs.

The intake is the traditional non-air gap type, it's rated from idle to 5500 RPM.

I do not have the cam specs but it's pretty basic, nothing radical, no significant lope, idle is smooth.
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1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-29-2018, 11:33 AM   #19
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by Mike C View Post
It sounds like once the carb transitions off the idle and primary circuit that it clears up. I too would be looking at jetting up and 4 sizes seems to be a good start.

Before that, try adding two full turns on the mixture screws to richen up the idle mixture and see if that doesnít improve things.

I assume that all of these issues are at a steady throttle application and not when you are ďpunching itĒ? Sudden application of throttle and response issues are usually because of insufficient accelerator pump shot. But Edelbrocks are not as affected usually because of the secondary air door that keeps from giving too much air that the accelerator pump canít make up for it.

Great looking truck BTW.
Thanks for the suggestions. I've decided to get a new Edelbrock tuning kit, the one I have is an older Carter AFB which does not seem to interchange numbers with the Performer carbs. I've played with the step up springs and metering rods but will try jetting the carb when I get the new kit.

I have adjusted the idle mixture screws every which way and until they're bottomed out or removed completely, there is not much change at idle.

I'm thinking about replacing the accelerator pump as well just to make sure. Punching the throttle does not do much off idle, it bogs and sputters however at a 30 MPH roll, punching it seems to be fine. That's what is baffling to me, still in a lower RPM cruise range punching it will allow good take off, just not from a really low speed or take off from a dead stop.

Thank you again for the comments, much appreciated.
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1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-29-2018, 11:40 AM   #20
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by SRT8-X View Post
Thanks for the reply. I did not account for the calibration in the distributor in setting the timing. I found TDC, verified, set initial to 16į at idle (950 - 1000 RPM) at the zero mark on the timing tab, then set total timing to 36į at 3200 RPM. I will be calling Performance Distributors to verify this but their instructions for setting timing comply with the method I used, not referencing the calibration specs.

The intake is the traditional non-air gap type, it's rated from idle to 5500 RPM.

I do not have the cam specs but it's pretty basic, nothing radical, no significant lope, idle is smooth.
Thatís why your numbers donít add up!
At 950-1000 rpm youíre getting into the mechanical advance in the distributor.
You need an idle lower near 700 to set initial.

Did you build the motor?
Who set the preload on the lifters?
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Old 10-29-2018, 11:41 AM   #21
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by HO455 View Post
Try putting your timing light on each plug wire and running the the engine up to the rpm with misfire and see if the light flashes indicate a misfire. Does the flashing show smooth movement as the timing advances and retards on each cylinder?. This should help you decide if the problem is fuel or ignition. My first thought was that you have a bad ground inside the distributor at low RMP (advance) and once the advance mechanism moves the plate enough the ground is restored and the engine runs as it should. Have you tried disconnecting the vacuum line to the vacuum advance and running it?
I would concentrate on the ignition side before diving into the carburetion side. It would be easier to swap the distributor with a simple point style to prove the ignition is good or bad than swapping carbs. The fact that the problem gets better with RPM leads me to believe that you don't have a cap or plug wire problem.
HO455, thank you for the suggestions. I'll give the timing light process you mentioned a shot. One thing to note, as I mentioned I am running Live Wires which are an 8mm wire with 2mm heat resistant cover. I noticed when setting the timing, the light would get odd RPM readings, sometimes half of what it should be or zero, when on #1. If I jiggle the induction pick-up it comes back where it should be but it "lost" the RPM several times each time I used this light.

Regarding the distributor, I started with a stock Delco HEI which had an Accel High Energy coil, switched that out for a new DUI cap, rotor and high energy coil, swapped that out for the entire new DUI drop in unit with same specs but an upgraded Dyna Module. The problem never changed with these upgrades and was present before I started "hunting". I doubt the distributor could be the issue since the various combinations produced the same issue, but its possible. I also ran a set of 8mm Taylor wires prior to the Live Wires with the same results.

I have run the truck with the advance disconnected under load but not since the carb / distributor were changed. I did this prior to the new carb and prior to the distributor upgrade but it was the same before and after.

Thanks again for your replies.
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Keith

1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-29-2018, 11:48 AM   #22
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by Coley View Post
Ok I'll weigh in with a possibility....you might not be getting full needed voltage to the HEI/coil (equivalent) at lower/idle speeds, noting that you list an HEI unit as the distributor.
If you aren't....then the engine will run like it misses at lower speeds and can be hard to start.
Anything above 2500-2800 rpm starts to smooth things out as the alternator puts out more voltage to compensate for the low end, low speed voltage deficiency.

You can test this by running a 'hot' 12 volt wire direct from the battery to your hei or coil....then start up the truck and see how it runs.
This will essentially bypass any original wiring that might be deficient or failing to provide the voltage lower down.

All good
Coley
Coley, good suggestions, I'll check this out. I had some electrical issues with the original harness last year which prompted me to rewire the complete truck with Painless Wiring's chassis kit so every wire on the truck is new, including homemade custom heavy braided stainless grounding straps in over a dozen locations.

My dad was an electrician and gear head so I know all about bad grounds and the issues they can cause in 12V systems. All the wiring has been installed meticulously and very clean but there still could be an issue with the coil wire when it comes through the Painless bulkhead. With that said, when I first set up the wiring harness, I ran a return 8 gauge wire "loop" per the instructions if running a 65amp + alternator but then removed it with some modifications as I had a parasitic draw that kept running the battery down. Not sure if the two were related but it has not had any issues since with the battery since.

I'll try running a dedicated wire from the battery to the coil direct and see if that helps. Thanks again for the suggestion.
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Keith

1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-29-2018, 11:53 AM   #23
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by geezer#99 View Post
Thatís why your numbers donít add up!
At 950-1000 rpm youíre getting into the mechanical advance in the distributor.
You need an idle lower near 700 to set initial.

Did you build the motor?
Who set the preload on the lifters?
Geezer#99, I'll give it a shot setting the timing at idle numbers lower per your suggestion. I appreciate you catching this!

I did not build the motor, it was purchased as a built long block which I went through and properly torqued all the main and rotating assembly connections. My father may have adjusted the valvetrain on the long block when we installed but I cannot recall. As far as I know, no valvetrain adjustments have been made. We were working on this project together for years and I can't be certain of everything he did prior to his passing 2 years ago.
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Keith

1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-29-2018, 12:01 PM   #24
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

Quote:
Originally Posted by 68 P.O.S. View Post
I think itís a lost cause and you should give up so I can take that sweet truck off your hands

Yes, your distributor should have 24 degreesÖ.was just trying to verify. Keep your total timing at 36, it should run very well there. Yes, you can plug your vac advance into the manifold vac port on the carb to see how much advance it provides. It should have no more than 10-15 degrees in it and be plugged in to manifold vac for it to work right. Another possibility, did you add the HEI and are you using the original power wire? The stock power wire has a resistor in it and wonít give the HEI the full 12 volts it needs. You can de-pin the wire from the harness and replace it with an un-resisted power wire.

Glad you kept the manual; it has lots of helpful info. Get the 1487 calibration kit, and together with the manual, youíll have everything you need to set it up correctly.

Geezer is correct on the pressure gauge. The heat under the hood doesnít agree with the liquid filled gauges and makes them read incorrectly. Maybe your Delco inline filter is making the fuel pump work a bit harder, reducing pressure? Heís also correct on your timing numbers too. I let that go since your total timing of 36 is more important than the initial.

I agree with HO455, make sure your ignition system is good to go, then move on to the carb. Test the distributor to make sure you didnít get a bad unit. It happens.

Thanks again 68 POS. I appreciate the comments, I love the results and progress we've made with the truck but it just sucks that this off idle issue exists.

I did a full rewire using Painless Performance wiring for the kit so every wire on this truck is new. I've also installed over a dozen heavy ground wires at the proper locations and then some so that won't be an issue. The coil wire is a straight feed for the under hood harness from the bulk-head / fuse panel however I'll give it a shot to make sure 12V+ is at the coil.

I will also try lowering the RPM for initial timing to see if that helps as well. I'll check the advance added under vacuum and run without as well under load so I can weigh the differences.

I can then move on to the carb, noting that the floats need to be verified and rejetting is a benefit that should be done anyway since these electric choke carbs are set up for efficiency more than performance out of the box.

Noting the fuel pressure gauge issues, I've heard that too with the liquid gauges.

I will be calling Performance Distributors too so I can run this by them as well since my ignition is all DUI with the exception of the plugs.

Thanks again for the update and added suggestions. I appreciate everyone's help and the comments about the truck.
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Keith

1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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Old 10-29-2018, 12:33 PM   #25
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Re: '69 C10 327 SBC Off Idle Stumble / Misfire Help - I feel like I've tried EVERYTHI

For all who have read and commented, I appreciate your feedback and suggestions. I wanted to point out the sequence and a few concerns I have that don't make sense to me regarding trying to diagnose this issue. Please see below and let me know if this changes any suggestions or opens up for more. Thanks again, y'all are great.

First drive, the 327 had an original GM OEM HEI with Taylor plugs and Autolite A86 plugs. It had a period correct Carter AFB 9605S 600 CFM carb with an 10" diameter 3" tall round K&N filter. It had a cheap parts store fuel pump with inline filter from tank, hard steel fuel line from pump to carb. Open headers were run while tuning and moving around in the driveway / garage then exhaust was installed. The original wiring was present at this time too. Below is a sequence of trouble shooting and upgrading the engine both trying to overcome this issue as well as upgrading for performance and aesthetics. With ALL changes below, this issue never improved. I'll group these as they were performed.

1. Rewired truck with Painless Performance full chassis wiring harness, replaced ignition switch, replaced battery with Optima Red Top

2. Added Power Brakes, Power Steering, changed all engine pulleys to Billet Specialties

3. Added 2" tall triangular Billet Specialties Air Cleaner, Added Hamburgers 1" spacer (originally to provide air cleaner clearance of the distributor), replaced valve covers with Chevrolet Performance Cast units and Billet Specialties PCV valve / breathers

4. Replaced distributor cap / coil with DUI / Performance Distributors 50k coil / cap / rotor

5. Replaced plug wires with DUI / Performance Distributors Live Wires

6. Replaced entire distributor with new DUI / Performance Distributors (same specs as above, 24¬į advance at 3000 RPM per build sheet), added zero gauge battery cables to starter and ground

7. Replaced Intake, Carb, Fuel Pump, Thermostat, Fuel Filters, Fuel Lines, Vacuum lines and ports, throttle cable, trans kick-down cable, throttle pedal

8. Replaced Spark Plugs

9. Replaced transmission modulator and power brake vacuum check valve at booster

10. Added DUI boot protectors at #7 & #8

Now to elaborate. Again, none of the above solved this problem. It seemed intermittent at times since the truck would start great cold, run decent cold but never had off the line good acceleration. I could drive 10 - 15 miles and run well, even taking off well at times but the longer I drove, the worse it would get. We went to a show last week and it drove excellent on the freeway at 75 MPH but could not get out of it's own way from a stoplight. Cruising at 35-50 MPH was fine too. Kick down was great. Idling was great. Any hard throttle from stand still would not do anything. Very light pressure on the pedal from a stop seemed to do better than even applying any additional throttle at that point.

The engine idle's on and is hard to start when it's warm. Cold starts are easy and effortless.

The baffling part is that it can run great for 10 minutes cruising then this situation occurs. And again, it's only in the 1000-2500 range. Beyond that it runs great. It's difficult to test every change to since it only happens under load but I'm trying. I will take all suggestions and try the carb settings / upgrades as well as resetting the timing at a lower RPM to see if this helps. It does act as if it's too far advanced based on the run-on and hard starts warm.

When adjusting the accelerator pump rod, when it comes out of the hole the engine immediately stalls. Is this normal? As soon as it's reconnected, she starts right back up with no problems. Can the choke setting do anything to driveablity or is this just at idle?

I'd like to upgrade heads and install a nice cam with roller rockers soon but I'm not ready to do this until this problem is identified as it will only make things worse unless of course the cam or valvetrain is the actual problem. Does anyone sense that the cam could be going flat or this could be a valve adjustment issue? I'm trying to rule everything else out before I go internal. I know low compression could be an issue too and will be checking this as well. Oil pressure is lower than I'd like at about 20-25 at idle and 35-40 cruising but that seems well within range albeit lower.
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Keith

1969 C10 Stepside (current project)
2014 Jeep Grand Cherokee SRT 6.4L HEMI (daily)
2011 Chevrolet Tahoe LT 5.3L/6A (wife & kid hauler)
2013 VW GTI 1.8T/6A (son's Euro rocket)
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