Fresh 383 SBC smoking, fouling plugs

[nikwho]

Hello all,
I'm stumped with my freshly built 385" SBC (3.75" X 4.040"). It is smoking, misfiring, fouling plugs and feels down on some power. It has not run properly since installed. Its an gen 1 SBC, 4 bolt main, Eagle rotating assembly. Has World Products heads, 224/224 @ 0.50", cam specs indicate 0.466" lift with factory rockers. Rockers are 1.5:1 roller rockers. Has new Quick Fuel Brawler 650 cfm carb. I live at 7,000' ASL. I re-jetted the carb from 70 (stock) to 66 primary jets and from 74 (stock) to 70 secondary jets. I also ran an Edelbrock 1406, rejetted for altitude, and it behaved the same way!

I have replaced the fuel filter. I have put an ohm meter on each plug wire, and they were all quite close, though at the moment, I cannot remember the reading. When trying to figure out my misfire, I pointed my laser thermometer at each header tube and a few were 200-300° cooler than others. So, not being 100% sure on the age of my distributor, I ordered a new Accel HEI Distributor, installed and had no effect. I pulled plugs and 5 had a good tan appearance, while the others were oily and fouled. Those were NGK UR5. I figured that I would be fine with a stock heat range plug, so I replaced all 8 plugs with NGK UR4 plugs. It ran noticeably better, and did not sound like it had a misfire at first. But, now with about 30 miles on the plugs, it has started misfiring again, and I believe it to be fouling the plugs again. It is smoking quite a bit, initially only on hard acceleration, but a bit more now, even at idle. Smells quite rich. Smoke is quite thin, so hard to call it a color. Wouldn't really call it very white or blue. Really light grey, perhaps? It looks slightly blue in color, I suppose, but not obviously blue. All four idle screws are 1 turn out. Adjusted to peak RPM, then 1/4 turn richer. Thinking intake leak, I adjusted all four idle mixture screws in and could not even get them all turned in to 1/2 turn out before the engine will die. I've played with timing, with no effect. I BELEIVE that it is sitting at about 14-16° advance at idle. No signs of water in oil, not consuming oil, that Ive noticed. I've sprayed around carb and intake with carb cleaner. No RPM change. Im running a Summit Racing branded mechanical fuel pump, and my fuel pressure regulator body cracked, so it currently does not have a regulator. The floats were set so that the fuel level is perfectly in the middle of the sight windows.

When driving, it feels loaded up, and bogs, seemingly the worst at about mid throttle, but it won't really clean up at any RPM! Seems the happiest at idle. I bought the World Products heads with a long block engine. They appeared brand new, but I didn't specifically ask. I supposed it could be a bad valve seal? I can say, that even when running at its best, it felt like it had less power than my previous 350 with run of the mill GM iron heads. I have not done a compression test, but likely will tomorrow. Obviously have not done a leak down test, either.

I'm kind of at a loss. Any thoughts? I trust the shop that did the work, though they didn't do the machine work for me. They machined the parts for a co-worker, whom I bought the engine from.

Tomorrow I intend to pull the vacuum modulator line off of the carb and plug the vacuum port, and see if it cleans up. I was thinking that a bad vacuum modulator could allow it to be sucking transmission fluid into the manifold, which could cause the smoking and explain the misfire and fouled plugs.

Thanks for any and all help! I can typically sort this sort of thing out on my own, but needing to reach out for a bit of help on this one.

Nik

[geezer#99]

Leave the modulator on but splice in a 6 inch piece of clear hose. Hardware store has them. Trans fluid will show up easily if it’s there.
Pull the carb off and have a look at the transition slots. They should look square.
You might need to lower your floats a bit to just at the bottom of the glass.
And locked in mechanical timing might be needed if nothing else works. That’s for later.
And how are your valves adjusted?
Could be holding valves open a thin hair too.
I’ve always set mine at 1/4 turn from zero lash.

That should keep you busy for awhile.
I’m old and off to snoresville! LOL!

[nikwho]

Originally Posted by geezer#99

Leave the modulator on but splice in a 6 inch piece of clear hose. Hardware store has them. Trans fluid will show up easily if it’s there.
Pull the carb off and have a look at the transition slots. They should look square.
You might need to lower your floats a bit to just at the bottom of the glass.
And locked in mechanical timing might be needed if nothing else works. That’s for later.
And how are your valves adjusted?
Could be holding valves open a thin hair too.
I’ve always set mine at 1/4 turn from zero lash.

That should keep you busy for awhile.
I’m old and off to snoresville! LOL!

I've got some 3/16" clear motorcycle fuel line. That should do the trick. Ill swap that in place of my vacuum line and see if its pulling tranny fluid up into the manifold. Im definitely thinking that its not a carb issue, though I have found that more often than not, when a problem is really kicking my butt, there are compounding problems. It has run the same with both my Quick Fuel Carb and my Edelbrock carb, so likely not carb related. Ill run through setting the valves again. I may have an intake manifild sealing issue along the valley. I have no leaks around the perimeter of the intake, but might have along the bottom.

When my first set of plugs were fouled, cylinders 3 & 4 both the front of the middle four cylinders. That may be indicative of something. Then I believe that it fouled 7 & 8 next. These are World Products iron heads. I've never run them before, but they may be the issue. I may just yank them and have my machinist go through them and verify that they are straight/flat, and make sure that valves all check out. Then reassemble with new head gaskets and intake manifold gaskets. If none of that resolves the issue, Im wondering if some of the rings were installed upside down? That could explain the smoking issue, but I wouldn't think that itd be this down on power, and feel so "loaded up"! But, I would expect it to feel loaded up if lots of oil (or fluid) is fouling plugs.

I believe that I went 1/4 turn tighter than zero lash when I adjusted all of the valves. Ive always done it this way, and never had a problem. But, I would expect some issues if it was hanging valves open slightly. But, wouldn't you expect hard starting issues with that, if it were hanging valves open? BUT, perhaps it isn't hanging valves open before oil pressure builds up, and once it fires and build oil pressure, its holding them open? Certainly wouldn't hurt to re-adjust. Though, IIRC, I re-adjusted all valves when it was first doing this.

I've played with advancing and retarding my timing, both with vacuum connected to ported vacuum source, and with vacuum advance disconnected. And, this issue has persisted with not jut two carburetors, but two separate HEI distributors. One a known good working unit from the trucks last SBC, and a brand new unit.

I do think that a compression test is in order! I'll try to get that done tomorrow, as I am carpeting the stairs in our house today.

Thanks for your response, and your taking time to try to help me out! I've always been able to work through little issues like this in the past.

Nik

[geezer#99]

Do the free stuff first.
Like lower your float levels.
Oil pressure likely not a factor in unseated valves. More likely heat. Valves heat quickly and expand enough to not seal tight.
Clear hose can be had at the hardware store too for bigger sizes. Use new ones. Old ones collapse easily.

[jayoldschool]

Get the valve covers off, re-lash all the rockers with it running and get back to us.

[Dead Parrot]

Since it behaves similarly on two different carbs, probably not a specific carb issue. Might check the fuel pressure and make sure it is in the proper range. Old style vacuum gauges often have a fuel pressure range.

I would think that a leaking modulator or brake master cylinder would tend to foul the back four cylinders but the clear tube or simply disconnecting is too simple a test to skip.

Any chance it just needs some more time to properly break in the rings?

PCV system connected and working? Poorly seating rings might overwhelm the PCV with blowby and mess up the carb fuel/air mix.

[paul mora]

When there are performance issues I always start as if you are starting for the first time. Verify the distributor is set to the right tooth. Next be sure are the spark plug wire are in the right order and pushed in all the way. Be sure all the vacuum line are in the proper place and not leaking. If you have fuel to the carb your read to start it up. If you are using the original carb it should start and run. If it isn’t starting and running properly dig deeper verify valve adjustment and be sure timing chain is in the right tooth. Remember spark fuel and timing are the key.

[nikwho]

You know, bringing up timing makes me really wonder if the timing chain was installed off a tooth! It is certainly behaving like a timing issue! I have disconnected the vacuum modulator hose and plugged the vacuum port with no change. I don't think that is it.

It is odd, the engine starts great! Fires immediately and idles well, but with an audible misfire. Runs worse as it revs, but rolling into the throttle fairly hard, it runs better with a load than without. As it accelerates, and I let off the throttle, it begins to run worse. For context, it is drivable. And makes decent power, but not great. Noticeably less than my old 350, that this 383 replaced.

I've re-set the timing no less than 5 times. My float levels are each just below half way up the sight glass. Im confident in the carb not being the issue. Both carbs run great on another vehicle. Verified that plug works are in proper order, and on all the way. With fresh plug, all cylinders were running at similar temperatures (temp taken at header tube for each cylinder).

Ignition system is new, and same performance with old and new. Ive set the valves twice, and Im pretty confident there, but I will probably readjust the valves again today. My Holley fuel pressure gauge agrees with my vacuum gauge, that fuel pressure is right at 6 psi.

Regarding time to break in, no. It has over 120 road miles on it with no change. It runs worse once warmed up. When I accelerate and let off the throttle it blows out quite a bit of smoke. Smokes at idle, too, albeit less. It drives like it has a stock 350, but misfires a lot. The more I think about it, the more it is seeming like the timing chain is off a tooth!

Before I go to the extreme of pulling the intake, oil pan and/or timing cover, I will verify that the PCV valve is good. Im sure that I have others.

I'll verify timing and run some clear tubing on the modulator and perhaps even the PCV valve today. Ill start at square one, and go through everything and report back. Finally finished the flooring on my stairs, so I'll have plenty of time to play with it today.

Thanks everyone!

Nik

[Dead Parrot]

Was the timing gear set one of those that lets you set the cam either dead on or advanced/retarded?

[MySons68C20]

Have you done the compression test yet?

[nikwho]

Originally Posted by Dead Parrot

Was the timing gear set one of those that lets you set the cam either dead on or advanced/retarded?

Negative. Straight up only.

[nikwho]

Originally Posted by MySons68C20

Have you done the compression test yet?

No sir. Trying to get to it today! I've replaced the PCV valve with another that I had, run a clear vacuum modulator hose and set the timing with the engine running. Adjusted to zero lash, plus 1/2 turn tighter. Still have a misfire. #7 cylinder. 1-6 & 8 are all showing roughly 400° at the header tube. #7 running at 140°, so not firing. Plug wire is good. Plug fouled. Second plug that cylinder has fouled.

[geezer#99]

Have you checked #7 isn’t flattening the cam lobe?

[jayoldschool]

Adjusted to zero lash, plus 1/2 turn tighter

To clarify: did you do this running? I see that timing was done running.

[nikwho]

Originally Posted by geezer#99

Have you checked #7 isn’t flattening the cam lobe?

No... I was wondering the same think today. I sure hope not, but I think that Im at the point of starting to pull this thing apart. At least the intake, possibly heads to start. May end up needing to tear it apart and start over.

[nikwho]

Originally Posted by jayoldschool

To clarify: did you do this running? I see that timing was done running.

Yes sir. Sorry for the lack of clarity. Set valve lash with engine fully warmed up, at idle. Made a bit of a mess, but got it done. Timing was set initially with a spark plug hole TDC stop, rotated in each direction, then balancer marked between two points, and timing degree tape added to that spot on the balancer. I've loosened the distributor and played with the timing in either direction, to see if there was any improvement, but there was not.

The smoke sucks, but isn't bad. Its the misfire that is really stumping me! I'm gonna pull the plugs and do a compression test soon. Probably a leak down test, too. I'm considering pulling valve retainers and springs after those tests are done, and inspecting the valve seals. I am still suspicious of the valve seals.

[AcampoDave]

Im wondering about the intake seal too. It's happened to me before and I had symptoms similar to yours as well as loading up on oil at an idle and blowing blue when i took off. At the time I was using fel-pro gaskests which are good, but even after I installed another set it happened again. After the second set of fel-pros became an oily mess, I switched brands to Victor Reintz and the problem was solved. Weird I know, but whatever I was just glad to be able to say "third time's a charm."

[gvw5400]

I had a oil use / fouling issue on a fresh rebuild. Found intake gasket pulling oil
from the valley on # 6-8 cylinders. It would start fouling fresh plugs in 25 miles,
and have blue smoke on decel and idle. I was freaked out about rings installed upside down, cracked rings, scored cylinders, flat cam and just about every major thing my mind could come up with!
Hopefully you find a easy fix also, these problems can become all consuming until fixed!
Hang in there!

All the Best
Dirk

[72blue]

Good luck man, I kind of have a similar engine I built 10 plus years ago and never worked the bugs out of. Bought a house, married and kids and there it sits still. Other issues with truck as well. I had a 1826 Edelbrock on it. That’s a 650. Seemed like too little carb and just got a bigger carb on it last night. After work today we will see if I can at least drive this thing while I finish/fix the rest of the issues.
I am keeping my fingers crossed for ya.

[nikwho]

Originally Posted by 72blue

Good luck man, I kind of have a similar engine I built 10 plus years ago and never worked the bugs out of. Bought a house, married and kids and there it sits still. Other issues with truck as well. I had a 1826 Edelbrock on it. That’s a 650. Seemed like too little carb and just got a bigger carb on it last night. After work today we will see if I can at least drive this thing while I finish/fix the rest of the issues.
I am keeping my fingers crossed for ya.

Thanks! Good luck to you, as well!

[nikwho]

Is there any chance that a bad fuel pressure regulator (and fuel pressure gauge) could cause an issue without the gas level going to the top of the sight glass? I swapped cleaned plugs, completed compression test (150-155 psi in all 8 cylinders!) and replaced my plugs today. Replaced a suspect plug wire, too. While this was going on, I swapped to a Nitrous Express fuel pressure regulator that I had, and fired it up. The engine ran smoother than it ever has before! I was amazed! Then, I looked down and the garbage Nitrous Express fuel pressure regulator was puking gas all over my engine, so I shut her down. Disconnected the regulator and bypassed it. Fired it back up and its instantly running like dog sh@t! So, I may have narrowed it down! I've ordered a new Holley fuel pressure regulator from Summit Racing. Now, kinda just waiting until that arrives to see if that makes it run well again! If I can get it running like it was at first with that NX regulator, I THINK that I may have this thing figured out!

[nikwho]

Well, I FINALLY have some resolution here! Got the new engine running perfectly! Lots of tuning and tinkering, and i.lroving lots of little things along the way, so it was not in vain, at least!

So, I finally figured that I'd torque the intake down, just to make sure that it wasn't the source of a leak... Well, I put a wrench on an intake bolt and it was LOOSE! Like, finger tight! Checked the others. Every single one, finger tight! When I install intakes, I put a bead of black gasket maker along the front and rear edge of the block, set the intake on, and finger tighten the intake bolts, and allow the gasket maker to set up, before torturing the intake down. I obviously forgot to go back and torque it! So, I had staryed and run this damn thing with the intake manifold finger tight! So dumb! Oh well! I torqued it down now, and it is running like a top! Need to start over from square one tuning the carb, but thats easy!

Thanks for the advice, thoughts and tips along tye way!

Nik

[paul mora]

Wow my first thought was a vacuum leak. I remember when the vacuum advance was not working the truck ran like a dud. In this case you had basically the same problem pro vacuumed and it was running like a dud.
Enjoy your truck. Nothing like a fresh good running truck motor.

[AcampoDave]

Did you put in new intake gaskets? Based on my experience, they are likely a nasty oil soaked mess.

[nikwho]

No, I didn't. But I was thinking the same thing. I'm probably gonna pull a set out of my tool box and swap 'em out. Ill torque the intake down this time! LOL