Truck won't start right up and backfires like crazy!
 

I have a 1971 Chevy Cheyenne Longhorn with a 396 and an edelbrock 1406 w/electric choke. My buddy and I recently installed an HEI distributor and new plugs(gapped at .045) and wires(8mm). Before installing this distributor the only issues that I was having with the truck was that it was missing and seemed to lose power and bog down and then stall for no reason while driving at cruising speeds on the freeway. I would feel it start to bog down and try to give it more throttle to keep it from dying but it would just die and then as soon as I would restart it would be fine again. So we changed the distributor and the only other change I made was that I bypassed the old fuel solenoid that was located underneath the bed of the truck that regulated the fuel from the two reserve tanks which are no longer installed.

Now the truck won't start up, I have to pump the accelerator and fight thru backfiring until I finally get it started and then I have to keep my foot on the accelerator to keep the idle up until the truck warms up and then it will run ok. It almost seemed as if the electric choke wasn't working so I replaced it but it still requires the same actions to get the truck started. The last time I started the truck which was about an hour ago it made such a loud explosion that it almost felt like the truck was gonna blow up, in fact I think it destroyed my mufflers because now the truck sounds like I'm running straight headers. We have tried restabbing the distributor many times and I currently have the timing at 10 ATDC but whatever we do it all seems to have the same result. Hard-starting and loud explosive backfiring. Sometimes flames will shoot out of the carb...we're baffled! I was thinking that the carb may be bad.

The truck ran fairly well before the HEI, it just had the loss of power and stalling out while at cruising speeds but it would always start and run at a nice idle. Now the truck won't start up with out a fight and when it does get running it seems to run fairly well but I have noticed a slight bogging when I shift into third. It is a stock 4-speed. Please help with any ideas of what could be wrong. I will try to take some pics of my set up and see if that helps with any suggestions you all may have. Thanks.

Re: Truck won't start right up and backfires like crazy!
 

Almost sounds like you have a crossed plug wire since it will start up. double check the firing order

Re: Truck won't start right up and backfires like crazy!
 

welcome to the board

you need to start back at square one remove the distributor disconnect all spark plug wires
set motor at TDC on compression stroke and follow directions in a service manual to install distributor and hook everthing back up

i hope when converting to HEI you ran a new power feed wire and are not using the original wires

Re: Truck won't start right up and backfires like crazy!
 

10 ATDC is waaaay retarded. Needs to be closer to 10 BTDC. Timing like that will create symptoms exactly like you have described. You are probably a tooth off.

Re: Truck won't start right up and backfires like crazy!
 

I'd say your firing order is wrong. Either a crossed wire, or you're one wire off all the way around. Put #1 cylinder at top dead center, and see which distributor terminal the rotor is pointed at. I got a dollar says it ain't pointed at #1!

The original problem sounds like fuel flow. Dirty filter or maybe the float level is set too low.

Re: Truck won't start right up and backfires like crazy!
 

I agree that your timing is way off. It should be between 8-12 degrees BTDC with the vacuum advance plugged. Check your firing order too. If you have a stock manifold it's cast into the manifold.

Re: Truck won't start right up and backfires like crazy!
 

Thanks for all the help everyone...I'm gonna go through and check each of these possibilities and see what I come up with. It may take me a day or two because I am sick as hell right now but I will troubleshoot all scenarios based off all of your suggestions and will post the results of what I find and if I remedied the problem. Thanks again all of you.

Re: Truck won't start right up and backfires like crazy!
 

One more thing...is all the backfiring going to cause any damage to the engine?

Re: Truck won't start right up and backfires like crazy!
 

I run a BBC and my timing is set at 12 degrees BTDC. Everything I have ever read has said that 10 to 12 degrees BTDC is a good starting point for timing.

Re: Truck won't start right up and backfires like crazy!
 

I bet you're one off on all cylinders. Is your #1 where this cap shows?

Re: Truck won't start right up and backfires like crazy!
 

Nope, it looks like it's a tooth off. The rotor looks like it is pointed directly between the #2 and #1 spot on the cap. I guess I will have to restab my distributor and go from there.

Re: Truck won't start right up and backfires like crazy!
 

How far can you move the distributor by just loosening the hold down bolt a turning it counter clockwise???
If the vac.advance is hitting the intake now, 2 teeth might be needed.

If you have enought length on all your plug wires, you could move each wire one position

I didn't know Schurkey had any Chevrolet stuff, thought it was all Pontiacs for him... :D

Re: Truck won't start right up and backfires like crazy!
 

He is a regular poster on the chevelles.com forum too.

Re: Truck won't start right up and backfires like crazy!
 

When the Motor is rotated to #1 TDC compression stroke, the rotor should point towards #1 spark plug, sounds like weak fuel flow was the initial issue, now sounds like your timing is off by a good amount.
Firing order on BBC is 1-8-4-3-6-5-7-2
This would apply to all SBC and BBC in automotive use. not the line form center of distrib thru #1 terminal will make aline to #1 spark plug.

Re: Truck won't start right up and backfires like crazy!
 

If you think all of the plug wires are correctly routed, then I'd say you are 180 degrees off from TDC. Being a 4-stroke engine, the piston will be located at the top of its bore two times in a combustion cycle. The first time, both intake and exhaust valves are closed during combustion. This is TDC. The second time the intake valve is closed and the exhuast is open during exhausting. This is not TDC, and this is probably where you are at. Rotate the crankshaft until you are at what you originally thought was TDC. Remove the dizzy. Rotate the crankshaft one revolution until the timing mark shows TDC again. Install dizzy. Set 10 -12 degrees advance with vacuum advance disconnected. Reconnect vacuum advance. Should run now.

Re: Truck won't start right up and backfires like crazy!
 

Ok, so I was able to get to what I believe is the correct TDC, I was off by a couple of teeth, and was able to get it timed and running fairly well. It is set between 10-12 degrees BTDC with vacuum advance disconnected. Only problem that I am still having and have been having is that when I start the vehicle the choke is not doing it's job and I have to manually hold the accelerator down to bump up the idle until vehicle is warm and then it will stay running. I also have the curb idle set at around 1100 rpms permanently because if it goes anywhere below 1000 the vehicle will stall. Does this sound right?

Re: Truck won't start right up and backfires like crazy!
 

A step in the right direction, great glad its running now. It sounds like you could have a couple more problems take them one at a time.
1. wont idle at proper rpm, look for a vacuum leak
2. Choke not setting properly, we need more info, what kind of carb? is it a elec choke or does it have a heat riser from the intake manifold?

Re: Truck won't start right up and backfires like crazy!
 

Hey naystcb ... :hi: and :welcome2: from Ohio. By the way how abouts some pics of your ride ...

Re: Truck won't start right up and backfires like crazy!
 

Thanks for the welcome. I will try and post some pics this week. Be forewarned that she is a work in progress, so she's a little rough around the edges. :chevy:

Re: Truck won't start right up and backfires like crazy!
 

I'll check for vacuum leaks tomorrow, and as for the choke it is an edelbrock 1406 carb w/electric choke, no heat riser off of intake manifold. I am running the vacuum advance off of the full-manifold vacuum port on the edelbrock carb since this is the port that is recommended for non-emission controlled vehicles. I have been getting lots of static about this because my friends have been telling me that I should running of of the timed vacuum port. Am I ok to have it running off of the full-manifold port? What is the difference between ports? Could this be contributing to the problem?

Re: Truck won't start right up and backfires like crazy!
 

There is lots of debate about the full vac vs. timed vac ports for dizzy advance, but for a performance application the full vac is much better. This way it is advanced during low load cruising, and backs off the advance when load increases and there is increased chance of detonation. As a side benefit it also allows a smother idle and lower idle temperatures. Timed vacuum was just a band-aid fix to lower emissions at idle.

Re: Truck won't start right up and backfires like crazy!
 

Welcome... personally I think a 600 CFM carb is a bit small for your big block. The edelbrocks run small anyway.... As far as the choke issue and what appears to be a fuel starvation isuue I would refer to the Owners Manual to properly setup the carb.... Just remember the 1406 is a 600 CFM carb jetted for economy over performance.... works great out of the box on a mild 350 small block.... runs like crap on my built 355, hence the 1806 and alot of tweaking.

http://www.edelbrock.com/automotive_...406_manual.pdf

Re: Truck won't start right up and backfires like crazy!
 

It sounds a bit like an improperly adjusted choke solenoid. I would recommend looking at it when its cold (californias version) with the key in the run position and see if the choke is closing. Look at it first with key off (should be open) then turn key on (should close). Remember you should not be touching the gas peddle to start with the electronic choke. If the butterfly is closed with the key on have someone crank the engine over, does the butterfly shudder like it wants to open? How many turns are your mixture screws? Did you make your wires or buy them? Did you check resistance on them?

Re: Truck won't start right up and backfires like crazy!
 

Automatic chokes whether electric or not, you must depress the gas pedal once to allow the choke to close, and set the high idle cam on the choke. So with vehicle cold press pedal once then see if choke is closed. That simple . If choke doesn't close check eldebrocks site for proper adjustment procedure.
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Re: Truck won't start right up and backfires like crazy!
 

I have not seen mention of what kind of cam you are running. Performance cams with lopey idle can benefit from the manifold vacuum to keep the vac signal up high enough where the advance kick in and helps it idle. With stock or stock-ish cams the extra vac at idle is not needed so ported vac is OK.