Unusual Backfiring Problems

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hawkgoalie31

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Hey guys I need a little help here. I have a 318 with a performer series edelebrock carburetor. I recently had a problem where my voltaged regulater was bad and the alternator would spike the system causing everything to burn up like the ignition box, coil, alternator etc. we replaced all that and it runs fine. However when I cruise between 40 to 60 mph it backfires. That's the only time it does it and only when I m barel on the. We rebuilt the carb and it still does it. We had the timing checked and it's perfect. I m open to all and any help.
Thanks
 
Did you check the timing with the vacume line to the distributor unplugged?
 
inertia said:
Do you have an exhaust, or header leak?
Click to expand...

X2, check for a header leak. Run your hands around each tube near the head flange and feel for a puff when it is running (easier if you do this right after you a start it from cold).
 
The ignition box may be on the way out.
 
Plug wires not on in the correct order. I have seen it where you only get the backfire when at a constant speed. Order should be 1,8,4,3,6,5,7,2, You may be getting cross firing from two plug wires as well.

Jack
 
Don't forget that a bad valve or stem or both can cause this.
 
Hey guys first off thanks for all the advice.
The timing was checked with the vacuum off.
We also checked for a vacuum leak and it was all good.
I have TTI headers and I checked for a leak and there was none.
We have tried adjusting the carb numerous times and before the electrical problem it didnt back fire.
We are going to try replacing the ignition box. Is there anyway to test it?
When we had the electrial problems we replaced the pick up coil and gapped it correctly.
Also double check the spark plugs and wires they are all good.

I will keep you updated about the ignition box. Also open to more suggestions

Thanks again
 
i had a misfire at part throttle cruise,it ended up being the pick-up module in my msd dist.i cleaned the reluctor wheel while i had it out.
 
I replaced the pick up coil and reflector I guess I could go through it and make sure it's all cleaned and proper
 
Possible broken valve spring. Does it misfire or backfire if you bring it up to cruise RPM w/ no load on it, or just while you're driving?
 
hawkgoalie31 said:
Hey guys first off thanks for all the advice.
The timing was checked with the vacuum off.
We also checked for a vacuum leak and it was all good.
I have TTI headers and I checked for a leak and there was none.
We have tried adjusting the carb numerous times and before the electrical problem it didnt back fire.
We are going to try replacing the ignition box. Is there anyway to test it?
When we had the electrial problems we replaced the pick up coil and gapped it correctly.
Also double check the spark plugs and wires they are all good.

I will keep you updated about the ignition box. Also open to more suggestions

Thanks again
Click to expand...

i still recommend changing the distributor cap ($5 bucks) before pulling the valve covers and all that. really. had a very similar issue and that's all it was. drove me nuts until i figured it out. the cap had a hairline crack in it.
 
ok guys here what i got I am so stumped right now haha.

I changed the ignition box and distributor cap and it still backfires. but only at very specfic time and speed. For example I will accelerate no problem no backing firing then ill let off the gas completely and when I am about 40 to 60 when i get back on the gas just a tiny bit barley pushing the pedal it will back fire pretty bad but as soon as i give it gas then its fine no hesitation or anything. We have re built the carb but maybe we missed something? or could the carb not be tuned right even though it backfired before we rebuilt it in the same way it does now.
 
You didn't post what rpm this is happening at, but as others have eluded to, sounds lean in that spot.

I can't give you a specific fix, but read here and see if the tuning info gives you some idea's?

[ame]http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf[/ame]
 
Accelerator Pump,, try putting the pump rod in the hole closest to the carb,, if it's already there, try the second hole...
 
I moved the accelerated pump hole closest to te carb and it seems to run worse :(. I think it may be lean but I m just confused because it never did this before. And after all the problems with the voltage regulator I can't figure out if its timing or the carb.
 
Also I don't have a tachometer so I m not sure what rpm this is occurring at
 
i have a 64 polara 440 auto . this 440 had a 750 cfm eldelbrock on it and it would run okay as long as u were not on it ! as soon as u floored it after 3 grand it would miss fire like crazy :banghead: so my engine biulder tells me its ignition :protest: not have all new electronic !! put a rebuilt 750 holley on it no miss fire pulls like crazy :burnout:just a thought might be the eldelbrock


mike
 
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