1991 Chevy S-10 Carb Backfiring

Tiny
LUDWIGCLASSICS
  • MEMBER
  • 1991 CHEVROLET S-10
Engine Performance problem
1991 Chevy S-10 V8 Two Wheel Drive Automatic 0

I have a 283 CI board.030 over engine. It has 10:1 forged pistons with a 480 lift cam. I am not sure of the duration. When I bought the short block, the guy said something about the cam having a 6% grind. It has aluminum heads with 2.02 intake valves with 190 intake runner. The brand name of the intake is Edelbrock torker. The roller rockers are 1.5 stock with a 650cfm double pumper Holley carb. It has an after market fluid balancer and Flowmaster shorty headers with 2.25 exhaust all the way out and Thrush ultra flow mufflers. This is all in an S-10 pickup.
I am getting an occasional backfire through the carb on acceleration. First, I had set my valve lash the standard way with engine running half turns after rattle stops. I backed off the half turn to only quarter turns to see if this would help. It did not.
Next, I started out with a Edelbrock 500 CFM carb on the engine. I thought it was too lean thus causing the backfire so replaced it with the 650 Holley. I came to this conclusion to change to the Holley after trying numerous timing settings. Now that the Holley is installed, I have set my initial timing to 16 degrees. The mechanical advance is 10 degrees and the vaccum advance is 10 degrees. This is a combined total of 36 degrees and still am having backfiring issues. I have tried setting the timing to 23 degrees intial and mechanical 10 degrees and no vaccum advance to no avail.
As a last resort, I have increased the exhaust valves to a half turn while leaving the intake valves at a quarter turn for valve lash. I did this thinking the exhaust was not staying open long enough to let the exhaust completely out before the intake opened thus allowing the backfire. However this doesn't appear to help my problem either.
Another issue is the passenger side of the engine, which I call the left bank, has a cylinder that only starts to fire as I accelerate. The collector of the header on that side gets to extreme temperatures, resulting in a cherry red glow because it is so hot. This bank and collector problem have been occuring throughout all changes to the engine.
Is it possible that the cam shaft might be my issue, possibly the root cause of my toubles? I am looking for any suggestions you may have to remedy my issues. It would be greatly appreciated.

Thanks in advance!

Ken Johnson
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Saturday, May 9th, 2009 AT 8:00 PM

4 Replies

Tiny
M_H_RITZEL
  • EXPERT
You do have a computer in the car? I am not much up on cams and durations, but have you reprogramed the computer to the engine? I don't know if this applies or not to your car. Try reprogramming the computer, to do this disconnect the battery for a couple of minutes, then reconnect the battery. On that year car the vehicle will probably have to be driven about 50 miles before it completly resets. The other question what octane fuel are you using. That could have something to do with the backfire. Other than the computer or fuel octane is all I can think about.
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Saturday, May 9th, 2009 AT 9:00 PM
Tiny
LUDWIGCLASSICS
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I started with 93 octain. Ran that out then filled it with 87 trying to dial this engine in. No computers
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Sunday, May 10th, 2009 AT 4:53 AM
Tiny
LE501J
  • MEMBER
Hey check your fuel psi it sounds like your not getting the right fuel pis. And what kind of pump are you runing? You sould be between 7, 9pis.
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Tuesday, May 12th, 2009 AT 6:35 PM
Tiny
M_H_RITZEL
  • EXPERT
Ken, just wondering, how is the compression in the left side, just wonder if there is something making the left side get so hot that a valve not closing all the way, if the valves not closing would it be possible that when the other cylinders are on exhaust stroke and one cylinder is on intake stroke that the exhaust is ignitiong the one cylinder making it back fire. That would also count for the extra heat.
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Sunday, May 17th, 2009 AT 9:13 AM

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