L36 backfire on hard accleration

[Dan Pepper]

I've set-up the engine according to the shop specs (i.e. idle, mixture, timing, dwell, etc.), but the engine loads-up / backfires on hard acceleration. It's okay if you ease your foot into it, but coughs when you stab it.

This is an AIR big block WITH the correct carb (air fittings blocked) but WITHOUT the pump and related tubes (soon to be put back on, although in neutered form).

Any suggestions to cure the problem?

Thanks,
Dan Pepper

[Jack H.]

Re: L36 backfire on hard accleration

Since she drives right now, why not consider visiting a shop with 'dyno' capabilities? Once you get the electrical characteristics on a scope combined with lock-step tailpipe emission analysis, virtually all of the guesswork and try this/that hints evaporate....

[Jack H.]

Re: L36 backfire on hard accleration

Since she drives right now, why not consider visiting a shop with 'dyno' capabilities? Once you get the electrical characteristics on a scope combined with lock-step tailpipe emission analysis, virtually all of the guesswork and try this/that hints evaporate....

[Duke W.]

Re: L36 backfire on hard accleration

Are you talking about "backfiring" through the carburetor, or "afterfiring" throught the exhaust?

If it's the former and occurs just after you got to WOT I would suspect a monentary lean condition and, the likely culprits are the accelerator pump or the the secondaries opening too soon.

If it happens higher up in the rev band after you've gone to WOT I would suspect something in the ignition system.

Duke

[Duke W.]

Re: L36 backfire on hard accleration

Are you talking about "backfiring" through the carburetor, or "afterfiring" throught the exhaust?

If it's the former and occurs just after you got to WOT I would suspect a monentary lean condition and, the likely culprits are the accelerator pump or the the secondaries opening too soon.

If it happens higher up in the rev band after you've gone to WOT I would suspect something in the ignition system.

Duke

[Pat L.]

Re: L36 backfire on hard accleration

How old are the spark plug wires? Before you start replacing things, check the spark plug wires. An easy way to do this is to start the car with the hood up in a dark garage. If you see fire jumping from one wire to the other, change the wires before doing anything else.

[Pat L.]

Re: L36 backfire on hard accleration

How old are the spark plug wires? Before you start replacing things, check the spark plug wires. An easy way to do this is to start the car with the hood up in a dark garage. If you see fire jumping from one wire to the other, change the wires before doing anything else.

[Dan Pepper]

Re: L36 backfire on hard accleration

The wires are new, dated repros, but I'll pop the hood in a dark garage and take a look to see if there's arcing.

[Dan Pepper]

Re: L36 backfire on hard accleration

The wires are new, dated repros, but I'll pop the hood in a dark garage and take a look to see if there's arcing.