Recently I have had a problem with pinging on acceleration when the engine is cool. I have not changed the timing in a long time and it never used to do this.

Also, as long as I drive moderately, the car runs smooth. If I get on it, it accelerates good at first and then will ping & be really rough and choppy, even after slowing down and parking at idle.

My plans are to:

change the fuel filter, check the exhaust for holes.

the plugs are good

Anyone had this problem and what did you do to fix it? Could it have anything to do with my carb tuning? The fuel pump is original and I have a mallory 5 port regulator...both have always been good in the past.

BTW, I posted this here because I didnt get much response in tech/general and because I have a carb.


Much Thanks.

 

Sounds like you're running it out of fuel under load. Fuel filter is a good place to start.

 

I replaced the fuel filter and plugs for the hell of it. Still pinging and bogging down on acceleration. I hear a popping noise on the drivers side in the engine bay too. Any ideas what the popping noise could be? Could the headers or exhaust be clogged up?

 

I'd start by inspecting more of the ignition, and do a fuel pump test. Just becuase it has worked in the past doesn't mean that it won't fail on you. Pop the distributor cap off and make sure the mechanical advance weights and everything works smoothly and isn't excessively worn. Check your vacuum advance (mightyvac does a good job of verifying if you have one), bypass the MSD box (in my case it went bad and my car ran a lot better after I finally stopped talking myself out of checking it), make sure one of your wires hasn't gotten fried on a header (remember it'll always happen on the side you can't see, use your finger). And again, I'd look into testing the fuel pump. Anyway, just a few things to look at next time you are under there.

 

Hmmm what size carb ?? is it popping or ( backfiring through carb)?? or actually backfiring through exhaust...very unlikely it has anythign to do with your exhaust..... sounds like either a low fuel prob under load......or archign in your distributer...... does it everty time ...dont knwo what ign u have mallory msd ect..... i would take your cap off...look for any cracks look at the rotor for black lines which would mean arching or a crack u cant see.... i would def swap out a new cap and rotor......their very cheap and this may fix your prob........ also i would buy a fuel pressure guage and air fuel guage........ this will tell u #1 if your running outa fuel....... #2 will tell you if your secondary jetting is to small and cuasing the motor to lean out under full throttle

 

I am pretty sure it is popping through the carb. Would that mean it's getting enough gas, but not enough spark to burn it? I have an MSD pro billet distributor. I took off the cap and rotor, everthing looked fine. I have checked the wires, plugs all that stuff.

Could it be the timing chain?

 

I agree with Bunker. Sounds like the springs on the weights have gone bad in the dizzy. Or your distributor clamp has loosened enough to throw the timing off. The backfire through the carb is from the charge igniting before the intake valve is closed.

 

Backfiring is usually from a lean condition. Lean can also lead to pinging.

However, as usual make sure the ignition is up to snuff. It isn't unheard of for a spark to get weak or weird for one reason or another.

Re-looking over your original post & my original reply, I doubt it's a fuel delivery problem. Perhaps your power enrichment circuit isn't doing its job. The "accelerates good at first" part is really strange, though.

 

I have done a lot to it today...

Since it is mostly a pinging problem, I:

checked springs - they are the heavy silver for slowest advance
the weights - moving freely
the bushing - the biggest one for the least amount of advance
jets in carb - 410's in front and 416's in back (did have 401's in back) I thought with more fuel, pinging would be less likely.
Ignition parts seem in very good shape.

It seems that if anything, the spark would be too strong (if there is such a thing). If it was weak, it seems like the fuel would barely burn - hence no detonation.

When I run with no vacuum advance, the pinging goes away with initial timing at 6*. Any lower, it barely starts and stumbles on take off. It doesnt idle very good and does not accelerate well.

With vacuum advance, the ping is back. I stuck a 3/32 allen wrench in the canister but couldnt find an adjustment screw. It idles good, takes off decent but due to pinging, the power loss is unbearable.

I am at a loss. I appreciate the replys.

Oh yea, my mechanic suggested getting a plain jane HEI distributor.

Can too small a spark plug gap cause pinging? Mine are at 35*.

 

Did you check your float level? Fuel pressure?

 

I guess I will do that this weekend. Ill have to run an extra hose or 2 from the fuel line into the car. I'll do a search to find out how to do it. I do have a pressure guage already attached in line. Maybe someone could ride in the engine bay and look at it while I drive...

 

I have heard of a bad EGR causing pinging problem. Normally it occurs only during cruise though.

 

Anybody heard of spark knock? What is your timing set at? If its up high and its pinging under load it might be spark knock. This basically is the pre ignition of the charge of air and fuel. If it continues you can burn holes in the top of your pistons and you will be F*#@ed. Just a thought. If you think this might be the problem retard the timing until it stops knocking. Oh and check your overall timing. It should be set to 34* or so. Do this by revving the engine up to about 3500 rpm or so and make sure you have around the 34* total timing. Be sure to have the vacuum advance unhooked and the vacuum plugged at the carburator.

 

I tried everything short of digging into the motor (which I don't want to get into) and I can't afford to get it fixed. I bought a 94 Mustang GT and am selling my IROC. The next time I get a Chevy it'll be a Corvette.

I appreciate all the suggestions and help over the past few years from thirgen.org and wish the best for your wishes for your hot rodding pleasures.

My new car (forgive me):

 

OMG...

disowned