Engine in my sig.

Running good most of the time, but sometimes I have a issue with what appears to me as running lean, and it wants to ping.

It does it only when I accelerate slow, and especially when it shifts gear, but not always.

It started to act like this one day I was testing with a G-tech. I made 5-6 good runs, and then it started to do it. If I accelerate hard everything is ok.

I have tried a new fuelpump, but it is still the same. I thought it could be dirt in the carb, but it didn't help cleaning it.

Could it be the power valve not opening as it should all the times? Power valve is rated at 6.5, idle vacuum is about 8-9 hg in.

10.6 compression alum heads you should be able to run 93 oct. gas, turn your timing down just slightly until this goes away.

I will try retard the timing slightly. Thanks for the tip.
What confuses me is that engine has run ok for nearly a year without problems, and then this occurs out of the blue.

Couple things: As time goes on you can build up some deposits in the engine, and this will help cause pinging. When the engine is new everything is fine. This is soon for that to happen, but I think the more you have the problem the more likely it is to happen, until you clean it out again.
The other thing is to try other brands of gasoline. I have had experience with that in cars, where a car would run better on one brand of gas, while another car would run better on a different brand. Octane (here, at least) is rated as an average of the "motor" and "research" octane ratings. One rating tests at high power levels, and the other tests higher timing advance levels. So, if one fuel has a higher "M" rating but a lower "R" rating it can have the same "octane" rating as another fuel but be better (or maybe worse) in your car.

try sunoco 93 octanr always had good luck with it, if you can get 94 get it, but just back the timing down 2 degrees i bet thats all you need.getmore is correct as you drive carbon deposits build up in chamber and retain heat which can lead to this problem, years ago we used to make a full out run on a desolete strech of highway, we called it carbon blowout ally haaa....

Still have the problem :(

I have tried: octan 99 gas (same as US 94), octan boost, retarding the timing to 32 deg., advance the timing, block the vac. advance, new fuel pump, new acc. pump, new spark plugs, new ignition coil, checked for broken valve springs.

The symptoms is getting worse and worse. Sometimes after nearly stopping by a crossroad, I can give full throttle trying to accelerate and nothing happens. Only thing is I can hear the barrels open. Cold or hot engine/weather is the same.

I have bought an a/f meter, and despite it acts lean when it does the thing, it shows 13-14.

All new ideas are welcome...

The symptoms is getting worse and worse. Sometimes after nearly stopping by a crossroad, I can give full throttle trying to accelerate and nothing happens. Only thing is I can hear the barrels open. Cold or hot engine/weather is the same.
Man thats more problem than pinging, sound like your dist. is way out...

The symptoms is getting worse and worse...

...I have bought an a/f meter, and despite it acts lean when it does the thing, it shows 13-14.

So, it's getting worse? If the A/F ratio is the same, but the problem is happening more often, I would suspect timing/ignition.

I would suggest rechecking your timing and see if it has moved (this can happen if your distributor hold-down clamp is not tight). Also check your plugs to make sure they're not fouling.

I had a lean miss on my 383 that I've tracked down to my timing curve being too quick. I had the right initial and total timing, but the curve without vacuum advance came in too quick...

Still have the problem :(

I have tried: octan 99 gas (same as US 94), octan boost, retarding the timing to 32 deg., advance the timing, block the vac. advance, new fuel pump, new acc. pump, new spark plugs, new ignition coil, checked for broken valve springs.

The symptoms is getting worse and worse. Sometimes after nearly stopping by a crossroad, I can give full throttle trying to accelerate and nothing happens. Only thing is I can hear the barrels open. Cold or hot engine/weather is the same.

I have bought an a/f meter, and despite it acts lean when it does the thing, it shows 13-14.

All new ideas are welcome...

probably have excessive carbon build up on the combustion chamber and intake valve seat .this excessive build up and cause hot spots that create "pinging" or spark knock what you're experiencing

to remedy this it is very easy ........get yourself one of those plastic spray bottles with the adjustable sprayer and set it to it's finest mist/spray setting . now with the air cleaner off and engine idling at 2000-2500rpm spray water into the carbs venturi's and do this for about 10-15 seconds then let the engine recover for a minute as it is probably stumbling while spraying the water .now repeat this process of spraying more water into the carb and letting the engine recover until the bottle is about half empty

now go and look at were your exh tips are and see if there's any sign of black sooty residue on the ground ,this would indicate carbon being cleaned out of the motor .then drive your car around to see if it still pings or not and hopefully this has stopped the pinging your experiencing

excessive carbon build up on the combustion chamber and intake valve seat we used to just take her out and run the bejesus outta her in the country somewhere. your method of remove carbon is alot safer than mine i think....... but ours was fun ha...

Right now i suspect the ignition box. I will try an old points distributor to eliminate the electronics, as soon as I can borrow one.

I have thought about the vacuum secondarys. Could it open too early causen this flat spot. I have tried several springs, but anyway...

Yes, I would take her out for a good long high speed run out on highway first, safely of course, and then evaluate from there. City driving can hurt a hi-po engine.

I always have to ask this. What spark plugs are you using? Also, I would agree to install a stiffer spring in the dizzy to bring the timing in a little later to avoid the ping.

As I now run the higher octan (94) it doesn't ping anymore, it is more like a stall or whatever to call it. When I ran 91 it was stall AND ping.

I ran NGK V Power FR5, when this problem occured. Now i run Bosch FR 8 DC+, which is same heat range but a better plug i think.

I have tried strip tied sec. barrels closed, but same result.

I'm borrowing af points distributor this weekend, so I can eliminate the ignition box.

You may want to try slowing down the Mechanical advance curve with a heavier spring on one side.

I had a similar problem with a firebird I had, tried everything nothing seemed to work. For grins I poured a can of 44K in the tank and the pinging, and dead spot went away.

Yes, I would take her out for a good long high speed run out on highway first, safely of course, and then evaluate from there. City driving can hurt a hi-po engine.


spraying water down the carb is easier and safer

I don't believe in carbon buildup in an engine with only 3500 km in it.
Especially not at the way it showed up. I was making 5 or 6 1/4-mile runs in a row with G-tech, and then it started to do it out of the blue.
But I could be wrong an everything needs to be tried.

I don't know why, but raising the float level by 1 turn seems to solve the problem:screwup:

It helped because 1 of two things are happening. You are uncovering a jet(s) when you corner causing a lean out....but by raising the fuel level in the bowl you are also effectively adding 1 jet size. So if your jetting was right at the ragged edge, you've richened up the mix by a few percent. If the bowl level is higher than it should be, but it runs better, then up the primary jets 1 size and lower the float a bit.

Also, if it was OK up to now, remember that refineries all over the world where they have winter weather are reformulating the gas for easier winter startup and lower emissions. Here in the Eastern states they add some alcohol and other chemicals like MTBE...so the BTU value of the gasoline actually drops about 5%. So a car that is perfectly jetted for summer will, with cooler air and reformulated gas, actually run a jet size or 2 lean.

I agree with you that it runs a litlle richer now. The problem must be in the transition circuit, because of the 2000 - 2500 rpm's. In my (cheap) 3310 holley carb. this area is non-adjustable:mad:

mine engine just started it a couple of days ago. it only has 250 street miles and 10 dyno pulls on it. i cant figure it out.

carb is a 750 mechanical dp

i put on my cousins 950 hp to see what it would do and still does the same thing. even when its getting all the fuel.

Might check to see that the cent. weights in the dist. are coming back to retard. With aftermarket weights and springs this stuff doesn't always work right.

i got a msd pro billet dizzy. out ill take the cap off and check it.