Pinging on takeoff

[Bonnewagon]

I have a 1979 Pontiac 301 4 barrel with a 4 speed Saginaw manual trans, 3:50 first gear, 2:78 rear gear in a 1983 Bonneville wagon. Overall ratio is 9.73 to one so I don't think it's lugging ( I consider 10 to one ideal for a stick car). When I take off I get pinging but no other time, just when I let out the clutch and start to move. If I ride the clutch and rev it a bit no pings. Uphill, towing a boat, WOT, no pings. It otherwise runs terrific, pulls strong and smooth. The motor was from a Firebird with automatic trans so the carb and distributor are for automatic too. Never had a problem in the Firebird even though it's heavier and had 2:41 gears. I just wanted to get some ideas what could be wrong before I start changeing stuff.

 

[olds307 and 403]

Maybe try an adjustable vacuum advance canister. That should be the 170hp version too.

 

[Bonnewagon]

I thought there might be too quick advance so I put a vacuum delay valve in the vacuum advance line. No difference.

 

[turbo78]

your pinging could be fuel related more than timing related, try increasing your idle air mixture screws alittle out to give it just a hair of fuel more. jmo

 

[megaladon6]

it sounds like you're going lean. look for any (probably small at this point) vacuum leaks at the carb and intake gaskets and of course the lines. if you're good there, yeah try the mixture screws. see if tuning them ups your manifold vacuum.

 

[Bonnewagon]

I'm allready on the rich side at idle. Vacuum is a solid 21". I was wondering if my off-idle circuit could be richened up. The Q-jet has an APT that raises the metering rods up out of the jets for good transition but right now they are at the original factory setting and I hesitate to monkey with that.

 

[MD13ailey]

The intial timing in the distributor could be a little much but it doesn sound likes its going lean I would try messin with that rod on the Q-jet

 

[turbo78]

perhaps the accelerator pump is on its lowest setting, that would cause it be a little lean off idle.

 

[Bonnewagon]

OK, worked on it today. The vacuum tree behind the carb was loose,so there's a leak. Then I noticed the THERMAC air cleaner had a check valve that was stuck so I bypassed that. It was getting only hot air instead of a 100 degree blend. Then I checked all vacuum hoses and wondered if the ported were right and a vauum gauge showed that the advance port was opening way before the EGR port. So I reversed them and now the EGR should kick in before the timing advance does. All this helped a lot but I still got some ping if I lugged the motor so I backed off the initial timing 2 degrees and that seemed to eliminate it finally. I didn't want to mess with the carb as it is so original the choke still has rivets and it will idle smooth at 400 rpm. Tomorrow I will test in real life traffic and see how she does. Thank's for the suggestions guys.

 

[turbo78]

well good luck on the test drive tomarrow, hope it all works and by the way, i think your wagon looks really cool on the rallye wheels 😀