not enough timing at idle too much under a load

[drewdude92]

Whats there to do in something like this? or could this even be my problem. If i retard my timing enough for it not to ping at heavy acceleration my truck will run really bad at idle and slow acceleration but run like a top when the rpms get up. Or I can also advance it enough to where I can drive it around town perfect but when I get to higher rpms it starts pinging again. Whats there to do? or am i just dumb?

[Leviticus]

Originally Posted by drewdude92

Whats there to do in something like this? or could this even be my problem. If i retard my timing enough for it not to ping at heavy acceleration my truck will run really bad at idle and slow acceleration but run like a top when the rpms get up. Or I can also advance it enough to where I can drive it around town perfect but when I get to higher rpms it starts pinging again. Whats there to do? or am i just dumb?

Nope you're not dumb, just getting your engine dialed in which has had us all calling our trucks names that we won't repeat here .

We need some more info on you setup though, cubic inches, intake, carb, dizzy, fuel delivery etc? Pinging has always been more of a fuel delivery/quality thing from my experiences. But timing could be the cause, not sure though.

Give us some more info, and what you have checked and what is new.

[drewdude92]

alright here it goes.....I put the motor in recently. 350 bored .030 over, 1.24cc domed pistons, 327 64 cc camel hump heads, HEI distributor (old), comp cams mutha thumpr cam, New plugs and wires, 1.6 roller rockers, all balanced, regular old mechanical fuel pump. thats all i can think of. if anything else let me know. And also if someone had a desktop dyno that would be awesome

[drewdude92]

and edelbrock performer intake, and edelbrock 600 cfm carb. Im looking for an airgap intake and holley carb as i type this

[Leviticus]

What are you setting your initial timing at?

[Leviticus]

And are you running a spacer between the carb and intake?

[drewdude92]

ill have to go get a timing light today. Because idk for sure. Where should i start it at since i have a pretty high compression ratio?

[drewdude92]

yes i am its a one inch spacer.

[Leviticus]

Originally Posted by drewdude92

ill have to go get a timing light today. Because idk for sure. Where should i start it at since i have a pretty high compression ratio?

Not sure on the high compression engine, but I run my 350 with mild bolt on's at about 10-12 BTDC initial timing. Are you getting enough fuel?

[drewdude92]

ill start mine at about 11 then thanks for the help. and im sure i am if i can retard my timing enough to where it runs perfect at the high rpms. it has to be in the timing im sure....

[bigsnookmaster]

Sounds to me like you might need more octane than pump gas, with a domed piston and small combustion chambers, I think this might be your problem. Good luck

[Mike C]

For one thing, you have pretty high compression for iron heads and today's crappy gas. Flat tops in a 355 are about 9.8:1, the dome probably has you about 10.5:1. Especially high in a heavy vehicle. A lot of other questions to answer as well: Are you jetted even close to correctly? What rear gear? How tall a tire? How much camshaft? Specs? What is your initial timing? What is your total timing? How much is centrifugal and how much is vacuum? Is the vacuum through manifold or ported?

It is possible to tune for a heavy vehicle with high compression, you need to do an in-depth search for info on setting ignition timing at (a) initial (b) at a particular rpm and figure at what rate it gets to the total mechanical advance (c) how much vacuum advance and is it to smooth out the idle or to get to the proper total advance.

[Tynee]

I suspect taht this thread will answer any questions you may have:

http://67-72chevytrucks.com/vboard/s...ght=faq+timing

There are others threads that do a good job of providing detailed instructions on adjusting timing, as well. Just run a search as recommended above.

Also, if I may make a suggestion, when you buy your timing light, spring for the model that will allow you to adjust the advance on the light itself. Something along these lines:

http://www.sears.com/shc/s/p_10153_1...0070921x00003a

It'll make your life easier in this process.