tuning help fouling plugs - Pontiac GTO Forum
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post #1 of 3 (permalink) Old 04-12-2019, 07:02 PM Thread Starter
 
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tuning help fouling plugs

I have a 1970 350 Pontiac believe it has been rebuilt before I got it and maybe a small "RV" cam. It has a 1405 eddy sitting on top of a single plane tomahawk intake. MSD ignition and distributor running no vacuum advance w/12 degrees timing at idle 23 at 2300 RPM, anymore and I would have a hot start/overworked starter problem.
My issue is I re jetted the carb due to an off idle stumble to a point of stalling sometimes, I could not tune out, the larger jets and rods fixed that. When I pulled a plug it was fouled some so my question is should I be worried about the fouled plugs? I don't have a heavy gas smell coming from the car when I drive it it idles at about 700 rpm 850ish in park.
as it sits now
Main jet .101
Secondary .098
Rods are .073 x .042
with the pink step up springs (car has 15-16Hg)
What jet/rod combos have worked for anyone running a stockish 350 ?
After more reading around I am thinking it might be my choke as it wont adjust where I need it and gives me hard cold starts second opinions are welcomed

Last edited by 1970lemonhead; 04-12-2019 at 07:33 PM.
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post #2 of 3 (permalink) Old 04-12-2019, 07:36 PM
 
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Originally Posted by 1970lemonhead View Post
I have a 1970 350 Pontiac believe it has been rebuilt before I got it and maybe a small "RV" cam. It has a 1405 eddy sitting on top of a single plane tomahawk intake. MSD ignition and distributor running no vacuum advance w/12 degrees timing at idle 23 at 2300 RPM, anymore and I would have a hot start/overworked starter problem.
My issue is I re jetted the carb due to an off idle stumble to a point of stalling sometimes, I could not tune out, the larger jets and rods fixed that. When I pulled a plug it was fouled some so my question is should I be worried about the fouled plugs? I don't have a heavy gas smell coming from the car when I drive it it idles at about 700 rmp 850ish in park.
as it sits now
Main jet .101
Secondary .098
Rods are .073 x .042
with the pink step up springs (car has 15-16Hg)
What jet/rod combos have worked for anyone running a stockish 350 ?

That single plane intake is not helping. You can sometimes get a poor mixture distribution with them. Velocity can be sluggish at lower RPM's and you could even experience fuel puddling. My experience on the older cars was to periodically "clean them out" by doing a good hard full acceleration. But assume you are already doing this.

The fouling could also be oil, often caused by worn valve guides or even dried out valve seals - this may account for the lack of heavy gas smell.

Try a step hotter spark plug and see if it helps. A hotter plug can sometimes help to burn off the excess gas/oil.
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post #3 of 3 (permalink) Old 04-12-2019, 10:43 PM Thread Starter
 
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Thanks for the quick response, i do baby it more then I should. The heads have been rebuild so hope its not oil, the intake was what I could afford at the time, waiting for it to give me a reason to spring for a OEM type this just might be it
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