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Discussion Starter · #1 ·
i have a 68 model 302 bored over and all that. i believe i'm running at 11:1 compression. i know that my carb isn't adjusted but i also cant get it adjusted. i'm now running a 750 holley vac sec. the car is constantly rich even with 65 jets in the front. i'm also having a lot of crank case pressure buildup. i guess just give me some ideas of whats goin on. i'm willing to tear it down and rebuild it ie. new rings and a little lower compression heads, but i don't want to if it can be fixed
 

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A 750 is really big for a 302, even with 11:1 compression. Stepping down the jets doesn't compensate for excessive flow, you might to go down to a 650 at the most, that should help.
 

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+1 with EagleAutosports.

I'd also like to add it's not so much that the carb is too big for 302 cubic inches... just yours. I back that up with I know a 306ci sbf running a 1000cfm dominator.
The reason a small cubic inch engine can take a large carburetor per se is the camshafts ability to manipulate the air charge along with the intake manifold. This is called carburetor "signal". A strong signal provides the negative pressure the carb requires to pull metered fuel along with air at the correct ratio throughout the rpm band.
What I'm saying is, it may not only be the carb but also the camshaft, camshaft indexing and intake manifold are not matched properly.

I assume you know the "need" to go through the engine and correct the blow by. Another concern would be an excessive amount of fuel mixing with oil and wiping across your bearing surfaces. Not good.
 

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Discussion Starter · #4 ·
i had a 670 street avenger and had the same problem. i have been thinking about it and i think that my valve springs may be to strong. i was adjusting the valves and noticed when i turned the motor over that one of the open intake valves slowly closed....maybe crushing the lifter, could that cause a problem that would act like timing fubar that would mess with the a/f ratio? thanks and let me know
 

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i had a 670 street avenger and had the same problem. i have been thinking about it and i think that my valve springs may be to strong. i was adjusting the valves and noticed when i turned the motor over that one of the open intake valves slowly closed....maybe crushing the lifter, could that cause a problem that would act like timing fubar that would mess with the a/f ratio? thanks and let me know
IMO, the only time a valve spring is too big... when the pressure takes out the lobes on the camshaft and/or beats the seat all to hell regardless of closing ramp on the camshaft.

My first thought is you have bad lifters going by your description of what going on. However, you must realize the lifter will depress just not as quick as you're describing.
Yes, you're correct... incorrect camshaft timing will disrupt good carb signal, response, acceleration.
 

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my 69 had a 750 dp manual second's and it ran fine stock holley carbs are easy to tune and i bet your problem lies with the idle mixture screws if they are not set right it will run rich as hell there are 4 screws on the bottom plate screw them all, all they way in then take them all 2 1/2 turns out and make 1/4 turn changes till you get the response you wan and so its not belching black smoke let me know how this does


Im runing a 4bbl vac seconds on my 69 302 of a 460 not sure the size right now so it gets gas mileage
 

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Check fuel pressure, float level, accelerator pump, and engine vacuum.

Often a high compression engine has a fairly radical camshaft. That big cam usually causes a low vacuum, which can make it tough to tune the carb. Low vaccum signals generally run better with a mechanical secondary carb.
 
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