I have a 600 cfm holley and it is hesitating. It pulls good at initial throttle app but at around 1700 rpm it falls off then picks up to full rpm very well, falls from 1700m to about 1000 then runs up till i shift. could this be the acceloator cam or am i missing something? It pulls very strong after it falls off, even before. I have it jetted to 60 and the #1 and #6 plug where carbon fouled but the others look to be clean, maybe rich I will try to lean it out but this is something new to me as the old manifold had the plugs running clean on all six cylinders. Should i clock the carb with the primarys to the front of the car or is this not nessasary. Sorry if this is a stupid question i just don't know where to go from here?

Thanks TF

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Even in moderation i am excessive!

Is this carb on a stock 225 SL6? What is the manifold vacuum at idle?
BTW, 600 cfm is a lot of carb for even a built-up SL6.

It sounds like the carb needs a higher rated power valve, you will need a vacuum gauge to figure-out what power valve will be needed. You should get yourself a book on how to rebuild and calibrate Holley carbs.
DD

The engine is built up, 30 over balanced and blue printed it has a joe delong cam head is ported and polished oversized valves. I will be purchacing a book for they holly shortly just havnt had much time after work to get one lately. I will check my manifold pressure to see what i get

Thanks for the advise TF

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Even in moderation i am excessive!

We had a similar issue with ours as well. Our 225's .060" over, Comp Cam kit running a Holley 390 carb. I believe it's jetted with 51's and we ended up using a power valve kit and that helped out our cause. Motor is really smooth thru acceleration now. I believe we used the yellow spring as recommended by the fine folks here.

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