Carb help....
 

Hi guys. Have some issues tuning my carbs and wondered if I could bet some ideas on jetting. ENGINE SEEMS TO RUN OK AT Cruise (3500rpm). When I go WOT, it starts to pop thru the carb and won't pull any rpms. I have a 500HP with a 256 blower and a set of Holley 750 blower carbs that are boost referenced from Holley. Jetting at the moment is 74 pri. 84 sec. with a 6.5 p.v. Plugs are black at idle and pure white at WOT. What do you guys think I should do as far as jetting goes? I have been screwing with this thing for a month and am at my ends wit! Can you lean down the primary jets and go bigger on the secondaries or do you have to stay with an 8-10 spread when running a pv???

You need to ck fuel pressure at wot make sure the system is keeping up, some parts of a factory system really restrictive, jetting does not seem all that off, what timing are you running ? you should have a max of 28 total, and would like about 18 initial to clean the idle up, you may even lock the advance as starting usually not a issue with the low compression...Rob

Fuel pressure at wot sets right at 6psi. distributor locked out at 34 deg. taking 1 deg. of timing out per 1lb of boost (taking a total of 6 deg. out).

Jetting has nothing to do with idle mixture.

Are you running primary and secondary PV's????

This search may help.
http://www.offshoreonly.com/forums/s...=2198798&pp=25

Popping is usually lean and jetting doesn't affect idle.
You may try 78's and 84's.
Check fuel pressure at WOT, must be over 4 psi.
Run a compression check, You may have damage already.
Timing should be 30 or less (total).
What boost are you running?

JB

Running a 6.5 PV in the primary side only.

Fuel pressure at WOT is at 6psi.. Did a compression test and all cylinders are good. running 6lbs. of boost.

Where did you connect the carburetor PV hose to?
Have you measured the PVCR openings yet?
JB

I am picking vacuum up from the intake. Basically ran each hose off of the carbs to a tee then one line into a tee off of the intake where my boost gauge runs off of. Not sure as to what you are referring to when you say PVCR. It's pretty sad when I can tune a 7 sec. race car and can't tune a damn boat lol!!!

A spread of 8-14 jet sizes is fine then.