Carb. power valve [Archive] - The Donzi Registry

tmdog

07-17-2002, 07:53 AM

Have a 18 Donzi Classic Chev. 350- 330 hp with a Holley 750 cfm carb. The problem is engine burning very rich at idle. Some time ago in Hotboat they descibed my problem and the remedy was to change the power valve to a 3.5. The conflict comes into play while reading the member's forum, it stated their is a formula to follow. Take a vacuum test at idle, halve it and add .5 and that shoud be the number of power valve to use. Any member have a comment on this problem. An answer would be appreciated. Jim (a new member)

Greg K

07-17-2002, 08:12 AM

Have you tried adjusting the idle mixture screws?

Rootsy

07-17-2002, 08:14 AM

and don't forget to check your idle with the boat in the water, in gear, idling....

RIGHT poodle??? wink

All Sorts of Reference Info Found Here... (http://www.holley.com/HiOctn/TechServ/TechInfo/FMCTech.html)

Donzified

07-17-2002, 12:07 PM

I bought a plug that is made to replace the power valve.That was the third time I had the p.vavle in my hand and also the last.I did not notice a loss of performance and some people will tell you that for our application a p. valve is not nessasery. When I catch my holley running poorly most of the time it has to do with the float levels.They can get out of wack after a good ride in the "rough Stuff".

tmdog

07-17-2002, 06:12 PM

Thanks for the reply. I had the carb. adjusted and I think I'll use Jamie's formula. Let yall know what happens.Putting a solid plug sounds interesting might try it if all else fails. Thanks again.

Rodger

07-17-2002, 09:01 PM

You should be pulling plenty of vacuum at idle to keep that power valve shut. Check to make sure the valve diaphram is not torn and that there is no dirt keeping the valve from seating tight. If you can turn the needle valves in all or most of the way and the engine keeps running then the emulsifier tubes are probably plugged. You might be able to clean them by spraying carb cleaner, using that thin red tube that comes with it, into the brass vent holes that you see when looking into the carb on each side of the accelerator pump discharge. If that doesn't work and the problem is in fact in the carb, then you will probably have to take it apart and clean it in solvent.