Loosing RPM's HELP!!

[BajaBennett]

Trying to help a friend work the bug out of a new engine. New block (454), forged crank, new pistons, etc., new Dart rectangular port heads, Holly (800). Original Merc. ignition (454 Mag.). Idles fine, gets on plane fine up to about 4300 rpms, then it starts slowing down. Back off and wait about 30 seconds and it will go again. We checked fuel pressure and have about 4 lbs. when running. Is this enough????

Any ideas guys. My friend had this engine built thinking it would be very dependable. However, it just won't run. Any thoughs would help.

Dail

[mats]

Sounds like lack of fuel. The float bowl gets emtied at WOT and when you slow down it is refilled again.4 psi is on the low side. Have you checked if the fuel pressure goes down at WOT?

[BajaBennett]

mats,

I'm thinking fuel too. The engine builder went out with us this afternoon and did a vacumn check. He got 8 - 10 and said it should be 10 - 15. So we pulled the intake. No indications of a leak. We had sprayed carburator cleaner around the intake earlier thinking there might be a leak, with no results. I am thinking we need a constant 7 lbs. of fuel pressure to feed this thing

Dail