High fuel pressure

videobobk · #1 10-09-2006, 08:53 PM

Our stock O-320 (carb) engine has a problem I haven't ran into before. It 885 TTSN and has been sitting for about two years, but pickled and well cared for (actually on the 9A awaiting the Big Day.) The only problem we found on first start was a leaking carb and rich mixture. Had new float valve installed. No help.

Today I checked the pressure with a calibrated gauge. It proved two things: our gauge is very close, and we have high fuel pressure downstream of the mechanical fuel pump. Electric pump gives 4.6 psi, mechanical 8.2! This is forcing fuel past the float valve. Bypassing the mechanical pump gave a smooth runup, through the pump gave a VERY rich mixture.

Looks like a new pump is the next step unless someone knows something that would safely fix this one. Also, anyone know why a pump would act like that? It is original to the engine.

Bob Kelly

mahlon_r · #2 10-10-2006, 04:46 AM

Make sure the engine breather isn't restricted. High crankcase breather pressure will cause the fuel pressure to increase, due to the fact that the fuel ump has a vent to inside the crankcase..
Good Luck,
Mahlon
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videobobk · #3 10-10-2006, 08:13 AM

Quote:

Originally Posted by mahlon_r

Make sure the engine breather isn't restricted. High crankcase breather pressure will cause the fuel pressure to increase, due to the fact that the fuel ump has a vent to inside the crankcase..
Good Luck,
Mahlon?

Thanks, Mahlon, will check that out. Doubt if that is the case, but it will be easy to check and it sure would be nice. Fuel pumps are kinda pricy!

Bob