CayFomula

I have an 89 Formula 272SR1 with twin gen VI 454s with the mechanical fuel pump on the raw water pump. These pumps use to maintain 7-8psi at all times (haven't checked it in a while though) however after upgrading the fuel lines from the pump to the carb I am now only getting 3psi at higher rpm on one motor. The other is about 6 at idle and maintains about 4.5 psi at WOT.

I have installed -8 lines from the suctions to the carbs and no difference. I have installed upgraded pump halves from CP that are supposed to deliver up to 120 gph, still no difference. I have swapped pumps, still no difference. I have installed Holley Blue pumps feeding into this mechanical and still same.

I am wondering if the cam lobe on the raw water pump hasn't worn out. Has this ever happened to anyone? Any suggestions guys?

Ian T.

Comanche3Six

See if you can disconnect the vent line at the fuel tank, then blow compressed air through it. If an insect, like a wasp crawled in there and died, it can obstruct the airflow. This can lower fuel pressure and drive you crazy trying to figure out what the problem is.
Good luck

mcollinstn

The cam lobe DOES wear out. More often than people realize.

Check both of them before you go nuts.

Krumbsnatcher

This just happened to me last weekend, I ran the boat fine all day then suddenly I lost fuel pressure, well of course i thought that the line was too long from the pump to the regulator so i shortened it, wow it worked great.

Now the real culprit was a billet fuel filter that got clogged with the minute rubber dust that was collected in the stainless lines. Anyhow, if you did not run stainless lines check your fuel filter.

Just a thought.

HP350SC

Couple other things to check:

You didn't mention if you have mech. gauges or electic senders. Try switching the senders side to side if electric.
One other thing that is a long shot...where is the small safety tube from the fuel pump routed to? If it "sees" any vacuum signal at all it will affect the pump diaphragm and cause what you describe. For instance, if your spark arrestor is dirty or restrictive and the tube is between the carb. inlet and the arrestor screen.

CayFomula

Thanks for your feedback guys.

I didn't mention it but I had also eliminated the following:
The fuel tank vent was clear
The gauges are mechanical
Swapped the gauges no difference
New fuel filters
Filter housings clear

The safety tube is one I hadn't checked out though.

I have installed a pair of Holley Blue pumps which worked fine.

Thanks again.