anybody know the flow rate of these pumps my pressure drops below 5 at WOT I am going to try bigger line from tankand a Mechnical guage right at the carbs

In a carb application this is kind of tricky. Just because your FP drops doesn't necessarily mean you're leaning out right then. If you try a bigger fuel line then that would do nothing to increase pressure to your needle & seat. But you should use the biggest line that you can from tank to carbonator. If you use a return regulator (and you should) then both the feed line and the return line MUST be the same size.

Don't exceed 8-9PSI on the carb or the needle will be overcome and you will flood the engine. Keep in mind that with carbonator pressure is not needed as is volume.

Roby

I am working through a fuel pressure issue with my new HP500 clone (OE Merc combo fuel/water pump)

At the carb I had 4psi at idle and 3 psi at WOT.

Replaced Carter pump BOTTOM with their strip pump bottom rated @ 7 to 8.5 psi/ 120 GPH ($64 @ Summitt). Merc fuel pump upper has a different lever.

New fuel pressure is 7psi @ idle Hope to test WOT over the weekend.

BTW; Holley Tech says 7psi max/ 5psi minimum for a 4150

Have you replaced your fuel filter?????????????

BTW; I change my gear lube annually (200hrs) in my Merc belt driven fuel/water pump.

Is the pump old i.e. 2 years or so, if so, get a new pump and get 7-8 psi idle with 5-7 psig at WOT. Definitely stay above 2 psi at WOT w/ a stock 500 HP and >4 psig with a blower motor. My 500 HP carb fuel pumps have to be replaced on a regular basis. I recommend changing fuel pumps before changing fuel lines especially if the boat has been running with the same 500 HP motor for a while.

klaw
After replacing the Lower on the fuel pump the pressure ended up being LOWER after a few minutes of run time. So I changed fuel filter and pressure continued to drop

Next step, I replaced the upper (diaphram). I'm back up to 7 psi at idle, hope to lake test this weekend.


To replace the upper, remove lever pin cap, drill a small hole in the other side of housing to remove lever pin with a punch. Then install Merc lever.

BTW OE pump had the same size check valves as the new Carter (M4889) Strip pump (Advertised 7 to 8.5 psi/120GPH)

CV products makes a replacement pump for the merc style.It puts out 130 gph @ 7-8 pounds.

What size fitting connections?
How much?

Inlet is #8 outlet is #10.I dont remember what I spent.It was around the time when I built my boat that I stopped asking prices on everything.I had Elephant ears for pockets in the end!

klaw
On water testing WOT I ended up with 4.25 PSI. With Carter 4889 (arm changed)

JCPERF
Who sells CV products?