klaw

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

robyw1

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

RickR

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

RickR

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

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

Thunderstruck

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.

RickR

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)

JCPERF

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

StrikinLightnin

What size fitting connections?
How much?

JCPERF

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!

RickR

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

JCPERF
Who sells CV products?