Yamaha 150 ProV fuel issue PLEASE HELP!

[Yamikid28]

First time poster, but I've heard a lot of good things. I have a 1986 Yamaha 150 ProV. Up until just recently she ran like a bat outta hell. But I began having fuel issues, mainly not getting enough. I ordered a manual and read it top to bottom. It tells me that a common mistake would be to point fingers at the fuel pumps or carbs, but to check everything else first. Well here's what I've checked/replaced and she still doesn't get enough fuel: fuel lines, fittings, connections, filter, fuel water separator, tank vent, primer bulb, I rebuilt both fuel pumps, fuel in the carb bowls, along with a few other nick nacks. I've even tried running it on a separate fuel source (5 gallon handheld tank) and she still won't run. I've got 115-120psi on all 6 cylinders, and good spark off all 6 coils. I am at a brick wall here and have it sitting on one hell of a hull that I can't fish out of! Any help would be greatly appreciated

[Sparkieboat]

what does "fuel in the carb bowls" mean??
you probably need to clean/rebuild your carbs..

[rodbolt17]

try purchasing a fuel vacum guage and a few T fittings.
then starting at the pump inlet check fuel system vacum at the problem RPM.
should be above 1"Hg and below 4"Hg.
less and look for air leaks between the T fitting and the liquid level in the tank.
more and your looking for a restriction between the T fitting and the liquid level in the tank.
myself I have a tool with a guage and a flow meter and a pump that I can run the tests at the shop with the engine off.
keeps from damaging pistons.

[Tucker]

Another good diagnostic tip from the rodbolt worth printing out. How can you rig the vacuum gauge to test the fuel pumps without pulling them off and inspecting the diaphrams?

[axolotl98]

....
myself I have a tool with a guage and a flow meter and a pump that I can run the tests at the shop with the engine off....

What kind of a flow meter r u using ? Model # maybe or photo if available would be appreciated. And what kind of readings do u consider as being OK and out-of-the-range ?

[Yamikid28]

I took all 3 carbs off last night, disassembled, cleaned, and reassembled them. I also checked for air leaks throughout the whole travel of the fuel from the tank to combustion and found none. Could it be a bad crank seal? Or would the lack of a gasket on the back of the fuel pump(s) cause there to be no vacuum to draw the fuel in? Again, it runs ok while fully choked, but nice the choke is released,it slowly shuts off

[Tucker]

Think you just solve your own problem kid, need a gasket for the fuel pump. I believe the gasket p/n is 10-650-24431-AO-00 $1.05 each.

[99yam40]

I took all 3 carbs off last night, disassembled, cleaned, and reassembled them. I also checked for air leaks throughout the whole travel of the fuel from the tank to combustion and found none. Could it be a bad crank seal? Or would the lack of a gasket on the back of the fuel pump(s) cause there to be no vacuum to draw the fuel in? Again, it runs ok while fully choked, but nice the choke is released,it slowly shuts off

If you want to test the fuel supply system then check this out.
HOW TO: Testing your boats fuel system.

But If you are saying the carbs have fuel in them but motor will not run properly then you need to make sure you are getting the proper fuel/ air ratio into the cylinders and the timing and spark is doing the proper thing at the problem RPM

Main thing I see right now is that you have not told us what problems you are having, just that you have not enough fuel getting to motor, which may or may not be the case.
Tell us what is happening.

[jb123]

running better choked is usually a sign of clogged carbs and those carbs are known to clog easily, i know as i have an '89... and be careful choking if you have the spring butterflies as they can suck them right in
if you pump ball while running and motor bogs, usually a sign of bad lp pumps

[Yamikid28]

Thanks guys. I'm waiting on the fuel pump gaskets and have all 3 carbs apart and in a cleaning solution. So hopefully this all works. I'll post the results of my struggles

[rodbolt17]

I simply have to ask.
why would you suspect the fuel pumps?


do you actually understand what a carburator does or are you winging this?

[Yamikid28]

It's a fair question. I do not have much experience with carbs used on outboard motors, but have torn apart and rebuilt many at my job(turf equipment manager). So I would say I have a basic knowledge of their function. The main reason why I suspect the fuel pumps is because they are usually the source of a lean running condition on the equipment I work on everyday. Even a broken hose clamp or pin prick hole can cause a problem, so I thought that due to the lack of a gasket on the back of the pump(s) could cause a slight loss in vacuum and it wouldn't be able to pull enough fuel. But that's why I got on this forum is because I thought I'd get the opinions and help from people that have more knowledge than I do in the wonderful world of outboard motors.

[rodbolt17]

why I asked?
because tapping the choke forces the fuel from the bowl up the emulsion tube bypassing the normal circuits.
if by tapping the choke it picks up it means that fuel is avalible in the float bowl.
anyway, its always advisable to rebuild/replace lift pumps when doing the carbs/

[Yamikid28]

Alright I'll definitely look into when I start reassembling the carbs. Thanks a bunch