225 ox66 starving for fuel

[jol1ymon]

I recently completed a complete rebuild of my 1998 225 OX66 and have been having a recurring problem since the rebuild, which never happened before the rebuild. The clear fuel filter on the port side of the engine is continually about half full. I can pump the fuel primer ball and fill it back up, but the filter always drains back down to about half full. This results in the motor stalling at low RPM's, especially when I have the motor tilted up while in shallow waters anchoring up at our local sand bar. Pumping the ball always results in the motor firing right back up. The high pressure fuel pump was replaced about 100-150 engine hours ago, and the low pressure pumps were replaced during the rebuild. I have since replaced the fuel lines from the tank to the fuel/water separator, the fuel/water separator assembly, and the fuel lines including the primer ball all of the way to the clear filter on the port side of the engine. I removed the anti-siphon valve on the top of the fuel tank and cleaned it...it seemed to be in working condition, only allowing flow one direction. I have removed and inspected the clear fuel filter and gasket, and it seems to be in good condition as well. I am not sure what to check next...any ideas? Any help will be greatly appreciated!!!!

[jb123]

to check if it is supply side issue, use an aux tank , hose and ball hooked to the motor filter
Brett ?

[jol1ymon]

Haven't tried aux tank yet....guess I will need to try this...and yep...it is Brett..good call John! If not a supply side issue...what do you think it is? My next guess is to replace the VST gasket. The VST is the only thing that I did not break apart during the rebuild (took it all off in one piece) so I have been reluctant to think that is the source of the problem.

[99yam40]

monitoring the fuel pressure/ vacuum would be my first thought to see if there is a fuel supply problem

[jb123]

if you have air in the motor filter it is from there> back
recheck the seating on the clear bowl and gasket
may want to remove check valve after that filter and install a fitting in case of future issues
could be tank vent issue,pinched or broken supply line
pickup tube clogged,airleak @ separator
the aux tank will help isolate the issue

some will also use clear tubing temporarily to 'see' where the air is coming from

[jol1ymon]

Finally have a resolution to this problem! After replacing everything from the fuel tank to the motor (tank pickup, anti-siphon valve, fuel line to the fuel filter, a new fuel filter and housing, fuel line to new primer ball, fuel line to motor mounted filter, new filter, cup and o-ring, check valve before low pressure pumps and cleaning and rebuilding the vst tank again with a new gasket) with no change whatsoever, I decided to replace the low pressure pumps again. One thing that I did not remember was that when I rebuilt the motor, I had replaced the low pressure pumps with aftermarket pumps, made by Mallory. It never even dawned on me that the pumps made by Mallory would be any different that the O.E.M. Yamaha pumps. In a final act of desperation, I replaced the new aftermarket pumps with the real thing, and presto...no more stalling engine! Apparently the Mallory pumps will not pump fuel at RPM's below around 1600 RPM or so....the engine would run fine at speed...but stall when running at low speeds. When I would pull the pumps off of the block and pressure test with the primer ball, they did not leak so I assumed they were fine. DO NOT BUY AFTERMARKET FUEL PUMPS FROM MALLORY!!! It is damn near criminal that Mallory would sell something that flat out does not work!

[99yam40]

you could have saved yourself a lot of time and money, along with aggravation by testing fuel pressures

[tonynorie]

I recently bought (haven't installed yet) the two low pressure fuel pumps from Boats.net. The faceplates read "Yamaha" so can I be assured they are original OEM replacements and not Mallory?

[Tucker]

That's another failure story for Mallory pumps. On the VST O-ring, I'm always a nervous wreck after cleaning the HP pump filter. Can't see for sure if that gasket is seated in the tank correctly, try to hold it in with grease. What are the symptoms of a leaking VSTgasket?

[jol1ymon]

To tonynorie: Yep...my aftermarket pumps were stamped "For Yamaha" not just "Yamaha" like the O.E.M. version.

[jb123]

Brett,do yourself a favor and buy the OEM pumps