Years of troubleshooting fuel problem

[Jim Hardesty]

I am finally done with a 4 year epic trouble shooting experience.  Here is the saga.

My first season with Shamrock changed all the filters (used 2 micron on the Racor primary) and sampled the fuel.  Looked good.

A season and a half later about 75 engine hours the engine would not reach full RPM.  Changed Racor, no change, changed OEM engine filter, problem went away.  Didn't make sense that the secondary filter should plug first.  But no problem.

Another season and about 75 engine hours the engine would not reach full RPM.  First changed the OEM engine filter, problem went away.  Make no sense to me.  The only thing that I could think of was fuel pump was weak.  So I got a spare pump.  But no current problem.  So I didn't change the pump then.

Didn't use the boat last season, so it was 2+ seasons and about 85 engine hours, the engine would not reach full RPM.  Left the filters and changed the fuel pump, problem went away.  A weak fuel pump was the root problem.

So, it took a while, but I learned that my boat will run with a bad fuel pump.  Just not well.  Very clean fuel filters will mask a weak fuel pump.

Now I'll go back to scheduled filter changes.  And get a new spare fuel pump to keep on board. 

Jim

[Dave DeAre]

I had a similar problem with my 2002 MK2. Engine would start and run good but sometimes slow down during extended motoring, from 2,600-2,800 to 2,000 rpm. Would continue to run @ 2,000; next time we used the boat all was fine. I too changed all filters several times.

Long story short, finally the engine would not start and a new fuel lift pump immediately resolved the problem for me. Believe this is a MK-2 issue, if you have a similar problem on a MK-2 suspect the fuel lift pump.

[Ron Hill]

Jim : When you say that you changed the OEM filter, I assume that you know there are 2 OEM filters!!

One is the screw on canister type and the other is an inline by the fuel pump.  I don't recall, but the inline may be screwed into the fuel pump. 

I've had great results with the Starbright enzyme additive vs. the Biobor.  A few thoughts

[Jim Hardesty]

My boat never had the small filter just before the lift pump.  The plumbing goes Racor filter--lift pump--spin on(OEM)--then high pressure metering pump.  When I did my first filter changes I looked and looked for that filter.  I don't see that it has any purpose, the Racor filters the fuel before and is a smaller micron filter.

[Ron Hill]

Jim : The newer M35BC engines now have a inline filter just before the fuel pump beside the screw on canister on the starboard side. 
Guess as a first owner you certainly know what came with the boat. 

Sorry for the bump steer as I didn't know that the older engines didn't have that feature.