Low RPM in gear

[Dave DeAre]

I had this same problem with my M-35, did most of the same fixes. Finally my electric fuel lift pump failed, engine would not start. I replaced it and engine runs at 2,800 all day. Symptoms were exactly the same, start well, run good for some time, then 2,200 max.

Others on this forum will say the 34 will run fine without the lift pump, but mine would not. When the pump was disconnected there was no fuel in the line from the tank. My boat is a 2002 MK 2, your configuration may differ.

[RV61]

Ran into this issue again this past weekend on Interlude . Was out motoring and RPM started to drop and finally engine died. Was able to restart after turning on bleed screw knob and leaving it open. Could motor but not get boat to go over 5.7 or full power with throttle all the way forward. So limped back to the dock.

I just change fuel fiter a few hours of run time ago thus thought OK I beeter finally clean the tank.   
I first wanted to look at the fuel by draing a small cup from the bowl of the seprator filter. I had ignition on so electric fuel pump would work. Noticed AIR BUBBLES. I remembered Ron's comment lack of fuel or Air is usually the issue when loss of power. Thanks RON!!!

Started to inspect fuel hose a found a hairline crack at the clamp on fuel intake to seperator. Repaired that and boat then ran fine for three hours and was able to achieve cruising and full throttle speeds. Still planning to pull and clean tank and put leather between clamp and hose as a maintence item.

Suggestion:You may want to inspect fuel hoses and conections and look at sperator filter while fuel pump running and check for bubbbles. Not sure if your electric fuel pump clicks but if it does is it clicking more than once every few seconds while engine is off and ignition on and bleed screw turned off ? If so that is a sign of AIR in the lines some where.
Let us know what you end finding your issue was.
Thanks
Rick

[pjcomeau]

Also, My RACOR filter is R20S (2 micron). Could this be a problem or only means will get dirtier quicker?

[Jim Hardesty]

It's not talked about much here, so I hesitate to bring up adjusting valves.  I did mine the first season I had the boat, they were off just a little,  did improve both idle smothness and open throttle power.  It's not hard to do.  Just be patient and don't have many beers till after.
Jim

[Ron Hill]

Pierre : You still haven't confirmed that the screen on the fuel pickup tube has been removed!!!

[pjcomeau]

I tought I did. There is no screen on the fuel pickup tube.

[Ron Hill]

Pierre : When was the last time you cleaned the fuel tank?  and when was the last time you changed your Racor and engine filters?  Is your electric fuel pump working? 

It sounds like the loss of rpm is fuel related (partial starvation) especially if it runs well when first started and then looses rpm.  A thought