Diesel - All Seems Fine, But ...

[rpwillia]

So in commissioning prep this year I replaced my spin on filter and my racor. To make it even crazier I had never replaced the racor in 14 years of owning the boat, and it had been a couple years with the spin on filter and I have never had a problem with fuel on this boat. So now with full throttle I am only hitting 2500-2600 rpm whereas before it was 2950-3000. What should I be checking? Did I mention the engine is starting up just fine and running smoother than ever and is an M25XPB?

 

[kappykaplan]

What does the exhaust look like? Water flow overboard? Any chance you have a small air leak?

 

[capta]

I'm guessing you didn't get the Racor or spin on to seal properly and you are getting air in the line. However, it is also possible that there was so much dirt in the Racor that a tiny bit got through the system and has fouled your fuel distribution pump. I had that happen once, with similar symptoms. This is not an owner serviceable item. You'll need to get it to an injector/pump service shop.

 

[Stu Jackson]

Diesel starts and runs? Check.

RPM different? RPM comes from the alternator on that engine. Belt drives alternator.

Where to check? Hmmm...

Good luck.

 

[Ron20324]

Mabye buildup on the hull and/or the prop?

 

[FastOlson]

Mabye buildup on the hull and/or the prop?

Yup. I would also start with some basics. Are your tach and speedometer providing correct info? Hull clean (as normal)? Prop and shaft not fouled? When running, is there any air or dirt visible in the bowl of the filter?
Does the throttle cable actuate the lever on the fuel feed on the engine same as usual? (Observe the movement at the engine while someone moves the lever forward and back).
Let us know what you find.
Good Luck!

 

[odaydokay]

You did pull the sieve out of the fuel pump and clean it out, right?

 

[rpwillia]

Will check the bowl on the racor, but it looked clear last time I looked at it. Do not think it is an air leak as the engine is purring like a kitten, just not roaring at WOT. Do not believe there is anything in the fuel pump like a filter but will check again. If a fuel injector were clogged it would be running rough, but again it is purring.

 

[Hello Below]

Have you actioned the suggestion alluded to in Post #4 above? Also verify that your analog tach is reading correctly using a digital tach.

 

[SycloneDriver]

Is the fuel stop lever at the pump returning to the normal run position? If it's not the injected fuel quantity may be limited, limiting the power output.

 

[Ken13559]

I had my Racor head foul up such that I could not run high rpm under load but can only do lower rpm. Have been replacing filters but not realising the Racor head could foul.

Ken Y

 

[jnorten]

Be sure to properly bleed the fuel system. I had almost an identical experience with reduced RPM this spring after a Racor filter change. It turned out I had use the the two bleed valves in reverse order. Bleeding is not hard, however it seems a little voodoo until you actually do it yourself. My Universal (different model than you) had the bleeding instructions in the manual.

 

[rpwillia]

Fixed it. Not quite a 1d10t thing, but it was pretty obvious. I made a checklist of all the comments and started working them through. It turned out it was the throttle lever connection on the engine. I moved it back and re-clamped it and then adjusted the set screw for upper and lower throttle setting and it is great now. The checklist is below and it was super helpful to go through it - thanks all!

• Exhaust
  • What does the exhaust look like? Water flow overboard? Any chance a small air leak?
• Racor
  • Didn't get the Racor or spin on to seal properly and you are getting air in the line.
  • Any air or dirt visible in the bowl of the filter?
  • Racor head foul up such that could not run high rpm under load but can only do lower rpm. Have been replacing filters but not realizing Racor head could foul.
• Fuel Pump
  • Possible dirt in Racor got through system and fouled fuel distribution pump. Not owner serviceable item. You'll need to get it to an injector/pump service shop.
  • You did pull the sleeve out of the fuel pump and clean it out, right?
• Alternator
  • Diesel starts and runs? Check. RPM different? RPM comes from the alternator on that engine. Belt drives alternator.
  • Are tach and speedometer providing correct info?
• Hull/Prop
  • Maybe buildup on the hull and/or the prop?
• Throttle and Fuel Stop Lever
  • Does throttle cable actuate lever on fuel feed on engine same as usual? (Observe movement at engine while someone moves the lever forward and back).
• Is fuel stop lever at pump returning to normal run position? If it's not injected fuel quantity may be limited, limiting the power output.