Diesel slows down RPM,s

[Terry in Naples]

I have an XP25 Universal diesel in my Catalilna 34. It runs and starts great but. when I first start motoring it runds at a brisk 27oo rpm and moves me along at about 6+ kts. After awhile (30 to 40 minutes) it starts slowing and will settle into a 2200 to 2300 rmp range and there is stays. It is then at about 5.5 kts. What could this be?
One thing I have noticed once was bubbles coming from some gas escaping from where the glo plugs insert into the block. I had washed the engine with degreaser and started it and saw bubbles slowly coming from the top cylinder where it is recessed and is screwed in. I tried to tighten these down but they appear tight. I ordered new metal seals but have yet to remove the plugs and install them. Could this be the problem? Is it possible this is from a clogging filter? I changed the RACOR and the filter on the secondary filter nearer the engine so ? if it could be that.
Any ideas appreciated?
Terry

 

[Maine Sail]

I have an XP25 Universal diesel in my Catalilna 34. It runs and starts great but. when I first start motoring it runds at a brisk 27oo rpm and moves me along at about 6+ kts. After awhile (30 to 40 minutes) it starts slowing and will settle into a 2200 to 2300 rmp range and there is stays. It is then at about 5.5 kts. What could this be?
One thing I have noticed once was bubbles coming from some gas escaping from where the glo plugs insert into the block. I had washed the engine with degreaser and started it and saw bubbles slowly coming from the top cylinder where it is recessed and is screwed in. I tried to tighten these down but they appear tight. I ordered new metal seals but have yet to remove the plugs and install them. Could this be the problem? Is it possible this is from a clogging filter? I changed the RACOR and the filter on the secondary filter nearer the engine so ? if it could be that.
Any ideas appreciated?
Terry

Terry,

Can you get it back to 2700 RPM with the throttle?

 

[Dan Johnson]

Terry...

if the answer to Maine Sail's question is NO, then it is possibly a fuel issue. It sounds like a filter is clogging. A compression issue (as mentioned by the "bubbles" would probably be present from the start. 30 minutes of running will cause heat expansion, possibly sealing the glow plug seating.

Change all your filters and give it a sea trial.

Last thought: does your fuel pick-up in the tank have a strainer on the end of it? If it does, this could be clogging as fuel is drawn in over time, then the gunk would settle off it while the boat sat without use for a period of time. Pull the pick-up and remove the screen.

 

[Bill Roosa]

Any smoke?

probably a fuel starvation problem. Could also be a clogged exhaust elbo or fitting. My Atomic 4 used iron pipe in places and it got pretty bad after a few years. The exhaust would flow fine at lower RPMs but after a time at 80%+ throttle it would build up back pressure enough to slow the engine.
To check get her to act up then slow to idle for a minute and try to get her to go back up to 2700. If she repeats the loss of RPMs immediatly then start thinking fuel problem if she repeats the gradual RPM loss then I'd bet it is the exhaust.

 

[Ted]

Diesel slows down

It could be the throttle is slipping and slowly reducing rpm's. Some systems use a clamp on the casing of the throttle cable to increase friction between the casing and the cable within it. If you have those clamps, slightly tighten up the bolt on the clamp to increase friction.