M-25xp loosing power.

[pjcomeau]

I've posted this problem before but still not solved.

Consistantly whenever I have a few hours of motoring ahead of me I get the following:

1) If I leave berth fairly soon after starting engine I can throttle to the max rpm of about 2800 (was more like 2500/2600 prior to new injectors put in 2 weeks ago) and getting to around 6.6/6.7 knots. From What I've been reading here that's more like cruising numbers rather then full throttle (I can actually throttle back a little without change/loss of power).
2) after about 10 minutes I feel/hear the engine "slowing" down (throttle same place at full) and the tach shows about 200/300 loss of RPM and speed goes down accordingly.
3) over the next 15-30 minutes (not fully timed) I feel/hear the engine "slowing" down in spurts of around 200 rpm until it settles around 2000/2100 rpm and around 5 knots or less.
4) It will then stay at this rpm for as long as I run (never really mototored more then 3 hours continously). At this RPM I'm running pretty smooth but I'm at least a knot and a half slower and when there is no wind (or on the nose) and when with a group of boats I'm usually 20 to 30 minutes behind on trips of 2.5 to 3 hours).
5) I also notice that when warm, that when I completely throttle back it vibrates/run alot harder then when cold (still runs pretty rough too). The RPM are a little lower when warm too, a little below 1000.

6) Note that when not in gear I can throttle up to above 3200.

Last summer I purchased/installed from a fellow C34 owner his original 3 blade prop (15" x 9 pitch) so should not be over propped.
As mentioned I just replaced injectors (new from Kubota dealer) which helped with getting more speed during first 10/15 minutes).
At same time I had the Racor filter replaced. Last summer had the Racor and primary fual filter replaced.

I can only seem to get a mechanic to do specific tasks (e.g. replace injectors), but not get one to actually try to determine problem/troubleshoot (they are busy and prioritize total failure).

There is some smoking so I can probably use some other work (mechanic suggested starting with valves). I'm totaly ignorant when it comes to engines.

The consistency in the symtoms in the amount of time or maybe temperature (definitely not at max temp 0f 160 when it starts to slow down, more like around 120) made me think that someone else might have encountered something similar.

I've read through various discussions (here and on other sites where M-25xp is used) and a couple of threads mentioned things that should never need work or be done, but in their case was the fix. One mentions injection pump and a couple mention breaking seal/cover and adjusting governor. How does one determine bad injection pump?

It runs pretty smooth for those first few minutes and the speed is pretty good, so I'd be so happy if I could keep that speed for the whole trip :)


Thanks,

Pierre

[Stu Jackson]

Pierre, was it this thread?  http://c34.org/bbs/index.php/topic,7019.0

Have you checked the throttle cable?  Have you checked the fuel lines for air leaks?

[Les Luzar]

I would first check all clamps on the fuel lines to make sure that they are tight. Also, as Stu said, inspect all fuel lines for leaks/air intrusion. Check fuel pump screen, and the tightness of the secondary fuel filter (mounted on engine) to make sure it is tight. Then, start your engine and open the knurly knob to bleed your fuel system. Tighten the knurly know and go for a motor and see what happens.  Perhaps another idea would be to take your boat out and when these symptoms occur, open the knurly knob to bleed out any air and see if the engine performance returns to normal. That may indicate air in the system. You may again change your fuel filters too just in case. Is your fuel tank full?

I once crewed on a boat that had a slow air intrusion in the fuel system. The boat would motor fine for a while and then lose power. We would bleed the system under way, and this would correct the problem for a while. Then air intrusion would occur again. Hope this helps...

[pjcomeau]

Thanks, I will take a look at the possibility of air. I was not sure how to tell if air was getting in, did not think of bleeding while it occurs.

As for cable, I will double check (I remember trying at the engine where cable is and I was getting same reaction - i.e. not able to throttle up and could pull lever back slowly for a bit without loss of power indicating that the possible additional fuel was not getting used.)

-PC

[mark_53]

I had a similar problem last year.  Mine was very straight forward issue.  The throttle friction screw under the compass was a little loose.  I'd motor for a while and rpm's would back down.  Easy to determine if that's your problem...just push up on the trottle and see if rpm's go up.

[tommyt]

This certainly sounds like you are getting air into the system and the ideas above make sense. Could be a throttle problem, but it sounds like you are trying to run it at the stops...so questionable.

The prop should not have an effect, but was it off a C34 with the M-25?

For those of you with the M-25 what is your normal crusing RPM and speed in flat conditions. On my previous boat with the M35 it cruised comfortably at 2100-2200 RPM at 6.1 average. I find it hard to believe that an average cruising speed is in the high 6's. This is more for my information than an answer to the problem.I guess the same question could be asked of those with the 35.

[lazybone]

Does the engine smoke more as the rpm's drop and if so what color is the smoke?

[Ken Juul]

I would check all the fittings and blank plugs on your racor.  Make sure the blanks are tight and that the oring on the pump cover isn't split.  Your symptoms definitely sound like your sucking air. 

Seperate thoughts after you get the air sorted out, remember the engine likes to run at about 80% for cruising.  80% of 3200 is 25-2600 for a cruise rpm.  You should also check the accuracy of your tach, your mechanic should have an infared tach he can use to verify/adjust to get the correct reading.  Or lots of threads/wikis about it if you want to try yourself.

[KWKloeber]

1) If I leave berth fairly soon after starting engine I can throttle to the max rpm of about 2800 (was more like 2500/2600 prior to new injectors put in 2 weeks ago) and getting to around 6.6/6.7 knots. From What I've been reading here that's more like cruising numbers rather then full throttle (I can actually throttle back a little without change/loss of power).

As mentioned I just replaced injectors (new from Kubota dealer) which helped with getting more speed during first 10/15 minutes).
At same time I had the Racor filter replaced. Last summer had the Racor and primary fual filter replaced.

I can only seem to get a mechanic to do specific tasks (e.g. replace injectors), but not get one to actually try to determine problem/troubleshoot (they are busy and prioritize total failure).

There is some smoking so I can probably use some other work (mechanic suggested starting with valves). I'm totaly ignorant when it comes to engines.

The consistency in the symtoms in the amount of time or maybe temperature (definitely not at max temp 0f 160 when it starts to slow down, more like around 120) made me think that someone else might have encountered something similar.

Pierre,

Sounds elementary, but double check to make sure you don't have a closed or partially closed fuel shut off.  Sometimes mechanics have it in their scope of services to only "close" the valve, not "open" it.

Also do you have a screen on your fuel pick up tube in the tank?  If so remove it.

Ken K

[Jim Hardesty]

Pierre,
You have already been given quite a list of good trouble shooting ideas.  I'll add another.  Had a similar problem with my M35.  It was a weak fuel pump.  The problem would go away, or improve, with fresh fuel filters and or a full tank of fuel.  Took me a couple of seasons to get to the root of the problem.  A weak fuel pump.  So, if your tank is half full try filling up and see if that helps.
And check to see that the vent is clear.  Or when you are having the problem, crack the fuel fill, and see if that helps.
Jim

[Ron Hill]

Pierre : I wouldn't worry too much about the fuel pump for an M25 & M25XP engines. The circular NAPA pump that you have will allow the fuel to gravity feed even if the pump is inoperable (tank at least 1/2 full).  
The engine will continue to run beautifully with out the lift pump!!

If your power loss continues to persist, you might want to read my Mainsheet article on "Re Building the  Injection Pump".

A few thoughts

[Dave DeAre]

I had the same problem with the M35 on my 2002, eventually it would not start. A replacement fuel lift pump solved the problem and it has not returned. The tank was full and there was no fuel in the line at the pump. My engine would not run with a faulty fuel lift pump.

[RV61]

An additional item to inspect is be sure your fuel tank air vent  is clear. Had a friend who would have intermittent power issues you describe and his mechanic found fuel air vent was clogged up with spiders. 

[Ralph Masters]

On a simple natural aspirated, non-electronic controlled diesel engine such as we have on our boats, if you have a power loss it's one of two things, 1) loss of fuel, 2) loss of air.  If you think you have all the fuel checked out, check your air filter.  If you have a good air filter, check your fuel system again.

Ralph

[Paulus]

I have  the same loss of power but the RPM have stayed the same.  Returned to Muskegon at end of summer it was determined that the thrust bearing(clutch) was slipping.
Paul