Chicken or the egg

[Ken Juul]

I have thought for a couple seasons that my prop was over pitched.  I can only get about 70% of the max neutral RPMs when in gear.  The prop manufactures says he has sold several of the same size and pitch to other M25xp owners who do not have a low rpm problem.  I confirmed the prop's size and pitch. 

So am I over pitched or is the engine not producing enough power?  New injectors made no difference, fuel filters are clean.  I've run injector cleaner through the system.  Clean prop or dirty prop results are about the same. 

The prop manufacturer suggested: "Is the exhaust riser clear and the back flow valve working and not stuck part way open? This is a common ailment with the Universal engines. Is the Exhaust hose clear and not kinked somewhere?" 

No kinks in the exhaust hose, as far as the riser and hose being clear I get good water flow out the exhaust, I would assume that means it is clear.  Do we have a back flow valve?

I've thought about the fuel injector pump. But power does not seem to be declining. Suggestions?

[prh77]

Have you checked compression?

[Craig Illman]

I'm interested in this topic as well. My compression is 370/370/420. It's not great, but it's still above minimums. I have a 15x10.5 3-blade and max out under load at about 2600. In neutral, I get to 3200.

Craig

[Kyle Ewing]

What prop and pitch?  Do you mean other C34 owners with the M25XP?  Other than engine type, the boat including bottom condition and weight can be a factor.

When you say in gear, is that under way or at dock?  When I installed my Kiwi prop it turned lower RPMs than expected in gear at dock but was closer to what I expected under way.

[Ken Juul]

The prop in question is a Campbell Sailor, 14x8.  I get approx 50 more RPMs under way.  Yes the other boats were C34/36.

[Ron Hill]

Guys : Be very careful spouting off RPM numbers unless you know that these are actual engine rpm numbers.  The tachs on our boats are too susceptible and notorious for error.  Either check with a mechanical or a laser tach and get the real numbers of what the engine is actually doing!!

Ken - I had a similar problem and finally had the injection pump rebuilt and that solved my problem - no power in gear.   

[Kyle Ewing]

Here's some info from Kiwi's web site regarding similar symptoms.  They suggest a blocked exhaust riser or valve problems.  http://www.kiwiprops.co.nz/power_loss.html.