was cavitation but now just doesn't have power

[Sculldog1]

Hi All, I have recently gone through a valve job, new manifold and exhaust rebuild! I got the engine back running quite well and then went to test her out. The trouble is that after sitting at the mooring for about 5 weeks during the engine work the prop had grown a lot of barnacles and the result was cavitation at anything over around 1200 rpm. After diving and scraping the prop, shaft and everything else the cavitation has stopped but the engine will not make power beyond about 1400rpm. It will go up to 2500 or beyond in both neutral and reverse. Any thoughts what to check? Might it just be in need of carb adjustment after resetting the valve gaps and having a new manifold that is free of carbon and therefore out of tune so to speak?

[Dave Neptune]

What is the diameter and pitch of the prop? And what RPM's were you getting before?

Dave Neptune

[Sculldog1]

Hi Dave, I am not sure of the size and pitch exactly but before the engine work there was no trouble at all with getting the boat to do hull speed at about 1800 rpm so I am doubtful that the prop size would be wrong. I am going sailing tomorrow and plan on checking whether the stuffing box may be too tight and also try disconnecting the shift cable and operating by hand to eliminate possibility of less than full engagement there. Engine idles great and revs up great in neutral and reverse so it doesn't seem to be fuel related. Haul out at the end of the month also so will have time for more extensive investigation over winter but also hope to find out as much as possible when I can put a load on the engine to troubleshoot this issue. What all would be additional things to check? If anyone has thoughts I be much obliged. Mike

[Dave Neptune]

A dirty prop and a dirty bottom can really slow things down. I would not be to concerned until you test after the bottom and prop are really clean.

As far as "carb adjustment" is concerned all you can adjust is the idle and float setting, neither will make much difference in power. If it is indeed a loss of power did you possibly bump the distributor or move the plug wires?

It does not take much to slow an over propped engine down so find out what you can about the prop.

For the stuffing box to be to tight to slow the engine that much it would be very hot and melt the wax out of the flax.

Dave Neptune

[Sculldog1]

Dave, thanks as always for your help. It seems that the prop cleaning has actually worked better than I immediately reported. On two subsequent outings I was able to get the power back up to where it was before the troubles. +/- 6knots at approximately 1800 to 2000 rpms. The outing I reported immediately after prop cleaning also felt significant vibrations which after running the following times has abated and things were, dare I say it, aok! I did use the engine sparingly to get on and off mooring with the fouled prop totalling about 4 or 5 hours till my diver friend came to my rescue. Could running with fouled prop have caused an imbalance that has now abated? Happy to have things running well again but a strange episode for sure. Thanks again, Mike

[Dave Neptune]

Absolutely, barnacles and such don't know to grow "evenly dispersed".

Dave Neptune

[joe_db]

Could running with fouled prop have caused an imbalance that has now abated?

Yes very much so!