help me capt. hawk!!!!

[bay idyll]

i'm sure your expertise extends to the yanmar 3gm30 that is in my boat! first off, the bottom job is done. it was 75 degrees and blowing 25kts all day so i took 3 days off to tear up the bay. i was the fastest thing out there with my smooth hull! really, those sort of days you live for- the rails buried all day long.my problem now is my engine. when the bottom and prop were dirty i could go maybe 3kts at 2k rpm. if i pushed over 2k the heat alarm would sound. now that the bottom and prop are clean i am at 4.5kts at 2k rpm, the heat alarm no longer sounds but if i go over 2k for 15 minutes the engine makes a revving sound and a puff of white smoke comes out of the exhaust.could this be bad fuel? the boat did sit for an undetermined period before i got it. do you have any clues for me before i have to pay a diesel guy $600.00 to go through the motor?thanks!

 

[CaptHawk]

Fuel Filter

BayIdyll;Sounds like dirty fuel FILTER........change it AND have the fuel "polished" if there is a fuel restorer in your area.He can run all the fuel in your tank thru a very complex fuel filtering system right at the dock [if he has a portable unit].It does take a few hours but makes the fuel as new.When a boat sits with diesel in its tank for a long period, algae builds up and as you bounce along in the waves this algae is washed from the walls of the tank and picked up by the filter.As the filter begins to clog it will cause a surging sound (RPM's) and will sooner or later shut down the engine.I would at the very lease add some Biobor-JF/...or BioGuard or other fuel additive[West Marine Store] to help clean the algae out.Also check for any air leaks in your system.I usually keep 2-3 filters onboard to change if need be.Hope this clears up your problemo!Cheers!CaptHawkROGUEWAVE