Strange 225hp

[NiVani 1]

Our 225hp with 1000hr on it is acting strange.

First of all, we run these engines hard, and in shallow water, on a few trips whilst ramping on the beach with swells caused engines to take in a lot of sand.
Once this was cleaned out and water ran strong out of tell tail engines ran fine.
after 4 days of sitting, we started up to do a standard check before doing a run.

Whilst at idle and after a few minutes the engine heat alarm come on and RPM increases and a large amount of exhaust bubbles out of the leg/prop and after a minute or two it drops RPM and goes back to smooth operation???

We did test run and all was fine during the run. after 6hr trip still all was fine, on the return leg and 1.5hr later during the trip, the engine Rpm would very for a minute and vibrate them goes back to smooth operation.

Any thoughts?

cheers

[artdf175]

do you have the engine interface cable installed so your instrument guage reads out engine temp?
if the engine is running a bit on the high side.. it may be the cause of some uneven firing.. also check the spark plugs for damage from overheating?

my only other thought.. have you taken out and cleaned the thermostat?
to me that is a something to do every once in a while.. and especially if have been in the situation you describe..
good luck.
art..