3gm30 on 355 smoke on up rpm +2200

[rgarand]

Hi all sailors,
I have looked thru previous threads to no avail...
Bought a h355 last year, engine had an complete tune up in aug. 2013 by a mec.
It starts fine, at 1800 rpm, engine runs very smooth and I get 5.5 K of speed.
But if I want to increase rpm, it starts to shake and smoke. Think it is grey smoke.

My question is, how come others have to go to 2600 rpm to get this speed, could it be a wrong sized blade ? I am afraid to get the throttle higher then 2200 so not to break anything, but if I ever get in emegency and need the extra power, don't know what will happen...

TIA
Robert

 

[RichH]

Grey smoke at high rpm when under load is a sign/symptom that the fuel injection TIMING is 'off' .... the engine is 'over-fueling' and that 'grey smoke' is principally unburnt fuel.

Black smoke usually means that the engine is lugging ... cant develop full rpm under load - usually due to too high a propeller pitch.

Could be a combo/mixture of 'both' situations.

If the injectors were found to have an acceptable spray pattern but the injection timing was not evaluated, consider to start with a re-assay of injection timing. Then, proceed to prop pitch. The more 'blackish' the exhaust (+ the accumulation of soot on the stern) points to 'over-propping'; Grey points to an injector pump timing situation.

 

[Benny17441]

It is a common occurrence to have tachometers provide incorrect readings. See if you can get your hands on a handheld laser test tachometer to verify the actual engine RPM and compare to the readings you are getting. There are many postings in the archives dealing with trouble shooting tachometers. Also run the engine in Neutral and see if you get the same RPM readings, the smoking and the shaking. Before staring to work on the engine make sure the propeller is not fouled by marine growth. That or a dirty hull may place an undue load on the engine causing it to overfuel. If the actual engine RPM are not close to where they should be check the exhaust mixing elbow for carbon build up.

 

[rgarand]

Hi Rich and Benny,
Thanks for taking time to answer me. I made some tests this week-end and saw that, the engine can run at 2800 rpm without any some or vibration (good ...), the problem really seem to be an overpiched blade, cos I ask friends with look alike hunters, and they need to be at 2600 rpm to get 5,5 K, I get 5,2 K at 1800 rpm.

So from what you say, it must be that the load is to high on engine when trying to accelerate (I see it like a car going at 20 mph on 4th gear, and you it the pedal...am i right?)
So if someone can tell me the size and pitch of their blade, I could verify this.

Regards,
Robert