Engine misbehaviour

[chas]

Today, my normally 100% reliable Thorneycroft T90 started doing odd things. It would suddenly speed up to about 2500 rpm, despite running smoothly for up to 20 mins at 1500 rpm. When put to idle, it would slow down, but only to about 1400rpm. When put ahead again, it would perform normally at 1500 rpm (except that the idle speed remained at about 1200 - 1400 rpm) - for another 30 mins or so, when it would repeat its sudden speed up. I would be grateful for any ideas about what is going wrong and any palliatives!

Thanks in anticipation

 

[Guest]

Hi, Chas, Your`e not the only one having problems with a misbehaving engine! In your case, have you checked the govenor? This controls the tick-over and stops the engine from racing away. It could be that the govenor is sticking, hence the increase in revs for no apparent reason. A question for you,have you any knowledge about plastic fuel tanks?
Cheers Davey

 

[vyv_cox]

Classic symptoms of an air leak. Check pipework upstream of the lift pump and the diaphragm in the pump. Leaks downstream of the lift pump are less likely as fuel will tend to come out, rather than air go in. Worth checking though.

 

[brianrunyard]

Have you disturbed anything in the fuel system recently?
Like changed the filter. Sounds like an air leak upstream of the lift pump.

 

[vyv_cox]

Plastic fuel tanks

Definitely the way to go. Most production boats seem to have them now. I fitted a Vetus 10 gallon to my previous boat, after suffering numerous engine cutouts due to flakes of rust coming through and blocking pipework upstream of the filter. Never a moment's problem after that.

 

[chas]

Thanks to all. Today I found a perished 'O' ring in the fuel distribution pump. I hope that was the problem!

For Davey - I am sorry but I have not had any experince of plastic tanks - mine is a good old fashioned 50 gal steel one. Seems to be alright.

 

[Jcorstorphine]

Sorry to put a damper on your discovery of leaking "O" ring but I had a similar problem on my BMC nearly 20 years ago and it turned out to be the governor sticking. Only solution was a strip down by old Joe Lucas. (CAV)

regards

John C.

 

[chas]

You are absolutely right. I thought that i had cracked it but the symptoms reapppeared after a bit. The idling speed is better though

Thank for your help. Mr lucas can hve my givernor when the boat is slipped.