Engine prob

[PabloPicasso]

3cylinder Volvo 30hp engine. All works well except occasionally revs drop to below tickover, for several seconds, and usually recover Clean fuel filters. No obvious fuel problem. Treated fuel. Any clues as to why the revs drop off like that?

 

[knuterikt]

Some type of intermittent blockage in fuel tank by an object that moves around in the tank.

 

[lpdsn]

Or perhaps gunk in the fuel pipes.

I'm probably getting boring recommending a vacuum gauge before the lift pump, but they are really handy when you have one.

 

[fisherman]

Air, due to occasional part blockage somewhere around the engine filters. I had this for ages, turned out to be a scar on the bleed screw seat on the last filter. When the final filter had sufficient gunk in it the scar would let air in. One such problem was found to be a dead bluebottle in the lift pipe from the tank, it would get to the 90deg bend at the top and stick, then when the engine was stopped it would drop down again.

 

[PabloPicasso]

Thanks lads.

 

[pmagowan]

Fuel supply issue. Start taking bits apart and cleaning them. You can get a kind of gunk forms in the engine if the fuel has been sitting for a long time, not just the tank. Might be useful to fit a vacuum gauge for the filters also. Two engines I have had did the same thing with a bit of gunk causing the problem.

 

[daverebbettes]

Sounds similar to an issue I faced. Engineers struggled to find the issue and racked up a bill of £7K+. Turned out it was a split fuel return line that could have been fixed for sub £50. Needless to say I negotiated the price down.

 

[Blue Drifter]

My experience was the same as Fisherman, air, in my case my Cav fuel filter had developed a slight air leak which resulted in an occasional drop in engine revs, almost stalling, before recovering to normal. Redid all the Cav seals carefully and problem solved.

 

[fisherman]

My experience was the same as Fisherman, air, in my case my Cav fuel filter had developed a slight air leak which resulted in an occasional drop in engine revs, almost stalling, before recovering to normal. Redid all the Cav seals carefully and problem solved.

When this happens you should shut the throttle, it will probably settle, but if you open up it drags more air in and stops.