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Posted: Sun Jul 26, 2015 7:36pm

Post Subject: Engine losing power

I have a problem. When I'm cruising along, I'm intermittently losing power, with revs dropping down towards tickover pace, then picking up again. At times it can go on for half an hour or more - losing power, then gaining revs. When the engine is in neutral, even when the engine appears to be struggling in gear, I can immediately rev it up to or beyond 200 revs, which makes me suspect that the issue isn't fuel related - I only ever lose power when in gear and travelling, and it seems to happen more at higher revs. I'm currently on a month long holiday on board, and if this issue continues, it's going to ruin my holiday, as I can't rely on engine to get me from A to B, so any advice would be most appreciated, thanks.


Posted: Mon Jul 27, 2015 8:46am

Post Subject: Engine losing power

First of all I assume that you mean 2000 RPM. Secondly I can not agree with your reasons for dismissing a fuel problem. The amount of fuel required relates to the power the engine is developing, not the revs. The power required to rev an engine in neutral is very little more than at tickover. An engine with a fouled prop running flat out at say 900 RPM will use more fuel than one driving the boat normally at 1500 or 2000 RPM. Having mentioned a fouled prop I assume that you have checked your prop is clear. I also assume that you have tried giving it a momentary rev in reverse in case fallen leaves or weed have packed into the prop disc. As long as you have adequate oil and oil pressure and there are no singes of overheating then it points to a fuel system problem but first of all check the gearbox oil is at the correct level and nice and clean. Make sure that your stern gland is not running hot. Once you have done that I would advise that you replace/clean all your fuel filters and water traps. Drain the old ones into a tub so you can inspect the fuel. Then take the old filters apart so you can inspect what they may have caught. If the fuel is discoloured, there is any signs of jelly like substances, or there are more than a few drops of water you have a fuel problem. If you have an older engine like a BMC, Perkins 4-10x, or older Lister then check the strainer and water trap that is under the fuel lift pump cap. Try blowing beak down the supply pipe into the tank in case it is blocked. You might have an air leak into the fuel system but as you do not mention difficult starting or the need to bleed the system this is less likely. The symptoms might indicate a faulty lift pump (especially if its a Vetus engine because they tend to have a little filter in the end of the pump that many do not know about) but check the filters first. Please report back about what you find in the filters or if you need more help.

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