Why is my engine on a bit of a go-slow?
Q My engine has been sounding less than smooth for a couple of months. It felt under powered at times and shook a bit as if something was loose. It first happened the day I filled up with diesel at a new place, so I wondered if there was water in the diesel tank, but I drained the plug on the fuel filter and it had only diesel in it. A couple of people advised topping up the diesel regularly and the water would work its way out eventually.
It seemed to be much better, but recently using high revs on a river, the engine slowed right down and conked out altogether. I checked the weed hatch (nothing) and tank (about 60% full). It started up again, but although if I kept the revs moderate it would keep going, it tended to die when I put it under more load. It still feels under powered,even when not spluttering, so I fear it’s serious. STEVE HALL, via email A TONY REPLIES: This is the classic symptom of a blocked breather on the fuel tank. Try running with the fuel filler off (but protect the hole from rain). If that makes no difference, change the filters (which might involve bleeding the engine). Check the old filters to see what they have caught, for early warning of bug/water problems. Note: a good installation will have more than just the main filter on the engine. There should be at least one more filter-like thing between the tank and engine.
BMC, Lister or Perkins engines are likely to have a gauze strainer under the domed cap on the fuel liftpump. Some electric lift pumps, typically found on Mitsubishi-based engines, have a small filter under the fuel pump end cap. These need checking as well.
If there is no improvement, look for potential air leaks into the fuel lines or a blockage at the fuel tank outlet. Try rigging a small tank feed the liftpump directly, to rule out the tank, pipes and filters.
Check the liftpump filter