Why is my en­gine on a bit of a go-slow?

Canal Boat - - Back Cabin: Experts -

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

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