Erratic engine power - cause?

[YachtAllegro]

Hi

I suspect I may know the answer to this one, but anyone got any other ideas / experiences to share?

I changed the primary fuel filter on Allegro last week (on a Yanmar 10GM) and when using the engine this weekend found the power was erratic - started ok, didn't seem to rev up very much when I increased throttle, then later did for a bit, then the revs dropped back again on their own... It didn't actually stop, and I was only using it for 10 minutes after which I had to head home in a hurry, so didn't stop to investigate at the time.

So what do you think is the most likely cause of that? I'm guessing I've not tightened something completely and there's a little bit of air getting in - would that do that? Or is there something else I should be thinking of when I head down to try and sort it out?

Cheers
Patrick

 

[Tranona]

Getting the filter bowl to seal is a well known problem and results in air getting in, causing the problems you have.

 

[lenseman]

Almost certainly sucking in air where you changed the fuel filter.

 

[dt4134]

If you have a glass bowl don't just tighten it a bit more. They do shatter, as I found out when I thought I had an air leak.

Take it apart and try again to get the seal seated correctly.

 

[Tranona]

Not a glass bowl. Metal and is secured with a locking ring. Difficult to get tight owing to the location and the sealing ring can distort as you try to tighten it.

 

[YachtAllegro]

Not a glass bowl. Metal and is secured with a locking ring. Difficult to get tight owing to the location and the sealing ring can distort as you try to tighten it.

These are helpful replies, thanks. Just to clarify, though, while my primary filter does indeed take a metal cartridge, it then secures with a bolt. A hard to get at filter secured with a locking ring sounds like what I'm calling the secondary filter. Now I changed this at the same time, but assumed that this wouldn't be the problem as, being beyond the fuel lift pump, it is under positive pressure, so failure to seal should produce a leak of fuel out, not of air in. Is that right, or could these symptoms be equally due to a failure to seal the secondary filter properly (which, I agree, is a pig to tighten round the back of the engine...)?

Cheers
Patrick

 

[srp]

I cured my secondary (engine) fuel filter problem by fitting a fatter O ring. The original is very skinny, something like 1 mm, so I put a bought a few 1.5 and 2 mm ones. You can get them from many on-line bearing suppliers. Mine leaked air in from day one. Have often thought the ultimate answer would be to bypass it completely and fit something else in a more sensible location.

 

[Spyro]

I cured my secondary (engine) fuel filter problem by fitting a fatter O ring. The original is very skinny, something like 1 mm, so I put a bought a few 1.5 and 2 mm ones. You can get thoem from many on-line bearing suppliers. Mine leaked air in from day one. Have often thought the ultimate answer would be to bypass it completely anDtion.

Do you know what size the o ring is? Never had any problems with the engine but I have slight weep from mine and I'd like to get a new one before removing the old.

 

[srp]

I should know definitely, but I bought a couple of different sizes and can never remember which is which. However, I've just had a look in the spares box and one of the packets also has a spare impeller in it. That pack is marked 45 x 2 mm, so I'm fairly sure they were the ones I used at the last engine service.
I got them from Polymax, but I think SimplyBearings also do O rings, try http://simplybearings.co.uk/shop/Seals-O+Ring+Seals-NITRILE+O-Rings/c19_4501_4705/index.html

 

[mickywillis]

Just in case you haven't seen this, have a look at the problems I experienced with a 1GM10!!!
Took almost a year to resolve!!

http://www.ybw.com/forums/showthread.php?t=312212

 

[Spyro]

I should know definitely, but I bought a couple of different sizes and can never remember which is which. However, I've just had a look in the spares box and one of the packets also has a spare impeller in it. That pack is marked 45 x 2 mm, so I'm fairly sure they were the ones I used at the last engine service.
I got them from Polymax, but I think SimplyBearings also do O rings, try http://simplybearings.co.uk/shop/Seals-O+Ring+Seals-NITRILE+O-Rings/c19_4501_4705/index.html

Thanks for that, I've bought before from Simply Bearing and found them good. I take it that would be 45mm internal diameter?

 

[srp]

Thanks for that, I've bought before from Simply Bearing and found them good. I take it that would be 45mm internal diameter?

Yes, or 49mm od if you prefer. Fairly sure that's the right size, but you could just measure the diameter of the metal bowl to be certain.

 

[YachtAllegro]

Just in case you haven't seen this, have a look at the problems I experienced with a 1GM10!!!
Took almost a year to resolve!!

http://www.ybw.com/forums/showthread.php?t=312212

That's very interesting - thanks for the link. Chance in a million if that's exactly what's happened, but I do remember when I tightened the secondary filter thinking it wasn't going round as far as it usually did, so I suspect that is where the problem's coming from. I'll definitely have a careful feel under the top of the housing to check all is clear before I refit it this time.

Cheers
Patrick

 

[Modulation]

Agree with all of above.
If the solutions offered don't do the trick, you could try changing your airfilter. I went through exactly the same problem a couple of year's ago and it turned out NOT to be the seating of the fuel filter bowl.
In desperation we methodically went through everything in Yanmar's trouble shooting guide. Changing the air filter was the one that did the trick. We were so amazed that we put the old filter back in just to see if the problem recurred - it did!!!! It looked fine but must have been clogged.

 

[KellysEye]

Sounds like a diesel leak letting air in. I've mentioned this before but put talcum powder around each joint and the filter(s) top and the top of bowl where the O-ring is. Diesel will go through a microscopic hole so you will find the leak. A forumite has used that and found the leak.

 

[nigelmercier]

Sounds like a diesel leak letting air in. I've mentioned this before but put talcum powder around each joint and the filter(s) top and the top of bowl where the O-ring is. Diesel will go through a microscopic hole so you will find the leak. A forumite has used that and found the leak.

Can you explain how this works?

 

[lenseman]

Can you explain how this works?

Yea! You start the engine and it sucks in the talcum powder. When the exhaust fumes off the stern smell like a freshly washed babies bum, you have found where the air is getting sucked in!