Yanmar 2GM20 running sluggish

Hornet_UK

Hornet_UK

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My engine seems to have started to run very sluggishly since I changed the oil and oil filter. The engine used to start fine witii7hout any extra throttle but now I have to give it lots welly to get it going. Once the engine has started it seems to be ok but has less power. Only thing I can think.of was the new oil filter was smaller than the old one. Could it be that I got the wrong oil filter and that has caused the problem?
 
Have you changed the fuel filter, and more important are you sure you have not got some sort of fuel bug that is turnuing the fuel to more like jelly? I had a 2GM20 and it was incredibley reliable. Have you changed the air filter?
 
The oil filter size on many Yanmars has been reduced, maybe to harmonise between the GM and YM? the correct filter is smaller than the old one.

However, there is no way that oil filter size could affect engine performance, assuming you put the correct amount of oil in it!

You need to be looking for something else, as suggested air and fuel filters are a possibility, although air filters don't clog much on a boat. You might also consider blocking of the exhaust manifold by carbon.
 
Hornet_UK said:
My engine seems to have started to run very sluggishly since I changed the oil and oil filter. The engine used to start fine witii7hout any extra throttle but now I have to give it lots welly to get it going. Once the engine has started it seems to be ok but has less power. Only thing I can think.of was the new oil filter was smaller than the old one. Could it be that I got the wrong oil filter and that has caused the problem?
Click to expand...

The oil filter can't have a bearing on how the engine runs. It's more likely that your symptoms are caused by either a fuel blockage or air in the fuel. Change the fuel filter, flush through, bleed the air out and try again.
 
Yesterday I changed the Air Filter and the Fuel Filter. The Air Filter was non existent, all that was left was the metal cone and a load of oil black **** in the air intake. I cleaned all the oily stuff from the air intake as and replaced the filter. Started the engine and it still struggled to start, after chugging slowly with the throttle almost fully open for a minute or so she was able to run on tick over. After a few more minutes she seemed to behave as normal, went to max revs. I turned the engine off and left her for about half an hour and started her up again same as before. Is there anything else I should look at or should I just give her a good run at high revs to clear out any much etc?:confused:
 
Hornet_UK said:
Yesterday I changed the Air Filter and the Fuel Filter. The Air Filter was non existent, all that was left was the metal cone and a load of oil black **** in the air intake. I cleaned all the oily stuff from the air intake as and replaced the filter. Started the engine and it still struggled to start, after chugging slowly with the throttle almost fully open for a minute or so she was able to run on tick over. After a few more minutes she seemed to behave as normal, went to max revs. I turned the engine off and left her for about half an hour and started her up again same as before. Is there anything else I should look at or should I just give her a good run at high revs to clear out any much etc?:confused:
Click to expand...

Assuming the oil pressure light works as expected (on initially, but goes off smartly on starting) two possibilities spring to mind....

1) There is an air leak in the fuel system (and your tank is below the level of the engine) - likely candidates are the bleed screw on the top of the fuel filter on the engine, or the metal bowl on that filter. If you have any diesel leaks in that area then try to get them sealed and see if the problem persists (diesel gets out when the engine is running & air gets back in when it's stopped);

2) You have a dose of diesel bug and have yet to locate all the filters / gauzes which it has clogged up (or water in the fuel, maybe).

Any black (or other colour) smoke at any time?

Andy
 
do you have any type of alternator regulator fited like stirling etc.

maybe the alternator is drawing lots of current and dragging the engine performance down.


Steve
 
Hornet_UK said:
Yesterday I changed the Air Filter and the Fuel Filter. The Air Filter was non existent, all that was left was the metal cone and a load of oil black **** in the air intake. I cleaned all the oily stuff from the air intake as and replaced the filter.
Click to expand...

There shouldn't be oily gunk in there, as there shouldn't be a mechanism for it to get there. I had similar symptoms on my 1GM10 and it turned out to be a blocked exhaust port in the head. There was only a 1/4" hole for the exhaust to get through, so a lot of it didn't and blew back through the air filter when the inlet valve opened.

I'd strongly recommend getting the exhaust elbow off and having a poke around both ways inside.
 
Bit of a long shot here but are you sure that your prop and bottom are reasonably clear. Do the problems occur in gear and underway? The drop off in engine performance is quite something if it is fighting heavy fouling.
 
it does accumalate there but only if the injector is not firing properly or if the valves are not seating correctly or worn, i just wanted to sound more positive about the outcome, i do agree on the elbow/ exhaust port.

To check if the valves are leaking turn the crank pulley by hand and listen at the inlet (without silencer/filter) and also at exhaust port, assuming you have elbow off.
If you hear the air hissing when its compressing then they are leaking


steve
 
Last edited:
steve28 said:
do you have any type of alternator regulator fited like stirling etc.

maybe the alternator is drawing lots of current and dragging the engine performance down.
Click to expand...

That's just reminded me. When I got Jumblie the engine would lose a lot of the little power it had after an hour or so of running, and would stall if asked to tickover. The fault turned out to be a bad alternator bearing which only stiffened up when things got hot.
 
Make sure the throttle arm is free to move through all it's range. Mine has lost 1/4 of its travel in the past.

BTW, the sponge in my air filter always looks like that except when I clean it. I used to be paranoid about it, but now only do it just before launching.
 
Update

Hi Guys, Thanks for all your advice, I have at last got to the bottom of the problem!

It turned out to be the Engine Stop leaver wasn't going back into the correct position at the engine end. Once pulled the leaver to start position it started first time no problem. So I'll have to investigate the cable and maybe replace it.:)
 
Hornet_UK said:
Hi Guys, Thanks for all your advice, I have at last got to the bottom of the problem!

It turned out to be the Engine Stop leaver wasn't going back into the correct position at the engine end. Once pulled the leaver to start position it started first time no problem. So I'll have to investigate the cable and maybe replace it.:)
Click to expand...

Thanks for letting us know - one to add to the list....

Andy
 
Hi all ,
Yanmar 2GM20F with high revs and reducing power ?
If you’re still boating I have a similar issue to problem above but have checked the following :
Elbow is okay
Stop valve is okay
Exhaust is okay
Cleaned jets - okay
Oil & air filter okay

As years have rolled on since this post was created, I was hoping time and experience may benefit it me ..
 
Jollybot said:
Hi all ,
Yanmar 2GM20F with high revs and reducing power ?
If you’re still boating I have a similar issue to problem above but have checked the following :
Elbow is okay
Stop valve is okay
Exhaust is okay
Cleaned jets - okay
Oil & air filter okay

As years have rolled on since this post was created, I was hoping time and experience may benefit it me ..
Click to expand...
A few years on and a few more sea miles, I had another similar problem a few years later, it turned out to cr@p in the fuel tank. Suggest checking Fuel Filers and take a look in the fuel tank.
 
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