Yanmar ysm-8

[Cre8tve1]

After a rebuild by a licensed mechanic, my YSM-8 runs well, in neutral. however, as soon as it is put in gear it bogs down to the point of stalling, despite opening the throttle to full.

In neutral the revs spool up and down in synch with throttle adjustments, the motor seems to run fine until put in either reverse or forward.

The shaft is free and turns easily by hand.

The mechanic is very good at scratching his head and saying that he does not know why this is happening. Any suggestions or ideas would be very much appreciated. Thanks.


Brooke

 

[Don S/V ILLusion]

did he also rebuilt the transmission?

 

[Cre8tve1]

reply

did he also rebuilt the transmission?

No he did not.

 

[Rob19574]

how is your exhaust system? Elbow and rest of system clean?

 

[Cre8tve1]

New elbow, checked and clean.

 

[alexco38]

Fuel lift pump screen

Does Yanmar has a screen inside the fuel pump? Same symptom if it is block.

 

[Benny17441]

Was the transmission working properly before the rebuild? If it was just check the oil level and perhaps crank the engine by hand to confirm there is no undue drag. I would then check the operation of the engine's throtle governor that regulates RPM when the engine is under load.

 

[kloudie1]

If there is not a lot of black smoke when you open the throttle, then you have a fuel delivery problem.(enough fuel to run without load, but not enough to run with a load) . First start with filters replace all and make sure their gaskets aren't letting in air.. Make sure the banjo connections in the fuel line are tight and not leaking air.. make sure the lift pump is working well.... make sure there are no air leaks in the line from the lift pump to the tank.. then the tank pick up line.. check that there is no screen on the inlet dip tube.. next be sure all air is bled out of system, all the way to the injector.. next is to check timing and governor and fuel rack on injection pump. the devil is in there .. ya just have to find him.. Happy hunting, Brooke !
EDIT: Be careful with the banjo connectors, they are easy to break off or strip..

 

[jrowan]

I also used to have a YSM 8. Strong lil engine, but when she had a partial fuel clog, she would want to sputter out. Enough fuel got through when in neutral, but would bog down under load.
Check the end of the fuel pickup tube in your fuel tank. Mine was almost completely clogged at the mesh filter screen placed INSIDE the end of the fuel pickup tube, used as a pre filter, pre clog. Also check the small (tiny) mesh screen located inside the intake side of the fuel pump. It is TINY & will easily clog. After rebuilding a motor, all kinds of debris can get into the fuel lines & clog em up. At the time, I thought that I had an injector pump going bad, when it was really just a partial fuel clog in the lines. I think a lot of sailors spend a lot of money on part replacements & engine rebuilds when a lot of these Yanmar diesels just have hidden fuel blockages. If the YSM 8 has clean fuel and air and cooling water, shell run forever. Good luck & tell us what you find.

 

[Ray Bowles]

I am not familiar with the YSM 8 but I am with a lot of other diesel motors on the farm. Check the above mentioned fuel system items. If they are all ok then I would check the injector pump timing. That will do exactly what you are experencing.
Ray

 

[Sail123]

Try a different licenced head scratcher. If you go fussing with everything, it could end up with more problems. Diesel engine's do not like sucking air in fuel lines, and that can be hard to trace.

The people at Torresen Marine are very helpful, maybe they can advise. 213-759-8596.

 

[Cre8tve1]

No sign of any "mesh/screen" in pump assembly thus far. Signs point to governor issue. Thanks for guidance and input. Will advise further.

 

[Chris Patterson]

In my years of diesel, the oddest things would pop up. Worked on one once that would run like a scalded dog, and just out of the blue shut down, or nearly. We did everything, pump pressure tests, purged it by blowing air back through the system toward the tank, it about drove 4 very experienced diesels mechanics to drinking. Problem? Somebody at one point in time lost a small piece of rag in the tank, and when the engine would spool up tight, it would suck that piece of rag up to the tube and stop it. After the engine shut down, the suction would stop, the rag would fall off, and it would start right back up.
Now while I doubt that is the case with yours, crazy things are what they are. Take a very clean container with fuel in it, get a cheap aftermarket electric fuel pump, (NAPA has one at about 25 bucks) and put a piece of hose in the tank, the other side to the injector pump, (purging the air of course), and see if that doesn't eliminate the problem. If it does, you know it's in the delivery system. If it's new fuel, in a new/clean can, with new pieces of fuel line, you shouldn't need to filter it for testing purposes.
If it still acts up, the problem is as said. Pump timing, (as indicative of the "pro" mechanic scratching his head, or other parts), rail pressure, or your pump was built back wrong. Period.

 

[Chris Patterson]

One more bit of useless information before I forget it. We had a "mechanic" in the shop, that whenever the opportunity could arise, whip a card out of his wallet proclaiming to be ASE certified. He was one of the biggest idiots that I have ever known. I walked by one day and saw him with an ALTERNATOR on the floor, touching a battery charger to the poles to test it, like you would a starter. And his helper was there with his foot on it in case it spooled up to keep it from running across the floor. I started to take him out right then and there, before he could inflict more damage on the mechanical world. So; just because your "pro" has some piece of paper, or a certificate or whatever, it don't mean a damn thing other than he conned somebody out of a piece of worthless paperwork. That said, another mechanic might be your best recourse..

 

[Cre8tve1]

In my years of diesel, the oddest things would pop up. Worked on one once that would run like a scalded dog, and just out of the blue shut down, or nearly. We did everything, pump pressure tests, purged it by blowing air back through the system toward the tank, it about drove 4 very experienced diesels mechanics to drinking. Problem? Somebody at one point in time lost a small piece of rag in the tank, and when the engine would spool up tight, it would suck that piece of rag up to the tube and stop it. After the engine shut down, the suction would stop, the rag would fall off, and it would start right back up.
Now while I doubt that is the case with yours, crazy things are what they are. Take a very clean container with fuel in it, get a cheap aftermarket electric fuel pump, (NAPA has one at about 25 bucks) and put a piece of hose in the tank, the other side to the injector pump, (purging the air of course), and see if that doesn't eliminate the problem. If it does, you know it's in the delivery system. If it's new fuel, in a new/clean can, with new pieces of fuel line, you shouldn't need to filter it for testing purposes.
If it still acts up, the problem is as said. Pump timing, (as indicative of the "pro" mechanic scratching his head, or other parts), rail pressure, or your pump was built back wrong. Period.

I've connected with another fellow, and the governor seems likely to be the culprit...so we'll see what happens.

 

[Cre8tve1]

Now while I doubt that is the case with yours, crazy things are what they are. Take a very clean container with fuel in it, get a cheap aftermarket electric fuel pump, (NAPA has one at about 25 bucks) and put a piece of hose in the tank, the other side to the injector pump, (purging the air of course), and see if that doesn't eliminate the problem. If it does, you know it's in the delivery system. If it's new fuel, in a new/clean can, with new pieces of fuel line, you shouldn't need to filter it for testing purposes.

Did that one already, and the bogging down continued. We/I am looking at the governor.