Yanmar loses power, slows down & kills

[Underwaterdog]

I remembered reading about something similar to this on the board, so I did a search for power loss under yanmar. It is gravity feed isn't it? If so, it is unlikely that the fuel bowl could be sucking air. There have been some issues with the plastic fuel bowls shrinking and leaking, but none that I recall sucking air. As far as the vent is concerned, we learned from one of Kenmac's post that the tank will implode if it is not vented. So the only way I can figure it to suck air would be if the tank is not vented and a leak developed in the lines or the bowl. I remembered reading about something similar to this on the board, so I did a search for "power loss" under yanmar.
Here is one thing that I found under "Loss of power in YM1700":

Originally Posted by jkelley8
I had a similar problem. It turned out to be a bend in the return fuel line sending the unused fuel back to the tank.
Had major loss of power most especially in the higher range gears.

Trying some different search terms will give different results , but my guess is the answer is already somewhere on this board.There were several suggestions, but they didn't post the fix. So please, when you do locate the problem, and I have faith that you will, give us the answer.

 

[tallyho8]

I have not checked the return fuel line and will try to do that later today. I have the original glass fuel filter bowl. I have changed the o-ring and do not believe that it can be the problem. The problem seems to be heat related since it runs fine when cold and acts up after it warms up for 10 minutes. Seems like some part is getting warm and opens a crack that lets air in. I should get my new bleeder valve in a couple more days and hope it makes a difference.

Maybe my thinking is wrong because I have never had a bad injector, but it seems like a bad injector would make it miss like a bad sparkplug and it never misses. It just slows down and loses power and finally kills.

 

[1danny]

I have not checked the return fuel line and will try to do that later today. I have the original glass fuel filter bowl. I have changed the o-ring and do not believe that it can be the problem. The problem seems to be heat related since it runs fine when cold and acts up after it warms up for 10 minutes. Seems like some part is getting warm and opens a crack that lets air in. I should get my new bleeder valve in a couple more days and hope it makes a difference.

Maybe my thinking is wrong because I have never had a bad injector, but it seems like a bad injector would make it miss like a bad sparkplug and it never misses. It just slows down and loses power and finally kills.

Take the muffler off.

Danny

 

[greatrandini]

I did not know that some of the original fuel bowl were made of glass?

 

[1danny]

I did not know that some of the original fuel bowl were made of glass?

Some of them look like glass.

Danny

 

[ProdaddyTX]

The ones I've seen that look like glass are coming over on the vietnamese reconditioned machines, and they're actually a clear and fairly brittle plastic that is prone to developing a hairline crack around the lip. I've never seen that allow air into the lines though... it just leaks fuel. Back when we used to buy and sell those machines we replaced a lot of fuel bowls with the better white-ish ones available from Hoye and Fredricks.
I'll bet the part you've ordered from Hoye solves your problem. Please report back!

 

[BruceR]

The ones I've seen that look like glass are coming over on the vietnamese reconditioned machines, and they're actually a clear and fairly brittle plastic that is prone to developing a hairline crack around the lip. I've never seen that allow air into the lines though... it just leaks fuel. Back when we used to buy and sell those machines we replaced a lot of fuel bowls with the better white-ish ones available from Hoye and Fredricks.
I'll bet the part you've ordered from Hoye solves your problem. Please report back!

You're not doing re-cons anymore ?

Bruce

 

[greatrandini]

The ones I've seen that look like glass are coming over on the vietnamese reconditioned machines, and they're actually a clear and fairly brittle plastic that is prone to developing a hairline crack around the lip. I've never seen that allow air into the lines though... it just leaks fuel. Back when we used to buy and sell those machines we replaced a lot of fuel bowls with the better white-ish ones available from Hoye and Fredricks.
I'll bet the part you've ordered from Hoye solves your problem. Please report back!

Yes, that is like the one I replace with one like you said! If he has one of those it maybe sucking air.

 

[tallyho8]

Still not working!

I installed my new bleeder pump. The pump works fine and does not leak fuel when pumping but it still runs the same.

I took the muffler off as Danny suggested and it still does the same thing, warms up, loses power and slows down. With the muffler off I can hear that it is not running as steady as I thought with the muffler on. When it starts acting up it appears to be running erratically.

I removed the fuel return lines from the injectors while it was acting up and ran it for a while and no fuel, except maybe a drop, is coming out of the injectors to the fuel return lines. Is there supposed to be a constant flow of fuel out of the return lines?

 

[chriswheeler]

As it starts to falter, loosen the lines to each injector. ( at the injector ) If one of the lines loose doesn't make a difference, I'd look hard at that injector.
Chris