1999 60 HP low RPM

[dhil1955]

My motor suddenly will not run up to WOT. Fact is it barely will run past about 1500-2000 rpm. I brought it in from lake and tore carbs down.(No sign of any foreign debris, they looked very clean). I've replaced the fuel filter. Second time to lake I verified good spark to each cylinder. It almost acts like its in limp mode or timing is off. It's pumping good water and not running hot.
I checked compression. 125 PSI to each cylinder.
Any ideas?

 

[cousinabe]

Re: 1999 60 HP low RPM

bad fuel pump. pump the primer ball while problem is happening.
try an auxillary fuel tank.

 

[dhil1955]

Re: 1999 60 HP low RPM

I did pump the bulb last time out. I also removed the air silencer and confirmed a nice mist of fuel to each carburetor under load which makes me think the fuel pump is good.

Thanks,

 

[yoyo133]

Re: 1999 60 HP low RPM

Start by telling us what kind of engine it is.

 

[Silvertip]

Re: 1999 60 HP low RPM

Knowing what you ae working on might help us. What do the plugs look like? Rough running at idle says you have a dead cylinder. With the engine running, give each carb a squirt of fuel to see if it picks up. If not, it is a spark issue. Spark timing does not just suddenly change and it does not affect one cylinder. Don't mess with timing unless you have a service manual and understand what you are doing.

Is the vent open on the fuel tank. Any air leaks in the fuel system. When was the fuel filter last changed. Have you checked for water in the fuel? How old is the fuel? Had the engine been layed up (stored) for a period before this happened? If so, was the fuel treated and the engine run long enough to suck up the fuel system treatment.

 

[EAVES]

Re: 1999 60 HP low RPM

Did you remove the tubes from the carbs ?? Maybe stopped up there from the fuel separating from the ethenol how long did it sit before this problem occured

 

[dhil1955]

Re: 1999 60 HP low RPM

The motor is a Yamaha 2 stroke c60tlrx year model 1999.

The motor has not been setting up. It's used weekly. It was running fine prior to it suddenly wouldn't get up to RPM. I first thought it was a fuel problem. I cleaned the carbs including the tubes that you were referencing. No sign of any obstruction. I've ran the motor without the air silencer and squirted a small amount of fuel in each carb while running the boat. It makes no difference on increased power. Last time out I inserted a short piece of vacumn hose on the spark plug to spark plug wire so that I could easily see if each cylinder was contributing power. I am getting spark to each cylinder and you can tell a power loss when the spark plug wire is removed. The motor idles pretty good. When you apply throttle the motor will run up to about 1500 rpms and began cutting out. Sure has got me stumped.

I was very concerned that maybe had a bad cylinder. Felt better after checking the compression. 125 each cylinder.

Could the CDI module cause these symptoms?

 

[cherisse]

Re: 1999 60 HP low RPM

is it possible the thermo/temp saftey is defective and throwing the CDI into safety mode?

 

[dhil1955]

Re: 1999 60 HP low RPM

The motor does act like its in a reduction mode. It's pumping lots of water and no indication of over-heat. The buzzer is not going off. I'm not sure how to check the thermo switch. The motor is not oil injected, I pre-mix the fuel. Is there any other things that would cause a reduction mode from the CDI?

 

[dhil1955]

Re: 1999 60 HP low RPM

Problem solved. I had checked the fire to spark plugs earlier by pulling the plug and observing spark to each one. A friend went with me to the lake and while running the motor under load we choked each carburetor one at a time. The #3 cylinder should very litte difference while the other 2 cylinders would almost kill the engine when carburetor was choked. I exchanged the spark plug with the #1 cylinder and the problem moved. Replaced the plugs and the motor is running wonderful again. I guess the bad spark plug would not fire under compression.