120 hp force performance issues

[pphandyman2]

I recently purchased an old 18' boat with a 120 Force motor. It runs great for the first 15-20 minutes, after that it starts acting up. It is dying out on full throttle and doesn't even want to idle. If I let it cool down for like 15-20 minutes, it will go for another 10 minutes and start acting up again. At first, we thought it was a fuel problem so the mechanic pulled both carburetors off and cleaned them; new gas filter, new fuel line, and the problem still exists.

Can it be something electrical? Please help and any advice or input would be greatly appreciated.

Thank you.

 

[pnwboat]

Re: Motor perforamce issues... what other possibilities are there? Please help.

Re: Motor perforamce issues... what other possibilities are there? Please help.

While you're under way at WOT, look at the primer bulb. Does it look like it's collapsed? If so, then there is either a blocked fuel line between the fuel pick up in the tank and the primer bulb, or maybe a bad primer bulb.

If it looks OK, try squeezing it while under way at WOT. If that helps, then may be a bad fuel pump diaphragm. Easy cheap fix.

Also check the primer bulb with the engine shut down, and the motor sitting level. You should be able to squeeze it and it'll be soft at first. After a couple of squeezes, you should feel it get hard. If it doesn't get hard after a couple of squeezes, then the needle valve in one or both carburetors is leaking. This can cause your motor to run rich and bog down.

As a side note, you might want to check the compression. Typical reading is somewhere in the neighborhood of 120LBS. Actual PSI reading is not as important as even readings in all four cylinders, plus or minus 10% max. variation. This will give you a general idea as to what kind of shape the rings and cylinders are in.

 

[john from md]

Re: 120 hp force performance issues

Here are a few checks to make other than those already mentioned.

When the engine dies at full throttle, feel the ball and see if it is soft. If it is, prime until hard and start the engine again. Have someone sit next to the ball and as the engine starts acting up, have them slowly pump the ball. If this will keep your engine running, you may have sticking check valves in the fuel pump. It appears that the alcohol in todays gasoline causes the flapper in the check valves to swell and stick. The new check valves are only $5 each and have a flapper of a different type of material. The valves that stick have like an amber colored plastic flapper. The new valves have a grey colored flapper.

Hope this helps,

John

 

[pphandyman2]

Re: 120 hp force performance issues

Thank you all for the input i will try the check valve, because we did try all the rest, and we did install all new.

Thanks Peter