25hp johnson cutting out at high rpms

[lcol8548]

I have a 1974 25hp johnson outboard (25R74) that has been running fine for over a year. In the last month, I have replaced the prop and changed the plugs. Engine was running well. All of a sudden the engine starts to cutout (misfires?) at high or maximum rpms. Runs fine at lower rpm. Idles and starts well. Water pump appears to be working. The only change before this happened was new fuel (and oil).

I have noticed that the bulb on the fuel line does not compress. Always inflated and hard to squeeze. Checked valve on fuel line that enters engine and when open allows fuel to flow. Have tried to squeeze bulb at high revs when engine was cutting out but did not fix problem.

Any help with this will be much appreciated. Thanks!

 

[tashasdaddy]

Re: 25hp johnson cutting out at high rpms

once the motor is started the bulb should be squeezable. if it is old and hard, time to replace. when were the carb last cleaned and rebuilt. you could also have a coil that is starting to fail. what spark plugs are you using, motor was built to run champions, other brands have been known to cause misfire problems. you should be running QL77JC4 plugs set at .030.

 

[lcol8548]

Re: 25hp johnson cutting out at high rpms

thanks for the prompt reply. I am using champion J4C sparks....only 2 months old. The bulb and fuel line are fairly new. Bulb can be squeezed when I manually depress valve at end of fuel line, and fuel comes out. When plugged into engine, bulb cannot be squeezed. As I mentioned, the engine was running great two weeks ago. Problem began suddenly.

Not sure when the carbs were last cleaned (over a year at least).

 

[tashasdaddy]

Re: 25hp johnson cutting out at high rpms

what do your plugs look like. do they both look the same, or is one a different color or one wet one dry?

 

[lcol8548]

Re: 25hp johnson cutting out at high rpms

Spark plugs look ok, in terms of gap and electrode. A little oil on both, about equal. Drained carburettor as well.....greenish solution came out. No particulates or "gunk". Looks like oil/gas mix. Noticed valve on fuel line may be sticking.....will replace to see if this helps.

 

[tashasdaddy]

Re: 25hp johnson cutting out at high rpms

if the bulb rubber is stiff and starting to crack replace. consider complete new hose. get an OEM hose, the after markets that say for Johnson, Evinrude, Suzuki, have the wrong O rings in the and will leak at the fitting.