Low power/won't "rev-up" 68 6hp Johnson

[OldJohnson6hp]

Hi guys I'm stumped. My little 6 won't rev up to full rpm. When in neutral it will run up, runs excellent on slow speed, idles like a champ, starts in 1 maybe 2 pulls. I have cleaned the carb, water pump, ignition new etc..

It didn't do this before not sure what to do. Go to take off, put in forward, twist the grip and.....up to what seems about half speed more will not wind out to full rpm. Every one in a while it seems to want to go and you can hear the motor try to rev up. Also replaced bulb with a new one so it stays firm. Could it be the fuel pump? I disconnected it on the carb side, pulled it over and fuel seems to be getting pumped, but is it enough? Or maybe the float level off? I thought it was even with the bowl.

Any help much appreciated!

 

[tashasdaddy]

Re: Low power/won't "rev-up" 68 6hp Johnson

is the time plate moving all the way around to wot. the some time get hung up on the neutral rev lever.

 

[OldJohnson6hp]

Re: Low power/won't "rev-up" 68 6hp Johnson

Timing seems good, the plate slides all the way over to the stop

 

[CATransplant]

Re: Low power/won't "rev-up" 68 6hp Johnson

Check spark, too. It could easily be running on just one cylinder. That's not uncommon, and you'll get about half power.

 

[OldJohnson6hp]

Re: Low power/won't "rev-up" 68 6hp Johnson

Nice spark. I put new coils, points, cond. Checked it again though all good. I did replace the fuel lines too as the old ones had got ruined. The hose running from the pump to the carb is slightly larger then the old one. It is on tight and doesn't leak..that couldn't be it could it? It does rev up just fine in neutral..you have to back the throttle down to avoid over-rev.

Compression is reading 88 on both cylinders exactly also

 

[CATransplant]

Re: Low power/won't "rev-up" 68 6hp Johnson

I hate to ask, but did you clean the main jet above the bowl plug? Any restriction in it will cause poor performance.

Also, track the linkage to the carb throttle and make sure the carb is opening fully at full throttle. Do this with the engine off.

There are only a couple of things that can cause your problem. If you have good spark and compression, then fuel is the natural next step.

 

[Brokeback Johnson]

Re: Low power/won't "rev-up" 68 6hp Johnson

Sounds like your main nozzle to bowl gasket may not be seating causing a rich condition. We had the exact same symptoms on an old 10hp. Easy fix that cleared up the problem and the motor ran perfectly.....

 

[OldJohnson6hp]

Re: Low power/won't "rev-up" 68 6hp Johnson

Will tear down the carb again..Like you said CA fuel delivery has gotta be it at this point..

 

[the machinist]

Re: Low power/won't "rev-up" 68 6hp Johnson

I agree with Cat. Sure sounds like it is only firing on one cylinder. Just because everything is new does not mean it is firing on them all, maybe just a loose connection. Pull one plug wire at a time when it is running is the old way to tell.