Johnson 9.9 Won't give full RPM

[Mystic Traveller]

Have the Following Motor:<br />Johnson 9.9 <br />Model 10R76H<br />Serial 16722<br />When in gear and have full power applied motor will not give full RPM/Power.<br />If I slip it back into Neutral, engine will rev right up. <br />Motor will seem like it is trying to kick into high gear so to speak, like sputtering. A couple of times It has gone to full RPM/Power but only lasted for a few mins at a time. <br />Now wont seem to go to full power no matter what I do. <br />Any ideas as to the possible culprits. <br />New Plugs, Gas etc already done. <br />Thanks

 

[Bear]

Re: Johnson 9.9 Won't give full RPM

Check your ignition coils, ignition cables and the "rubber cap? thing" (boot) between the ignition cable and the spark plug.<br /><br />Remowe the cowling and start it up when it is dark outside and check for sparks. There shouldn't be any visible sparks anywhere.<br /><br />Revving in neutral but not in gear also indicates low compression. But low compression never is intermittent like this problem of yours.<br /><br />When was the last time you cleaned the carb. I might be some dirt or water in the fuel bowl. Drain it and tell us what you found.

 

[the machinist]

Re: Johnson 9.9 Won't give full RPM

On that motor, it is not designed to fully raise the tiller/speed handle when twisting the speed knob. <br /><br />If you raise the tiller/speed position, it can dissengage the cogs from the handle shaft to the other mating cogs on the motor shaft. If you then, while the handle is still up, twist it back for slower, you can slip 2 cogs. <br /><br />This will still allow you to operate at slow speed, but will not allow you to get more than about 1/2 speed out of the motor.

 

[Mystic Traveller]

Re: Johnson 9.9 Won't give full RPM

It is not the Cog problem. <br />Even if I remove the engine cover and manually push the Throttle to full still wont get full RPM. We are gonna clean the carbs as previously recomended. <br /><br />I have tried adjusting the mixture, between Lean and Rich and no difference in performance. <br /><br />Once in awhile, the motor will kick into High speed and last for at most 5 minutes then drops back down to about 1/2 power. <br /><br />The rest of the time it runs steady at 1/2 power, or sputters like it is trying to get to full power, and eventually it will one time out of 10 say, and again last for up to 5 or 6 minutes and then drop back down again.

 

[optisoft@istar.ca]

Re: Johnson 9.9 Won't give full RPM

I have almost the exact same problem. The only difference is that the lack of RPM is there whether the engine is in gear or not. With the cowl off, the throttle reaches the stop.<br /><br />Did anyone resolve the previous post's problem?

 

[Xcusme]

Re: Johnson 9.9 Won't give full RPM

You mentioned that you replaced the plugs, gas etc.....already done...<br />Have you looked for water in the tank?? Does pumping the primer bulb make any difference? Have you checked the link/sync? As already stated , a carb clean-inspection would be next. Address what seems to be a fuel delivery problem first, then move on to a possible ingition problem.

 

[Chinewalker]

Re: Johnson 9.9 Won't give full RPM

My money is on a bad coil. The "shifting into high gear" description is typical of an ignition problem. If it's a bad (cracked) coil you may hear a snapping sound with the hood off as a spark arcs from the coil to the block.<br /><br />Also, I can't remember if '75 or '76 was the last year of the low-tension magneto with the maker points under the flywheel, but you may want to check the points, possibly replace them if it has them. If it does not have points, you'll have a 5"x2" black box mounted near the cylinder head...<br /><br />- Scott

 

[Michael P]

Re: Johnson 9.9 Won't give full RPM

This sounds like what I was experincing with my 9.9. If you read my post from today it lays out what the problem for my motor was. The mechanic said that the wrong plugs along with a cylinder that was a little weak was enough to rob the engine of its ability to come up to full RPM.<br /><br />Taking a motor to a dealer and having a mechanic work on it is not cheap but in the long run it is fixed and the irratation facter is a lot less.<br /><br />Mike