'91 115 Johnsonspeed problems

[Sebrof]

Ok Problem solvers......91 johnson115 2 stroke. The engine won't come up to cruising speed with wot( with a loaded boat). It is not overheating and the voltage seems ok across the slow diode. If I remove the engine cowl, then the motor jumps up to running speed in an ok manner . Still not 100% but at least it will go up in plane and eventually top out at it's usual speed. The voltage meter I have in my dash registers a little lower than the past. At wot it logs about 12-12.2 and it used to go up to 12.8-13.3.
At first I thought the engine was air starved as the old foam in the cowl was loose and seemed to be near the carb intakes. I removed the foam to not difference. At idle and revving out of gear, it seems fine no break down in performance so this happens only out on the water.

Is the cowling draining juice from the wires?( new last season), or what???
Please help Seb

 

[Captain Jeff]

Re: '91 115 Johnsonspeed problems

Make sure there aren't any hornet nests in the cowling intake vents. Those volt meters aren't known to be super accurate but it is something interesting to note. It is possible that the coil stays cooler and can produce more voltage with the cover off, check the voltage with it off. Your coil may be breaking down or leaking voltage.

If you are getting the correct RPM for WOT and still not getting to a normal cruising speed make sure that the prop isn't slipping and that your boat is loaded evenly and you are trimmed out optimally.

 

[Sebrof]

Re: '91 115 Johnsonspeed problems

Thanks capt'n Jeff
air intakes are all clear. Unfortunately my tach doesn't work well so I don't know what rpm it gets up to but I bet that it's no where near what it should be at wot. Like I said in my first post, even when it does get up on plane the hole shot is nowhere near what it used to be and moving people fwd is the order of the day until on plane, then they can go anywhere. ( the engine powers a 19 proline). The boat has never had a "fast" hole shot but now it doubled the time with the cowl off.
I'm tearing down the carbs tomorrow just for fun and see what condition they are in.
Keep those ideas coming
Seb

 

[ezeke]

Re: '91 115 Johnsonspeed problems

Look under the starboard side of the flywheel and make sure that your spark advance rod is connected to the timer base.

 

[Solittle]

Re: '91 115 Johnsonspeed problems

Your symptoms point to an exhaust leak which displaces the oxygen needed for combustion. When you take the cowl off the exhaust dissipates.

 

[Sebrof]

Re: '91 115 Johnsonspeed problems

Brilliant!!, Thanks guys for some starting places, Probably won't be able to work on it until the weekend but I'll update this site with progress
Thanks
seb