120 johnson breaking up under a load

[Bonanza79]

I have a 120 johnson that runs perfect in nuturel and revs up fine but once I put it in the water and get going it cuts down to about half power. Its not running hot. It will speratically kick back to full power here and there for a second or two and then drop back down. It seems like an electrical problem.I have checked all the grounds and they are good. Could this be a problem with the powerhead? Does anyone know what might be happening?

 

[jonesg]

Re: 120 johnson breaking up under a load

rather sketchy information you got there,
no model number, no yr, no tests done yet?
compression , spark gap test? engine history?

it all helps to get you help.
Got a manual?
www.outboardbooks.com

and rebuild the carbs with rebuild kits.

 

[CharlieB]

Re: 120 johnson breaking up under a load

You may be right about it being an electrical problem.

However, because ignition parts get expensive you should NOT change anything without testing to prove a part defective, there is NO RETURN on electrical parts, so be sure BEFORE you buy.

Search this forum for instructions on DVA testing your ignition.

Your stator may have developed a crack or shorted winding in the high speed coils, failing to produce enough voltage to consistently fire the plugs under load.

Test to prove it before spending any money.