Johnson 9.9 hp gas problem

[Bobby D.]

This 1985 Johnson starts and idles fine but under load it breaks up. I changed the fuel pump, carb., tank, hoses, bulb and connectors. The only hose not checked was the hose from the motor connection to the fuel pump. Any other thoughts?<br />Thank you

 

[BF]

Re: Johnson 9.9 hp gas problem

My thoughts:<br /><br />1) Clogged or painted/fiberglassed over vent holes in the cowling? A trial run w/o the cowling on would tell if you it's restricting the air to the motor. I had a dirt bike with this problem once... was the tool kit blocking air to the breather. Of course once I noticed something not right I started carry an extra wrench and plugs etc... hey the problem got worse! <br /><br />2) dirty main jet (you did clean/change it with the carb?)<br /><br />3) you did clean the little screen filter in the fuel system?<br /><br />4) dirty screen in fuel tank<br /><br />5) electrical problem? bad plug (even brand new ones can be bad), cracked wire, bad cap. Does it idle good, or maybe is able to run but still misfiring? (or on 1 cylinder)<br /><br />Brent

 

[Solittle]

Re: Johnson 9.9 hp gas problem

When was the last time you changed the water pump? A 9.9 will act like that if it gets hot.

 

[JB]

Re: Johnson 9.9 hp gas problem

It will also act like that when it has no spark to one cyl.<br /><br />That is your most likely problem.