225 engine idle running away..

[cobbcfi]

When I fire up my 96' Johnson 225 Oceanrunner, it does fine but when it starts to warm up the idle climbs up to 1,100 rpm... That's a bit to high but then it runs away to 3,500 rpm and I turn the ignition off.. It continues to run at that rpm for another 10-15 seconds before it finally shuts down.. This is out of water on the earmuffs... Is this a bad ground or a vacuum leak?? Any help is greatly appreciated..

 

[jimmbo]

Are the carbs fully closed, Is the Throttle linkage all the way back to Idle, with the control cable disconnected? Were you or anyone else 'tinkering' under the cowl?

 

[oldboat1]

Interesting, and a little scary. 1,100 rpm is about what it should be on muffs at idle. Does it shut down with the key switch at that point?

If you can find a large enough barrel/plastic trash can, run with water about half way up the leg to provide back pressure. It may be running too lean (surging rpm) on muffs.