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purchased used pontoon with 1995 Johnson 48. rebuilt carbs, with boat on trailer and muffs on, rpms run away for no reason? Idles great, put in gear idle up slightly, rpm's continue to climb and will run up to 4 to 5K. Pull back into neutral, motor goes back to proper idle.
 
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Not sure but will check. have been told that these motors are notorious for running away on muffs. in the water should not be a problem. thoughts?
 
is it truly running that high s rpm or is it running about 2k rpm which should be close to the fast idle levers limit?....have you run the motor in the water since you bought it?what was the reason for doing the carbs?

i cannot see it of course but i think you got the linkage to the carbs and/or timing advance messed up....
 
Motor had sat up for about 3 years with old fuel, hence the carb rebuild. After dropping in gear, keep in mind that it is on a water hose and muffs, I will ease up to about 1500 rpm's, it will run steady for about 3 minutes until all hell breaks loose and will hit 5k. pull throttle back to neutral, settles down into a perfect idle. I just talked to a mechanic at a local boat shop, he told me that these engines cannot run on muffs and that it all has to do with back pressure. he said put it the water and run it, should be fine.
 
Not prudent to run an engine on a hose above idle...don't know where the 'back pressure" theory originated but the fact is most hoses can't supply enough water and you can damage the impeller inside the pump....hopefully, you drained the fuel tank and lines as well. putting it in the water and then taking a cruise will tell you if the engine has any residual problems...
 
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