225 idles fine then rev on its own

[GDB]

I have a 1988 Johnson 225. Starts up fine and will idle properly on the muffs. Then after a few minutes it will rev up to 1500 RPMs without any change to the throttle and will stay there. Fuel is fresh, filter is new. I recently removed and cleaned jets on the carburetor. Any ideas?<br />I have woned OB motors before and it seems to me that there is excessive "carbon drip" from exhoust when I shut it down. Will a Decarb will help this problem?

 

[v12mac]

Re: 225 idles fine then rev on its own

Does it do this in the water too?<br />Mac

 

[GDB]

Re: 225 idles fine then rev on its own

I will run it in the water tomorrow. By the way compression checks good (about 110 psi per cylinder). <br />If compression is good, is there any other reason to decarb?

 

[v12mac]

Re: 225 idles fine then rev on its own

Read some of the other posts here, it looks pretty common to have a higher idle due to no back pressure on the exhaust when on the muffs.<br /><br />Decarb see FAQ section lots of good stuff<br />Mac

 

[GDB]

Re: 225 idles fine then rev on its own

I put it in the water and it idles fine... but my original problem still exists.<br />Boat starts fine and will run at 1500 RPMs fine. If I try and accelerate it dies at 2000 RPM. I can keep it running by pushing the key for the enricher and lowering throttle to below 1500 RPM. After about 5 minutes, the engine will "kick in" and it will accelerate and run fine at full throttle for remainder of the day. I have fresh gas and replaced filter. Compression is good.

 

[tonyscj5]

Re: 225 idles fine then rev on its own

fuel pump?<br /><br />rebuild carbs?

 

[GDB]

Re: 225 idles fine then rev on its own

I removed and cleaned all "fixed jets" and sprayed carb cleaner throughout while the throttle body was still on the engine. I am thinking fuel pump next....

 

[lark2004]

Re: 225 idles fine then rev on its own

so you haven't actually 'rebuilt' the carbs then?<br />Doing what you have said, is only a part of the job, you really need to pull them right apart and put a kit through them to be able to rule them out of the problem.