increasing idle rpm w / 96 john 60hp

[Beaux]

Had the little 60 hp on the water muffs after some speckled trout chasing and had a surprising thing happen. After cranking on muffs and letting run for approx. 3-4 minutes at normal idle (when on muffs) at about 1000-1050 rpms(normal when on muffs), the motor had a increase in rpms of about 100. Then I heard it increase again at about the same increment. After probable 30-45 sec., and an increase to 1400 rpms, I went up and shut it off. Anyone heard of this phenomenom before? I read on a search about runaway engines while on mufs because of carbon buildup. Does this sound like the same thing except not quite hot enough to "runaway"? Any help is appreciated.

 

[Waterbugtoo]

Re: increasing idle rpm w / 96 john 60hp

Most likely backpressure issue.

 

[KennyKenCan]

Re: increasing idle rpm w / 96 john 60hp

It idles higher because the exhaust is not in the water and the motor has insufficiant backpresure

 

[Beaux]

Re: increasing idle rpm w / 96 john 60hp

I understand the lack of back pressure increasing the rpm's. That is why it normally idles at around 900 rpm in the water and then idles at 1000-1100 on the muffs. That is normal and the motor maintained this steady rpm for 3-4 minutes with no problem. Then all of the sudden, it started increasing Rpms at a rate that I could easily notice while listening. I turned it off at 1400-1450rpm and it sounded like it was going to increase in rpm speed again as I turned it off...that is why I killed it. My question is whether this can be explained by some mechanical problem or related issue like excess carbon (like the runaway motor postings). Thanks for your suggestions but are there any other ideas about cause or concerns? again all ideas are appreciated.

 

[Hooty]

Re: increasing idle rpm w / 96 john 60hp

Hey Beaux,<br />I would doubt it's a runaway. To increase speed it's either more fuel or more timing. I think I'd start with the fuel. Is the linkage viberating and opening the butterflies? Could it be a stuck float or leaking needle & seat?<br />Just a few things to consider.<br /><br />c/6<br /><br />Hooty

 

[Beaux]

Re: increasing idle rpm w / 96 john 60hp

I will check the linkage. Thanks for the reply.