High speed stutter?

[fishndirk]

Had my Tohatsu 20 hp a little over a year now. Its fully broken in. A while ago I ajusted the throttle linkage cause it was'nt quite maxed out at full tiller turn. After that the motor seems like it skips a beat while at WOP and a light load (sounds like cavitation almost) but when i back off the throttle just a tad bit it stops immediately. Im thinking maybe I adjusted the carb barrel to where it opens just a tad bit too far. Like it gets too much O2 and throws off the timming. Anyone ever heard of this?

 

[levi_tsk]

Re: High speed stutter?

without knowing the model it may now be advancing the timing to far causing it to shutter as youve mentioned

 

[fishndirk]

Re: High speed stutter?

But the spark advance has already stopped moving well before the throttle barrel gets to this point. The difference between the sputter and no sputter is only about 2-3 degrees of carb barrel rotation and no noticeable difference in RPM, just a slight difference in tiller handle rotation.

 

[pvanv]

Re: High speed stutter?

Check it with a tach to make sure, but you are probably exceeding the max 6100 WOT RPM, and engaging the ESG. If so, you could go with a slightly steeper pitched prop.

 

[levi_tsk]

Re: High speed stutter?

pauls probably right i forgot these things have a rev limiter.....

 

[fishndirk]

Re: High speed stutter?

Yeah the prop thing would make sense as pvanv said, however im not sure I wanna move to a slightly higher pitched prop. When the boat is under a heavier load it does'nt do it. It only does it when im under a light load and on a straight run and smooth water at max speed. But the thing that confuses me is when I back off the handle just a tad I hear no loss in RPM and no loss in speed but the shutter stops instantly. Wierd! Could the carb barrel really be that sensitive at WOP? Ive only seen that kind of sensitivity on carbed engines at low speed.

 

[pvanv]

Re: High speed stutter?

The ESG is a go/no-go circuit. If you are running at X RPM, it does nothing. If you attempt X plus one RPM, that is detected, and the motor is limited to X. So yes, the ESG is indeed that sensitive. Only a tach can tell you for sure, but based on your symptoms, I'm 95% sure.

 

[fishndirk]

Re: High speed stutter?

Thanks that does sound like a logical explanation. So basically I just had it adjusted to where it might have been rotating a couple degrees to far it sounds like.