vacillating idle

pauljames

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May 20, 2015
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OK with a brand new 2006 Tohatsu 2 HP (old stock) 4 stroke, the idle vacillates up and down. I increased the idle screw just barely so that it wouldn't stall at idle while in gear. Now when I take it out of gear the idle increases too much, my guess is about 500 RPM increase. Consequently, I believe it is too fast of an idle and it slams into gear. The motor is not running rough under any circumstance. If you just let the motor idle, it will vary all on it's own. Is this normal for this motor?
 

Sea Rider

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Sep 20, 2008
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12,345
Welcome to Iboats.

It's not normal, probably carb is dirty inside ? idle rpm should be adjusted to a point that provides a dry gear clac and engine doesn't die when shifting into gear, If dies adjust idle screw a tad CW.

Happy Boating
 

pvanv

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Apr 20, 2008
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6,500
You must use a tach to adjust idle. If the motor was run years ago, even just had the carb filled, and then allowed to dry out with fuel in the bowl, the carb likely needs cleaned. Tohatsu did not make a 2 hp 4 stroke. What is your model?
 

pauljames

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May 20, 2015
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Thanks for the reply gents. The model is MFS 2A. The manual covers the 2A and the 3.5A models. To be more clear, when the motor is running (at normal temp) the idle will change gradually (within 10 sec time frame) to the higher RPM. It will remain there for a while and then lower back down (maybe) all of this on it's own, i.e. no throttle adjustment has been made. I try to rev the motor to bring the RPMs back down so I can shift into gear without slamming the trans. Sometimes that works and sometimes not. If not, I choke it a little to lower the RPMs and put it into gear. I have only put a couple of hours myself but it is brand new. I don't believe it is
 

Sea Rider

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Sep 20, 2008
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Do you have a smooth operation throughout the whole throttle system ? Probably carb doesn't achive a full idle rest, kind of jams somewhere when fully reversed. Lube all rotating and sliding throttle system components, check if carb has been completely reversed to idle rest position when throttling down. If it's not a throttle related issue, clean carb.

Happy Boating
 

pvanv

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Apr 20, 2008
Messages
6,500
Ah yes, Tohatsu did sell a few MFS2.5/3.5 motors with that smaller 2 hp carb, about 10 years ago. One solution would be to install a carb for the 3.5. Failing that, you likely need to go through the carb with a good soak. I bet the carb was filled with fuel at one point, and then allowed to evaporate, leaving deposits in the tiny passages of the low-speed circuits. As a result, in order to get any idle at all, the idle stop is probably set to open the throttle plate to the point that you are right on the edge of the transition to the power circuit. In any event, if it was recently sold as new from a dealer, you are under warranty, so see your dealer.
 

pauljames

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May 20, 2015
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3
OK, Thanks for the answers gentlemen. That will give me something to start working on. I appreciate your time and knowledge.

Paul
 

Sea Rider

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Sep 20, 2008
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All of these up down revs happens when you been running for some time and then come to a complete boat stop while reversing throttle to idle ?

Happy Boating
 
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