1994 Tohatsu M40D rpms dropped to 3400

[eaglecries]

I have had this motor for 4 years now it is a 1994 and has run fine on my pontoon and would run just above 4500 RPM until a couple weeks ago. I had just run down the lake to a favorite spot and I idled around there for a bit. When I started to leave and head back to the slip, I could only get from 3200 to 3600 RPM. There and been no warning signals of any kind. . I checked the spark plug firing and all three are firing. I checked the Carbs and everything else I could think of then tried looking through my service manual for the answer and could not find anything that helped. I have run the boat a couple more times to see if the RPMs were still low and they are still between 3200 and 3500.

Today I was picking up something about 150 miles from here from a boat mechanic and when I explained my problem he stated right away that he would almost bet me 100% that it was the stator going bad that was causing my problem. My question is does that sound reasonable or what else might do it when there are no warning signals such as oil or temp.

Thanks in advance for any words of wisdom.
Bill in Northwest Arkansas

 

[pvanv]

That motor does not have a stator. Your Factory service manual has full diagnostic info for the ignition, as well as fuel and mechanical systems. The problem could be "almost anything" so it is best to test, instead of guess.

 

[Sea Rider]

If still with original delivered factory prop, perform a prop slip test to check if internal hub is is 100% in good working order. If engine works good throughout the full throttle range but with less rpm, don't think it's an electrical component related issue.

Generally speaking engines with electrical issues starts to fail, have erratic performance or even drops dead dpending on which component is the culprit. With engine off at full throttle, check 3 carbs opens fully all the way ? if not, check remote box, throttle cable for hidden issues.

Happy Boating

 

[eaglecries]

Thanks for the thoughts. Paul.. actually I misspoke when I said Stator because I was actually referring to the coil plate assembly.

Sea Rider .. the prop that is on it is one I bought new from here at I boats and installed a bit over two years ago. However I have not checked it for slipping and that could be a possibility. Also will recheck the carb and throttle linkage. Motor sounds as if it is running normal and everything dopes fine until I try to open it up for more speed. That is when it will only make 3200 to 3400 rpm. Motor sound does not really change that I can tell. It appears to be oiling normal and does not run hot. I hope to get the chance to do further checking on it as soon as the Dr lets me resume normal activity from the cataract surgery I had on the 14th. I am restricted from lifting or straining for two weeks after the surgery. Thanks again for the information.

I will let you guys know results when I can.

Bill