# 40 tohatsu missing while at full throttle



## Brett (Jul 16, 2008)

Are you sure you aren't activating the rev limiter?
Aerated water in the tunnel will let the prop spin up
and that will cause the rev limiter to kick in until the prop bites clean again.


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## James4302 (Apr 17, 2011)

I will test it in the am.... I will run the prop in clean water on the JP at 0. On a good day with that prop I have only seen 5400rpm the motor is rated at 5150-5850 just asking- do you think the rev limiter would kick in not getting above 5400? Just askin'?


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## Brett (Jul 16, 2008)

Interesting thing most don't know about tachs,
many are not accurate, right out of the box.
It's recommended they be calibrated before use.

http://www.se-r.net/electrical/top_speed_speedo.html


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## Gramps (Nov 1, 2007)

It sounds like you've got a lot of cup in the prop. What make and material is the prop? I'm currently running a custom cupped 13 pitch and only hitting 5400rpm, I'm talking down hill with the wind to get there but the 13 pitch stocker & an 11 pitch cupped prop ran out to 5800 without ever hitting the rev limiter. 

With that said, I'd have to side with Brett, it sounds like you are hitting the rev limiter. Tiny-Tach's are a good option but $50, maybe a local Tohatsu dealer can hook up his computer & data log for comparison? Otherwise I'd suggest finding another tachometer to verify the operation of the OEM unit.


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## James4302 (Apr 17, 2011)

Ok... I started to look in to this issue... I decided I would start with the spark plugs... Bang!!! I found it... My top plug was missing all of the ceramic all the way down to the threads... 12.00 fix... Man I am relieved...


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## makin moves (Mar 20, 2010)

easy fix nice


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## Gramps (Nov 1, 2007)

Very cool. It's always a relief when _something_ on the boat is cheap to fix. ;D So, when we fishin?


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## James4302 (Apr 17, 2011)

Well.... I just thought I had the problem solved after a few months of trying to get it proper out I was talking with the guy I bought it from and he said he was getting low 30's out of that motor and I could only get 25.2 on an incoming tide...

Well I have done a hillbilly compression test on it where u pull off the plug off the cyl and crank it over with your finger covering the plug hole on the top cyl and super low compression compared to two other ones.  I am thinking that the guy knew it had some issues so he would push it over on someone else... Can anyone ball park me on specifics on what this mint be.  

Best cast senior blown head gasket???

Worst case senairo busted ring and lots of scaring and piston damage???

When is being a boat owner fun??? Ever??? ;D ;D ;D


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## Brett (Jul 16, 2008)

Get a compression gauge, thumb test is fun,
but not accurate enough for diagnosis.


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## mmjamp (Jul 3, 2011)

If it is a 4stroke motor it could be many things, head gasket, intake valve, exhaust valve, rings, etc. Only way to tell is pull the head. But like mentioned before get a good guage and test it first.


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