Tohatsu M40C surging

[elong0916]

I have a 2000 Tohatsu M40C that starts and runs good at idle but seems to be surging when running wide open in the water. It will do good the first few minutes, it will be humming along and then it dies down and then comes back, sort of like you were goosing the throttle. Thinking maybe it is doing it after it warms up, maybe getting to warm?
I have checked the compression and spark, all good. This motor does not have the pee indicator on it, but when it is idling the exhaust relief ports have water just barely trickling out.... I know this motor is thermostatically cooled, but I'm not sure how much water I should be looking for? Also, what reading should get with a IR temp gun?

 

[pvanv]

Re: Tohatsu M40C surging

Temps should be around 150-160, depending on where you take a reading. Check for any possible air leaking into the suction side of the fuel system, and confirm the fuel vent is clear.

 

[elong0916]

Re: Tohatsu M40C surging

Thank you Paul. I just removed the carb to make sure it was clean and I found that one of the two pieces of the housing that holds the pin for the float is broken. So the pin is not secured on that side and allowing the float to move around.
I am pretty sure this is my problem. I guess I wil have to replace the carb to know for sure.

 

[pvanv]

Re: Tohatsu M40C surging

If the rest of the carb is serviceable, you can still get:
CARBURETOR REPAIR KIT: 40C 2-STROKE
Part # 345871223M
$63.67

But if the carb casting itself is damaged, you will need:
345032000M CARBURETOR ***'Y $202.72

 

[elong0916]

Re: Tohatsu M40C surging

Unfortunately it is the casting so i will be buying a carburetor. Hopefully this resolves my issue, I'm still not sure if I should have more water coming from exhaust idle relief ports. I will be able to shoot with temp gun once I fix the carburetor.

 

[bcbit01]

Re: Tohatsu M40C surging

That should fix the problem. Proper operation of the float needle that lets fuel into the carburetor is critical to keep the bowl from overfilling, forcing unmetered fuel up the main jet and flooding the engine. I will defer to PVANV's advice but, if you still have the pieces of casting, you should be able to fix it. That structure receives ZERO load (in fact I can't believe it broke...sounds like rough treatment by a mechanic) so you should be able to JB Weld it back into place and put the pin back. You should NOT have to buy a whole new carburetor just to remedy that. I would also have a conversation with my technician and how he takes care of your motor.

 

[elong0916]

Re: Tohatsu M40C surging

Yes, I actually traded motors with a guy who was overpowered, this motor he had bought just a couple months before from a boat center and I can't help accusing them of breaking the carb because I'm pretty sure they prob had the carb apart. The piece is actually not in the bowl so somebody had it off.... I thought about using JB to build a new end but I was not sure if JB will stand up to being submerged in gas?

 

[pvanv]

Re: Tohatsu M40C surging

Ymmv.

 

[bcbit01]

Re: Tohatsu M40C surging

I recommended "gluing" the piece back on with JB Weld. If the piece is gone, I would not "build up" a new ear and drill it. Its only held on by that tiny interface with the rest of the casting. PVANV is right....get a carb. $200 well spent. Keeps you from getting stuck out on the water.