2006 Tohatsu 18 carbed 4 stroke, hard starts, fuel under cowl, and leaking out of TB

[lmuss53]

My first impression is to pull the carb off and look for something in the needle valve. I did notice that when I pushed the ignition switch in, nothing clicked and it had no impact on the running engine, is there an issue of the enrichener sticking open. I'm a pretty good OMC and Merc 2 stroke guy, but have very little experience with these 4 strokes. It will start eventually and then it runs ok for a few minutes and starts to spit and sputter and eventually shuts down. It will run fine with the throttle open and on plane.

Any help is very much appreciated.

 

[pvanv]

OK, so your model is MFS18B2. That's critical. Year is irrelevant for servicing these.

There is no choke, and pushing in on the key does nothing. It does have auto-by-starter enrichment. That has a heater which expands over time with the power on. You can apply 12v to the ABS when cold, and see whether, over the course of a couple of minutes the needle extends. If not, the ABS is shot (that's VERY rare). You can also see whether you are getting voltage to the ABS when running.

HOWEVER, if you are actually spilling fuel, the carb is flooding. Probably a needle/seat thing.

 

[lmuss53]

Thanks Paul, I got the carb off today and took it down to the parts and pieces. It was clean as a whistle when I took it apart, float was level when upside down and all in all it looked fine. I put it in the ultrasonic cleaner anyway and gave it 40 minutes at 50C. I took it out and got it dry and blew choke cleaner thru every orifice and passage, everything is open and clean. I had had enough of the 20 degree outside temps in my shop with a small propane heater so I called it a day. I will get it back together tomorrow and see what it does. Any additional tips or suggestions?

 

[pvanv]

Pay very close attention to the tip of the needle and the seat. If that weeps, the carb will over-fill and spill fuel. Of course, at that point, it will be very rich-running. If you prime the carb with the bulb, and it continues to accept fuel after full, the needle is leaking. When I do those carbs, I run the heated ultrasonic for several hours at 50C, and then blow everything out with carb spray. Is the bowl passage that transfers fuel to the small bowl for the accelerator pump and ABS clear? That is a common stoppage area on these, if the carb isn't always run dry at the end of the day.

 

[lmuss53]

I did not pull that tiny snap ring out at the bottom of that small accelerator pump bowl, and since I'm not familiar with how the carb works I'm not sure what should flow where. I'm going to go tho one of the parts pages and look at the blow up for this carb. Thanks for your interest and responses.

 

[lmuss53]

The needle and seat looked perfect and I could not push fuel past the needle with the ball when I first got it here. I'm going to look that accelerator pump over again and put iti back together and install it.

What was the test for that ABS plunger, do you do it with 12 volts?

 

[pvanv]

Yes. There is a heater and a wax capsule. When powered from cold, the heater causes the wax to expand and push the needle out. This takes a few minutes. Yes, it is 12v. Again, if you are overflowing the carb, the needle and seat was not shutting off fuel.