2010 Tohatsu MFS6B won't stay running

[rsnyder518]

Glad I got a sailboat so I could sail back to the dock.

I brought a tank of fresh gas up to the boat this morning. Hooked it up and pumped the primer...but I couldn't get it hard. Usually it pumps up quickly, so this was weird. Out of curiosity I started the motor and all seemed fine. I gave the bulb a quick squeeze after it had been running for a few minutes and it seemed to have firmed up a bit. I figured it was a fluke (and maybe it was) so I left the dock and sailed for a few hours. At the end of the day I started the motor and it seemed normal. After a few minutes of motoring the motor just suddenly quit. I tried to restart it and it started back up but died almost immediately after putting it in gear. Then I couldn't get it to restart until I squeezed the bulb which was firm at this point. Then it started, ran and again died pretty quickly after putting it in gear. Got it started again, by squeezing the bulb. Thinking that maybe it was a fuel pump I tried to keep it running by squeezing the bulb but it didn't work. Even out of gear, it eventually stalled out...just not as quickly.

I'm a fanatic about gas. I had bad gas problems the first year I had this motor. But now I change the gas every 2 weeks, I use K100MG, I run it dry at the end of every outing, I clean the carb at the beginning of every season (4 hour soak + spray) and I use 91 octane. If this current problem is due to a dirty carb I'm going to be extremely disappointed because there is literally nothing else I can do to keep the carb clean. I don't think it's realistic that 3 weeks into the season it's already gummed up given that I totally cleaned it at the beginning of the season and have used fresh gas + stabilizer and have run it dry.

My gut feel says fuel pump issue, but not certain why I couldn't keep it running with pressure on the bulb. Thoughts, suggestions?

Thanks!

 

[Sea Rider]

Re: 2010 Tohatsu MFS6B won't stay running

Did you opened the tank's air vent ? If engine when running starts to die and you prime bulb again and engine catches rpm up, it's a fuel pump related issue, seems not your case. If there isn't and debris found inside carb, definitely you have a clean carb. What about when giving throtttle, the engines dies too ? Or it's just a idle rpm issue when dying ?

The bulb doesn't need to be stone hard, just firm and start engine as usual. Pull choke, place throttle grip to match start position, some hard pulls, push choke back in, let engine gain working temperature..

Happy Boating

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B won't stay running

Vent was open.

Idle in nuetral is fine, off idle is fine...for a few minutes. After a few minutes, revving it up induces stalling. In gear its the same story but the "few minutes" becomes "few seconds".

I guess I will be pulling the carb off....again. I am more fanatical about clean, good gas then anyone I know. Yet I have the most problems. Very frustrating. Not bashing Tohatsu but I have the only one at my marina and I have the most problems. I get a lot of people saying that the "bargain basement" motor is the problem. No one listens when I try to explain that they also make most other brands of small motor too.

 

[Sea Rider]

Re: 2010 Tohatsu MFS6B won't stay running

It's incredible that people probably having same rebadged brands talks silly things about Tohatsu, no real difference if being Nissan, Mercury exact same portables. That's the issue of being "the new kid on the block"...

Happy Boating

 

[pvanv]

Re: 2010 Tohatsu MFS6B won't stay running

You may still be under the 3-year warranty, so check the date of warranty registration. The MFS4/5/6B (which is identical to the Nissan, Mercury, and Evinrude) is almost indestructible... I have a fleet of these motors on rental sailboats in Buffalo, and they get abused like crazy... yet only need periodic maintenance... But, your problem could be a lot of things.

A weak fuel pump is probably not your issue, as the primer will push fuel past the pump... so, if squeezing the primer doesn't keep the motor running, you probably are getting enough fuel delivered to the carb.

If your oil is overfilled, that could cause your issues. Along those lines, if you have a blown fuel pump diaphragm, you could be getting fuel in the oil, resulting in a too-full crankcase. When a primer won't get firm, there is either (compressible) air in the system, or the fuel is leaking out somewhere, possibly either at the fuel pump, or at a stuck-open carb needle.

It's also possible that you have a thermally-failing ignition component. In other words, an ignitor that works OK when cold, but gets cantankerous when hot.

K100 works well to slow fuel "rotting", and will help keep any small amounts of water suspended in the fuel (instead of separating out)... but the real trick is to always run fuel less than 30 days old (as you are already), so I doubt that fuel quality is the issue. In western NY state, some of the NOCO 91 octane fuel is also non-ethanol, which is a real plus.

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B won't stay running

I have taken the motor off the boat and transported it back home for inspection/repair. I don't really have a dealer conveniently close to me. There's a Mercury dealer up the road and I know they'd have the knowledge and ability but don't know if they could do it under warranty.

1. I checked the oil level and it is good. I am aware that these motors are sensitive to oil level and very easy to over fill but I am 100% certain this motor is not over filled.

2. I had been suspecting a fuel pump but as you indicate that appears to not be the issue. But I did have a spare, so I've swapped it on just in case. (Yeah, I know that "throwing" parts at it is bad form, but I already had the pump so I figured what the heck)

3. I pulled the carb off and took it apart. Everything appears to be in working order and clean. But since I had it apart anyways I did another full cleaning. The float isn't cracked, the level looks good. The needle appeared to operative freely with no noticeable damage to the tip or seat.

4. I hope that it's not an ignition component that behaves badly when hot. I hadn't thought of that. In my experience with other small motors such as lawn mowers and snow blowers I've never had an ignition related problem with the exception of spark plugs. I don't really have a good way to get the motor nice and hot at home since I'm just running it in a bucket. Everything seemed fine until I was in gear so if it's thermal I think I'd need some load on it to build the heat up and I can't put it in gear in the bucket.

5. Pulled the spark plug. The gap is good, and it's clean with some slight lightish brown.

I'm starting to wonder if it's my fuel line and/or the connections? It's new this year and it's a West Marine "make your own" since the standard Tohatsu line doesn't really work well on my boat (location of the primer bulb is problematic). I bought the fittings from Tohatsu and hose clamped them onto the West Marine line. Everything appears to be good and tight with no leaks. But I have noticed that sometimes it's a little difficult to make the connection to the tank. Maybe it wasn't on tight (even though I removed and reconnected it a couple times)? There's an o-ring in the tank fitting, maybe it's swelling a little with age making it hard to get the connection? Maybe some air was getting in? I'll bring up a spare line to the boat and see if that affects it. Maybe I'll replace the tank fitting? Probably quick and cheap to replace the filters too.

It's a learning curve. The first year with the motor was terribly problematic something that I've now learned was due to poor gas management. Last year was no problems. I've sailed twice this year and am having problems. Let's hope it's something simple! It's very frustrating to have a nice day of sailing only to have it end with motor issues. Sailing in isn't always an option depending on wind!

Thanks again for all the suggestions, please keep them coming!

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B won't stay running

Update: So I cleaned up the carb and replaced the fuel filter, checked the spark plug and all seemed well. It bugged me because I never found a problem and still didn't have a good idea as to why my motor cut out on me. My main problem is that I couldn't run the motor in gear in my garage. So I brought it to the local outboard mechanic. He's not a Tohatsu dealer because there isn't one that I trust near by. But he's a Mercury dealer so he's familiar with the motor and came highly recommended from some local boaters.

Glad I did that. Turns out pvanv was right! I had a bad ignitor. I'm going to miss sailing this weekend because he needed to order the part but I'm glad that he found the problem. Just wanted to update everyone.

 

[mikehoyt]

Re: 2010 Tohatsu MFS6B won't stay running

How do you check for a bad ignitor?

 

[pvanv]

Re: 2010 Tohatsu MFS6B won't stay running

How do you check for a bad ignitor?

You need a good analog (not digital) ohm meter, and use the Factory service manual as a guide to test the ignition system.