2010 Tohatsu MFS6B Carb Rebuild

[rsnyder518]

I have a 2010 Tohatsu MFS6B. I pulled the carburetor for cleaning and found the float bowl full of what looked like sawdust? Not sure where this came from or exactly what it is (I doubt it's actually sawdust). I've attached a picture, and I'd love to hear what people think this might be. It's not evident anywhere else in the system, didn't see it in the lines. Cut the filter apart, didn't see it there. It's a mystery to me. Believe it or not, it did run although the idle quality was a little poor.



So I cleaned and rebuilt the carb and because of the contamination I'm pretty much going to replace the rest of the fuel system. It may be overkill, but better safe than sorry I guess especially since I don't understand where it came from.

At any rate, I'm reassembling the carb and I don't know how to adjust the pilot screw? I have a service manual but all it says is that it's not adjustable. Maybe I'm not supposed to be adjusting it but I removed it for the purposes of cleaning. I did count the number of turns and have put it back to where it was, but it seems as though there has to be some method of actually verifying the adjustment.

Any advice would be appreciated. Thanks!

 

[pvanv]

Re: 2010 Tohatsu MFS6B Carb Rebuild

I have seen that before... actually a few times. It is a result of bad gas, or contamination in the fuel. Sometimes that stuff is dispersed in the gas, and it's small enough to pass through in-line filters. Sometimes it happens as the fuel decomposes. Seems to happen more with E-10, with stabilizer added, when some water gets into the gas. Definitely try to run the carb dry at the end of each and every day. That reduces the fuel in the carb bowl to under a teaspoon. If there's no fuel, it can't rot. If practical, add a water separator filter. And always run fuel under 30 days old.

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Thanks. I've never seen anything like that before so I really wasn't sure what I was looking at. I definitely had some gas problems last year so I guess this isn't surprising. You mentioned that this happens more often with E10, water and stabilizer. I'm stuck with E10 sadly, I can do my best to minimize water intrustion. Should I continue to use the stabilizer? Also, I hadn't been running the carb dry when I was done. I (perhaps incorrectly) assumed that keeping it full was better, along the same line of thought as keeping the fuel tank topped off.

Thanks again for the advice! If anyone has a procedure for adjusting the pilot screw I'd love to hear that too!

 

[Sea Rider]

Re: 2010 Tohatsu MFS6B Carb Rebuild

I call your sand dust, coconut dust, happens when E contaminants are filter bypassed at plant, deliverd to gas stations and badly filtered there too, have had it in several occasions, definitely bypasses mesh filters to be deposited inside carb bowl and produces bad performance from 3/4 to wot as the engine needs more juice and has it rescticted. If repeats frecuently, buy gas on cans and filter with coffee meshs before adding gas to tank. Could add a water separator as recommended, but costier for such a small engine and a nightmare if placing, removing from boat frecuently.

Don't replace fuel line, just clean tank and internal filter well, remove engine's entrance line to filter, place a container and squeeze bulb several times to let gas pass through hose system if thinking having unwanted sanddust remains inside bulb or line. Check container. Place a new filter.

Don't know 4 strokes motors but for what have read seems to have fixed unremovable air/gas screw, it that's your engine case, seems you have removed the idle rpm screw...

Happy Boating

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Yeah, also glad to hear I'm not alone. I internet surfed and didn't see anything similar.

It's definitely the pilot screw that I took out and it's definitely adjustable....after you remove the security cover they put over it. I couldn't see leaving it alone given how much stuff there was in the carb. I counted the number of turns and put it back to where it was, but the spark plug tells me I'm somewhat rich. So I was wondering about the adjustment procedure. I didn't really notice terrible performance from 3/4 to WOT, but I'm on a sailboat so it's not an area that I operate it in too often. My idle on the other hand wasn't great and I did have some intermittent stalling problems.

During the winter I bought the Tohatsu fuel filter/separator. I'm trying to figure out a decent place to mount it as anywhere convenient is tight with space. Here's my latest and greatest E10 plan for the upcoming season:

1. Keep tank full (>90%)
2. Keep gas fresh (less than 30 days at most)
3. Run carb dry after each use
4. Install filter/separator
5. Filter gas as I put it into the tank
6. Sta-Bil
7. Pray and hope

 

[pvanv]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Setting the pilot screw is a bit of combined art and science. Yes, it doesn't affect WOT much; mostly idle and some effect on the transition (tip-in) from idle. Setting it correctly in the field requires a very accurate shop tach, a good ear, and you must be in the water (not just on muffs). Typically, start at about 1-1/2 to 2 turns out, and get the motor fully warmed. Cycle the throttle up a few times, and then check the idle speed. Adjust the idle stop to get within specs. Then make a quarter turn on the pilot (whichever direction increases RPM and produces a more pleasing intake note), and repeat the throttle and idle stop procedures. Listen very very carefully for a change in the intake note. Repeat until you have found the maximum idle mixture RPM. Then add about 1/16 to 1/8 turn richer for stability.

Fuel stabilizer is OK to run. We have found the K-100 products to be about the best (they don't contain any alcohol -- many others do). They make an MG formula (marine/gas), which is a stronger blend of the chemistry than what they market for road use.

BUT... stabilizers only slow the "rotting" of the fuel. They don't remove water, and don't clean the gas. And... they can produce a "gel" when they are run in water-contaminated fuel. Personally, I do run K-100MG, and I haven't had any issues. But the best practice is to run only fresh gas, and always run the carb dry at the end of each day. You can dump any gas over 30 days old into the car to get rid of it.

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Paul,

Thanks for the tips and advice, it's really appreciated. It is clear to me now that I've been pretty sloppy with fuel management and gunked up the carb as a result. I'll try the K-100MG this season and make sure I keep the fuel clean, full and fresh.

With regard to the pilot screw adjustment: How accurate does the tach need to be? I have a TinyTach but based on your post I think it may not have the resolution I will need for the adjustment. I may be able to borrow a better one from a mechanic friend.

I did set the screw back to where it was which turned out to be 2-3/4 turns. Maybe I should just leave it at that?

 

[TOHATSU GURU]

Re: 2010 Tohatsu MFS6B Carb Rebuild

It's an ear thing. Detecting the right point to set it is not a set number of anything, however, if you set it back to where it was originaly you should be fine. The reason it was hidden is that it is not legal to alter the setting...It's also unnecessary to remove it for cleaning as the acid in carb dip will work it's way everywhere in the carb without anyone having to touch it.

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Yeah, I probably should have left well enough alone and not messed with it. Water under the bridge now I guess. But I'll know for whenever the next time is!

 

[pvanv]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Right you are! The tiny tach may be accurate enough. You need that to reset the idle stop after adjustments and throttle cycling. The big thing, as Elvin noted, is a keen ear to listen for the intake note. At worst, most newbies set the mix a little on the rich side, which works OK, but results in plugs fouling faster. If you end up within about a 1/16 - 1/4 turn of the Factory setting, you are probably just fine.

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

So, based on what you saw in my carb are there any other fuel system components that are suspect? The lines look ok, I've replaced the filter. Should I be concerned about the pump or anything else?

I'm hoping to reassemble and try to get it running this weekend. Wish me luck!

 

[pvanv]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Just flush everything (the pump included) to make sure no gritty stuff is in there... otherwise, if any is remaining, it could possibly end up in the carb.

 

[Sea Rider]

Re: 2010 Tohatsu MFS6B Carb Rebuild

If this stuff is capable to bypass mesh filters, will surely bypass complete gas pump as well and definitely end on carb's bowl.

Happy Boating

 

[Davem3]

Re: 2010 Tohatsu MFS6B Carb Rebuild

this makes me glad i use non-ethanol fuel only in my motors, but regardless, this is a awesome thread, should be stick'ied, because the info paul, elvin and sea rider provide here is very valuable.

RS, this was a bad experience, but we have all gotten some great wisdom from it, and i am printing it out, for future use.

so, the fuel line/ball pump must be changed from time to time is what i am getting, because at 75 dollars a pop, this is a big ouch.............

 

[pvanv]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Dave,

If the fuel line fittings develop a vacuum leak over time (due to worn o-rings), and start allowing air into the fuel line, you can replace just the ends. If the check valves in the bulb start leaking, you can buy just the primer bulb. Often, the fuel hose starts to harden and become brittle around the same age, so if the while primer hose is shot, it's easier to just change out the whole hose, for about $60+.

 

[Sea Rider]

Re: 2010 Tohatsu MFS6B Carb Rebuild

If wanting complete hose to last much longer, don't let it exposed to sun/UV or with E fuel inside for long periods of time. Before shutting engine off or while in the process of runiing carb dry while flushing, disconnect hose from tank and while pushing open internal valve with finger let engine suck E fuel leftovers untill engine drops dead. Will take it's time but it's worth it if you want to save some $$$ due to premature wear.

Happy Boating

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

I finally had time to reassemble everything and I'm going to claim "moderate" success but I think still have a bit to sort out.

The motor started on the second pull (my first pull was a little half hearted). I let it warm up for 10 minutes and found that the idle was a little low (~950 RPM) so I adjusted the idle screw to ~1300 RPM (factory spec for operation in nuetral). My tach indicates that the RPM's actually fluctuate up and downa bit, so I actually shot for 1250 RPM so the +/- kept it between 1200 and 1300. It seemed to idle at least as well as it ever has. I revved it up a bit and it seemed fine. However, if I goose the throttle from idle real fast it stumbles bad. I'm on a sailboat so I really don't go around goosing this thing, so I can't honestly say whether or not it did that before I cleaned/rebuilt the carb. Any thoughts on the stumbling when I goose it fast? I also noticed a small air bubble in the inline filter. It did not go away as I ran it. Possible air leak or normal? Can that contribute to the stumbling? BTW: total run time 45 minutes tonight if it matters for anything.

As you may remember from earlier in the thread, I messed up and removed the pilot screw when I took the carb apart. At least I remembered to count the number of turns for the screw and I put it back to where it was to get it going. For "fun" I also tried to follow pvanv's and TOHATSU GURU's instructions and started 2 turns out and played it by ear. I ended up more or less where I orignally was at 2.75 turns. I guess that's kind of comforting.

Thanks again everyone for your help and patience! I've done this with lawnmowers, but I find they are a million times more forgiving that the outboard. No emissions standards, one speed operation, can't leave me stranded in the middle of a lake. So this is a little new to me.

 

[pvanv]

Re: 2010 Tohatsu MFS6B Carb Rebuild

The MFS6B does not have an accelerator pump in the carb, so it needs to be as rich as possible during tip-in (transition) to avoid a too-lean condition. If your cleaning did not include a 4-hour bath in real carb dip, that might help. Likewise, a super-dose of Chevron Techron in the fuel may, over time, help dissolve any varnishing in the low-speed passages. YMMV with the fuel additive. We have had only mixed results.

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Well, it didn't include 4 hours in carb dip but it did include some time in an ultra sonic cleaner. I thought that would actually be better. Is that a correct assessment? If not, then what do you consider "real" carb dip? I have some Seafoam additive, any experience with that?

It only stumbles when I snap the throttle from idle to WOT, but I suspect that it shouldn't stumble right? Or without accelerator pumps is some stumbling inevitable when I snap the throttle?

 

[rsnyder518]

Re: 2010 Tohatsu MFS6B Carb Rebuild

Additional info and question. As you could tell from the picture in my first post the carb was pretty dirty. I'm able to believe that my ultrasonic cleaning didn't get everything and that's contributing to the stumbling. My plan is to disassemble and clean again using pvanv's advice of a 4 hour dip and cleaning to see if it helps.

So I went out and bought a bucket of carb cleaner made by "Gunk". There are warning all of it not to put plastic in. So my question is do I have to worry about the linkages and choke plates, etc...? I didn't remove those items for the first cleaning.

Thanks.