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Tohatsu 6HP 4 stroke hard starting

D

Dabnis

New member
Bought it new in 2012, ran perfectly right out of the box, but a bit cranky to start, still runs perfectly,
trolls way down for hours without dying, & puts out full power. However it is getting more difficult to start
when cold. Get a couple of weak pops, then nothing, after about 20 or so pulls, it finally catches

What I have done:

1. Use the exact starting procedure as described in the manual
2. Tried full choke, about half throttle, not much difference that I could tell.
3. New plug each year, no difference.
4. Drain carb if not used for about a week.
5. Use an additive in the fuel
6. Squeeze the primer bulb until firm
7. Inspected all fuel line connections, all appear to be OK

The fuel filter looks clean but after running there is an air gap in the top, which I am suspicious of.

Would appreciate any suggestions
 
You didn't mention model (year is irrelevant); Probably MFS6C.
Usually a carb issue, but could be many other things.
A POP usually indicates a too-lean condition.
If you have an internal tank, you may not have good fuel delivery through the pump by gravity. If using external tank and primer bulb, that should not be a factor.
Choke only when cold. Sometimes a little extra throttle helps, but 4-strokes generally should not need to be started over 1/4 throttle. The choke on the 4/5/6 automatically adds some throttle.
Some fuel additives help prevent "rotting" of the fuel, but in general, they aren't especially helpful. Fresh gas is what you want; fresh non-ethanol is even better.
Running dry or draining the carb when sitting for a few days is a good practice, but after 4 years, it only takes one time to get some varnishing in the low-speed circuits, and cause hard cold starting.
The fuel line between the pump and tank is under vacuum when running, so a small bubble in the filter is OK. That air compresses when under pressure, but is still there; under vacuum, it grows a bit.
If it were my motor, I would check over everything (you already checked spark), and then do a Proper carb cleaning, then re-test.
 
pvanv said:
You didn't mention model (year is irrelevant); Probably MFS6C.
Usually a carb issue, but could be many other things.
A POP usually indicates a too-lean condition.
If you have an internal tank, you may not have good fuel delivery through the pump by gravity. If using external tank and primer bulb, that should not be a factor.
Choke only when cold. Sometimes a little extra throttle helps, but 4-strokes generally should not need to be started over 1/4 throttle. The choke on the 4/5/6 automatically adds some throttle.
Some fuel additives help prevent "rotting" of the fuel, but in general, they aren't especially helpful. Fresh gas is what you want; fresh non-ethanol is even better.
Running dry or draining the carb when sitting for a few days is a good practice, but after 4 years, it only takes one time to get some varnishing in the low-speed circuits, and cause hard cold starting.
The fuel line between the pump and tank is under vacuum when running, so a small bubble in the filter is OK. That air compresses when under pressure, but is still there; under vacuum, it grows a bit.
If it were my motor, I would check over everything (you already checked spark), and then do a Proper carb cleaning, then re-test.
Click to expand...

It is an MFS6B. I have used the internal tank some time ago, couldn't tell much, if any, difference when I went to the external
tank. IIRC, I haven't missed draining the carb but---. As it seems to be somewhat progressive, you likely have a good point
with the carb cleaning, although it runs perfectly at all speeds once it fires, trolls way down there for hours on end.

On closer look I can see some "Staining" in the fuel filter, which I will replace. If that doesn't work, I will clean the carb.
Thanks for your help.
 
Dabnis said:
It is an MFS6B. I have used the internal tank some time ago, couldn't tell much, if any, difference when I went to the external
tank. IIRC, I haven't missed draining the carb but---. As it seems to be somewhat progressive, you likely have a good point
with the carb cleaning, although it runs perfectly at all speeds once it fires, trolls way down there for hours on end.

On closer look I can see some "Staining" in the fuel filter, which I will replace. If that doesn't work, I will clean the carb.
Thanks for your help.
Click to expand...
Make sure the valve to switch tanks is closed, so that you are not trying to suck air from the integral tank, and so that priming goes directly to the carb, instead of filling the integral tank. Never hurts to change the fuel filter, but if dirty, that would restrict flow at high speeds, likely not prevent starting, since you prime through it. Keep in mind that a flaky spark plug can cause similar symptoms -- whether new or not. We often overlook that.
 
pvanv said:
Make sure the valve to switch tanks is closed, so that you are not trying to suck air from the integral tank, and so that priming goes directly to the carb, instead of filling the integral tank. Never hurts to change the fuel filter, but if dirty, that would restrict flow at high speeds, likely not prevent starting, since you prime through it. Keep in mind that a flaky spark plug can cause similar symptoms -- whether new or not. We often overlook that.
Click to expand...


I will check the valve, & get a new plug. I always try to do the simplest & cheapest things first, didn't even think about the plug.

Come to think of it, the problem started to get worse after putting in a new plug at the beginning of this season.

"Keep it simple" :) Thanks again for the feed back.
 
Well, well, with the help of Mr. Moon, on Sailing Anarchy:


"Sure. Cold starting procedure is to attach fuel line, pump up until I'm reasonably sure the bowl is filled, give the throttle a couple of twists to wide open and back, then set it to the start position (1/3?) , full choke. Usually catches on and runs on the first or second pull. Cut back to half choke for about 15 seconds, then choke off and away we go."

Tried it 3 times over 6 hours & it works, 3rd or 4th pull, fire!! I hope I am not speaking too soon, will try it again in the cold morning.

Not sure what turning the throttle all the way open a couple of times does? Maybe there is a small accelerator pump, or equivalentin the carb? In any event, it appears to be the answer, Many thanks, Moon.
 
johnnygjr said:
happy boating,good luck
Click to expand...

From Istream on Sailing Anarchy:

"Glad you got it working. There's no accelerator pump on these carbs that I'm aware of. Maybe your butterfly valve is sticky or the cable is binding or has stretched a bit, preventing the plate from opening without more significant throttle. Any of those could be helped by exercising the system with a few full twists of the throttle. I'd get in there and clean + adjust and see if there's a root cause you can find. "

I will test again this morning & do the "Clean & adjust" procedure he suggested..

Anyway, many thanks to all who replied here, much appreciated.
 
Update to an old post. About a year, or so ago, I thought I had it fixed, but it went back to hard starting. Long story short, I was going to order the high altitude jets kit. A dealer in the area suggested removing the brass cap over the low speed air screw & open it up from 1/2 to one turn. I opened it one turn, & it started on the 2nd pull in cold weather, & idled just fine. Will fine tune it on the boat under load in a few months. If you plan on drilling out the brass cap, I suggest you center punch it exactly in the middle & use a drill about 1/16 to 1/8", & drill very carefully just barely through. Then start a self tapping screw just enough to hold, then pull it out, kind of like pulling a tooth. Be very careful & gentle to avoid drilling into the pilot air screw, easy does it.

As I corrected an overly rich condition, at 6,700 feet, I hope the EPA Police won't be breaking my door down. Again, many thanks for all of your suggestions.
 
Um. The high altitude jets are LEANER. Increasing the pilot screw makes it RICHER. Something else is happening here.
 
pvanv said:
Um. The high altitude jets are LEANER. Increasing the pilot screw makes it RICHER. Something else is happening here.
Click to expand...

Yes, that is what the dealer said, about the jets, that is. He also said that the low speed mixture screw allows more air when opened up. In any event, the factory setting was 1-1/2 turns out. Per the dealers suggestion, I opened it up one more turn. Whether it was richer or leaner, the result was 2 pull starts instead of 20 to 30, pulls. As mentioned, I will fine tune it under trolling speed load in a few months.

I have seen some carburetors where opening the low speed mixture allowed more air, only know what the Tohatsu dealer told me about Tohatsu's. In any event, it helped with the hard starting. 2 pulls is better than 30.
 
pvanv said:
Um. The high altitude jets are LEANER. Increasing the pilot screw makes it RICHER. Something else is happening here.
Click to expand...

"Something else"? Forgot this:

Same plug
Same gas as last summer
Exactly the same starting procedure

Only change was to open the low speed screw one turn, which appeared to solve the hard starting issue. I will know for sure when I start fishing in a few months. Being a Tohatsu dealer, I think?, you know way more about them than I do. It appears the dealer in our area & you have differing positions on the jetting issue. His suggestion seems to have worked, time will tell. Appreciate your input.
 
Yes, I'm a dealer. I have worked on a hundred or so of these, and the truth is that adjusting the pilot can be an issue. They are set by instrument at the factory, so should be spot on when delivered. That said, richening the pilot can cover up some for varnishing in the idle/slow speed circuit. However, once the carb is cleaned properly, that setting then makes the slow speeds too rich. Check the plug; if it gets dark fast, you are too rich.
 
pvanv said:
Yes, I'm a dealer. I have worked on a hundred or so of these, and the truth is that adjusting the pilot can be an issue. They are set by instrument at the factory, so should be spot on when delivered. That said, richening the pilot can cover up some for varnishing in the idle/slow speed circuit. However, once the carb is cleaned properly, that setting then makes the slow speeds too rich. Check the plug; if it gets dark fast, you are too rich.
Click to expand...

Yes, I have checked the plug more times that I can remember, it always looks just a bit off color, never dark or wet. Have also replaced the plug many times,
"Just because". When I had the carb off I dropped the float bowl & it was perfectly clean inside, not a grain of residue or any discoloration, & as mentioned, once started it runs perfectly at all speeds, all day. Once it starts, it smokes, a bit, blackish, not severe, but more than I think a 4 stroke should. The hard starting was present from the first time I started it when it was brand new.

I am anxious to try it in the water, might even launch through the ice to try it. Again, thanks for your help.
 
pvanv said:
Verify that the oil is not even a drop over full. Mid-way between the hash marks is good.
Click to expand...

Oil level is right at, but not over, the top mark with the dipstick screwed in. Motor is level. Last oil change I filled with exactly 15 oz

Model is MFS6CD Serial # 007976AB

Thanks
 
Well, it looks like I finally broke the code. As mentioned in post # 12, per a dealer near our area who suggested I open the low speed mixture screw one turn,
I did just that, after removing the metal cap. After three separate starts on different days, this morning, on the boat, in the lake at 6,000 feet elevation, & at 34 degrees, took three pulls, started smooth, clean, no smoke as before the adjustment. Trolled perfectly, actually had to back off the idle speed screw a bit.

Our local dealer said opening the low speed mixture one turn would allow more air, resulting in a leaner mixture. PVANV here stated the opposite. Whatever, I don't know, & don't care, it worked. Should have done this when I first bought the motor, about six years ago, all those 20 to 30 pull starts for six years, good exercise, I suppose, but very frustrating.

Please note, in fear of the EPA police force, I am not recommending anybody do anything, just passing along my own experiences.
 
Glad you got it going. Yes, I have adjusted quite a few of these, but I typically don't recommend a consumer do that, because they often overdo it. Proof is that you were able to lower the idle stop speed. That indicates that you now have a better idle mixture. Opening the pilot screw dumps more fuel at low speeds, which is apparently what you needed. In the event that the carb gets cleaned well in the future, you MAY end up a bit rich at idle... but you now know how to adjust for that.
 
pvanv said:
Glad you got it going. Yes, I have adjusted quite a few of these, but I typically don't recommend a consumer do that, because they often overdo it. Proof is that you were able to lower the idle stop speed. That indicates that you now have a better idle mixture. Opening the pilot screw dumps more fuel at low speeds, which is apparently what you needed. In the event that the carb gets cleaned well in the future, you MAY end up a bit rich at idle... but you now know how to adjust for that.
Click to expand...

Right now it is starting & running perfectly, using the starting procedure as shown in the manual. If it was too lean at 6,000 feet I can't imagine how it would have run at sea level. The lowest elevation we ever ran it was ta about 3,000 feet. Anyway, at this point I plan to leave it alone. If it starts to become hard to start again I think your thought of the low speed jet varnishing up is spot on. Thanks for all of your input, much appreciated.
 
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