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Tohatsu 4 stroke 6HP starting procedure

13921 Views 8 Replies 3 Participants Last post by  dabnis
About 2 years ago I bought a new Tohatsu 4 stroke 6HP outboard, I think the same as Nissan & Mercury & same basic motor as the 4 & 5 HP. It ran/runs perfectly right out of the box, even at 6,000 feet elevation with no jetting changes.

HOWEVER, it has always been a bit "cranky" to start. I had many cases of it flooding, & tried many different starting procedures. I think I have finally solved the problem. The tank has a vent-in only cap. I think what was happening was that when trailering the boat pressure would build up in the tank from the gas being sloshed around, resulting in gas being forced by the float needle. Being lazy, I do not disconnect the hose each time I use it.

So, what I did was:

1. Cut off the one-way duckbill valve in the cap, allowing venting in & out of the tank, eliminating the pressure build up.

2. Only squeeze the primer ball just enough for it to firm up, no more.

3. Follow the starting instructions EXACTELY

Last two trips out, starts on the 2nd or 3rd pull, clean with no smoke.

Am curious if anyone else had similar problems & if so, what was the fix?

Paul T
1 - 5 of 9 Posts
I had a 4-stroke Tohatsu 5 on my 22. I never had to modify anything to get it to start, but I did eventually develop a meticulous procedure.

  • Open air valve on tank
  • Pump the bulb (just until it has pressure)
  • Pull the choke all the way out, regardless of ambient temperature
  • Throttle at the "start" marker
  • One slow pull (with no intention of getting it to start on this pull)
  • One fast pull to start
  • Make sure that it's running well and water is pumping, and then slowly push in the choke.

I have no idea what the slow pull did, but if I did a slow pull first, the next pull just about always started it. If I neglected to do the slow pull, sometimes it would buck and act weird on the fast pull. On the very rare occasion that it wouldn't start on the first try using my usual method, I'd push the choke about halfway in for the subsequent pulls. If the engine was warm (from having just been run...I never saw much difference in the way the engine started just from the air temperature) I would do nearly the same thing, but without the priming bulb or setting the choke.

I don't think that this matches any of the typical advice, but my engine loved this approach and was uncannily dependable.
I also do the "slow" pull, just to make sure the shift interlock isn't engaged, then started doing two slow pulls. On my motor when you pull the choke all the way out there is a linkage that also opens the throttle a small amount, maybe to where the "start" part is?

I think the problem I had was the one way in only vent on the tank created enough pressure to over ride the float valve, resulting in flooding. Since I "modified" the cap so it will vent both in & out, it started on the 2nd or 3rd pull. In the beginning, not knowing what the problem really was I was squeezing the ball past the point of it being firm, no doubt making the problem worse?

Curious to know if you have one of the newer tanks that only vent in, or an older conventional two way tank vent?

Thanks, Paul T
I'm honestly not sure. It was a genuine Tohatsu tank and the vent was a little knurled plastic screw in the middle of the fuel gauge. I assume the tank came with the engine, which was a 2006. I didn't personally buy either...they came with the boat.

I always treated it as if it were a 2-way vent and closed it when leaving the boat, but I'm not sure.
It being at least 8 years old it may be the "old style" 2 way vent? The new ones, like mine, only vent in, allowing pressure to build, up to about 5 pounds, I think, which is quite a bit. I first noticed it when disconnecting or connecting the fuel hose & getting sprayed all over with gas. So much for the "vapor free" tanks. It finally came to me to loosen the filler cap first to blow off the pressure, more vapors in the air.

Anyway, thanks for the feedback.

Paul T
The EPA cap can be a problem. The older caps are available, and will fit.
You must disconnect the fuel hose and run the carb dry at the end of the day, or risk varnishing in the carb.
If you don't disconnect the primer hose, and the tank gets very pressurized by sunlight, you can blow the fuel pump diaphragm, which will then fill the crankcase with fuel when running.
If the carb inlet needle is working, the primer will firm up when squeezed, and that's all the fuel that will go in.
Yes, the choke does increase throttle past "restart" Also, a warm motor will need some more air to start well. Do not choke a warm motor.
Agree, leaving fuel in the bowl can lead to a carb cleaning, I forgot once, what a mess. I ran it "dry" & then later opened the drain screw & found there was still a little bit of fuel left in the bowl. I don't know if just a little bit will cause a problem, but don't want to find out. draining & shaking is easy & quick. Nice motor, for a 4 stroke. :D

Paul T
Yes, draining is best, but any sludge in the very bottom of the bowl is at least not in the passages, so running dry works during the season. If you know for certain that you will be running again tomorrow, no big deal... but if that could turn into a week or 2, best to get the gas out of the carb.
Agree, I generally use about a week or so as a target. If I don't drain, I give the primer ball a squeeze every other day to keep the bowl full. Don't know if it helps or not, but so far, no problems.

A couple of years ago we downsized our fishing boat & gave our bigger boat to my daughter & son in law. I suggested he drain the carb. He didn't. He had a shop clean the carb. Ran OK at low speed, but wouldn't pull a load.

Coming up soon, one brand new carb. :D

Paul T
1 - 5 of 9 Posts
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