Tohatsu etc. 3.5 2 cycle carb issue

[Rick D]

I have a Mercury (Tohatsu clone) that has an annoying carb problem. For background, I have had this engine for ten years. I had a Tohatsu twin of this for another ten years. It was a one-pull start engine. This one was one of the last two strokes sold by WM in CA. As such, it is a CARB certified engine that runs so lean I finally figured out I had to choke it even when it was still warm and had to run 50% choke for the first 30 seconds or so of acceleration when cold started to warm it up enough.

It sounds like I hate it but I don't. To the contrary, it is light, compact and reliable and had plenty of torque for our needs.

However, with the gasoline formulation changes in the past couple of years, it has become a PITA. Mostly, it's due to the fuel going stale in less than six weeks. Now I always put fresh fuel in it before a trip, add Stabil always and run the carb dry before storing. This after several carb overhauls. Now my problem is that the float valve hangs up upon fresh use and the carb bowl overflows and the engine floods. Happened too many times to be a piece of debris. Once torn apart and freed, all is well for the duration.

It isn't complicated, but I cannot figure out why it does it after a run-dry. Or, what to do about it.

Any ideas most appreciated.

 

[RichH]

Get a carb rebuild kit and be SURE to replace the needle valve that controls the level of the float chamber. This needle valve 'should' be rubber tipped, the OEM rubber probably has become soft and deformed over time due to contact with the ethanol in your gasoline.

 

[Steve Dion]

Rick:

One thing you may want to consider if putting a fuel filter on the inline hose from the tank. While I realize that this is NOT going to remedy your immediate problem, it should help prevent getting crap-O-la in the carb.

I am wondering if some of this problem is caused by using gasoline with alchol in it. I suggest that you drink alchol & only use fuel without alchol added (if possible).

PS: This is not another Jabsco Fiasco is it?

 

[Don12364]

Too Much TLC?

Sounds as if the evaporating fuel may be leaving a gummy residue which either sticks the float to the bottom of the float chamber or prevents a seal at the float valve. Apart from giving it a healthy whack with a baseball bat to free it up after turning the fuel on, I wonder if not running the carb dry each time would leave enough in the float chamber to keep it moist and prevent this effect.
Nowadays float chambers are sealed to the outside so the fuel should not evaporate. Of course there is a path via the carburettor itself, but only through the tiny jets so evaporation should be minimal.
I never run dry on any of my 3 engines and the Yamaha which lives in my stern locker only sees the light of day once a year at best.
Then it sometimes needs six pulls to get it going - but it never fails.

 

[Mike Holibar]

A few drops of Fuel Set works wonders removing gum and varnish and when used routinely seems to prevent oxidation of the fuel. I'm not sure where to obtain it over your way.

Regards,

 

[Charisma]

I was having carb problems with a new to me 6hp Merc. After posting on this site I used the advice of others and cleaned everything with "seafoam". So far it seems to have fixed the problem, and I am able to start the motor with 2 or 3 pulls and after the initial strart-up it runs and starts on the first pull for the remainder of the weekend. PS I also use the seafoam now as a gas stabilizer. Chris

 

[Rick D]

Thanks everyone!

Rich, I'm going to order a kit. I have OH'ed this carb so many times, it will only take me 30 minutes. Don, you may be on to something. Maybe I'm causing more problems than solving by running the bowl dry. Mike & Charisma, will explore your suggestions. Steve, it is way cheaper than the Jabsco issues!

 

[David Knauer]

Rick,
I don't have anything constructive to add to this discussion except that I seem to have the same problems with my 9 YO Tohatsu 3.5. I did rebuild the carb once and that seemed to help. Now, I have to shut the fuel tank and let the carb run dry before it will start again anytime in the near future. I discovered this by trial and error. Besides that it is a good engine for all the reasons you mentioned.
David Knauer

 

[kenn]

We have a 1983 Suzuki 5 hp two-stroke. This is our 4th season with it. It generally starts third or 4th pull at the beginning of the season, and after that it usually starts first or second pull.

I don't run it dry except at end of season. So far, for maintenance I periodically blast some carb cleaner into it while it's running. I only use premium Shell gas (which claims to have no ethanol), good 2-stroke oil, and fuel stabilizer.

It's my belief that the ethanol-free gas lasts longer and doesn't cause as much build-up issues. So far, so good...

 

[Rick D]

Yea Ken, I think You Identified One Problem

My older identical Nissan never had this problem. However, I am told that the 1999 model Merc I have is CARB (California Air Resources Control Board) approved and for it to pass emission tests, is set to run very lean. I think it was the last year two strokes were available in California if I recall. Thus, I am told, it is finicky to start with and any debris or varnish renders it troublesome. I can believe it, altho it appears to be more of a problem the last few years, and not only in this, but also several other gas-powered items I own. I do use a stabilizer and premium fuel. So, I think the 'solution' is to overhaul the carb and maybe see if I can get a richer jet, assuming it's replaceable. I guess I need to get a manual while I'm at it.

 

[Rick]

Re: Yea Ken, I think You Identified One Problem

Rickkkkkkkkk...... DONTTTTTT! I have the identical motor. Exactly the same symptoms. Tried MMystery Oil... Hell I would have treid Moose twit if someone would have recommended. Do this first...
Take the carb apart. Under the bowl you will find a single jet. Unscrew it. Clean it out and put it back in. Vhwaaaaalaaaah! My problems were cured. About a three month periodical maintenance thing. I hope this works for you too.

And cheers. I sent you a private message a while back. No worries.

Rick

 

[Rick D]

Rickkkkkkkkk...... DONTTTTTT! I have the identical motor. Exactly the same symptoms. Tried MMystery Oil... Hell I would have treid Moose twit if someone would have recommended. Do this first...
Take the carb apart. Under the bowl you will find a single jet. Unscrew it. Clean it out and put it back in. Vhwaaaaalaaaah! My problems were cured. About a three month periodical maintenance thing. I hope this works for you too.

And cheers. I sent you a private message a while back. No worries.

Rick

OK. I have blasted through that jet with carb cleaner on a bunch of occasions, but not actually pulled it. I'll give it a try.

I'll PM you back.

 

[shemandr]

I have the 3.5 Tohatsu of that same vintage and find that I do have to run it a long time with the choke on too. Now, I know why. I did put a fuel filter in line which has helped its performance - in particular the starting. There was crap in the carb and I ended up buying a new float chamber housing since the existing one was flaking chips of aluminum, or whatever finish is on the aluminum, which were clogging the jets. I only run it dry for the winter lay up. I liked the results so much I bought a new cover for it. I was ready to deep six it.