Tohatsu 3.5Hp Starting Issues

[Sailathon]

I had similar problems with Tahatsu 3.5.
Took first issue to mechanic. He changed carb
since after cleaning still could not make it work.
Then I had same issue again. Bought a new carb
and changed it myself but I found that someone
opened box and that one did not work either. So I returned it and got an unopened new carb from factory and now it works. Last summer motor worked well to my surprise. I also use airplane fuel now. Hope this helps.

[sowwaninii]

Outboard needs 3 things to run: fuel, air, and spark.
As others have stated, fuel is the most common problem,. Old or contaminated gas will make starting difficult or impossible. And obviously any interference with gas flow, I.e., clogged jets in carburetor or fuel filter. Rarely is air flow a problem. Lack or weak spark could be due to fouled plug or bad wire to plug.
I would recommend cleaning main jet in carburetor, check fuel filter and consider replacing, and fresh gas, pull the plug and examine it. If it looks okay, ground the plug to the engine and have an assistant pull the start line and observe if you’re getting a spark. If not, try again with new plug. If still no spark, replace spark lead.

[EmeraldCoastSailor]

I have had a few of these over the years labeled Mercury and currently have a Tohatsu 3.5. They all seem to get clogged in the carb jet. Can be cleaned fairly easily as described above but I sometimes have luck preventing it. I also always drain fuel out of tank as well as run the carb dry. Even just for a few weeks of non use. I am not sure you can get it all out but I try. I burn the fuel in my car and always use fresh non-ethanol gas in the 3.5. They generally suck but not sure propane or electric is overall better.

[donradcliffe]

Try a shot of the quick start. If the engine doesn't even fire, you have an electrical problem. If it revs up and dies, its the carb. If it revs up and keeps running, you have shaken the clog loose.

I would also pull the fuel hose off the carb. If nothing comes out, you have a clog in the tank/valve/hose. If fuel comes out, take the opportunity to drain the tank and put fresh fuel in.

[Boatwright]

It's the gas. $20 / gal "Tru-Fuel" works. 92 octane, ethanol free, sold at Home Depot, etc.. It smells like aviation gas. 2 year storage life.

2 gallons is enough for the whole season in our dinghy dock to mooring trips, so $40 is a small price to pay according to Barb who takes it personally when I exclaim #**%##! at things mechanical.

[grahamj]

It may or may not be significant that these motors, and their carburetors were designed in a country with no ethanol in its gasoline.
There are many instructive YT videos showing how to detox E10. Makes sense to me.

[srbaum]

Kurt,
I have the same outboard on my workbench, with the same symptoms. Took the carb apart, placed it in an ultrasonic cleaning machine (Harbor Freight)., blew it dry, reassembled it and it runs like new.
The outboard is made by Tohatsu and they also sell the same outboard labeled as Mercury.
Lastly, I buy my parts on-line at boats.net , their site is easy to use...
PS, I repair a few dozen of these smaller type outboards a year and sell them in the spring, to help pay to keep my boats running. All of the small outboards are subject to the very same issue, because of ethanol. I recently worked on two almost new 2.5 hp Suzuki’s and could not get the internal orifices cleaned properly and had to condemn the carbs and buy new ones...
Best regards,
Steve Baum

[NorthCoastJoe]

Most of the time with small engines it's a fuel problem. Give it a shot of starting fluid if it fires that tells you everything else is ok and the problem is fuel delivery. I bought a small ultrasonic cleaner that I use on small carbs, it cleans them up.

I always run my small engines dry when I am done with both 2 and 4 stroke. My 40-year-old chainsaw to this day has never had the carb touched.

[MarkSF]

Well, I'll be the dissenting voice here, and say that none of these problems are due to ethanol, and it's a waste of time trying to prevent them by switching to non-ethanol gasoline.

Ethanol is an alcohol that burns very cleanly, and does not create varnish. Gasoline creates varnish, or rather, contains it. Evaporate any gasoline and you'll get a little varnish, whatever grade and whether it contains ethanol or not.

Ethanol can cause problems with much older engines where the rubber etc. is not compatible with it. Your engine has compatible materials throughout.

The problem you have is that you have a carburated small 4 stroke. This means that passageways in the jets etc. are very small, easily prone to blocking, and hard to unblock.

That makes the engine very sensitive to good practice - by which I mean, fuel stabiliser, keep the gas very fresh, always run it dry.

I am wondering if you might benefit from an inline fuel filter, as my recollection of my Tohatsu 3.5 is that it didn't come with one. But that was a while ago.

[Shrew]

I have a Tahatsu 4HP and it seems to have the same hard starting issues both my Honda dirtbike used to have and my Honda 2HP outboard. Aside from what was said above about fuel, as long as you're using a fuel stabilizer and run the carb dry you basically doing everything right.

Mine starts very, very hard if I use the internal tank. If I use an external tank and prime it with the squeeze ball it starts much easier (be sure not to flood it).

1) Open the Choke

2) Give the starter a few slow, complete pulls. At some point, about 1/3 or so out, you will feel some resistance after 1-2 pulls. Stop there and hold tension on the starting cord.

3) Open the throttle all the way.

4) Now give it a good sharp pull. (Be sure to be quick to chop the throttle and be ready to reach for the choke)

It should start.

[Westcliffe01]

OP, try the leaded aviation fuel. Its not like the other trash consumer gas and its storage properties are vastly superior. You wont need a lot of it for a small outboard on an annual basis and in my case, what didn't get used in summer goes in the snowblower tank and gets used up for sure...

[SRQsailor]

Alcohol containing gas is the worst thing you can do to a small engine that isn't used regularly. Many marinas sell it, as well as airports and stations listed at puregas.org. I use it in a least a dozen small engines including outboards, generators, mowers and RC airplane engines. No storage issues. BTW, the last information I saw recommends leaving gas engines "wet" with gas in the carb instead of running them dry. I only do this with non-alcohol gas myself. Alcohol attracts moisture and corrosion for sure.