Tohatsu 3.5 two stroke probs.

[Elemental]

My Tohatsu 3.5 two stroke OB is usually bomb proof. One pull and away it goes. However, last time out it simply wouldn't run. It fired, a short bust into life, then died. I suspected water in the carb.

So I took it home and ordered a carb service kit, from Pacer Marine. This basically consists of all the brass bits in the carb, plus new O rings/ gaskets etc. As the fuel tank has leaked fora while I also ordered a new tank and plug (the one with internal resistance).

I stripped, cleaned and re-assembled the carb (which did have water & crud in it), and fitted the new tank and plug. I also cleaned all the fuel pipe, tap etc. Running it up after the service (in a wheelie bin of water) it fired first pull, but whilst it was happy idling, seemed very reluctant to rev when I opened the throttle. Opening it would result in misfiring leading to stop 3/4 time. If I closed the choke it behaved better at lower revs but (as expected) wouldn't rev highly unless I open the choke again. It seems like fuel starvation but the whole fuel system is brand new...

The fuel is a last year's , (held in a 5L can in a cockpit locker) and I noted that it ran very smokey. I added a splash of fresh unleaded directly into the tank and it seemed to behave better, but by then the engine was well warmed up. I'll try again tonight from cold, but could old, possibly over oiled, fuel cause probs that look like fuel starvation? Should I adjust the main jet to run slightly richer (the needle has a bunch of preset settings you can select - mine is currently set to default).

 

[rbmatthews]

The fuel is a last year's , (held in a 5L can in a cockpit locker) and I noted that it ran very smokey. I added a splash of fresh unleaded directly into the tank and it seemed to behave better, but by then the engine was well warmed up. I'll try again tonight from cold, but could old, possibly over oiled, fuel cause probs that look like fuel starvation? Should I adjust the main jet to run slightly richer (the needle has a bunch of preset settings you can select - mine is currently set to default).

I think that completely new fuel should make a difference, but you will need to drain all of the old stuff out first, not just add the new to the old. Old fuel from last year (i.e. >3-4 months old) will cause all sorts of gummy deposits from the additives, which will block the little passageways and jets in the carb. Did you blow these out with compressed air when you refurbished the carb?

If that doesn't work, then it might be something else, but more often than not stale fuel causes these poblems, so at least eliminate that as a reason.

Rob.

 

[VicS]

+1 on the fuel.

It is possible to keep fuel from one year to another if stored in ideal conditions . I usually do but always filter it and mix it 50:50 with fresh the following year

Full tightly capped metal cans.... to prevent loss of lighter fractions and to minimise exposure to air and light.

BUT if you are having problems and are attempting to use old fuel the first thing to do is replace it. I know my Seagull does not run well on stale fuel nor did my old petrol Flymo. I never chance it in the Evinrude.

 

[Dino]

Hi folks,
I recently has some engine problem with my Tohatsu 3.5hp outboard. It wouldn't start at all so i decided to clean the carbureter. After some googling I found this very useful link http://seaweed.thebilge.com/tohatsucarbrebuild.htm
It outlines all the steps for rebuilding the carb with step by step photo's. a number of the small parts in the carb were badly corroded and the petrol had crystallised in the bowl around the float.

The author of that article used a carb repair kit but the few Irish and UK dealers I contacted never heard of it and wanted to sell all the bits seperately. Anyway a bit more googling brought me to this... http://www.maxrules.com/fixnissancarb.html

And in case you need to order any other parts... here's the parts list http://www.maxrules.com/TOHCatalogs/Tohatsu/2stroke/M2.5A2_3.5A2_3.5B2_2003.pdf

I ended up buying the carb rebuild kit from Bill Higham Marine.

 

[rbmatthews]

BUT if you are having problems and are attempting to use old fuel the first thing to do is replace it. I know my Seagull does not run well on stale fuel nor did my old petrol Flymo. I never chance it in the Evinrude.

All our old fuel, both mixed and unmixed, goes into our Suzuki Swift at the end of the season, which seems to thrive on it, and we start with fresh fuel for the boat engines at the start of each season. Minimal problems that way, but, all the same, water did somehow find its way into the carb on the T3.5 this year. Still haven't worked out how.

Rob.

 

[seumask]

Always change the spark plug and carry a spare to facilitate it. Its a quick and easy one to rule out and one that has got me out of a pickle with these small engines twice in the last 5 years.

 

[Elemental]

It was definitely the fuel. I made up some fresh 50:1 mix and it runs like a dream

The carb. service kit (same as at above) came from Pacer Marine. Prompt delivery too.