Tohatsu 3.5 OB Not well

[davidpbo]

I did post briefly on someone else's thread.

Towards the end of last season the sound of my outboard changed between outings developing what I can only describe as a rattle when running.

Normally when I started it it would start fairly easily with choke closed, I then imediately had to open it.

When the noise came I had to fiddle with the choke far more usually leaving it in a half way position.

Now testing it in a tank it start OK but when I engage drive it labours and stalls. Rattle is still there.

I have stripped and cleaned the carb which had some gunge in the bottom of the float chamber but not anywere else. Have not tried new fuel yet.

I am wondering if some water ran back up the leg and has damaged a bearing. When I take the motor off it is usually laid on its side on the pontoon whilst I get out of the dinghy then carried up the pontoon by its handle which should mean I would have thought it has had a reasonable time to drain. The motor is stored vertically at home.

 

[VicS]

Requiring some choke to run is usually a sign that the carb is not clean.

Take another look at the main jet assembly. Poke a soft copper wire through it.

If you have not already done so fit a new plug. Don't know why but it often seems to cure what are unrelated problems.

Chuck out any fuel that has been in the tank all winter. It'll keep in a full sealed metal can but may not in a partly filled tank. I always filter any stored fuel before using it too. Normally there's nothing to filter out but the one time I did not bother saw me in all sorts of trouble.

Cant help with the rattle.

 

[davidpbo]

What did you use to filter the fuel? I have done it in the past with kitchen towel. Wouild use a coffee filter if can cadge one. I presume it is to filter particals and any emulsified gunge.

 

[VicS]

What did you use to filter the fuel?

A syphon tube with a filter element in it when there are canfuls to do.
Cannot remember for sure where I got it from although I do know I did not buy it! It is Motorcraft part no 70HF-9155-BA. Had it for ages and probably nla.

But for small quantities, ie the mower fuel tanks and the Seagull tank I always use a funnel with a gauze filter in it

 

[steve28]

whats the compression like, it could be a broken piston ring which would allow for the slap you are hearing, this would also explain why you need choke to keep it running.

Steve

 

[davidpbo]

Compression OK.

Drained and flushed the fuel tank, cleaned the internal filter which had some gunge and a dead insect around it.

The fuel had a very definite pink tinge to it. Are there any 2 stroke oils that would give this? I don't recall using any. The other petrol I put in was virtually colourless. I am wondering whether the fuel was contaminated.

Cleaned the plug. All OK with running now, however it still has a different tone to what it used to. Will look at that another time.

Does the Tohatsu 3.5 have a mixture adjustment screw? The only adjustment I can see on the carb looks to me as though it is an idle speed adjustment.

Amazingly the 8HP Mercury boat engine started first pull, I then tried to break it by stripping and cleaning the carb which had no serious build up of gunge, including poking a bit of copper wire through what looked like a blocked jet. I did not succeed, it started first time again.

 

[VicS]

I dont think you have told us the year or full model details so not sure i have the right diagram

Is it like the one below?
If so the only external adjustment does appear to be the idle speed, but can the mixture be altered by altering the position of the needle # 1.8 in the throttle valve #1.9 by moving clip #1.7 .

I think if there is any suggestion that the mixture is incorrect then you should take another look at the jet assembly #1.10

 

[Elemental]

Compression OK.

As a bit of a mechanical duffer, I've often wondered how you can tell this? Did you put some kind of pressure guage into the spark plug aperture and pull the starter cord? And how did you know what pressure to look for - I don't recall having seen any guidance in my owners manual. (3.5T)

The fuel had a very definite pink tinge to it. Are there any 2 stroke oils that would give this? I don't recall using any. The other petrol I put in was virtually colourless. I am wondering whether the fuel was contaminated.

The two stroke oil I've been using is distinctly pink. The last last bottle I had was dark blue...

 

[PembrokeshirePromise]

I have one of these - which also developed a bit more of a rattle - but has been running fine for several years despite this.

Every time I have the symptoms you describe its dirty carburettor / jet. I've found even the smallest bit of gunge anywhere near the jet causes exactly the symptoms you describe

 

[VicS]

As a bit of a mechanical duffer, I've often wondered how you can tell this? Did you put some kind of pressure guage into the spark plug aperture and pull the starter cord? And how did you know what pressure to look for - I don't recall having seen any guidance in my owners manual

Yes that is basically it. My compression gauge is a home made one, Small gauge fitted to the body of an old spark plug. Car tyre valve set in so that it records the max pressure achieved over several yanks of the string.

Take all plugs out of multi cylinder engines.

Not aware of compression readings being specified, for 2 strokes anyway. Should run if over 60 psi, but it'll run better if over 80. 100 would be good anything much over either a bonus or an incorrect gauge. Generally expect to get higher readings with an electric start than a rope start

All cylinders should be within 10% of each other

 

[davey]

Fuel and oil problems

Compression OK.

Drained and flushed the fuel tank, cleaned the internal filter which had some gunge and a dead insect around it.

The fuel had a very definite pink tinge to it. Are there any 2 stroke oils that would give this? I don't recall using any. The other petrol I put in was virtually colourless. I am wondering whether the fuel was contaminated.

Cleaned the plug. All OK with running now, however it still has a different tone to what it used to. Will look at that another time.

Does the Tohatsu 3.5 have a mixture adjustment screw? The only adjustment I can see on the carb looks to me as though it is an idle speed adjustment.

Amazingly the 8HP Mercury boat engine started first pull, I then tried to break it by stripping and cleaning the carb which had no serious build up of gunge, including poking a bit of copper wire through what looked like a blocked jet. I did not succeed, it started first time again.

Please could you let us know (approximately) where you live and what brand of fuel you use? Years ago I had a Puch Maxi moped in Cyprus (it was too hot to walk and my car hadn't arrived and the Puch was the only wheels that were for sale) The Puch had a 2 stroke engine which was OK but every few weeks it would break down. The problem would always be the spark plug and every time it was noticed that the plug would have a yellow glaze on its insulator. The glaze is lead fouling which conducts electricity. Hopefully with modern lead-free petrol the problem won't arise. Honda 50s used to fail in a similar fashion getting only about 500-1000 miles per plug (this was in the UK not Bongo-Bongo land!) Diesels don't hav these snags.

 

[rob2]

I gave an old, very small Johnson to a friend whe I bought my Tohatsu 3.5. It rattled like it had no main bearing at all. A couple of years on, he wanted to use it so he cleaned the carb out and filled with fresh fuel. It ran quietly and smoothly! Apart from the possibility of gunge in the jet altering the fuel/air mixture, I believe using old fuel which has lost its higher end fractions due to evaporation will cause pinking and in an outboard there is little mass to dampen the sound.

Clean the carb again and use a fresh mix of fuel.

Rob.