Tohatsu 3.5hp 4 stroke Auxilliary.

Callum B · 09 May 2020, 14:18

Hi all,

Im at my wits end with this wee outboard!!

It starts and ticks over beautifully, but it doesnt like accelerating.....it can be coaxed up to full throttle, and stays there happily.

The carb has been through the ultrasonic cleaner with carb fluid for about 90 minutes at 60 °C, which cured the slow running, and ive proven the jets....the fuel is brand new dear stuff.

Heres a link to a wee vid.
https://s.amsu.ng/Jpe48HtIoUhN

I think its gotta be internal in the carb??.... i dont have an air line, but ive blown through the air ways, with a straw....and cleared out the jets with some skinny wire, in addition to ultrasonic cleaning

Any thoughts are most welcome!!

camarine2009 · 09 May 2020, 17:03

To clean these properly you need to drill out the EPA cap that covers the idle mixture screw and then screw in until it lightly seats counting the turns. I then fully strip and soak in acetone for a couple of days before blowing out with an airline. Be very careful when you drill the cap out just use a 1mm drill bit and go lightly. Once through you can use a small self tapping screw to pull the cap out. If you go at it too hard you will catch the mixture screw. These are are always troublesome as they have very small passageways and block easily. I now run quicksilver quickclean in every fill and run it over regularly which has definitely made a difference.

Callum B · 09 May 2020, 19:13

Thank you camarine.

There are 3 valves.....the float valve, the slow running, and the fast running.....both the slow and fast running jets are screwed home, to a hard stop.....there are no adjustments on these valves.....the only adjustments on the carb, that i can see, is the tick over speed.
There is one brass stud, with what looks like a raised capital D, presumably for a specific tool....i havent removed that one....and not sure of its purpose.....is this what you refer too??

beerbelly · 09 May 2020, 19:42

the idle mixture screw he is referring to adjusts the amount of air going through the pilot system which controls mixture from tick over up until it goes onto the main jet 3/4 throttle on .as you say you have to coax it up to some revs this could be part of your issue but first I would check to make sure your not drawing air anywhere .would give the similar symptoms. also check your float Hight is within spec if your fuel level in the float chamber is incorrect it could cause lean running issues

camarine2009 · 09 May 2020, 19:48

There is a little brass cap that covers the mixture screw. Its there trust me. As I mentioned before you have to be really careful when you drill this out. There are a few posts kicking about that mention this you look hard enough.

camarine2009 · 09 May 2020, 19:54

Beerbelly is spot on do check for air leaks but more than than likely its a carb issue. Spaying cab cleaner around the carb gaskets etc will cause a change in rpm which may help but my money is on carb.

camarine2009 · 09 May 2020, 20:09

Sorry meant to say carb cleaner.

Davie · 09 May 2020, 21:24

Quote:

Originally Posted by camarine2009

There is a little brass cap that covers the mixture screw. Its there trust me. As I mentioned before you have to be really careful when you drill this out. There are a few posts kicking about that mention this you look hard enough.

I have yet to see one of these engines run without drilling the cap and giving it at least a half turn. They don’t run when new out the box without a massive flat spot. (Not in cold Scotland anyway)!

Callum B · 10 May 2020, 13:40

Thanks fellas ..... I'll head off in that direction....

Callum B · 10 May 2020, 17:08

Quote:

Originally Posted by camarine2009

There is a little brass cap that covers the mixture screw. Its there trust me. As I mentioned before you have to be really careful when you drill this out. There are a few posts kicking about that mention this you look hard enough.

Hi,....ive had a look, but im a little wary.....im sure youre right....i think its the fuel air mix....i have attached some pics of the carb. The only thing that looks like it may be fuel air mix, is the brass stud, with the D emboss....it looks solid, like a stud,....not a cap??.... im guessing theres a special tool??

Callum B · 10 May 2020, 17:31

Sorry...ive found the carburettor adjustment tools on ebay....stand down!!

camarine2009 · 10 May 2020, 17:48

Its the little brass cap which is recessed on the righthand side if your first picture. The only way to successfully clean and adjust these carbs is to remove the cap by carefully drilling it out. I cant stress how careful you need to be and if you are in any doubt take it to shop. If you use marineengine.com you can see an exploded view of the carb which will give you a better idea of what you are looking at. Hope this helps and good luck

Callum B · 10 May 2020, 19:07

Ok thanks.....thats the brass stud, ( maybe not clear from the picture), with the D emboss on the top.... ive ordered a set of carburettor adjustment screwdrivers, including the D one, to asjust it

I'll report back in a week, once these tools arrive!!

Thanks for your help.....and patience!!

camarine2009 · 10 May 2020, 19:38

To remove/adjust these once the cap is removed is a small flat blade screwdriver. No special tools are required.

Callum B · 16 May 2020, 20:22

The head of the brass D stud, controls the fuel/air mix...... its a little fickle, and very small adjustments, make quite a large difference.

No drilling required!!

Problem solved,....thank you all...

Limecc · 04 February 2021, 22:39

Quote:

Originally Posted by Callum B

The head of the brass D stud, controls the fuel/air mix...... its a little fickle, and very small adjustments, make quite a large difference.

No drilling required!!

Problem solved,....thank you all...

I have the exact same issue with my Tohatsu 3.5hp aux.
Now I know why the seller was willing to travel and meet me half-way of the journey. I would not then see it running. It only revs from idle on part choke.

I drained and replaced stale fuel, removed the jets and blew some compressed air around. No change.

Can you elaborate on the adjustment tools please? I couldn't find them on ebay.

I attach a pic of the pilot screw cap. You are saying no drilling required, camarine2009 is saying to drill a cap off to access the screw. Did you prise the cap off because you said you did no drilling? Is the 'cap' simply the head of the adjusting screw without a screwdriver slot? Confusing.

I have a new 5hp carb upgrade being shipped from the US, but I want to sell the 3.5 one with a good conscience. It will be quite useful for someone who wants to uprate their 2.5 engine. Maybe they think they have a faulty carb but it's actually this issue.
Many thanks!

Fenlander · 04 February 2021, 23:27

In your left hand pic I'm pretty sure your cap has already gone and the brass part is the idle mixture screw. You can see the slight flat on one edge and usually a small screwdriver of the exact right size will fit snug between that flat and the alloy bore and be used to turn the screw round. It did in my case with no special tool.

Limecc · 04 February 2021, 23:36

Quote:

Originally Posted by Fenlander

In your left hand pic I'm pretty sure your cap has already gone and the brass part is the idle mixture screw. You can see the slight flat on one edge and usually a small screwdriver of the exact right size will fit snug between that flat and the alloy bore and be used to turn the screw round. It did in my case with no special tool.

Perfect thanks Fenlander. I zoomed in using the OP's carb pic so I'll have another look at mine and report back how it goes.

I found this guy also had the same hesitation on a brand new 3.5 engine, further confirming Davie's statement that it's a common issue:

https://www.youtube.com/watch?v=l4s2...ature=youtu.be

Limecc · 05 February 2021, 14:25

The 'cap' was still fitted to my carb and it would be better described as a 1/4"x1/4" solid plug of brass. Heartstopping stuff, I successfully drilled it out with the care of a brain surgeon.

Unfortunately adjustment helped but did not cure the issue.
Stupidly I did not check the float height or use any carb cleaner. More later..

Limecc · 05 February 2021, 22:05

All fixed!
Problem was the float height and to set it correctly I had to connect the fuel pipe with the float bowl off so I could see what height it was when the needle valve shut the fuel off.

Not shown in the exploded parts view was a little 4mm rubber bung that blocks a jet (adjacent to main jet) and is held in place against the bottom of the float bowl. No idea what this arrangement is, I was lucky to find it again when I lost it on the floor of the garage.

By trial and error I set the pilot screw 2.1/2 turns out, there's still a little hesitation when the throttle is blipped but I can live with it and couldn't be bothered with any further pilot screw adjustment or float height tinkering. Maybe this is normal, I welcome any comments.