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Old 09 May 2020, 08:18   #1
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Tohatsu 3.5hp 4 stroke Auxilliary.

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 įC, 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!!
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Old 09 May 2020, 11:03   #2
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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.
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Old 09 May 2020, 13:13   #3
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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??
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Old 09 May 2020, 13:42   #4
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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
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Old 09 May 2020, 13:48   #5
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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.
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Old 09 May 2020, 13:54   #6
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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.
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Old 09 May 2020, 14:09   #7
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Sorry meant to say carb cleaner.
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Old 09 May 2020, 15:24   #8
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Quote:
Originally Posted by camarine2009 View Post
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 donít run when new out the box without a massive flat spot. (Not in cold Scotland anyway)!
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Old 10 May 2020, 07:40   #9
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Thanks fellas ..... I'll head off in that direction....
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Old 10 May 2020, 11:08   #10
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Quote:
Originally Posted by camarine2009 View Post
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??
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Old 10 May 2020, 11:31   #11
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Sorry...ive found the carburettor adjustment tools on ebay....stand down!!
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Old 10 May 2020, 11:48   #12
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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
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Old 10 May 2020, 13:07   #13
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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!!
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Old 10 May 2020, 13:38   #14
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To remove/adjust these once the cap is removed is a small flat blade screwdriver. No special tools are required.
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Old 16 May 2020, 14:22   #15
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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...
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