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Old 16 May 2017, 13:07   #21
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Hmmmm ......... if it was running ok and then this fault delveloped, it must be a fault rather than a mixture issue.

The only way to adjust the mixture on that carb is to move the collar on the needle ring groves ....... it should be on the second grove down from the top.

I think at this stage you may need to check the spark ........ a weak spark from the coil will give the same symptoms as a lean mixture
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Old 16 May 2017, 13:27   #22
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Hmmmm ......... if it was running ok and then this fault delveloped, it must be a fault rather than a mixture issue.
Well, that's the thing - I've really only used the engine (many times) to travel a couple of hundred yards from a cold start. So I'd naturally start with a bit of choke and then back off - but I'd expect to do that as the engine warmed anyway - I may simply have missed the issue through having a touch of choke on. I don't really run the engine flat out as the dinghy won't plane with it so best displacement speed is my aim.

Thanks to everyone who has contributed so far - even though the engine is no further forward, I've learned a lot!

I have a day afloat tomorrow and I'll get that over before I open the engine again - just in case I give myself a day's rowing for my pains!

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Old 17 May 2017, 01:49   #23
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Well, that's the thing - I've really only used the engine (many times) to travel a couple of hundred yards from a cold start. So I'd naturally start with a bit of choke and then back off - but I'd expect to do that as the engine warmed anyway - I may simply have missed the issue through having a touch of choke on.
Aha! So now we've got a whole lot of doubt to deal with! It's best that you know exactly what's going on in the operation of the carb - I'd like to give you the benefit of the doubt but you said something about lifting the slide and that is not what you have to do so I'm gonna go ahead and explain how a slide carb works then you can choose what to do.

Firstly, the needle is a taper and though it looks even it normally isn't, it tapers in short steps. Different needles for different applications have different diameters down their length to match the engine requirement for fuel for that engine.

The needle fits into the jet, the jet is a fixed diameter. When at idle and the mixture is correct and the needle taper is correct, when the slide is lifted it lets air into the engine and the correct amount of fuel is let into the carb venturi through the annular space between the jet and the needle.

Now, when something in the engine changes from the exact manufacturing tolerances, the fuel requirement will change and this appears to be where you are with your engine. If the fuel requirement changes then the needle you have in the carb will not be an exact fit within the jet to provide the required mixture.

Given your circumstances of use for this engine, the fact that it's plainly short on fuel, you've checked it over and it appears to be ok and that there is an option to richen the mixture built in to the carb, then, imho, you should use this option and see how the engine performs before starting to mess around with it in other ways.

Your option is to lift the needle in the slide so that it provides a bigger annular space around the part of the needle in the jet so letting through a little more fuel. Since the slide will be in the same position as previously then the air flow will be as before so with the lifted needle the mixture will be a little richer. Note though that the mixture will be richer right through the rev range not just at idle. That's why you have to give it a try and see if you're happy with the way it performs generally.

I suspect that since the air and fuel requirement for such a small engine is so little and there is manufacturing tolerance and inevitable useage wear, keeping that fine balance between air and fuel will be difficult throughout the engine's life, especially so when there in no variable mixture adjustment - it may even have been marginal when the engine was new and you've just tipped the balance too far with engine useage.

The fact that there is three mixture settings possible suggests that it is known that there is the likelihood for some adjustment to be necessary in some circumstances.

Lift the needle and give it a go.

If lifting the needle proves to correct the idle mixture but provides an overly rich mixture from the rest of the throttle opening then there is a few things to be looking at... but leave that until you've tried it.
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Old 17 May 2017, 07:40   #24
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Lift the needle and give it a go.

If lifting the needle proves to correct the idle mixture but provides an overly rich mixture from the rest of the throttle opening then there is a few things to be looking at... but leave that until you've tried it.
I will do so - maybe tomorrow. I used the wrong terms above (soz) but understood what adjustment to make. To be completely honest, there wasn't much to that carb - even I could see it was simple and understood the general workings. Hey - this is like school again!
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Old 17 May 2017, 08:39   #25
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I Hey - this is like school again! :

Has anyone thrown a board duster at you yet?
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Old 17 May 2017, 13:51   #26
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Has anyone thrown a board duster at you yet?


I bet if he starts stripping the carb down on the kitchen table, he'll be getting six of the best[emoji12]
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Old 17 May 2017, 15:20   #27
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My handwriting hasn 't improved!
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Old 24 May 2017, 18:27   #28
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Does this story have a happy ending?
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Old 24 May 2017, 20:29   #29
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My handwriting hasn 't improved!
I'm impressed. It's like a style-board from one of Laurence Llewelyn-Bowen's 60-minute makeovers. I normally take the approach of dismantle and reinstall and hope there's no bits left over!
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Old 24 May 2017, 20:52   #30
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Does this story have a happy ending?
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I'm impressed. It's like a style-board from one of Laurence Llewelyn-Bowen's 60-minute makeovers. I normally take the approach of dismantle and reinstall and hope there's no bits left over!
Well TBH I'm no further forward. I've done the various adjustments and swapped out the plug and so forth, but just the same. I have also made the decision to spend not a single penny on this motor so any further advice will be of great use to the next owner.

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Old 27 May 2017, 14:45   #31
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You moved the circlip on the needle down a notch and this made no difference? Is this the older engine with points?
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Old 27 May 2017, 15:49   #32
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You moved the circlip on the needle down a notch and this made no difference? Is this the older engine with points?
I did that - same result. No points - looks like a CDI thingy.
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Old 04 June 2017, 17:01   #33
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Any suggestions for further checks? I might try to sort it and sell or keep as a backup. Other than this issue above, it's very clean and starts first time.
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Old 04 June 2017, 20:15   #34
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Anyone local to you that knows Tohatsu engines?

They'll have 2-stroke oil under their nails!
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Old 04 June 2017, 20:59   #35
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Anyone local to you that knows Tohatsu engines?
No. Oddly, there are very few capable outboard mechs close to me - and far less one who won't charge me the market value of the motor to effect what I suspect is a very simple repair. I'm not prepared to begin a process of renewing the entire "spark" side of the engine on general principles, but if I could narrow it down to one possible part - I'd gladly replace it myself (once my new engine has arrived - I can't be without a tender ATM)
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Old 05 June 2017, 22:30   #36
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There is I think an idle screw adjustment on these carbs also which you have not mentioned. Turn it fully in and count the half turns.Then take it out and spray carb cleaner.Refit it with same number of half turns.Might be worth fiddling with that
https://www.marineengine.com/parts/j...ion=Carburetor
Part 21 same carb
Also clean main jet part 16
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