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Old 01 February 2010, 16:11   #1
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Tohatsu carb float setting

I`ve just stripped the carb on my Tohatsu M12A 2 stroke O/B and reset the float as per manual - height 15mm from top face because the float as it was set was low.
No fuel was getting past the inlet valve so I bent it down as before. Fuel is getting through now and she starts fine.
In the top of the inlet valve stem there is a little spring loaded inner pin and it is this which was offsetting the float level.
Is this some form of dampener to reduce bounce ?
What will happen if the fuel level is either too low or too high in the bowl.

Second question - will this O/B get my Avon 3.4m roll away on the plane OK with 2 adults ?

Thanks

Bob
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Old 02 February 2010, 11:48   #2
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Not had one of them in bots before, so apologies if this is more of a question than an answer....

The spring might be there to allow the fuel to "slop" slightly when bouncing through waves (i.e allow the valve to be more constantly open or closed as the float bobs up & down) Any Pics? Is it between float arm and valve pin, or acting directly on the pin? Also what is its "extended" setting - valve closed or valve open?

The float valve is basically there to stop too much fuel getting into the carb bowl. Once the fuel is in the bowl it's sooked up by the vauum in the carb passage, so a reasonably constant level in hthe bowl is needed. The fuel pump only moves the fuel to the carb bowls, not into the engine airflow, coz that's called fuel injection! If your float is too low, the slightest amount of fuel in the bowl and the valve closes, so the engine is starved. Likewise float set too high & the engine "drowns" at idle as the fuel is literally pumped into the engine at far greater quantities than the engine can dispose oif at idle.
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Old 02 February 2010, 15:22   #3
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The inner spring loaded pin is actually built into the fuel level valve. The spring force is just sufficient to support the float when inverted. Travel of the pin is probably only about 2mm, measured from fully flush with the jet pin top to 2mm proud, but the arc from the float hinge to the bowl equates to about 10mm travel.
The main pin is about 2.4mm square terminating with the needle point.
The inner pin is about 1mm dia and reacts something like the spring loaded pins which secure your watch to the strap.
I guess the only way is to set it with fluid, ensuring I have flow at height 15mm+ as per manual and fuel stops at 15mm or less.
Have tried compressed air but the air will not positively displace the pin form the seat, it finds its way round the sides.
No photos as I don`t want to strip the carb again till spring.
Thanks very much for taking time to reply
Cheers
Bob
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Old 03 February 2010, 08:16   #4
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That sounds like the spring is just there to stop the float "over closing" the valve - I've seen these valve pins mangled to the point they get stuck in the hole.

Its usually obvious when it's way off, sounds like you got it running again, so problem solved?
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