Tohatsu M40D float bowl adjustment help

[nathanhawaii]

I have a seloc manual for this engine and in the carb overhaul section when it comes to the float adjustment part, it just says to adjust the tab to change float bowl height. The 3 carbs on my M40D don't have any tabs. The required setting is supposed to be 9-10mm. The top and the middle carb measures perfectly at 9mm, but the bottom carb with the fuel pump measures 7.5mm. How do I adjust these carbs? I'm just guessing, but would adjusting the main jet/nozzle on this non-adjustable float assembly be equivalent to adjusting float height? Would 1.5mm too low on only 1 carb cause any difference in idle/WOT? The couple of times I've taken off my carbs, I've noticed that this particular one with the 7.5mm float height has excess fuel sitting in the throat. Is this normal or is it due to the low float setting? Timing is spot on, new plugs, newly rebuilt fuel pump and carbs, every single fuel line is brand new(no more leaky fuel lines), engine cranks instantly; but at idle it stumbles and misses quite often. Could this be a result of float height? I still have yet to test my choke solenoid which could show the same symptoms. I would like to correctly set that single "off" carb before moving on to testing the choke solenoid. I have a hunch that fixing this one carb will take care of my problem. Thanks for any and all help!

 

[pvanv]

Re: Tohatsu M40D float bowl adjustment help

If I were working on that motor, the first thing I would do would be to get a Factory service manual, Part # 003-21036-1, $45.00, available from any dealer, including me... and use that aftermarket manual (that claims to be for "all Tohatsu motors of all sizes, from before recorded history until the 21st century") for its best purpose: woodstove tinder (or a doorstop if in warmer climes).

No, the setting is not 9-10 mm. The float should be precisely parallel to the carb housing when the carb is inverted. Period. With plastic-tabbed floats, if the setting is off, the float geometry is damaged. You might get lucky by removing the float, heating the tab arm, re-shaping it slightly, and then allowing it to cool in the new position. In our shop, we don't do that -- we just install a new float. If your lower carb float is 2.5 mm high, yes, that will cause flooding in that carb throat. No, you cannot reasonably dial that out by tinkering with the main jet and emulsion tube "nozzle". The procedure for the pilot screw adjustment and idle stop adjustment is in the Factory service manual, and is pretty straightforward.

The new float would be ordered as: 3C8031250M, FLOAT, $13.18, and it will fit any carb on either the 40D or the D2.