Adjusting idle on Tohatsu M40C

[jondavies]

I recently bought a rebuilt 40C and it's started to idle a little low and stall out. The mechanic offered to adjust but rather than drive 100+ miles round trip, I'd rather do it myself. He gave me general directions on what to do (turn screw 1/16" clockwise) and even though I have the service manual I want to make sure I'm turning the right screw. It's the one that the pencil is pointing to in the pic, right?

Thanks for helping out a clueless newb

Jon

 

[pvanv]

Re: Adjusting idle on Tohatsu M40C

Correct. That's the throttle stop, and you want to tighten the screw clockwise until you reach the correct warm idle. A shop tachometer would be great to have, but if you don't have one, just raise the idle up until it's stable and doesn't tend to stall as easily.

Keep in mind that something else may have changed to decrease the idle. Could be some junk in the carb, normal wear-and-tear compression loss, or even a change in fuel or oil. If you have to turn the idle up a lot, then odds are you are masking another problem.

 

[jondavies]

Re: Adjusting idle on Tohatsu M40C

Thanks.

I'm running with ~33:1 for the break-in so it might have something to do with that. The mechanic speculated that the plugs may be getting fouled by the extra oil so he's sending me a couple to swap out when the break-in is done. I may have to back off the screw a little at that point.

If I invest in a tachometer, I'm looking for 850-950 rpm at warm idle with the clutch in, correct?

Cheers,

Jon

 

[Sea Rider]

Re: Adjusting idle on Tohatsu M40C

Thanks.

I'm running with ~33:1 for the break-in so it might have something to do with that. The mechanic speculated that the plugs may be getting fouled by the extra oil so he's sending me a couple to swap out when the break-in is done. I may have to back off the screw a little at that point.

If I invest in a tachometer, I'm looking for 850-950 rpm at warm idle with the clutch in, correct?

Cheers,

Jon

If it's a 2 stroke 40 C : 1,000 rpm in neutral ; 850 in gear, if you buy a digital tacho, tiny tach type the numbers will go wild, readings are very sensitive, use a needle tacho for the adjustment if possible. If not using a tacho, adjust so as to have a slight clak sound when gearing forward, engine must remain idling ok, and not stall out. Slight readjust needle CW if needed. After breack in period, if you have new plugs, just cleam them well with acryclic thinner using an old toothbrush, regap tight to 1.0 mm and put back on, should perform well.

Happy Boating

 

[vilemd]

Re: Adjusting idle on Tohatsu M40C

hey i have a 2003 nissan 40hp. same thing justs differnt name. im having problems with my engine starting up and staying running in idle. i was wondering what the other screw on top you were pointing to does