Why is it so hard to tune my Tohatsu M40C?

[jondavies]

I bought a rebuilt M40C from a Tohatsu dealer a year ago. It took about five return visits and a new carb to get the thing running smoothly. After that it's been running flawlessly for about 80-100 hours.

Last week I took the motor to a different Tohatsu dealer for its annual tune-up (plugs, impeller, carb cleaning etc.) and I took it out for a test run yesterday.

Now, when the motor is hot, it tends to bog down and stall when shifting into gear. If it stalls, it's *really* hard to start again. The only way to get it to start is to give it choke, get it to fire once, then put the choke in and try starting again. This is pretty much the same trouble I had when I got the motor.

So I'm wondering if:

a. The 40C is a particularly finicky motor (not what I've heard).

b. There's a specific issue with my motor.

c. There's no way to really tell if a motor is adjusted properly until you get it out on the water and warmed up.

d. I just have bad luck with mechanics.

e. Other ...

I'm leaning toward D but would appreciate some expert insight.

 

[pvanv]

Re: Why is it so hard to tune my Tohatsu M40C?

a. No. They run well.
b. Yes, or it would fire right up.
c. Proof of the setup can only be determined on the water, but basic adjustments can be done on the bench or in the tank.
d. Possible.
e. Idle may be set too low.

 

[jondavies]

Re: Why is it so hard to tune my Tohatsu M40C?

Thanks Paul -- that confirms my suspicions.

When I bought the motor last year, I took the motor back to the dealer 3-4 times and he couldn't get it to run properly. In the end he put on a new carb and that resolved the issue. I'm hoping it's an easier fix this time.

Is it usual for the motor to start easily and idle fine when cold but not do that when it's warmed up? If so I'm surprised that both mechanics (both of whom are Tohatsu dealers) had trouble taking that into account when setting the idle.

Regards,

Jon

 

[TOHATSU GURU]

Re: Why is it so hard to tune my Tohatsu M40C?

Most outboard mechanics do not know how to clean a carburetor...The field has hgh turnover and the new people who are entering the job market have no feel for the macvhines they work on. IE If there isn't a piece of test equipment to say "good or bad" they are completely lost.

 

[jondavies]

Re: Why is it so hard to tune my Tohatsu M40C?

Thanks Ervin. It makes me want to learn how to clean the carb myself but I might be just digging myself a deeper hole. I have the manual but the exploded diagram looks a little intimidating. Any tips on how to approach this with limited experience working on motors?

Also are there any tips for keeping the carb cleaner? I have a water sep. and an inline filter, I turn over the fuel regularly, run the motor frequently, run it out of gas after every trip etc. I've heard mixed opinions on the value of additives.

Regards,

Jon

 

[Sea Rider]

Re: Why is it so hard to tune my Tohatsu M40C?

Those are reliable engines, if dies once warmed, check/adjust air/gas and idle screws. If correct, probably pseudo mechanics (not sufficiently skilled) have moved/played with throttle/timming adjustments, check gaps with other no problem engine to see if matching factory parameters.

If having excesive side play in throttle, timming linking areas, replace all worn metal & plastic parts with new ones, will improve acceleration and performance.

Happy Boating

 

[jondavies]

Re: Why is it so hard to tune my Tohatsu M40C?

Thanks for all the feedback. I adjusted the idle and it seems to be running much better now, even after it warms up. I"m hoping to give it a proper shakeout this week.