C40TLRY Operating temp

[de32sailor]

I have a 2000 40 hp three cylender that does not idel well. I replaced the thermostat with a new unit and the engin seems to run cool. I tested the thermostat and it opens at 130 deg. What should the temp be.

Also how do I test the crankcase pressure and what should it be?

Thanks

[Sparkieboat]

the stat seems to be working fine. my guess is that you need a good carb service...idle passage probably clogged

[99yam40]

Book says around 120F start to open and full open at 140F

What crankcase pressure are you speaking about?

Check you timing at idle and WOT. My c40 was running at 12 ATDC at idle it was suppose to be 7ATDC when warmed up. Had to replace the CDI to get it corrected

[de32sailor]

Thanks for the info about timing and t stat.

As far as crankcase pressure, it is my understanding that 2-strokes will not idel well with low crankcase pressure. Is there a spec on this?
Thanks

[99yam40]

only pressure I know about is compression of the cylinders. If the cylinders are not even the motor has problems

[de32sailor]

The crankcase pressure is what operates the fuel pump. It also forces the fresh fuel charge into the combustion chamber on the down stroke. I know that the reed valves (behind the carbs) seal off the crankcase so this pressure can build up on the down stroke. I just don't know how high this pressure should be, or how to check it.

BTW- all three cylenders hase 120 psi compression.

Is there a way to get one of the yamaha tech to look at this?

Thanks,
Jack

[99yam40]

I have never heard of someone checking that or how you could check it.
It is not in my Yamaha manual specs sheets that I can see.
If compression is good then the rings are sealing properly, as far as the reeds go you can look at them to make sure they are in good shape and maybe measure
Where did you hear about trying to measure crankcase pressure?


Might try to get Rodbolt17's attention to see what he has to say. Modify the title some to get his attention is my only thoughts

[rodbolt17]

there is not a good way to monitor PRIMARY compression.
it can be done but you will need a decent balanced and dampend guage.
you can use the oil inlet nipples on the intake to measure primary compression.
typically if SECONDARY ( cylinder) compression is good the PRIMARY usually is.
with your compression numbers my guess would be a fuel or linkage adjustment issue.

[99yam40]

Hey Rodbolt, His motor is a C40TLRY according to the title

[de32sailor]

Thanks for all the info. I now think I must have a timing issue.

Thanks again

[99yam40]

Have you checked the timing? What did you find it at?

like I said before my C40TLRX had a problem with the CDI.
Actually it was with the wiper but can not be fixed because it is made into the CDI