JT2M? compression pressure
I guess that is why I never could find a compression pressure in any of the Yamaha JT documentation, and Yamaha does not even show a compression gauge as a tool to be used anywhere.
So my next steps will be to follow RT325s advice and check the exhaust, cylinder and rotary valve. I will take a compression measurement to satisfy my curiosity!
DT50 runs great... in fact I rebuilt the top end because of the low compression even though it was supposed to be a low mile engine by the speedo... runs the same and compression didn't get any better.
JayB wrote: I have a yellow JT2M that has been languishing in the basement for 22+ years. Years ago I got it running but it had very little power, not enough to move itself. I suspected compression was bad. Does anyone know what the measured compression pressure should be for the JTs? I looked at the shop manual and didn't see a compression pressure. I want to measure it before I do anything else.
All I can offer is what my two JTs read for compression. My better running JT reads 120psi and my not so great running JT reads 90psi. Don't know if that helps you at all.
"Someday, you'll own a Yamaha"
Schu wrote: All I can offer is what my two JTs read for compression. My better running JT reads 120psi and my not so great running JT reads 90psi. Don't know if that helps you at all.
^^^ there's some good data, if you have a similar gauge.
P.S. The DT50 has a "slot" that raises the center of the exhaust port quite a bit... I think that's the main reason the cranking pressure is so low? A plus is you can literally start it with your hand, very easy to turn over and start.
Thanks for the replies Schu, MarkT and RT325 !
Check the air filter too... foam can go bad (if it has foam) and common place for mice and other critters to make nests.