Hey all,
I've just about finished restoring my 1980 it175, but the jetting here is causing me to scratch my head. I've leaned it out a whole lot and it still seems to be running rich, returning blackened plugs after each short ride. Power delivery seems fine enough with these jets.
At an elevation of 5200, here are the current jet sizes:
Main: 180
Pilot: 35
Needle: 6F21
Needle jet/emulsion tube: 159 P8
Needle position: leanest, clip at the top
Air screw 2 out
It did run a bit better after hooking up the power jet properly, but still running rich.
Referencing the manual the main and Pilot jets are much smaller than what's called for, 210 and 60. I'm at a bit of a loss for next steps to take to help lean it out, the last thing I have yet to try is running the 1:20 premix ratio called for by the manual rather than 1:40. Any other suggestions?
Is it sucking gearbox oil through the clutch side crank seal or between the crank cases?
I've replaced the seals in the engine, so I dont think that's the case. I'll have to check the oil level to confirm.
A pressure test is the only way to confirm there are is no leak.
A leaking float valve or float height too high, will also cause the bike to run rich.
Pressure test meaning compression?
The Shop
Luxon 4-Post Bar Mounts
$189.95 - $239.95
DeCal Works Huge Plastic Inventory of UFO and Polisport kits.
Negative, a pressure test, some people call it a leak test...
Seal the exhaust port...
Fit a pressure gauge to the reed intake...
Pump the pressure up to 5psi, it it loses pressure after 10 minutes, there is a leak...
https://www.thumpertalk.com/forums/topic/432226-pressure-testing-a-2-stroke/
I'll have to take it to a friend of mine with Guage like that. I checked the oil level and it is still full.
I've tried going back to the stock jet sizes which are much bigger but are now giving me a clean plug. The new issue is that rpms do not increase past half throttle, just before going into the power band. It doesn't bog either, just remains constant. Could this be an electrical problem?
Randomly pulling the plug isnt telling you much. A throttle position specific test will
As far as throttle position goes, RPM stopps climbing at about 1/3 to half throttle without a bog. Slight improvement switching out the 210 main for a 165. I'll try swapping out the needle and needle jet for leaner set.
It could be, the 1982 model's manual has instructions for checking the electrical system...
https://www.manualslib.com/download/1486962/Yamaha-Yt175j-1982.html
I swapped the needle and needle jet to 6dh4 159q2, no real improvement. Seems like major jetting changes aren't giving me much difference.
Really hoping it's not electrician as id like to run this bike in a race next week...
Ice ordered a new cdi and coil to try to eliminate those as potential problems.
I do have the manual here for the 1980 but it's not so descriptive about adjusting timing. Could that be a potential cause?
Yes, ignition timing would stop the bike reving.
I've just pulled off the stator cover to check, looks like timing marks are all lined up.
I would suggest only one jetting change at a time. so just change needle jet or needle at a time.
Post a reply to: 1980 IT175 jetting