My new Yamaha YZ85 chamber exhaust performance!

Discussion in '2 Stroke Bicycle Engines & Kits' started by StevenMain, Dec 12, 2016.

  1. StevenMain

    StevenMain New Member

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    None.....there was nothing gained over the long high mount ebay chamber I had been running. I was shooting for better top speed with a 44 tooth and the bike is only running 38 mph still.. back to more dremeling for performance I guess. On the plus side it looks and sounds wicked. Will post pics soon.:-||
     
  2. StevenMain

    StevenMain New Member

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    Pics of the new YZ85 pipe.. To fit this bad boy i cut off the flange and 2 inches of head pipe, i the made 6 pie cuts on the end of the pipe and used a torch to smoothly close all the "fingers". This made the head pipe small enough to put on a china girl flange. Then i cut the pipe in half at one of the bends, rotated the head pip 90 degrees and welded the chamber back to it. Took about 2 hours, for $35 dollars you cant get a better pipe! I sort of got lazy after finishing and slapped a 50cc four stroke muffler on the end with bailing wore so its not so loud. Next ill make myself a muffler. To be fair I can't give it an honest test. My clutch is suffering, it's slipping really badly and not putting the power down. I tried two different used clutches to no avail, I even pulled out all the glazed pucks and roughed them up on some concrete and that helped marginally. New pucks will be here later today and I'll replace them all. Until then I can't really go over 1/3 throttle until I'm over 30 because the clutch will just go right back to slipping.
     

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    #2 StevenMain, Dec 12, 2016
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  3. StevenMain

    StevenMain New Member

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    Cleaned clutch and installed new pads, still slipping for sure...Have to ease into the throttle until at a relatively high speed. Guess ill have to give it more clamping force from the countershaft spring. 38.8 MPH on a 44 Tooth using speedometer I programmed for my bicycles exact tire rollout. (81" exactly on the front wheel with my weight) I was hoping for 11,000 RPM but 9,100 seems to be all it can pull. Transfer Duration 118 Exhaust Duration 190 and 36* Blowdown.

    A teardown inspection showed a bit of discoloration on the piston and head temps about 350 after a hard pull. Also gets a bit of pre-ignition after a hard pull. I probably need to find a fatter main jet.

    This motor just plain sucks though no matter what you do to it. Going to tig up my crank case some to add metal, then machine it for this jug kit in the near future for a Piaggio scooter http://www.racingplanetusa.com/cylinder-airsal-racing-70cc-piaggio-p-7550-1.html#prettyPhoto
     
  4. StevenMain

    StevenMain New Member

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    Update: used a torch tip cleaner to file open the main jet.
    Installed a #7 NGK to stop detonation I was getting..
    Ported a new jug with less aggressive timing.. came up with a new heart shaped exhaust port.. there is a ring bridge to support the ring at the middle of the port as it grows as wide as possible. This setup yielded 41.5 mph on a flat. It seems to have two power curves.. about 8000 it pulls very hard.. then if you stay in the throttle it will ever so slowly continue accelerating.. if you tuck.. once at 36 it will start picking up steam again when it hits the pipe. Pulled to 41.5 and was continuing to accelerate. Heard nasty rattle and thought my bottom end was letting go so I let off,... exhaust stud stripped out of the cylinder... went and drilled and tapped for M8 Allen bolts.
     

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