First Generation Ascots > Tech Section
Dyno tuning
WTF304:
You sure your I.D and O.D isn't mixed up ?
scottly:
The needle has an OD of .071", at the point in the taper where the needle meets the ID of the needle jet, with the slide fully open.
scottly:
Wide open throttle tests on the dyno with the drilled needle jet showed an improvement in the air/fuel mixture from 3200 RPM up, but now the bike is waay too rich at lower speeds and small throttle openings. Next up is a Mikuni 36mm carb that was fitted to the same XR500 that the WBX-1 cam came from.
scottly:
I put the bike with the 36mm Mikuni on the dyno today, and found that the air/fuel was actually rich at small throttle openings, when I thought it was lean. The carb has a #35 pilot, while others have reported using a #25. The #220 main jet appears to be very close to perfect.
Just because you can snap the throttle wide open at 2700 RPM, it doesn't mean you should, as the motor can't take that much carb until about 4000 where the Mikuni starts overtaking the stock carb. It's interesting that the HP basically flat-lines from about 5600 RPM to about 6850, while the stock carb started dropping off.
Just for grins, I'm posting two versions from the same two dyno runs; the first is the stock carb in blue compared with the Mik in red, plotted against RPM, and the second is plotted against MPH. As usual, tests are run in 4th gear, WFO.
WTF304:
Nice ... that mik has an accelerator pump? .... this is good stuff to know.
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