First Generation Ascots > Tech Section
Dyno tuning
J6G1Z:
Can you use a small washer to shim the needle up like on a regular slide operated carb?
Good luck & keep up the good work.
J.
scottly:
I rode the bike a bit today with the 178 main and a 60 idle, and I have to say it ran pretty darn well, but I still believe the stock carb is worth more HP. ;)
I've found some .023" thick washers to use as shims for the needle. Here is a pic of the stock assembly:
scottly:
I made some dyno runs with the needle shimmed .046", and the improvement was very slight.
Does the factory manual give any theory of operation on the "air cut" valve located on the left side of the carb?
scottly:
I played a bit with the "air cut" valve; it appears to control when the slide is allowed to rise. With no spring, the motor wouldn't idle at all, but ran OK at 3K or more. With a weaker than stock spring, it would idle, although poorly, and seemed to pull better at lower RPM than the stock spring. Not much, if any gain, can be found there, so I would not recommend messing with it.
The bike is currently jetted as follows:
idle 58
main 185
needle shimmed .046" (not sure if this is worth messing with, either. ;))
J6G1Z:
I have not had one of these carbs apart other than removing the float bowl.
Does the throttle slide have a vent hole in the bottom, next to the hole that the needle drops through? I just installed a DynoJet kit on a VT Ascot. Part of the kit is a drill bit, sized to enlarge that throttle slide vent. This (along with a lighter spring) is supposed to allow the slide to respond to throttle input faster. It's kind of a leap of faith type of thing, taking a drill to your parts & permanently changing the part. I have some more work to do on the VT Ascot, but initial impressions of the DynoJet kit are good.
Keep up the good work
J.
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