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Is there a fast idle kickdown on a YFA?
Mine seems to drop idle drasticly about 1 min after letting off the throttle.
I cant seem to find any fast idle speed adj.
Yes, the YFA has fast idle. Unfortunately the procedure is not so straightforward with these; the adjustment is made by bending a metal rod. Here are some scans of a rebuild sheet, pay particular attention to figures 4 and 9. I didn't see any copyright information on them when I scanned them in so I figure it's OK to post. They're pretty much everything you need to know about setting the choke and fast idle on these carbs. The choke shown in these figures is an auto choke but the fast idle setup is the same.
I screwed the fast idle screw in quite a bit and it seemed to help. It is my opinion the spring in the auto choke is either too soft or too hard. I'm not sure which, but it seemed the more pressure that was placed on the screw, made it catch on the next lowest step instead of dropping right down to the lowest step.