High Revs when hot
 

1991 660z - When bike gets hot (temp gauge reading normal), revs go up to nearly 2k?! If I turn the revs down its too low when bikes cold?? Any ideas would be great, Cheers :)

If I remember rightly you were previously having trouble with popping on the overrun? Did you ever get that sorted? I think both issues are closely linked. Your bike is almost certainly running too lean at idle.

First try calming the revs down on the hot engine with the pilot air screw, rather than the throttle stop/idle screw which you have been doing. Standard setting is 2.5 turns out, but that is fairly weak anyway. You may need to go as far as 4-6 turns out. However, much beyond 4 turns out would suggest that the pilot jet is either gummed up or too small. I went up from a 48 (standard) pilot jet to a 52, with the pilot air screw set back to 2.5 turns out, in order to get a smooth idle on the 1994 3YF I had.

Hi, thanks for reply :) Yes I did have the popping backfiring issue. Managed to get that sorted by getting a carb gasket and float valve kit :) But now, when pulling up at lights etc its over revving. Have tried turning down the stop/idle but revs drop too low and cuts out. There doesnt seem to be any middle setting with it. Will have a go at trying your suggestion of turning the pilot air screw down as when backfiring stopped we returned it back to 3 turns out. Seemed to be ok but when hot its NOT !! Doing my head in lol :) Thanks for suggestions, will keep you posted :)

If the high tickover does settle but slowly then it could be tight valve clearances. Worth a check before delving into carbs.


Sent from my iPhone with a smile :)

Hi sorry it took so long, been riding the Vmax for a while instead of the XTZ :D
Anyway, got it to 4 turns out and tickover is steadier but revs dip and bike cuts out. Any other suggestions would be greatly appreciated, Cheers :)

Next thing I'd check then is vacuum leaks, often a cause if erratic idle. Also take the diaphragm cover off the carb and check the diaphragm is seated correctly and/or isn't perished. It is very common for it to jump out of its slot when refitting the cover after a carb overhaul.