Carb probs

[nick]

Been a (long) while since I've been on the forum, long story........

Anyway, I've got a prob with the hybrid which appeared on it's last track outing. I can get it started on full choke but after a little while the revs get very erratic. Knock the choke off and it just stalls. I've cleaned the carbs thoroughly but the problem is still there. The bike has run fine in the past so it's a mystery. I do have another set of carbs which I've tried out. Good news is that the bike ticks over just fine and throttle response is good. The only problem is that when you rev it up the revs rise and stay up even though the throttle has returned to the stop and the butterflies look shut. Err?????

So, I've got two set of carbs which between them are ok!!!!!

Any ideas??

[Evilchicken0]

It's a track bike so it kinda needs to be right because it's going to be at higher revs than a road bike ... so honestly

Take it to a dyno

[nick]

Anyone know what the standard setting is for the pilot screws on cat carbs? Thinking that might be the problem with the set that won't run at low rpm

[Evilchicken0]

1 3/8 turns
fuel level 11.5 to 12.5mm
idle speed 1200 to 1300 rpm

[nick]

Made some progress......

Tried and failed to find a problem so I picked another set of carbs which run fine.........well, most of the time!

Blipping the throttle feels ok, good pick up, no hesitation or duff notes but very occasionally the revs just linger before returning to tick over. Throttle returns fine, butterflies close, cable is free and easy. Odd!

Could it be an air leak? Airbox appears well sealed ( it's modded with a mix of 3tj and cat bits). If I put my hand over the intake I can feel a good "suck" so I'm fairly confident that's not a problem. Any other suggestions?

[barryfzr]

just a possible stab ...have you got any leaks/cracks on the inlet rubbers?

[nick]

Not that I've noticed, but I very small split might be there. Made me think about the carb balance pipes though.....

Will check these out as well, ta :-)