3C Idle mixture

P

pfg49

New member
Location
Southampton UK
When attempting to set up the carbs, I was trying to adjust the idle mixture. Two outer carbs adjust fine, but no matter where the centre carb screw is adjusted to, it makes absolutely no difference at all. When riding the bike at low revs, when the carbs are presumably using the idle circuit, it feels down on one cylinder, but roll the throttle and your back on to three cylinders. Very difficult to get it to idle too.

Advice please.
 
plugged pilot circuit in the center carb, may just be the jet
roll on throttle and you have pumpers allowing the center cyl some fuel to pick up and go

while i would pull the rack and check them all you could drop the center bowl and pilot jet to have a look see
 
can also be a sign of crumblying pick up wires, losing the chuff at tickover and just beyond, but coming back in as revs and raisins rise a bit.
CLEM
 
Could also be an air leak on the inlet stub: spray with easy start when idling and see if the revs pick up..
 
Thanks for your replies. I have synchronised the carbs, so I guess it's carbs off time. Eurocarbs want ?125 per carb to overhaul them, ?two hundred and something for a new one. Look see first I think!
 
It's not difficult to disassemble and clean them yourself. Have a tray handy to put all the little bits in so you don't lose them.

As previously mentioned, your problem is likely to be a blocked jet, which will be obvious if you hold it up to the light and look through the orifice. If you can't see daylight through it, it's blocked. Blow it out with compressed air (or your mouth if you can blow hard enough). If it's a stubborn bit of muck, you can also un-block it by poking something through.
 
Might also be one of the air bleeds for the idle circuit blocked...
As Andy stated the insulators can start to break up and cause you grief ... but would have thought you would have got some reaction from the mixture screw even marginal but as you say you have sync then we can assume that you have some vacuum at the carb.. 
So before you pull the carbs and send off to someone else why not check the basic's

Take the bowl off, remove the idle jet have a look at it, ( you can do in bike ) and if you are careful you can get the mixture screw out in situ, have a look at the rubber oring there.  Then you could try to spray a little carby cleaner in there and also in the air bleeds at the bellmouth of the carb and see if goes through.
 
Hey Kev, was that on a Mikuni or Dellorto?

I believe it's not unusual with Mikunis which have a very fine tip on the idle screw.
I've never heard of broken idle screw tips with Dellortos. Not saying it can't happen, but the tapered tip is a bit blunter on Dell screws. Would be worth knowing if they can break off.

Cheers,
Cam
 
[Sealing] Oring in place around the pilot screw? If not, this will alow excess air into the idle fuel metering.
 
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