Topic: stumble off idle??

[cbr-eric]

hey guys, hoping to get an answer here... I have an 82 cm250c that I have cleaned and set all the carb setting to stock.  I replaced the air filter and plugs. has a new to me coil and wires, lots of spark and all tests out ok.  when it is at idle I have to really go easy on the throttle to get the rpm up.  open it even a little too fast and it just stumbles and will die at times. any thoughts? thinking I will take the carb off yet again (probably the 20th time now) and see if it gets better. anyone else had this happen? how did you fix it?  thanks guys!

[w1sa]

I think the carb is a CV unit. Usually they can be more dependant on clean jets and especially the air bleed passageway. They tend to run rich if the air bleed is clogged or restricted, sucking richer mixtures from the slow and mains jets.

If you've double checked all the other tuning items, take the carb off and remove the jetting, air cutoff cover, valve, inspect all jetting/needle components to eliminate all crud from jets and holes, including the float valve. Remove the top cover of the carb and inspect the seals and condition of the piston and the cover/cylinder bore.  Blow carb cleaner thru the air bleed passageway to the aircut-off valve and from the air cut-off valve to the lower jetting passageways. Clean air  passageway should allow good exit of cleaner at the jet positions and into the carb throat when re-assembled. (Don't spray cleaner to the passageway with the air cut-off installed and covered)

When re-assembled,  make sure the piston slides freely from closed to fully open. Also plumb some clear tubing to the installed carb (at the drain) to check the actual fuel level inside the carb with fuel turned on and flowing   (s/b say 2-3mm below carb body/float bowl joint line)..............lucky its not multi cv carbs..........good luck
 

 

[cbr-eric]

great info, thanks!  I will double check everything again

[cbr-eric]

well I took it off again, cleaned it...again, and now it is holding gas (it had started pouring gas from the overflow when gas was turned on and idling) but now it is right back to having a good stumble when the throttle is first opened.  I hate this bike, its for sale ad I just want it to run decent and sell lol!  I have a spare carb, maybe I will go all through that one and swap, see if it changes.  amazingly this one simple carb gives me problems, and the 4 carbs on my 88 cbr 600 or even my k8 I am able to make run fantastically. 

[Uncle Ernie]

If it is a CV, check the diaphram for cracks or holes.  If it's not perfect, cutting a new piece of rubber (inner tube?) will get you home- but you need to replace it.  There are no fixes for an old, damaged diaphram (and that inclued silicone and tape).

[cbr-eric]

no diaphram in the carb.  I just cleaned the spare, took everything off it, soaked it for a day, blew air through everything and re-assembled.  everything is spotless. runs better, but not right.  with the idle srew turned all the way in the idle is just barely high enough. still a bit of a stumble off idle.  I will try and take a vid tomorrow and show you guys. really aggravating the heck out of me.

[Uncle Ernie]

Usually, you screw the idle jet in all the way and then back out a recommended number of times- according to the manual.  Then a little adjustment either way to fine tune.  I doubut you're supposed to screw it in and just leave it there.

Also, chasing those threads is a very good idea.  You want to be sensitive so as to just >touch< the bottom- not mash it down.  Mashing will put an indent (ring) aound the screw's pointy end and make it harder to adjust proper flow.

[cbr-eric]

oh, I mean the idle adjustment screw, not the pilot jet. sorry for the confusion.  I notice it seems a lot better with the choke pulled out slightly.  any possibility the valves might be adjusted wrong and it would cause this? thinking maybe valve clearance adjustment time...  thanks guys!

[cbr-eric]

update: I sold it for $360 and now it is someone elses problem lol!