funky carb problem - '76 kz 400

hi all, im new, posting for the 1st time.

i own a '76 kz400 with keihin slider carbs (non rubber diaphragm, i think mine are called the cvb36??)

anyways, i have had this problem since i have owned the bike of the engine/carbs choosing to idle realy high (5-6000 rpm) after riding it for a while and then stopping at a stop sign. then i'll reset the idle to 1000 rpm and then ride some more. when i come to a stop again it becomes too low and the motor quits. so i am consatnatly fiddling with idle speed. when choked when cold it also seems to idle high (3-4000 rpm). furthermore the left carb does respond to idle mixture adjustments whereas the right doesn't at all. another anomaly is that the plugs rich foul after prolonged idling. the idle speed problem is intermittent in nature and i have cleaned the carbs, set the float levels properly, and checked for induction leaks by spraying brake cleaner around the area with no indication of induction leaks. things i haven't yet checked is carb sync, and see if one carb is jetted differently than the other. if any one has any insight and advice, please help!

thanks,

paul k

Sounds like the carburetors' pilot circuits were not adequately cleaned. It would be helpful to have a description of jetting and any airbox / pipe mods.

It is very likely that the sooty plugs have nothing to do with jetting. Could be dirty air filter, clogged internal passageways, poor spark, lack of valve clearances, ignition timing problems.

i am 100% certain the carbs are clean as can be. the carbs were adequatly cleaned/soaked with carb cleaner twice. i checked all passages with spray (brake cleaner) to make sure they stuff came out of the right passages and unrestricted.

i am using an oem airbox and filter. the exhasut pipes are oem but i hacksawed the mufflers off due to rot and put slip-ons, but there's 3 ft. of originl pipe on each side from engine to muffler.

jetting is the only thing i haven't made certain of, i haven't played with the jets but i wonder if they have been messed with in the past.

i will check ignition timing/strength and valve clearances, i have neglected those factors as i was too focused on carburation, thanks for the reminder! i'll also have a closer look at the air filter too.

as for the right carb's idle mixture adjuistment's lack of reaction to adjustment, could that be a sync. problem as maybe the left carb/cyl. is doing more work as it reacts to change in idle mixture adjustments?

thanks w.g. and i thank in advance for any other inputs!

paul k

Trying to tune carburetors if you have not done ALL the other tune up steps recommended in a factory or Clymer manual is pretty much a waste of time.

While you may feel you have done a great job cleaning, without removing the jets and actually cleaning the jets, I doubt you have cleaned adequately. The method you used doesn't get 100 percent of gunk/obstruction especially if the jets are still dirty. Buy carb kits for your model... Keyster kits would be a good idea. Did you clean the air jets under the slides?

i have had the carbs apart completely, every piece, and soaked it in carb cleaner. i sprayed brake cleaner through to make sure that all passages were unobstructed after the thourough cleaning i had done.

the only tuning step i have ommitted up until now is the carb sync-ing which i intend to do. i have a friend who has vaccuum guages and i'm gonna check that out.

on a slightly different point, do those carbs have an eccelertor enriching system/circuit?

after much fiddling around with my carbs i did find a completely plugged slow jet whuch remedied my lack of adjusment on the right carb idle mixture.

i have also found that my unstable idle rpm is caused by an internal and external vacuum leaks caused by worn throttle shaft and the bores that it rides in. i have discovered that there are little felt washers behind little retainer cups on the ends of the throttle shafts that dry out and need to be lubed with oil. so when you disassemble and dunk/clean your carbs, be sure to pry out these little retainers and remove the felts.

so... does any ony know what can be done to repair/ rebush worn throttle shaft bores? the shafts can probably be re-plated or replaced with new oem if still available.