BS34 carb issues

Hey guys been lurking on this forum and posting on the 650 forum, just starting to post here I've got a an 82 kz650 with a set of bs34 carbs on it. I bought it and the carbs had seized pilot jets which i could not remove so i replaced them with another set of bs34s. The current set had 37.5 pilot jets in them and i could not get the bike to start without spraying a shot of starter fluid in the carb throat. The mods I know it has are a pipe and pod filters. The PO said it has internal mods but he wasnt sure exactly what was done although removing the carbs it appears the engine ports are ported & polished. I've been trying to get the reciepts for the bike build but i think hes in jail so im giving up lol Neways I switched to a larger set of pilots which were 40's and it would start on its with full choke after turning over a few times. It immediately revs to 5k then i put it on 1/2 choke where it sits (usually backfiring out of carbs) until its warm where it revs to 5k and i turn choke off and shes good to go. It barely starts unless the fuel pilot screws are almost 6 turns out. I've got some 42.5 pilot jets on the way, i've cleaned and rebuilt the carbs and checked for leaks (none). Does it just need jets that big? The carbs I put on had 117.5 mains and i rode it around then i changed the mains to one in the old set which were 137.5's which gave the bike a ton more power and made the ride soo much more fun Just wondering if those size pilots were common for these carbs, on the 650 forum not many guys run the bs34s on their bikes. The 82-83 models were the only ones that came with bs32s.

Hello,

I have similiar issues, let me save you a lot of time.

Adjust the pilot jet at least to a 45. Then move the needle jet richers. Air/Mix screw will likely be about 1.5 to 2 turns out. Sync carbs and you should be golden!

See my post GPZ on KZ650 carb issues. its a lil older.

Well last night i pulled them and installed the 42.5 pilots. I also gave them a cleaning one more time using a posted picture with some cleaning methods from another thread and found one choke passage to be plugged. I got it cleared and fired the bike up today. Now I got new problems! The bike revs sky high on full choke then revs to 5k on 1/2 choke and stays that way with choke off!! I've gotta go outside and mess with it but as far i can tell the throttles not blocked and the adjustment screw is all the way out with next to no tension on throttle. Does it ever stop :side:

Air leak would be a prime suspect.

Good Fortune!

Alright I just finished up some more tinkering (the wife kicked me outta my garage too much noise). I pulled the carbs and checked the throttle cable it had more tension than i remember. The metal bracket that goes on the throttle cable into the throttle cable holder is broke off the cable, meaning it slides on and off. I had to take it outta the carb bracket and just let the cable in it. However its still being very temperamental about it for some reason. It will start on full choke and shoot to 5k (its done this since I got the bike running). Then on 1/2 choke it goes down to 1500-2k idling sweet, at first it died at that point but adjusting the screws out the 3 1/2 from 2 1/2 turns fixed that. But if i barely touch the throttle to rev it then sometimes it going way to high again. The only thing i did differently was when the carbs were apart this time i sprayed carb cleaner on the outside to clean off the gunk, perhaps it dried the springs out a bit. I soaked it all with some wd40 and came back inside. I'll mess with it some more tomorrow but in the meantime i agree with needing 45 pilots then it should be at 2 1/2 turns. I checked for leaks before after i removed the carb holders and used some gas sealer on them but dint find anyone. I will check again tomorrow. Thanks for the help!

omgbossis29 wrote: Alright I just finished up some more tinkering (the wife kicked me outta my garage too much noise). I pulled the carbs and checked the throttle cable it had more tension than i remember. The metal bracket that goes on the throttle cable into the throttle cable holder is broke off the cable, meaning it slides on and off. I had to take it outta the carb bracket and just let the cable in it. However its still being very temperamental about it for some reason. It will start on full choke and shoot to 5k (its done this since I got the bike running). Then on 1/2 choke it goes down to 1500-2k idling sweet, at first it died at that point but adjusting the screws out the 3 1/2 from 2 1/2 turns fixed that. But if i barely touch the throttle to rev it then sometimes it going way to high again. The only thing i did differently was when the carbs were apart this time i sprayed carb cleaner on the outside to clean off the gunk, perhaps it dried the springs out a bit. I soaked it all with some wd40 and came back inside. I'll mess with it some more tomorrow but in the meantime i agree with needing 45 pilots then it should be at 2 1/2 turns. I checked for leaks before after i removed the carb holders and used some gas sealer on them but dint find anyone. I will check again tomorrow. Thanks for the help!

Could disconnect both throttle cables at the carb bell crank, and re-test idle stability after blipping throttle by hand.

This could help rule out possibility of a sticking cable and/or twist tube at handlebar.

Should be an audible click when the the bell crank closes against the idle thumbscrew.

Good Fortune!

Alright spent a few hours on it today. The throttle situation is worked out after lubing everything back up. I'm still in the same situation though, once its warm i still cant idle below 1500 (it just dies). I can get the rpms lower dialing out the mixture screws but I'm already back around 4 turns out just to idle around 1200 and it lean misfires out of the carbs and makes all kinda internal noise.
At this point im giving up on the carbs and ordering a book to do a valve clearance check. I've pulled these carbs off at least 20x and im sick of it..... I also got my new pods today as most of the old ones were so cracked it left large gaps when they were on. I believe that helped as my full choke no longer shoots directly to 5k it takes a few moments then starts slowing creeping. 1/2 choke also is not shooting high in rpms i actually had to turn the idle knob to keep it just under 2k. The bike wont even start unless the fuel screws are at least 3 1/4 turns out it just keeps hardly firing till i keep turning the screws out. No matter what i do i cant get it idle/choke drawing through the pilot jets.......

what is the current low speed jet size?

past 2 turns out means the jet is to small...pretty sure its 2 turns on bike carbs also

my jetski carbs are 2 turns past and u need to go up a size...


either way im thinkin ur to small on that low speed jet bud

Stock carbs would be bs32s, I'm running the bs34s. I have no idea what the pilot jet size is on the bs32s but I'm assuming for the 34s its larger than the the 32s. The stock pilot size on these carbs was 37.5 and I gone up one size at a time to the current 42.5. I can go up again but feel its best to do a valve clearance check in case the intake side is off causing low compression at low rpm but I'm not sure. I ordered a valve cover gasket to do the job anyway. I'm a bit nervous on tacking the job as it sounds daunting but I'm pretty good mechanically so it shouldn't be too bad.