78 kz1000 idle problems

I've got a 78 kz1000, from what i'm told it has a 1200cc big bore kit, cams, individual air filters, and a vance and hines 4 into 1 exhaust, i recently did a bunch of stuff to the bike, all pretty much looks no engine mods, the only problem is i can't get it to idle well, if i turn the idle screw in too much, the engine holds a high idle as soon as i rev the engine, if i turn just a little bit the idle comes back down to around 1000-1200, but after a second it drops down to like 500-600, some times it stalls out some times it just feels likes its going too, i've already taken off the carbs and bench syncronized them, they are all extremely close to being even, i'm also not exactly sure what carbs i have, one person said they are vm29 smoothbores and another said vm33 smoothbores, if anyone can help me out with what i should check and/or how i can figure out what size carbs i have i would greatly appreciate it

Here's a link to Z1E's carb id section.

Z1E Carb ID

according to that page i'd like to say they are vm29 thanks

My son has a 74 900 (pods and 4/1 star w/ baffle dyna S)and after cleaning the 29 smoothbores that it came with I had set the idle mixture screws to 1 turn (as that's what seemed to be good jumping off point for alot of the Mikunis). We started the engine and set the idle to 1100 rpms, but when we cracked the throttle it would idle high (2-3000) and want to linger there quite awhile. But I had kept in the back of my mind what Wired George had advised someone awhile back that the idle mixture for the 29s should be at 1/2 turn. Did that and it idled perfect w/ great throttle response w/ the idle retuning immediatley (have only done the bench sync so far). Don't know if it's the same for a warmed over 1000 engine. Hope that helps. Pat

rx8driver23 wrote:

...78 kz1000...can't get it to idle well... bench syncronized ...vm29 smoothbores....

Unstable idle could result from air leak (i.e., intrusion of outside air being sucked into the mixture).

Possible sources of air leak: vacuum caps (faulty sealing due to old hard cracked rubber); carb holders (ditto), especially if running pods without rear support for carbs; carb holder clamps (loose); fitment of carbs into carb holders (somehow misfitted).

Could test with engine running by spraying around carb intakes with WD40 (or propane gas or starter fluid) and noticing whether there's any change in engine performance or smoke from the exhaust.

As always, should address carbs LAST after all other components are up to snuff -- ignition timing, compression, valve clearances, spark quality, new plugs, cam chain adjustment, ample fresh fuel supply, in-line fuel filter, clean air filters, fresh oil and oil filter.

When ultimately get to carbs, would first assure correct service fuel level in float bowl using clear plastic tube method.

Good Luck!

already checked for a vacuum leak with starting fluid, none found, as for fuel i put on a pingle fuel valve and fuel seems to be getting to all the carbs ok, although i haven't checked base engine(compression, valve clearance etc) has new plugs and boots, brand new air filters and i just changed the oil also, the thing that makes me think its the carbs is that it ran good last year until someone at my work took it all apart and put it back to stock settings, i've been playing around with the air jet(one on the bottom) and it seems to help a little but then it gets worse

The 29s usually have too-large pilot jets installed relative to the slide cut out. Set the float levels (23mm inverted from the gasket mating line to the top of the float) and figure out what slide cut outs you have (there is a number on the slide... should be 1.5, 2.0 or 2.5) and what pilot jets you are using. The correct combo of pilot jet matched to slide cut out makes tuning the idle circuit a lot easier. Unfortunately, Mikuni chose to put air holes in the air mixture screws that make tuning the pilot circuits a bit touchy.

rx8driver23 wrote:

... been playing around with the air jet(one on the bottom) and it seems to help a little but then it gets worse

Perhaps misreading this, but my 29's have pilot air adjustment screws on the side (not on the bottom). :huh:

dbl post -- pls delete

i don't have a good picture of the carbs, i'll try and take a pic tomorrow, after a little research i may not even have smoothbores, i think its the stock vm 28, i've really gotta stop listening to other people that have no idea what they are talking about, my pilot jet is on the bottom back near the engine side of the carb bowl, i'm sorry if i don't seem like i know what i'm talking about, this is pretty much the first carb i've ever worked on and everyone that i know that keeps helping me out keeps making me just look for information that isn't even relative to what i have, i'll try and take a pic tomorrow and maybe someone on here can tell me what i do have, thanks for all the help

Pilot jet? If you are referring to the pilot mixture screw on the bottom of the bowl, they aren't 28s anyway. Most likely 77/78 VM26SS.

i took a look at another thread and then measured them when i had them off today and they are the vm26ss, sorry for my lack of knowledge, they are currently set at 2 turns out, 2.0 slide cut out, 25mm inverted on the floats, have a 130 main jet on the very bottom needle setting and has a 17.5 pilot jet, and a i've got the carbs off of the bike so any other question i could probably get it pretty quick, again thanks for all the help