Mikuni VM29 problems.

I hope someone can help me, I have a 1978 KZ1000 that has a 1075 kit in it and a set of Mikuni VM29's on it. The jets are: 20 pilot jets and 120 main jets. The needles are in the third notch or the middle. I've had the carbs ultrasonically cleaned twice now.

The problem I'm having is that when I come to a stop sign I have to bump the throttle to get the idle to drop from about 3000rpm to 1500rpm.

I've been living with this for a while, but I need to get it fixed. My gas mileage is only 20 to 25 miles/gal.

So far I've:
checked the the fuel level, used a color tune, pulled all the jets and needles and cleaned them, replaced some but not all the O-rings, cleaned and oiled the linkage and cable, and checked for leaks around the boots.


Thanks for the help,

what are your airscrews set to? do you have pod filters?

What setting on the air screw? 1.5 turns out is a good starting point.

Do you know what slides are in the carbs? If not, pull a top off and look down at the top of the slide - you'll see either 1.5 or 2.0 on the top. Your jetting is good for the 1.5 slides, but very lean on the pilot jet for 2.0 slides

The air screw is between .5 and 1 turns out. I did that based on the color turn.

The slides are 1.5 if I remember, I'll have to check again.

my airscrews are at 3/4 of a turn out, but I don't have the 1075 kit. confirm were your airscrews are there is sometimes a big difference between 1/2 turn and 1 full turn. I'd put them at 1/2 turn and see how it runs. it is easy enough to put them back if it doesn't help,before you start changing parts. sounds like your close.

I just checked all of the air screws and they are all 1/2 turn out. My plugs all still look rich, and my gas mileage sucks.

if you were rich at idle it would blubber and try to stall be slow to rev. are you letting the bike get up to operating temperature before tunning? reading the plugs only works really if you change them for new every time you tune. is this the bike in your avatar? maybe your gearing is contributing to your poor gas milage?

I changed the plugs out the last time I worked on this, I warm the bike up and then run a fan on it while I'm tuning it. It does try to stall when I try to adjust the idle below 1500.

I was thinking someone before me might have filed out the holes in the needles trying to clean them but I don't know how to tell.

Yes, it's the same bike in the avatar, and I think the I have a 17 tooth in front and a 44 in back, I'll have to check the front.

someone may have filed the holes on the needles? can you clarify that? not sure what you mean. I was just thinking if you are turning alot of RPMs to get highway speed there goes your MPG. still sounds lean to me. are you sure about things like ignition, timing, valves, carb sync, ect.? it should idle below 1500RPM, thats some of your MPG also.

My bad I type needles but should have type jets.:blush:

The ignition is a Dyna S with green 3Ohm coils, the timing is spot on, the head and valves were just redone by RLM here in San Antonio, and I synced the carbs with a mercury manometer.

Try a new cable. If it's frayed inside the housing it won't matter how much you lube it. Should 29's have a push/pull throttle due to vacuum pressure? Sounds like blipping the throttle is creating enough of a drop in vacuum for the slides to drop. IDK?

Both cables are brand new Motion Pro, I put them on this past fall.

If the rubber caps on the choke plungers are old and hard could that cause problems?