VM29 Jetting Trouble

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Post edited by: Patton, at: 2007/05/15 14:48

Post edited by: Patton, at: 2007/05/15 14:49

Thanks and apologies Wiredgeorge:whistle:! I'll replace that spring. I'll just get a new one and call it good.

Thanks again Patton. I've got a Dyna ignition and coils on the beast and timing is on. You're right to mention it though because, as you say, I'm probably not the only one having problems!

Everyone on here has been great. Hopefully I'll get the old girl running like she should. I'll post a pic of her as soon as I can.

Thanks and apologies Wiredgeorge:whistle:! I'll replace that spring. I'll just get a new one and call it good.

Thanks again Patton. I've got a Dyna ignition and coils on the beast and timing is on. You're right to mention it though because, as you say, I'm probably not the only one having problems!

Everyone on here has been great. Hopefully I'll get the old girl running like she should. I'll post a pic of her as soon as I can.

Sandy, i just installed my vm 29 smoothbores, after that i saw this post. What is in your opinion the correct way to instal the vent lines? I am using the Z1B airfilterhouse with an K&N airfilter, i only changed the mains from 120 into 117,5.
Greetz from Holland

Post edited by: willemZ900, at: 2007/05/17 12:52

Willem,when I first got My 29's,I was told to run the ventline from one set(of 2 carbs) over to the other...WRONG...run 2 individual lines and let them hang down over the swingarm.
I went through hell with these,as I was told to bridge the line,which made no sense to Me,but after running them individually,it was all good.

Sandy, I had the same problem as you in regards to connecting the vent line. Once I ran the vent lines seperately the 29's purrs like a kitten at an idle and pulls like a freight train with the throttle wide open. The only problem I have is when I open the throttle fast it hesitates then picks up. I'm still trying to figure the hesitation out but so far I'm loving these 29's and I barely have to use the choke when starting.

What is a good starting ajustment for the pilot air screws on the 29's?

Sandy, i run the vent lines seperately but they are only 15 cm long. As i understand you well i have to put long ventlines on the carbs to hang them over the swingarm.
tw, try one size bigger pilot jets (20.0), for the air screws starting point is 1.5 turns out.
GreetZ from Holland
Willem

tw.. wrote:

...when I open the throttle fast it hesitates then picks up....

Could be the pilot air screw adjustment. Would test with 1/8 turn increments. Screw in for richer and out for leaner.

As to routing vent hoses, might prefer running them to underneath the seat. On Z1 there's room between the air box and frame rail to do this. On KZ900 there's a hole provided in the frame whereby the vent tubes run underneath the seat and attach to guides made for that purpose which are cast into top of the air filter cover.

I forgot to check but are the points set right? or do you have electronic ignition.

smooth bores will never idle very well. 29's 33's all of them. they are racing carbs. they stumble at idle and fall on their face on unloaded acceleration

they are fantastic at half open throttle to wide open throttle. that is where these carbs are designed to perform and shine bright.

I have a set of vm29's on a street 1075 kz with .395 cams mild port job stock valves stock compression
I have 15 pilots 135 mains and needle on #2 position( one below middle notch) dyna electronic ign. too

my drag bike has 33's and same thing.- gs 1100 14/1 compression .425 cams 17.5 pilot needle at #2 position 142.5 mains floats set level 26mm +- 2 mm from body surface

I also need to add the float heights are very important on these carbs.

if you want smooth running at idle and smooth transition at lower revs you need CV carbs.

otherwise you will be chasing something that will never happen

Post edited by: trippivot, at: 2007/05/19 10:25

trippivot wrote:

...stumble at idle and fall on their face on unloaded acceleration...have 15 pilots...needle on #2 position( one below middle notch)...I have a set of vm29's....

As pilot jet controls allowable mixture range at idle and first 1/4 throttle, am wondering if #15 pilot is too small thereby causing poor idle and stumble during first 1/4 throttle opening. Attempted compensation by raising jet needle (enriches mid-range) won't much help stumble coming right off idle.

Recommended pilot jet is 17.5 or 20 for VM29's.

Just trying to help out a little here because my Yoshi-head Z1 idles smooth and stable at 1000-1200 rpm, and almost on par with the stock VM26's on KZ900 with 1015 kit and stock cams.

Maybe the idle problem is agravated by the .395 cams???

Just food for thought. Regret seeing anyone unhappy with their 29's for any reason.

Good luck with the chase!

Patton, the last sets of 29s out the door from Mikuni had #25 pilots installed. The pilot jet size has to be appropriate for the slide cut out. MOST of the 29s you will find on KZs are 1.5 slide cut outs. The larger slide cut out flows MORE AIR at lower velocity. The larger the slide cut out, the larger the pilot jet is required to get the bike to idle properly. A #17.5 pilot jet is FINE if you are running pods with a 1.5 slide cut out. The airscrew needs to be turned out about 1/4 turn. Neither of these settings is "recommended" by Mikuni or Sudco. I figured this out because it works. The smaller #15 pilot jet that trippivot is running would need to have the air screws closed to provide an acceptable idle... NONE of the larger pilot jets shipped originally with the 29s will work well (#22.5 or #25) at any air screw setting with a 1.5 slide cut out. With a 2.0 slide cut out, a #20 pilot jet will work. I tune and test quite a few of these things after rejetting and I have found this to work. The 33s respond pretty much the same way as the 29s and idle fairly well with a #17.5 pilot jet. If you use a stock airbox, the #15 pilot jet is the way to go with either. The type pilot jet used is the VM22/210; same as the VM24. Oh yeah, that tiny "air jet" you refer to... please be careful when deciding an air jet is missing. There are two air jets on a 29. One is for the main jet and the other the pilot. The pilot jet is a brass sleeve press fit into the carb body and the main jet is just a cast hole. Neither screws in or is removable. The 1 and 2 carbs have the pilot air jets on the left while the 3 and 4 carbs have the pilot air jet on the right. They have no slot in the head so I am mostly sure they are pressed in and not changeable although I could be wrong on this point... I have never attempted to remove an air jet on these carburetors as I am pretty sure you would just damage the jet.

Post edited by: wiredgeorge, at: 2007/05/19 16:28