VM 30 Jetting?

MILLENNIUM FALCON

MILLENNIUM FALCON

EL Guapo
Messages
211
Reaction score
2
Points
18
Location
Pennsylvania
I am just switched to vm30's and I was wondering what you guys are running for jets. so far I have found 150 main, 25 pilot. Does anyone else have any info. My carbs came with 250 main, 40 pilot...I know that is super rich. The bike is a 82 xs400 with 2-2 (Free flowing) exhaust and K&N filters. Any info would be appreciated.

DSC_0276.jpg
 
The VM32,which fits a Dt400 dirt bike among others uses,on mine,a 50 pilot jet with a 160 main. With pods,you'll need maybe a 170 main,maybe a 60 pilot. Set it up like that,see how it runs,do a plug chop,then adjust from there. lha
 
running 50 pilot and 142 mains using dohc carbs on a sohc bike. pods and small baffle in the exhaust.

best to run it and see how it goes. those carbs will be off dozens of times :D
 
lhaolpa said:
The VM32,which fits a Dt400 dirt bike among others uses,on mine,a 50 pilot jet with a 160 main. With pods,you'll need maybe a 170 main,maybe a 60 pilot. Set it up like that,see how it runs,do a plug chop,then adjust from there. lha I mistakenly told about the vm32,when you were talking about vm30,which fits a Dt360 dirt bike.It takes 180 main jet,a50 pilot jet and a 5ej8-3 jet needle,and air jet out 1-1/2 turns. I've got specs on all VM carbs from dirt bikes,of couse it differs with the application. lha
Click to expand...
 
I'm running VM30s as well. Pod filters and straight pipes. I called up sudco and they recommended 25 pilot and 150 mains so thats what I'm running

I have yet to extensively run it, and plug chop yet so I cant really tell you how it performs. But It is still rich with black smoke and flames shooting out when revved hard.

Mine also came with 250 mains and 40 pilots in the beginning.. stupid stupid rich lol
 
The carb was made for a 2-stroke monster machine with radical porting and other racing mods.they require lots of gas to cool the chamber,or you'll hole a piston in a 2-stroke. Four strokes have other needs,and these carbs will work great with milder jetting. Get a few jets and experiment with the jets and do plug chops and change them until you get it right. My carb has the jet on a hollow bolt that you can change the main jet without removing the carb. I would start with am 170 main and 60 pilot and go from there.The difference in jetting between the VMs and BS carbs are in that they're made for different bikes. lha
 
Did some riding today with the 150 mains and 25 pilots. It would start up and idle but you had to gradually give it gas or it would fall flat on its face if you gave it full throttle. So I'm thinking the mains are way too big. I may go down on the pilot as well.
 
Thanks for the info. let me know how you make out. I didn't order my jets yet.


Campbell45 said:
Did some riding today with the 150 mains and 25 pilots. It would start up and idle but you had to gradually give it gas or it would fall flat on its face if you gave it full throttle. So I'm thinking the mains are way too big. I may go down on the pilot as well.
Click to expand...
 
Campbell45 said:
Did some riding today with the 150 mains and 25 pilots. It would start up and idle but you had to gradually give it gas or it would fall flat on its face if you gave it full throttle. So I'm thinking the mains are way too big. I may go down on the pilot as well.
Click to expand...

What do your plugs look like after this riding? If it's too rich,they'll be black and sooty,if it's too lean,it'll be pale colored and dry....lha
 
They are black and sooty. I need to sync and get the pilot system tuned in first but I already know I'm way too rich. I fouled one plug already.

Does anyone know the procedure on how to jet the mid range? I understand the pilot and main system but confused on the jet needle and needle jet.


I heard VMs come stock with the primary type nozzle and need to be converted over to bleed type for 4 strokes
 
The midrange is jetted by moving the needle up for richer and down for leaner,by moving the clip[ up for lean,down for rich],which lowers the needle or raises it in the needle jet.If your plug is black and sooty,your carb is set too rich,and you should get some jets,a couple of sizes smaller,and change them one size at a time,then run it,check the plug,repeat.I'd change the pilot as well. lha
 
I'd get the pilot and mains dialed in,then if you can't adjust the needle up or down enough,then worry about it. What you want is there to be a smooth transition from slow speed to mid,then high speed.That should be able to be handled with the clip.Remember.move the clip down to richen,up to lean. lha
 
Well this is starting to get frustrating..

Trying to check the pilot system I put new plugs in and started it up and let it idle for about 5 mins. Killed it checked the plugs and they still looked new. Can you check the pilot system off the plugs?


After that I tried messing with the air jets and didnt really get much so I turned them 1 1/2 from seated.

Then I raised the clip on the needle one notch wanting to lean it out. Before when I gave it 1/2 throttle before it would have some black smoke with some fire shooting out on backfires.

Once I changed the needle height I noticed things got a lot crisper, throttle flowed easier, and didnt have black smoke anymore (but still backfired some fire), so I took it for a drive and performance was much better. Right before I got it back home though it died and I couldnt get it to start back up. Pushed it home and pulled the plugs, they were white.

I finally got it started back up by adjusting the idle waaay up. Granted I didnt go on a very long ride but I thought it wouldve shown something



I'm not really sure where to go from here...
 
Last edited:
its still sounds too lean to me, I've tried colortune and didn't like it. (couldn't see a thing really)
 
Going up in pilot jets worked great! idle to 1/8 throttle is so much better! but beyond that it fumbles around. I took it for a ride and came back and the plugs looked like this:

e1c1e4d2.jpg



That is white on the top btw. I think its because of the mid range and main being out of whack but I could be wrong

What do you think?
 

Similar threads

H
1979 XS250 Rich idle issue
Replies
0
Views
479
Hesketh308
H
82xs400dude
Vm34 jetting help
2 3
Replies
43
Views
4K
amc49
A
sandmanred
Needle position question 78 XS400
Replies
19
Views
2K
amc49
A
Gra900
4G5 carb jets, pilot plugs, power and general
Replies
7
Views
1K
Gra900
Gra900
RockyRo217
1978 Yamaha 400XS one cylinder won’t run!
Replies
14
Views
2K
RockyRo217
RockyRo217
Back
Top