Mikuni vm38

[SpaghettiOs]

Anyone have any idea where to start with the needle jet and the others running a 2 into 1 manifold and straight pipes with pod filter. Currently the carb has a 247 Q-2 needle jet and a 6DH7 needle which I think is rather extreme (right?) the air jet is out and it has a 180 main and a 22.5 pilot. Bike starts right up but there is a slight smoke at idle and if you crank the throttle a poof of black so I'm thinking its dumping too much gas in because the needle jet is huge... of course I very well could be completely wrong! Thanks!

 

[ThePirate]

Dude ,
Dont you think vm 38's are a tad bit big...vm34 are more than enough...even for a rather modified motor...but then again what do i know..seriously not much

 

[SpaghettiOs]

Honestly I thought the same thing, but I had it so I wanted to try. It runs on the rich side but with nothing being done to the engine itself she goes like a bat out of hell. There is no issue with lack of low or high end speed I'd just like to make is so she doesn't smoke at all.

 

[ThePirate]

SpaghettiO's...i tried to edit my post but dunno what happened..one vm38 might work i couldnt say for sure...if they're snowmobile carbs..put em back on craigslist or kijiji and look for a set of 34's...or just buy a set from one the companies doing xs650 specific carbs...
Running rich is definately bad for yer rings and just about everthing else from the exjaust valves back

 

[SpaghettiOs]

the carb is off a 750 and its just the one. It seems like it would be fine with the right jetting but I can't find anyone that can point me in the right direction. It doesn't run all that bad, if it did I would say junk it too. I think its just a matter of finding the right formula. At least I hope.

 

[gggGary]

I have a thread with VM38s on a hot rod 750cc XS650

This thread http://www.xs650.com/forum/showthread.php?t=28289

VM38s with 200 mains, down around post #38 there's couple videos of it running.
As far as jetting I think you will find one carb or two doesn't make that much difference.

 

[SpaghettiOs]

Trying to read this on my tiny phone in the sun so I may have missed it but did you say the needle size and needle jet size? Thinking that's my issue, it's a 247 Q-2 with a 6DH7 needle... I can get flames out of my exhaust, cool and all but horrible for the paint!

 

[gggGary]

Here's an in-depth VM thread http://www.xs650.com/forum/showthread.php?t=6570

These were on a 750 kitted cammed engine with omar's head pipes and big megaphones with little baffling,

the 38s on the bike
body 38 N9
N 6DP-1 3rd slot
NJ P8 166
MJ260
PJ 25
Slide 1.5
Float valve 3.3

 

[TwoManyXS1Bs]

gggGary, here's your other VM38 thread:

http://www.xs650.com/forum/showthread.php?t=28326

 

[TwoManyXS1Bs]

Here's a 2-into-1 intake thread:

http://www.xs650.com/forum/showthread.php?t=27063

 

[DIRTY DOG]

i RAN A WISEGUY 2-1 intake with a vm36 I ran a 22.5 pilot, 190 main, needle 6f9, and needle jet 159,p-8. I can't remember what slide 2.5 I think mix screw out one full turn. set needle circlip in middle ring. should get you in the ball park ( ran very well

 

[SpaghettiOs]

Thanks everyone, looks like I have some parts to get!

 

[DIRTY DOG]

I know the vm36 works very well you may email joe wiseguy about the vm38 he may have some advise on it