Mikuni VM22 Jetting Suggestions

Bow

Bow

Member
#1
#1
Gents,

This is my first Mikuni and I would like to hear what most of you run for Jetting.

I understand it comes with a 95 -100 main jet and a 15 Pilot.

When I ordered the Setup (Inverted Intake/Mikuni VM22), GoKarts USA suggested a 170-180 Main jet with a engine with the Inverted Intake and Exhaust, so I ordered a 170 and a 180 to go with it...

Looking around the forum, that seems pretty large.

I found a 130 main locally, so I got that today.

My current setup is:
ARC Billet Flywheel
Isky Black Mamba Jr Cam
18# springs
ARC +0.020 Billet Rod
Walbro fuel Pump
Home Brewed Header with EMGO "muffler" (glass pack straight thru)
GTC Torque Converter
Governor Removed
Low Oil Sensor removed

I notice when I fired it up the other night on the stand with the Mikuni (stock Jetted) it idled great, revved up good (no Load), but I had fuel coming out of the Overflow, so I am thinking I might need to Tee off the Fuel line to recirculate the excess fuel back to the tank...

Thanks for the assistance, like I said, I am a Mikuni Virgin... this is going on a Cyclekart, not a Mini Bike.
 
TheDullCarbide

TheDullCarbide

Active Member
#2
#2
That overflow is not "supposed" to be an overflow, it's a vent to keep the fuel bowl from trapping air that would prevent the float from coming up. If you have fuel coming out of there, too much fuel is going into the bowl. The obvious thing to do is check the needle valve seat and float height. I'm assuming the fuel pump is a pulse pump, not electric, right?
 
KMC3420

KMC3420

Member
#5
#5
My vm22 is running pretty well on a 15 pilot and 120 main. I have a 1/8 to 1/4 throttle stumble that might be air screw related. I might also go to a 12.5 pilot if I can't get the air screw right with the 15 pilot. I too am having fuel that I think is coming from around the main jet screw. I thought it was the bowl screws not tight enough so I tightened those and am still having excess fuel on the bottom of the bowl after a hard ride.

I am not running a fuel pump though.
 
Last edited:
TheDullCarbide

TheDullCarbide

Active Member
#6
#6
KMC3420 said:
My vm22 is running pretty well on a 15 pilot and 120 main. I have a 1/8 to 1/4 throttle stumble that might be air screw related. I might also go to a 12.5 pilot if I can't get the air screw right with the 15 pilot. I too am having fuel that I think is coming from around the main jet screw. I thought it was the bowl screws not tight enough so I tightened those and am still having excess fuel on the bottom of the bowl after a hard ride.

I am not running a fuel pump though.
Click to expand...
Could it just be the bouncing around that tricks the float into opening longer than it should?
 
KMC3420

KMC3420

Member
#7
#7
TheDullCarbide said:
Could it just be the bouncing around that tricks the float into opening longer than it should?
Click to expand...
That's a good point. I was running the heck out of it making sure the rings were seated. I didn't have time to let it idle, but have ran it for 30 minutes and will change my oil and see if it leaks fuel as I can allow it to just idle now.
 
ole4

ole4

#10
#10
Looks like you are running a real vm22 not the chikuni. I have not used one so scratch the jetting info. Those settings are for the oval bore chikuni.
 
TheDullCarbide

TheDullCarbide

Active Member
#12
#12
Bow said:
Not yet.. one would think a brand new carb would be right from the factory
Click to expand...
Ehhhhh...I'm not sure...I would check it just to be sure. IDK if they would check that in factory and you gotta remember the hell called shipping that it endured to get to you. It's coming all the way from Japan, ya know...
 
Bow

Bow

Member
#13
#13
I see your point...

I need to drop the bowl to put the 130 Main Jet in anyway... I have a digital caliper and few morals...

Also, for anyone interested, the Inverted Intake from Go Karts USA, yeah, it doesn't exactly "Fit" the Hemi Predator with the Fan Shroud on or an ARC Top Plate on the engine... bit of False Advertising... I plan to cut the shroud and the top plate to clear it, if the Intake was about 0.25"-0.5" taller, it would be fine...

Longer intakes are good for making power and tweaking power bands....
 
TheDullCarbide

TheDullCarbide

Active Member
#14
#14
Bow said:
I see your point...

I need to drop the bowl to put the 130 Main Jet in anyway... I have a digital caliper and few morals...

Also, for anyone interested, the Inverted Intake from Go Karts USA, yeah, it doesn't exactly "Fit" the Hemi Predator with the Fan Shroud on or an ARC Top Plate on the engine... bit of False Advertising... I plan to cut the shroud and the top plate to clear it, if the Intake was about 0.25"-0.5" taller, it would be fine...

Longer intakes are good for making power and tweaking power bands....
Click to expand...
Is the intake worth some extra room on the recoil side of the engine? Does it protect the carb and air filter any more than a short intake?
 
Bow

Bow

Member
#15
#15
I think it will. it puts the Carb above the Fan Shroud and the air filter facing Forward. You can see the problem that required the Fan Shroud to be cut in these photos

But that should also give you an idea of where the carb gets placed.

IMG_20170914_194917_606.jpg

IMG_20170914_194904_603.jpg

IMG_20170914_210234_103.jpg
 
KMC3420

KMC3420

Member
#18
#18
I had this thread saved and is the reason i have not pulled the trigger on the inverted intake, I hope you get yours running correctly. I am tempted to make one of these, it would be out of steel and not chromed, they have just welded two 90's together, but I would make mine long enough to clear all the tins. So far nobody has much luck getting one to run correctly besides Del Ray.

Inverted intake issues
 
TheDullCarbide

TheDullCarbide

Active Member
#20
#20
Once again, I'm talking out of my :asshole::

What is the finish on the inside of the intake? Is it rough, polished, chromed, etc? My point being that the intake needs to be rough for the fuel to atomize better and maybe the manufacturer overlooked this.
 
You must log in or register to reply here.
Top