Need help with predator and inverted intake w 22 mikuni carb.

[Cornishrooster]

Hi erbody need some help here. When I fire up the engine it starts at half throttle, I can give it gas without it dying but can't get the throttle to go down. Maybe I need to put smaller jets in it, the mikuni has the stock jets in at the moment, 100 and 15 pilot I was lead to believe that with the inverted intake I'd have to go with way bigger jets since the distance is much greater. Engine is running rich, sooty spark plug. Anyone have an idea of how far down I'd have to go jet-wise? Realize all engines are different but curious where someone else would start.

Thanks


edit

Well I pulled the bowl I was wrong... I guess somewhere along the way I put a 120 main and 17.5 pilot in there. Changed back to 95 and a 15 and I'm still having the same issue.... engine starts at half throttle

 

[TheDullCarbide]

How does it sound when it's running? A video would definitely help. Maybe your float isn't adjusted or assembled properly or the bowl isn't level?

Stupid question: Did you turn off the choke?

 

[TheDullCarbide]

Okay here we go...

My buddy had a VM22 on his 200cc two cylinder ATV. After he rebuilt the carb, it ran pretty much the way yours is. I dug in and found the needle retainer plate was missing. When the throttle was closed, the needle would push up into the piston and let fuel flow out the main jet. We ended up loosing the retainer plate so we hacked one out of a plastic washer.

Also, the main jet size will do nothing to adjust the idle mixture. It is only for 3/4 to full throttle.

Here's an exploded view of the carb. The retainer plate is 7:

 

[Cornishrooster]

Okay here we go...

My buddy had a VM22 on his 200cc two cylinder ATV. After he rebuilt the carb, it ran pretty much the way yours is. I dug in and found the needle retainer plate was missing. When the throttle was closed, the needle would push up into the piston and let fuel flow out the main jet. We ended up loosing the retainer plate so we hacked one out of a plastic washer.

Also, the main jet size will do nothing to adjust the idle mixture. It is only for 3/4 to full throttle.

Here's an exploded view of the carb. The retainer plate is 7:

So before I was using a mikuni knock off and I installed a real one this afternoon. Fired right up and I rode it around the block but it definitely sounded bogged down. After my ride I pulled the plug and it didn't have any color it but it was definitely soaking wet, dried it off and tried to start again but no luck this time. Ordered some smaller pilot jets to see if that helps. To answer your questions, yes the choke is off and the retainer piece was definitely in there. Should have shot a video while it was running, I had it idling between 1600 and 1800 by messing with fuel air and idling screw. Weird that it would run so well then have the plug get wet, is that a float height issue? When I got the carb I took the bowl off and the float wasn't even on the rod (part 22).

 

[Cornishrooster]

Grabbed this from a gokart forum I came across. Not sure if there's any sticky on this forum with this info but in all my search travels I haven't seen this info here.



I am posting this thread to clear up some things about the Mikuni 22mm Carb that alot of people are using.
First is the CHOKE or STARTING system as Mikuni calls it:

There is a lever that has the word CHOKE on it. If this lever is pushed down on the end with the lettering then the CHOKE is ON, (this lifts the plunger up). If the lever is raised on the end with the lettering then the CHOKE is OFF, (this pushes the plunger down).

Next we will explain what jets are active at what range of engine throttle:
Closed to 1/4- of Throttle Valve Opening (TVO) is using the PILOT JET and AIR SCREW.
1/4 to 1/2 - of TVO is using THROTTLE VALVE
1/2 to 3/4 - of TVO is using JET NEEDLE
3/4 to Full - TVO is using NEEDLE JET, MAIN JET and AIR JET
Before Tuning make the following checks before swapping jets and adjusting.
1) Check FLOAT LEVEL on the VM22 it is 24-26mm
2) Make sure the CHOKE LEVER is in the correct position ( OFF) before making adjustments
3) Valves Adjusted
4) Plenty of fuel

If its idling rich, black smoke, fouling plug (wet) then go down a step on the PILOT JET. after you have done this, follow these steps
First turn Fuel Air Screw in clockwise until lightly seated then back out 2 1/2 turns as a starting point.
Air dry plug if fuel soaked
Make sure the CHOKE is in the correct position
Start engine and get it warm
Turn Fuel Air Screw clockwise until the engine reaches its highest RPM and then turn Idle screw(the one that makes the slide barrel move up and down) counter clockwise until you reach the target idle you want then repeat the process until no further changes in rpm can be made.

Above 1/4 to 3/4 TVO if its rich you will Move the E-Clip on the needle up a notch.
The needle has 5 notches. Starting at the top from 1-5. 1= leanest and 5= Richest
When the needle comes up out of the Needle Jet it is allowing more fuel to enter. So, the lower the clip, the more it opens up and the lower the clip the less it opens
FULL OPEN - Main jet- the best way to gauge which one to use is to run the Kart at the Track and record your peak RPM.
Go up 1 size bigger jet and record peak RPM. Keep doing this until the RPM decreases and then go back with the jet before it fell off.
It took me about an hour to tune mine but I had a Mikuni knockoff which required me to remove the bowl to change Main Jets. I have since bought a Genuine Mikuni and Main Jet changes are done by removing the Bolt at the bottom side of the bowl. The jet is in the end of the bolt.
I will try to attach some pics of the 2 carbs so you can see the difference. The Real Mikuni VM22-133 is much larger and heavier. I could never get my knockoff tuned right. I did not know that were knockoffs out there. I ordered mine as an upgrade with my enigine build kit and thats what got delivered.
I went to SUDCO and ordered a new one. The jets will not interchange so If you buy a genuine mikuni you will need to order xtra Pilot Jets and Main jets for tuning.

Look at the size difference in the 2 carbs. The larger one is the genuine Mikuni vm22-133

I had one of my Techs detune my carb so that I could practice retuning. That Jive Turkey changed out the Pilot Jet, The Main Jet, Moved the Clip on the Jet Needle and messed with both Screws. I still had it diagnosed and tuned in about 30 minutes

I hope this helps anyone out there having a fit with a Mikuni.
Attached Thumbnails
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[TheDullCarbide]

I've read in other threads that the Chinese carbs are junk. The switch to a genuine Mikuni is a step in the right direction.

Just curious: What intake adapter are you using and did you P+P the head?

When's the last time this engine ran? What changed from the last time it ran? What spark plug are you using? Any information could help. I'm far from an expert on these carbs so I hope someone else can chime in.

 

[Cornishrooster]

I've read in other threads that the Chinese carbs are junk. The switch to a genuine Mikuni is a step in the right direction.

Just curious: What intake adapter are you using and did you P+P the head?

When's the last time this engine ran? What changed from the last time it ran? What spark plug are you using? Any information could help. I'm far from an expert on these carbs so I hope someone else can chime in.

Hey hey. Thanks for the reply. It sat for several years after my second kid was born. Changed the oil and put new gas in it, ordered a new plug but it hasn't arrived yet. It ran today and sounded good, or so I thought, after I put the real mikuni on. After reading that thread I found I'm going to try a new pilot. Not sure what p+p is to be honest, repaired a few engines but mostly from watching YouTube.


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[TheDullCarbide]

P+P means "Port and Polish." There's plenty of Youtube videos on it. I'm glad you got it running. A good tune and you're golden.

Thinking about it, how can China make such a solid Predator...but they can't be trusted with a carburetor?:shrug: Who knows? It's all hit and miss.

 

[Cornishrooster]

P+P means "Port and Polish." There's plenty of Youtube videos on it. I'm glad you got it running. A good tune and you're golden.

Thinking about it, how can China make such a solid Predator...but they can't be trusted with a carburetor?:shrug: Who knows? It's all hit and miss.

I'll check out the port polish vids. I know years ago I put a billet flywheel and crank arm in, pretty sure I put in stiffer springs. I don't know
Enough about engines to understand why it worked well when I started it but the wouldn't start again after I shut it off. Going to try smaller pilot and new autolite spark plug and see what happens from there. Def open to suggestions.


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[TheDullCarbide]

Just thought of something:

If it could run 1/2-full throttle, but would idle rich and wash out the cylinder at idle-1/2 throttle, wouldn't that mean the idle air passage is clogged? I don't have a VM22 in my hands right now, but I have an old VM34 from my snowmobile to look at. Maybe some carb cleaner and compressed air in the screw's seat and whatever hole on the air cleaner's side looks like the idle air could do the trick. After letting a carburetor sit that long, anything could happen.

 

[danford1]

If the engine sat like that, it is likely that air hole has a spider's nest in it. Take the carb all apart and clean EVERY hole you can find.
Post up some pics of the intake and a video of it running.
Thanks
Danford1

 

[TheDullCarbide]

If the engine sat like that, it is likely that air hole has a spider's nest in it. Take the carb all apart and clean EVERY hole you can find.
Post up some pics of the intake and a video of it running.
Thanks
Danford1

I totally agree. Spiders have no sense of decency.

 

[Cornishrooster]

If the engine sat like that, it is likely that air hole has a spider's nest in it. Take the carb all apart and clean EVERY hole you can find.
Post up some pics of the intake and a video of it running.
Thanks
Danford1

Thanks but I actually put a new mikuni carb on the other day and now it's up and running. Strangely the real mikunis come with a 30 pilot jet which is way too high for just about anything you would use that vm22 carb for. I had a 17.5 pilot and a 20 laying around so I tried those and it's still fouling the plug, ordered a 10, 12.5 and a 15 to get the idle dialed in. No idea how far up I'll have to go on the main but it came with a 100 jet. Still was able to ride it around for an hour yesterday and holy hell this thing is really really fast, faster than I'm willing to go without putting on some hockey equipment first.

 

[Cornishrooster]

I totally agree. Spiders have no sense of decency.

:laugh:

 

[TheDullCarbide]

If the engine sat like that, it is likely that air hole has a spider's nest in it. Take the carb all apart and clean EVERY hole you can find.
Post up some pics of the intake and a video of it running.
Thanks
Danford1

Just realized that spider thing sounds like that movie where the snail got sucked into a carburetor. That probably sounds terrible if you don't know the movie. Sorry for being fftopic:.