Jetting a Mikuni 22mm on a Predator Ghost

#1
Hello All,
I am new to the site and excited to be here.
I've got an MB200X Hurricane minibike and I've swapped the stock 196cc engine for a Predator Ghost. I swapped the cast flywheel for an ARC with a .045" coil gap. The exhaust is a GoPowerSports Super Pipe. After breaking in the Ghost it became apparent that the stock carb was running way too lean. Bone white plug, running hot and just plain inconsistent performance, stalling and hard cold starting. The carb may be fine on a kart but not on a minibike with the GPS superpipe...so I bought a Mikuni VM22-133 for it. Bolted it on for an instant boost in performance. Checked plug and still running lean so I changed the pilot jet to a 22.5 and got good plug color and drivability at part throttle operation. High speed run still running hot with white plug so I began increasing the main jet size. Started with a 130....now all the way up to a 290 and she's still looking for more fuel. I've done a thorough check for vacuum leaks as I was shocked this motor still wants more fuel. To note the drivability and performance has increased with each increase in jet size and the plug is starting to get some light color after a high speed run. Nothing inconsistent about this experience except the size of the jet this motor wants is shocking...

Has anyone else put a 22mm Mikuni on a Ghost and jetted it properly?
What are you using for an exhaust system?
What main jet did you end up with?
 
#2
Is the throttle pulling the slide all the way up? If it's not past 3/4 throttle the main jet will have little effect, its the needle and needle jet controlling the mixture. make sure the head side of the throttle slide is all the way out of the carb bore at the top.
 
#3
Is the throttle pulling the slide all the way up? If it's not past 3/4 throttle the main jet will have little effect, its the needle and needle jet controlling the mixture. make sure the head side of the throttle slide is all the way out of the carb bore at the top.
Thank you for the reply. Yes, the slide is all the way up when I turn the grip.
 

River Rat Ron

Well-Known Member
#6
Is the fuel cap vented or plugged ?
Start with the cheapest, easiest fix first
Or in my case it will always be the most expensive solution…:D
 
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#7
290 should be pig rich at full throttle. Are you using a fuel pump pulsed off the intake?
Yes, I am using a pulsed pump and agree 100% it should be running real rich. That is why I posted the original question. I spoke to the tech guys at GPS and they've not built and tested a Ghost with this combination of parts. They are waiting for a call back from me once I get this sorted out to see where the jetting ends up. As I mentioned I am using the GPS super pipe exhaust. I know this exhaust leans things out since I've run it on 2 different engines with 3 different carbs. All got lean when I installed it. This is the 1st one I've tried to dial in by jetting. The increase in power has been very impressive as I have jetted up. My plan is to trail ride with this bike, however, in the end it may have too much power to be tame enough to ride on rough hilly trails without dumping me off the back. :)
 
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#11
I had some eye surgery last week and have to wait for the doc to clear me to active duty. This should be on Tuesday. I plan to continue tuning late Tuesday.
 
#12
At some point the larger jet will yield nothing. Not to beat the horse but it’s starving.
Pull the carb and blow it out…bad pump, stuck float…..it’s always something stupid
I'll run through it again and see what I find. It's a brand new carb and brand new pump. Not to say I didn't get a carb with a bad float setting even Mikuni tech support says very few arrive with the end user that don't need a slight tweak.
 
#13
I really appreciate all of your feedback. As implied above when you get something like this going on it's always something simple and stupid that's not obvious when you get in too deep.
 
#14
When the jet is located in the float bowl it connects to the bottom of the needle jet thru a Oring but there is an orifice on the bottom of the needle jet where it seats in the float bowl. Verify that hole is at least as large as the hole in the 290 jet or it is now acting like your main jet.
 
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