Mikuni V22 tuning assistance

[sbagnato]

Last year, I pulled my go kart out of storage and went about fixing it up. While I had run it earlier in the year, it sat long enough, with fuel in the carb bowl, that the entire carb was shot. Along with some other upgrades, I replaced the stock Predator 212 carb with a Mikuni V22. I know that it is not a true Mikuni carb, however, I know it should work. I got everything installed early this year but ended up setting it aside (stored in the garage).

This week, I went back to it, and last night, I was finally able to start it. I worked on it more this evening, but now I am stuck. The engine will start with the 'choke' (fuel enrichment) on, but if I turn it off, even after the engine is warm, the engine dies. With the choke on, if I give it any throttle, it dies. And it sounds, and feels, like the idle is too high. What I mean by this is that, not only is it louder, but the RPM's are high enough that the torque converter is starting to engage, and the kart wants to pull forward.

I've already disassembled and reassembled the carb multiple times in the last two days. It is clean. The main jet is brand new. The other jet is clean and not clogged. The fuel is fresh and flowing into the carb (the bowl is full). It really does not seem to matter how I play with the adjustment screws either. At the moment, I'm really not sure how to proceed. Again, it starts, and will stay running with the choke on. But I can't turn the choke off, and I can't give it any throttle at all. The symptoms would point to it running lean, but again, the main jet is new (and large), and fuel is actively flowing...

 

[Master Hack]

My experience with Chikuni carbs was similar to yours, except mine ended in the trash. And the genuine article went on. It was plug and play. End of story.

oh and l lived happily ever after!

 

[Whitetrashrocker]

Im gonna bet the carb is still plugged.

Sorry to say but it happens all the time, your oem carb was the best one. It just needed proper cleaning.

Can you see throught the jets?

Look the the throat of the carb. See the little holes? Those have to be clean too.

There some passages on the sides of the throat, sometimes brass. They need to be clean.

Do you know how to set one to "factory settings" ? Idle air screw all the way in and then back out 2 and a half turns usually. Some carbs can differ.

 

[sbagnato]

Ha yeah, I don't WANT to junk it. However, I also don't want to go insane either. The old one literally cracked, so I had no choice there...

I can see through the jets, as well as blow air through them. But good point on the other little holes, I did not focus on those. Part of what I hate about these is they all seem to have different screw locations, so I have to mess with figuring out which is which. However, afaik the screw on the side (which essentially "pushes" into the throttle 'piece') is the idle screw, meaning the one on the bottom is the air/fuel.

I will give it another go this evening.

 

[Master Hack]

Some of dem adjustment screws work opposite of watcha might think.
Some even work in reverse. Good luck figgerin that out. Typical chinese, no instructions at all.

 

[Grizzlymi]

I've had a couple of those china Mikuni's, and had decent luck with both. Never had them in harsh conditions, but always went back to stock. Well stock appearing. My favorite is a stock Honda/clone carb bored out .675 with a #36 jet. Best performing carb IMO on a 212 or comparable engine on your typical kart or mini bike.

 

[Minimichael]

This sounds like an air leak. Even the high rpm part. Have you made sure all mating flanges and gaskets are air tight? Maybe raise the needle a notch, and/or go richer on the airscrew to sweeten up the mix. The jet numbers are different between real mikuni and chikuni, but screws should tune about the same.

 

[AnthonyG]

What size main jet are you running? Is your 212 stock? If not what mods do you have on it? Where did you buy the carb from?

 

[panchothedog]

The seal between the carb and manifold is VERY easy to mismatch. I had the exact same problem the 1st time I put one on. Air leak. Pull the manifold and carb off. Now center the manifold over the O ring on the back of the carb and tighten. Now put the manifold with carb attached back on the engine as one unit.

 

[sbagnato]

Okay, so made some progress. I took everything apart again and made sure to give extra attention to cleaning all the tiny ports on the carb. Put it back together, tried to start it, but nothing. Go figure, the float didn't seat correctly. After fixing that, tried again and it started. Initially rev'd a bit high, but then backed down a bit, and it stayed running, albeit not the best, with the choke off. I think had it warmed up more the non-choke running would be smoother.

Currently, I have both the idle screw and air/fuel screw out 2 turns. I gave it some throttle, but there wasn't much response (though it didn't shut off). I shut it off and pulled the air filter back off and noticed that the throttle slide seemed to be stuck part way up. That led me to also noticing the linkage was loose. Even though all the stock throttle linkage is gone, the stupid cable I have isn't a solid sleeve from one end to the other. There's a threaded gap maybe 6" from the throttle end, for some reason, and the only way to keep tension on the cable is to jerry-rig something to keep that gap extended. And that was loose.

I will fix that tomorrow, but the other possible issue I noticed is that the slide does not appear to be seated all the way down. If I unscrew the total of the throttle assembly and use a screw driver, I can push the slide down until there is just a small gap for air to pass through. However, with the assembly screwed back together, if I pull on the throttle cable, I can pull the slide and needle all the way up, but it does not return fully to that bottom position. It's close, but if the gap with it all the way down is like 3mm (I don't know how big it is exactly), then it's like 6 or 7mm when it returns. Not sure if this is actually normal, or what.

Regardless, some progress is better than nothing.

 

[Whitetrashrocker]

Your slide should be spring loaded to shut it. If its sticking theres bore damage or crud holding it.

im gonna bet it's your cable adjustments thats what's holding the slide open.

 

[AnthonyG]

Your slide should be spring loaded to shut it. If its sticking theres bore damage or crud holding it.

im gonna bet it's your cable adjustments thats what's holding the slide open.

I have to agree. The cable might not have enough travel

 

[sbagnato]

Hm. Well no bore damage, and everything is clean, so I'd agree with the damn cable situation. It does make sense. I don't recall exactly where I got the cable, so there's no "description" to go back and read, but I'd assume it's probably purpose-specific, and designed this way for that reason. Regardless, I'll figure out how to 'correct it' and let you guys know. Thanks for the help so far.

 

[Master Hack]

If the overall length is ok, but the inner wire is too short, cut a little off the outer jacket.
simple fix.

 

[Whitetrashrocker]

Pull the cable out of the way when you cut. Don't use crimp type cutters. Use a cut off wheel. This way your not crimping the sheath that will effect the cable sliding through.

 

[sbagnato]

Okay, wasn't able to do any work on it for the last week or so. In the meantime, I planned for (what I thought was) a better setup to bridge that weird gap. FYI, this is the cable - https://www.gopowersports.com/75-mi...adid=&gad_source=1&gad_campaignid=22898833881

In that picture, under the fat black part on the left is the threaded piece I referred to. Regardless, my plan didn't work well, and I can't cut anything shorter. The cable length itself is borderline long enough, but it's the outer sheath that I wish was longer. The way this carb is, there's only maybe an inch or two of the cable itself that is not in the sheath, and at the throttle pedal end, it's also only an inch or two. I don't know why the cable is designed this way...I guess the use case is supposed to be for more cable being exposed.

Cable aside, I figured out the issue with the throttle slide not easily sliding all the way down. The needle has the slightest of bends in it. Not sure why because besides the last time I updated here, the engine hasn't run with this carb yet. That and the little metal piece that the needle slides into (and is above the jet) looks like it was compressed a bit. Again, don't know why, but it doesn't matter. I do think that if I got the cable crap squared away that I might still be fine, but I guess we'll see.

 

[Whitetrashrocker]

Pics of "your stuff" instead of a screen grab of a product really helps us out here.
Your description is good and I understand what your saying but we're blind here with out your help.
Does your sheath make it from point A to B?
How much inner cable is protruding?
Can you reroute the sheath and trim it to make for more cable?

 

[panchothedog]

That " weird gap " is a threaded length adjuster. It allows about an inch of adjustment to compensate for different carb and pedal situations. Move it in or out to lengthen or shorten the outer cable sheeve and keep proper tension.

 

[sbagnato]

Ha yes, pictures certainly help.












Okay so from first to last, the first pic shows the length of exposed cable at the pedal. Less than 2", and I have that adjustment piece set as far back (aka, pushing the sheath back) as far as it can. Second pic shows the threaded length adjuster, and third pic shows the end with the little "nub" on the end that attaches to the throttle slide (which is why the majority of cables would not be compatible since they don't have anything on the end, and a ferrule would not fit). The final picture is with the cable reattached to the carb, the sheath slid to the end, and the remaining gap of a bit over an inch.

Again, I fully suspect this is considered normal, but with the orientation of the carb leading to the cable having to come straight up and out vertically (as opposed to the original throttle linkage on a stock Predator where it's essentially horizontal) it basically "requires" me to shove the sheath as far towards the end of the cable as I can simply to support the 120ish degree bend it has to make...

 

[Whitetrashrocker]

Awesome. I can see your issue.
This gap needs to be closed. Thats the fine adjustment.



To do that, your gonna have to move this bracket back about that same distance.



This way the 2 pieces of the sheath are tight against each other.

Make sense?