GX200 and Mikuni jetting

[bboulier]

Did not find anything definitive on this, starting new thread.
Brand new Honda GX200 (governor removed). Inverted intake, Mikuni VM22, trumpet exhaust. Live at 6800 feet (Colorado).

I believe stock 22s are 95-100 main not sure pilot (can't read either). Ran super rich. Air 2-turns out. Center clip needle.

Gokartsusa white paper says most start this mod on the GX200 and Clones with a 130 main and a 12.5 pilot. Because I had it I put in a 130 main, stock whatever pilot. Still rich.

I ordered a gambit of both pilots and mains yesterday. I'll keep this thread updated.

Note: I'm a massive vintage 2-stroke guy, lots of experience jetting, I know the gig especially at this altitude. 2-strokes are very finicky, 4-strokes more tolerant but still need good jetting through trial and error. This thing is just a pig at this point all through throttle range. So far out I'm going to start with small pilots and mains and work up.

 

[minibiker]

Stock pilot is 15 on all my mikuni clone carbs.

 

[Doc Sprocket]

Did not find anything definitive on this, starting new thread.
Brand new Honda GX200 (governor removed). Inverted intake, Mikuni VM22, trumpet exhaust. Live at 6800 feet (Colorado).

I believe stock 22s are 95-100 main not sure pilot (can't read either). Ran super rich. Air 2-turns out. Center clip needle.

Gokartsusa white paper says most start this mod on the GX200 and Clones with a 130 main and a 12.5 pilot. Because I had it I put in a 130 main, stock whatever pilot. Still rich.

I ordered a gambit of both pilots and mains yesterday. I'll keep this thread updated.

Note: I'm a massive vintage 2-stroke guy, lots of experience jetting, I know the gig especially at this altitude. 2-strokes are very finicky, 4-strokes more tolerant but still need good jetting through trial and error. This thing is just a pig at this point all through throttle range. So far out I'm going to start with small pilots and mains and work up.

It's too bad I had to mothball my kart for awhile. I am facing a similar situation, when I get back into it.

I have a GX200 clone with a VM22 Mikuni that I fabbed an adaptor for. Carb origin unknown, and I cannot remember the current jetting. I removed the governor and built a straight pipe for it.

Before I fell sick and put it away, my shakedown runs revealed that it was leaning out hard in the top end. At anything above 3/4 throttle, she'd fall flat on her face.

I'm gonna have to crack it open and see what I have now. I WILL be watching this thread to see what jetting results you get, I suspect mine will be similar, if not a somewhat richer due to the altitude difference.

 

[tundrabeagle3]

There is a number on the side of the pilot jet tells you the size after checking my jets I had a 15 and 22.5 in my stock mikuni type carbs

 

[bboulier]

There is a number on the side of the pilot jet tells you the size after checking my jets I had a 15 and 22.5 in my stock mikuni type carbs

hahahahah ---- you can see it.... I wear glasses and use a magnifying glass and can't read the numbers unless they're really clear. 15 pilot, thanks! I purchased a pack of 4 15's I can drill out and some other packs and some mains. This is running really rich on the top but falls 0-1/8+ throttle - so pilot circuit there. Once I get that dialed in onto the mains and clip position.

 

[minibiker]

I would go with 12.5 pilot that's agks recommendation and I remember these engines run better with a leaner pilot. Never seen a 12.5 pilot in the motorcycle shop but there probably online. A 15 pilot may work also but there is no need to bore it.

 

[bboulier]

Thought I read somewhere it comes 12.5 from Mikuni but I can't be sure on this. Found a 12.5 on eBay/ordered. Will advise the final outcome. I live at 6800 feet so nothing is easy here jetting wise BUT I will be riding this at relatively low altitude in May and always bring my jetting box for the other motorcycles. (Deals Gap annual 2-stroke meet).

 

[bboulier]

Getting Jets in now (130-150 in 5 increments), a 12.5 pilot came today and so it begins.

 

[minibiker]

Nice you will find it like that . I agree much easier than two strokes to jet.

 

[bboulier]

I ordered several smaller mains and a couple of smaller pilots too - Just because. I emailed gokartsusa (who I bought most of this stuff from) but have not heard back from them . I did say their techtip section for their Mikuni kit is wrong. No way a 130-180 will work with this setup.

I did put the stock GX200 carb back on and it ran fine so the new engine is good.

Note on cable crimp ends: I bought the "crimp type" ends for the throttle cable where it goes into the slide. It seemed good when I pulled on it pretty hard but it did come off today. I was worried about this since if it came off while in the carburetor it would have sucked into the engine. I've since ordered some of the solder type - I'll probably start another thread on that if there's not one already. I've found some good tips on the web about how to do these so I'm curious how it will work.

More to come.

 

[bboulier]

After tons of trying different jets and starting to think this new Mikuni has a bad fuel or air circuit, I tried a different tack. Jet needle is not for Large Hex. When I bought the kit from gokartsusa they sold me a range of jets for it too - large hex, which is what I've been buying trying to box in the issue. But I did have a VM26 and 28 that are a different taper. I tried the 26 needle and it finally ran where I can do something. But I bought a new VM22-133 Mikuni on ebay - just throwing money at this thing. I'm Pissed at gokartsusa (1) they sold me this and (2) they have yet to respond to my two support issues on this. Picture here is the 26 needle I put in the slide - and I'm holding the one that came with the VM22 they sold me.

 

[bboulier]

We can close this one. I ordered another VM22-133 from another supplier, installed it today and it works. I still need to box in the main and clip settings but I'm close.

Understand I have 40+ years experience working on VMs - I have a lot of bike with them - I KNOW these carbs and there's not that many things that can go wrong but I guess in this case it was a bad one from Mikuni. Now I have another I could spend time swapping around needle jets and such to find the problem but I'm done. The new on works and I'm moving on to other things on this DB30.

I don't know what gokartsusa will do, I told them what I found but I doubt they'll reimburse me for the VM they sold me and forget anything about all the jets I bought. My smallest VMs are the 30's on my H2 Triple, plus some VM34s, 38's and some older VMs too.

 

[landuse]

I am glad you got it running eventually