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Also Alleyoop you were correct, new carb (er well not exactly new) is set considerably leaner, after 45 mins of running on the new carb after setting mixture plug is nice light coffee color with no soot.

Previous carb was set with needle two notches lower than the current one (not by me).

The dirtbiker neighbors seem to think my plug looks good "Pretty damn close" says the Old Man.

Now I have no bogging or gas stink from exhaust, but I still have the stumble

The carb has been adjusted as follows: mixture screw was seated, then turned counterclockwise until the highest rpms,then set 1/8 clockwise. I don't think the carb is the problem.

I thought it may be the CDI, but after swapping my Hoca with a known good one, still had the same problem. Did the same with the coil.

Running out of ideas, I took off the CVT (lots of belt dust and chunks of belt in there) and kickstart and then left the kickstart off and put the CVT back together and started the bike. The belt flopped like crazy at 5000 rpm (where my stumble occurs). I am thinking the belt might just be the problem. I ordered a new Gates Powerlink belt from Napa that will be here today.

I also removed my carb and freshly cleaned and rebuilt my spare carb and put that on. The carb made no difference.

Other than having a shredded belt, the rest of the CVT looked good after I cleaned it. No flat spots on the rollers or heat checking or glazing on the clutch bell or shoes, no broken springs.

The belt was a Zhianping? Could a screwed belt cause stumbling if it's flopping around? Isn't 700 miles a bit soon for a belt to fail?

And lastly, my brother suggested running the bike sans belt to see if it was truly the CVT and not an engine problem. I told him that would cause my rollers to go flying out of the variator. Is it okay to run the engine without a variator? I would guess not as it's probably counterbalanced by the CVT.

So on my 2011 Baccio vx150 I have had a stumble (misfire?) Between 3000 and 5500 rpms.

So far I have done the following to no avail:

Changed carb to Keinhin 24mm w 105 main

Changed petcock to high flow Miniki vacuum pump

Changed CDI to Hoca unlimited

Changed coil to Hoca

Removed PAIR and blocked off exhaust port (and confirmed no leaks)

Changed exhaust to scrappydogscooters one piece can.

Changed plug to c7hsa NGK R

Adjusted valves to .004 intake .005 exhaust.

For one day it ran excellent, no stumble. But then after a 20 mile ride the stumbling returned. And then has become worse progressively to the point where I am only getting 30mph on flats, all the while bogging /stumbling.

This problem has been present since uncrating. It's a real head scratched as none of my other bikes have done this. Everything seems properly adjusted.

My PAIR did fail, causing lots and lots of backfiring around 400 to 450 miles. I am wondering if this may be a damaged exhaust valve?

Compression is spot on, no smoke or excessive oil venting.

What could this be? Why would this problem still be present after changing the entire fuel system and ignition system? Is this indication of inner engine valve damage?

You know, hard as it is to believe there are different laws in different places.

I was unaware that's how things work in Louisiana. That's not how it works in my state.

If Sugarscoot never speaks to me, then no harm done. She's quick to throw personal insults around and swear at people, people who call others "twit" and "negative asshole" don't really have much grounds to call others negative, especially when I'm not.

I'm fine with her replacing carbs to fix tight valves, I mean changing unrelated parts to fix a problem is cool I suppose.

And no I never charged to fix someones car before I was a licensed technician, because in CT that is a crime.

Yes you learn by asking questions and by doing, no argument there.

But if this is how stuff goes in the south, I'm happy to be a Yankee.

So you charged 86 plus 130 for a combined total of 100 worth of parts? That's called making a profit. You did profit. Not much of a profit, but still profit none the less.

It's not cool to misrepresent your skill. It's not cool to make a profit from misrepresenting yourself.

It basically shits in the face to those of us who pay union dues and went to school to learn how to be technicians (not that anyone can go to tech schools for scooter repair).

I am a trained automotive technician. Sure I'll charge to fix your car. But I'm not a trained scooter mechanic, so it's unethical to represent myself as a trained scooter mechanic, so I can't charge to fix scooters. And neither should you.

Can I ask why you are charging to repair scooters when you clearly are not scooter mechanics?

Carbs are pretty basic knowledge that you should have pretty much memorized and automatic before you go into business as a scooter mechanic. The fact that you do not know how to adjust or diagnose carburetors is proof that you should not be repairing customer bikes.

I, along with many other posters are rather versed in carb theory, and repair. It would behest you to research and learn basic carb theory.

Since you represent a business that claims to understand and repair scooters, when you clearly do not, I feel that aiding you in a for-profit repair procedure would be unethical.