Carb settings?
 

OK. Working on a Kazuma Viper that has what almost looks like a Mikuni carb instead of the standard vertical engine carb. Problem with the bike is that it only runs at half choke. I already went through all of the passages in the carb & cleaned the tank. It runs fine at top end with partial choke, but let off the choke & it's getting too much air & dies. Will idle all day long, but if you give it gas & let off, it dies. My problem lies with the two screws for air & fuel mixtures. When the carburetor is mounted, they are directly facing the frame & there is no way to adjust them. What are the factory setting for these? 1 1/2 - 2 turns out is what I'm thinking, but not sure. Any help is appreciated. Trying to think of a way to tune the screws with it running since that would be my best situation.

I'm failing to visualize two pilot mixture screws. Got a pic?

http://www.scooteratvsales.com/media...viper_carb.jpg
http://www.scooteratvsales.com/parts...-shipping.html

Not sure if the link will work, but that's the carb & the two screws in the pic. If it doesn't load, then I'll try something different.

Seems to me like the one nearest the inlet would be the low speed air mixture screw & the one in the neck would be for idle speed, but I haven't ran across this carb before & don't want to throw off the settings too much since I'll have to remove it every time I adjust. With it only running when I have it set at 1/2 choke, I'm GUESSING that I would need to turn the mixture screw in? Idle speed is good, might need to come up just a hair but seems close.

are the screws against the frame or against a panel? taking the carb off to make such minor adjustments must be such a pain.

thats correct. thats a copy of a keihin carb, which i am very familiar with frommy old honda... the one closest to the inlet is the ide air screw,to adjust the mix at idle/slow speed, and the one in the main barrel of the body is the idle speed screw...

as for getting your bike running right, i would double, if not triple check the pilot jet is clear, as i had similar issues with my honda, had a bit of crap in the jet that i had to clean out, wouldnt run right at all...if thats clear, i would start turning the idle mix screw (near the inlet) inwards a quarter turn at a time, and see if that helps... if not, i would try raising the idle abit... a video of the idle speed, and what its doing would also help tremendously in figuring out whats going on... :D

Is the Kazuma Viper a two-stroke? It's common for two-stroke bikes to have an air screw at the carb inlet, whereas a four-stroke usually has a fuel screw at the carb exit. It's a pilot mixture screw in any case.

a quick check of google shows it being a 110cc horizontal engined pit bike. that carb looks identical to the carb on my old honda, including the air screw placement...:)

It's a 4 stroke 110. I messed with it last night & still couldn't get it right. Got it running almost perfect with 1/4 choke, but as soon as I opened it up, blah. I've ran across this problem in cars before & it's usually a stuck float. Finally figured out how to wiggle a tiny screw driver in there to adjust it on the bike, but the lack of clearance is crazy. Guy said carb was rebuilt last year, but when you turn on the gas & let it sit for a few seconds while it's not running, gas pours out one of the vents. I never noticed this before. Gonna either tear it down & find the float specs or buy a new carb. I'm at the point of believing it has to be the float out of adjustment. I took the pilot jet out & can see right through it.

given the bolded part, your float height is too high, take it apart, and when holding the carb upside down (floats facing the sky) bend the little tab for the float needle so that the float arm sits pretty well level... that should get you real close. if it still does the gas pouring, i would be suspect of your float needle not sealing properly...

Thanks for confirming what I suspected. It's gotta be a float problem. If we don't have any more storms rolling through, I'll check it out tonight. This weather is crazy in Oklahoma.

OK. Just a little update. Float was way off so I bent the tabs to set it. Still the same results. I also noticed the carb size was 16mm :O ! Seems like Kazuma built this a little undersized so I replaced it with a 20mm carb from a different 110 that I have laying around & guess what? Still only runs on choke. :(

Maybe the 20mm carb is too big, but I doubt it. The gas doesn't leak out anymore, but it shouldn't have to run on choke. Possibly an intake leak? Got a compression tester, what's the compression supposed to be on these? I've gotta get this one running by Saturday if possible & it's so close.

I would guess the bare minimum on compression would be right around 90psi.... I thinknyou may be on to somethimg though with the intake leak idea... We have confirmed its not a bad carb with the switch to the other carb.... All thats left is compression or intake leak...

Wow, 90 psi isn't much at all! I'm used to cars so maybe it just seems low. Definitely gonna check it out after work. Anyone ever try Indian gasket or silicon on an intake? Might just buy a small piece of that cut your own gasket. Just don't have time to wait on shipping from ebay right now. Cutting too close to my oldest son's birthday on the 10th.

I'll get this knocked out hopefully tonight.

check the frame grounds!