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Daughter and I were riding (20-30 minutes), she rode hers up to mine and it just stalled out. I tried to restart it without the choke, no luck. I decided to try it again with about 50% choke and it started right up. As soon as I turned the choke off it idle very low and finally stalled out. A couple days went by and decided I’ll look into it again. From this cold start with the choke fully engaged it started pretty regular. I let it run a few minutes at 50% choke. Once at operating temperature I turned the choke off and took it around the yard. I would get it up about 50-60% throttle then left off and it would backfire. After a few minutes of riding, it just stalls out and I must use the choke to get started again. It will run if I leave the choke out about 25%. Here is what I have done so far.
Replaced plug, Drained and replaced gas, New inline filter, Verified carburetor float system, New air filter , Inspected air filter box and lines at least 3-4 separate times.
Removed carburetor, completely disassembled, cleaned and re-assembled.
Put machine all back to gather and it runs the same. Backfires at idle and when letting off throttle, runs rough, stalls, but no black smoke from exhausted. It seems to have plenty of power and appears to run normal between 30%-90% throttle.

Next day

Removed carburetor again, completely disassembled, cleaned and re-assembled.
Adjusted the Idle mixture air screw – notice a change in both directions but no large improvements.
Changed positions of E-clip on Jet needle – no improvements.
Noticed when it backfires there is a small flame that comes out of a small 1/2” breather tube. This tube is located on the small intake between carb and cylinder. There are two. One has end plug the other is open. I plugged the open one and noticed no improvements.
I checked the CDI unit according to the service manual with my meter. It seems ok. I do have some experience in electronics and this type of unit usually functions correctly or it is faulty, no in-betweens.

One thing worth mentioning, from day one (bought new from dealer) I did noticed it would backfire SOMETIMES when I would run it full throttle for 10-30 seconds then completely remove my thumb from the throttle. But performed normal in all other conditions. This Quad has less than 10 hours of riding time.

I am starting to suspect a factory problem, maybe the valves. Any additional help would be greatly appreciated.
Thanks,
Brian
 

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prob carb

i would say it was a piece of dirt in the idle jet. did you inspect all jets and clean them. i use torch tip cleaners with the ends broke off( the rough part that is like a file) you dont want this part of the cleaners, it will get stuck and make your holes bigger. remove the rough part and sand the ends nice and smooth and then clean the jets and blow out with a air hose. carbs are very sensitive when it comes to jets. anyway thats my best guess not knowing what you have. you prob need to hit the carb with air too.
 

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Discussion Starter #3
Carb has been dis-assembled COMPLETELY and cleaned very well. I feel can eliminate the carb being the problem.
 

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Try the old spark plug. Use some dielectric grease inside the boot, just not too much as it will creat an airpocket and the boot will want to pop back off.

Really can't see the valves being off far enough to cause the problem unless the cam lobes got wiped out due to incorrect break-in procedure.

Another cause may be in the electronic limiter for reverse. Try running with the override button held in.

You sound pretty capable, so I am just throwing out some ideas.

I would also check the ground wire off the ignition coil aas well as any connectors/plugs leading to it, including the main terminals at the battery.
 
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