Chinese Roketa 150 problems with throttle  By  johnathonkreider (Read 2,872 times)

First, welcome to the site!

Have a bone for your hard work...

I rode a Chinese 150 for 7 years and experienced some similar problems (along with all the other typical "things Chinese" that we find on these scoots...)  Square wheels, rotted tire-valve-stems, rotten, off-size fuel-lines, disintegrating mufflers, all nuts and bolts cross-threaded, etc.... LOL!

Each Chinese GY6 seems to be unique, and what fixes one may (or may NOT) fix another one. I had MAJOR grief with my carburetor, and like you, replaced it. Still I had major problems. With mine, I found the WORST problem was actually the AIR FILTER setup. I could NOT get the motor right with the factory filter... Period.

You may be experiencing more than one issue, but FIRST, I recommend you try tuning your carb with NO air-filter or ANYTHING attached to the mouth of the carb. (Mine would not run right with even a short tube for an aftermarket filter on the carb).

With nothing attached to the carb-mouth, I was able to get the engine running perfectly. I then installed a UNI "sock" filter and the tuning stayed OK. But the motor acted much like yours with ANYTHING on the carb, EXCEPT the sock filter.

I finally DID get the carb "right" with snappy throttle-response and clean acceleration from idle to WOT.  But it took some time and experimentation.

Here's an old pic of the scoot where you can see the UNI sock filter, Bando coil and my exhaust.  I used a 2-stroke "chamber" pipe (which runs GREAT on a 4-stroke)... a trick I learned back in the 1960's while racing 2-stroke go-karts. but the important part is a full-one-inch header.  The stock headers are SMALLER than the exhaust-port, choking the exhaust-scavenging right at the head where it causes the most trouble.  You can also see the extended cooling-fan intake, which lowered my oil-temp by 20 degrees on 100 degree days.

You don't want to run the motor sans-filter more than necessary, but for me, it allowed me to finally get the carb "right" and then add the sock filter. It ran fine for 6 years and was still running fine when I traded it on my current old Kymco 250 (which I do LOVE!).

The mods I had to make on my carb were a richer main-jet and a lot of playing with the needle to raise the slide at just the right point of throttle-opening. The idle-jet in the new carb was OK. The carb was a Mikuni, but NOT a performance one, rather, a factory replacement identical to the factory Chinese carb.

My experience with the air-filter is NOT common. But it DOES happen with some individual scooters. Since the frustration I encountered, I always recommend tuning these with NO air-filter. If proper running is obtained, you probably have one like mine that does NOT like ANYTHING on the carb, but should work with a UNI-sock filter.

If you get it running right with nothing on the carb-mouth, then re-attach the factory filter setup and it runs like garbage again...  You'll KNOW you have a cousin to my Xingyue... LOL!

You may also be experiencing a air-leak somewhere (like the manifold) or bad vacuum lines. My manifold had a crack in it! If you still have a vacuum operated fuel petcock, it also may act up, shutting off fuel at certain throttle openings. I also replaced my vacuum petcock with a Briggs & Stratton manual petcock, just to eliminate any vacuum problems there.

I realize this advice is pretty generic, but you are facing some of the same multiple problems I had, so I hope this may help. But definitely, I'd try tuning with NOTHING on the carb-mouth to see if the factory air-filter may be your problem.

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Other simple mods which truly helped overall riding and tuning on my individual 150 included a "blue" no-rev-limit CDI, a Bando coil, iridium plug, a FULL, 1-INCH EXHAUST HEADER and experimentation with roller-weights in the variator. I found 11 gram rollers gave great acceleration but 45 mph top speed at 9K rpm. 12 gram rollers gave a 65 mph top speed, with NO acceleration or hill-climbing ability.

So... I mixed 3 11's and 3-12's staggered and got good acceleration/hill-climbing AND a 62 mph top speed.

We tend to ask a LOT from these 150's, but first of all they need to run right. I hope this may at least get you on the right track with your new carb.

Ride safe!

Leo in Texas