Need help tuning Chinese 49cc dirt bike

Flapjack

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As long no clips fell apart, just reassemble. You want to run sea foam in the gas. Those little pilots like to crud up easy.

Yup just throw her back together and try to start it!
They had a little crud. It really wasn't that bad, surprisingly. I made sure absolutely everything was cleaned and put together correctly. The float moves well, too.

The problem is still there. You start it and it pretty much goes right up to full throttle.

 

weather man

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Starting to seem more like a bad throttle cable than anything...


Yes, to be at full throttle, the slide in the carb is full open. Can you see if the guillotine is moving up and down with the twist grip?
 

Flapjack

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Yes, to be at full throttle, the slide in the carb is full open. Can you see if the guillotine is moving up and down with the twist grip?
It does move. Like I said in a post above, my gut is that something is wrong with it. At first glance, it looks like the boot is just worn and cracked. A little downward pressure though, and the cable will move down to the point where you can see the cable behind the throttle plate.

There is a lot of play in the throttle grip itself. If you roll it all the way back (decel), it will keep moving that is . You have to turn it forward (accel) quite a bit before it actually moves the guillotine (tubular black plastic thing) down into the airway.

Could the guillotine be installed backwards? I had it out several times before I got the carb cleaned, before it ever started....

**EDIT**
Ding ding ding! That was it! The guillotine can go in two different ways. Wow....

I'll attempt to tune it tomorrow....

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weather man

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**EDIT**
Ding ding ding! That was it! The guillotine can go in two different ways. Wow....

I'll attempt to tune it tomorrow....

Sent from my Verizon Galaxy S4

Well? :popcorneat:
 

Flapjack

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Grrr....

So I pulled it out of the garage when we got home. Today's my daughter's birthday, so I was really hoping to get it running.

The good news is that it started on the first kick, and was idling exactly where I left if after fixing the throttle. I was ready to tune it.

I followed the directions, which was really easy to do this time. Started at two turns counterclockwise on the mixing screw (after turning it in clockwise all the way), then adjusted the bike to an "easy idle", which the author of that page described as as low as it with still run, but still have good throttle response. It instructed to then adjust the mixture screw until the highest idle rpm is reached, then adjust the idle screw again. Repeat until perfect.

It only took a few cycles of that step to perfect it. I was about to test ride it when I noticed a few loose bolts. Hearing these things needed loctite all over, I shut it off, pulled it in the garage, and started working on the nuts holding around the rear wheel (all were loose).

As I was working on the loose bolts, I noticed the vent was leaking fuel.... dripping steadily the entire time. It didn't do that before I tuned the carb. I was a little worried, but figured I'd just finish up and start it back up.

No go. When I was all done, it wouldn't start. I tried everything (even carb cleaner in the air filter). I even reset the carb and idle screw back to where it was. The only way I could start it was to roll it down the hill and pop start it. I was able to drive it around, but it leaked fuel out if the vent the entire time it was running. It kept leaking until I shut it off and closed the fuel valve.

Very frustrated....

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Flapjack

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I've been trying to find a place to pick up a replacement float, assuming that is what's wrong. I've found a bunch of sites with floats for only a few bucks, but I'm not sure if they'll work.

Gonna take some pics of the float assembly tonight. Maybe you guys can give me an idea.

One thing I've noticed is that it seems to be a bit different in design than most. Everything about the carb's design seems to match the one in this video, with the exception of the float. It seems the one here is just a float-alone donut that moves a u-shaped lever. The float on mine is actually connected to the body via the same pin as the u-shaped lever in the aforementioned video. Mine also has a little round pin type thing that rides under the float. Not sure if that is what cuts off the fuel or not.
 

Flapjack

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Alright i had to watch like 20 videos but here you go,


Great video, especially since it's basically the same carb. I've done all that, but it does look like the float needle is either a little different, or I'm missing a piece (the little arch on top of it).

Tearing it back down to see if anything is amiss....

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VectorPat

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That float sticking is not going to make it rev like that. It will only make it run super rich or no fuel at all. It sounds more like the throttle plate is stuck open.
 

Flapjack

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That float sticking is not going to make it rev like that. It will only make it run super rich or no fuel at all. It sounds more like the throttle plate is stuck open.
I edited that post a few days ago. I'd installed the guillotine backwards.

The problem now is after I tuned it, it started pissing gas out of the vent tube. That would indicate the float, but it looked fine last I had it apart. I'm taking it apart again right now.
 

Flapjack

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Seems to be fine now. Took everything apart again, and cleaned it again, just for good measure. I still didn't find anything wrong, but it started right up, I adjusted the carb a bit, and drove it around. No fuel leakage.

Hopefully it stays that way. Almost wish I had found something wrong. Now I don't know if it's going to do it again.

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skwerl

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If fuel was coming out the vent then either the bowl was stuck down or the needle was stuck open. Glad you finally got it going.
 

weather man

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Seems to be fine now. Took everything apart again, and cleaned it again, just for good measure. I still didn't find anything wrong, but it started right up, I adjusted the carb a bit, and drove it around. No fuel leakage.

Hopefully it stays that way. Almost wish I had found something wrong. Now I don't know if it's going to do it again.

Sent from my Verizon Galaxy S4

You now know why fuel injection is so popular. Chasing carb issues can drive you nuts. Seafoam is your friend!
 

Flapjack

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If fuel was coming out the vent then either the bowl was stuck down or the needle was stuck open. Glad you finally got it going.

Good to know. When you say "needle", do you mean the thing the float is connected to (that travels with the float)?


You now know why fuel injection is so popular. Chasing carb issues can drive you nuts. Seafoam is your friend!
Yes. Seafoam is good stuff. Still have half a can, which I'm sure I'll need in Spring after that thing sits all winter....

Sent from my Verizon Galaxy S4
 

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