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Need some help! Keep blowing the carb loose!

1K views 42 replies 3 participants last post by  Atvrunner2 
#1 ·
I cannot remember what model pocket bike this one is, nor is it all that important to me to figure the model of the bike out at this time. However, it was originally a 49cc 2 stroke bike that has since had a 54mm bigbore kit installed, as well as a full circle crank (didn't want to but I had to have a crank with a correctly sized connecting rod bearing hole for the BB kit)a rocket key, and an aftermarket "performance" carb, intake tube and carbon fiber reeds. I accidently overtightened the pinch bolt on the performance carb inlet and broke the inlet off of it. Gotta love cheap cast aluminum... so I bought a similar carb from Amazon that also had a jet kit included. The bike runs SO much better with the correctly jetted Amazon carb, cept that EVERY SINGLE TIME I wide open throttle it, the carb pops off of the intake tube. I cannot figure out how to prevent this from happening and it is driving me insane!

The only possible cause I can figure might be the exhaust system I custom built. The only original exhaust part is the first maybe 8 inches coming off the exhaust port of the engine. The expansion chamber is made from exhaust adapter flanges tapering up to about 2 1/2 and then back down to roughly 1" tubing, which runs into my favorite part of the whole "custom built" system. A gutted spray paint can that I ran the 1" tube through. The pipe inside the spray can exhaust can has a whole crapload of holes neatly drilled through it the entire length of the inside, and the can is packed with exhaust packing. It is held together by a cotter key and a spring. I think it looks pretty fantastic all in all. But I can completely understand the expansion chamber being placed wrong, or incorrectly shaped which wouldn't be any help to the motor, but could it be enough of an issue to cause the dang carb to pop off no matter how snugly it is mounted? I'm afraid to tighten it much more than I have because I really don't want to break another carb needlessly..

I can post pictures of any part of the bike that anyone thinks will be helpful in identifying the cause of this annoying problem.

Thanks in advance guys!
 
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#31 · (Edited)
Don't worry your family will learn how to get along with pocket bikes and learn to love them. 🙂

I use a soda pop bottle and some fuel line take the carburetor off the bike and bring it to the sink

Adjust the float height until water stops squirting out the overfill.

Make sure you have the flot in the proper direction the smooth flat ring goes up ( some of them don't have that )

Make sure you get it adjusted so that when it drops down a little bit it turns the flow of water on running you will see when you have the float bowl off and you can push on the little ears with your finger to turn the water flow on and off how it works...

Once you're done using water you have the choice of spraying WD-40 all over it and wiping it off or completely disassembling it and putting it in the oven on low for 15 or 20 minutes to evaporate the water if you don't plan on running it for a while.
 
#32 ·
I've worked on many carbs over the years, but each one is a little different it seems. Idk what happened to cause the float needle adjustment to get so off though. Must've unintentionally messed with the little ears while I had it apart. That, or the float needle did fall out at one point.. might have something to do with it. Haven't had a chance to look at it yet, but may before I go to bed tonight.
I'm about tired of my hands smelling like gas constantly though.. haha

I've actually got a gallon can of carburetor Chem dip I could drop the carb in, just have to make sure I don't forget any gaskets. I'm pretty sure it would take care of the water. But WD40 would be more than sufficient. That is some magic stuff, lemme tell ya.

Your pop bottle and fuel line idea is a fantastic idea. I've used a similar contraption to siphon gas before. Just deflate the 2liter and if you've got the hose in the fuel you can hear bubbles. Then pull the bottle back apart to create suction and you're done. Keeps you from getting a mouthful of gas and you've got a bottle to catch a decent amount of gas in at the same time. 😉. 20oz works best, but they don't hold much. Haha
 
#34 ·
Well I've done the petcock mod, taper bored the stock carb and used a micro drill bit set to rejet the stock jet. I think I went a little over on the jet size, because I cannot get the carb to tune in. It runs fine until I try to wide open throttle it, then it bogs hard. I've tried adjusting the needle clip, and it's best at the top position, but still doesn't run like it should. I guess my only option is to order a jet kit and cross my fingers.
It also will not quit leaking fuel through the overflow. I've adjusted the float and it's better, but still won't quit peeing fuel.

Any advise is welcome.

On a side note, I managed to put myself in the hospital last weekend while racing my neighbor. Took a corner too tight with it nearly topped out, and both tires lost traction. Wouldn't have been bad if it had low sided, but it instead grabbed and high sided me, HARD. I still can't use my right shoulder like I should, and my chest is still quite yellow and green from the bruising.
I wasn't gonna loose the race though by god!! 😂
 
#35 ·
I realize my last post was somewhat redundant because I just restated a large bit of information from previous posts.

Anyways.. if I'm bogging down at wide open throttle like it is, even with the needle clip at the highest setting (which puts the needle as low as it can go) then either my jet is the wrong size, or the float is too low and is starving the bike for fuel. Figure it is probably one of these two issues, or a combination of both.
It's too bad that a pumper carb will not stay attached.
I'm curious if I could retrofit one of the many other carbs I've got in a box to work for this engine.

I broke the newer pumper carb trying out a possible mounting solution. Dang cast aluminum is garbage!

Hope to hear back from one of you guys this week sometime.
 
#41 ·
Adjusted fuel mix, and rejetted the carb with one from the jet kit I ordered. It runs pretty good now all in all. Still doesn't compare to the pumper carb sadly, but at least I don't have to worry about the carb blowing off now. Now if only I could get it to quit peeing gas I'd be happy. I don't think it is a float adjustment issue, it looks more like the petcock that is leaking for some reason. I know I didn't botch the petcock mod, so it's gotta be one of the seals.
In other news, I need a set of forks for the red bike I posted a picture of awhile back. My son just smoked a curb (not quite sure how he managed it) and he bent both forks to the point that the tire catches the exhaust when you try to straighten the front wheel. Unless someone has a spare set they'd sell me for a good price, I guess I'm gonna have to order a set from Alibaba and hope they will fit correctly without major modification.
Has anyone gone from solid forks to actual oil filled forks on one of these little bikes and had good luck with it? It would be nice to have some suspension travel with how rough the pavement is around here. I'll attach a pic of the damaged bike. (My boy is perfectly fine thank goodness!)
Tire Wheel Vehicle Automotive tire Motor vehicle
 
#43 ·
Ouch. That was a good job. Last one I saw was a victim of getting run over in the driveway after being parked behind. I bought it for the spare parts. I thought I saw some on ebay, non suspension. Ill see if I can find them. I haven't converted to suspension style, should be fine as long as they are not too much longer than the original.
 
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