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Discussion Starter · #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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It's off balance because of the full circle crank making it shake like crazy...

You're going to have to JB weld the carburetor to the intake manifold.
 

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Discussion Starter · #3 ·
It's off balance because of the full circle crank making it shake like crazy...

You're going to have to JB weld the carburetor to the intake manifold.
Wait, really? Seems rather drastic doesn't it? Would epoxy putty work in place of JB weld? Epoxy putty like Steel Stick or maybe waterweld? I have both on hand is why I ask.

I can't understand why anyone thought that the carb slipping onto the intake like it does was at all a good design idea! Why the heck does it not bolt on?? Hah

Thanks for the quick response btw!
 

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Yea it's a really bad design and eventually you will keep tightening it and then the carburetor housing will just crack and it will fall off... So before that happens make sure to make the carburetor one piece with the intake manifold with whatever epoxy you choose I recommend JB weld.
 

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Discussion Starter · #5 ·
Already happened with the first carburetor like I said in my original post. I was so frustrated when that happened too, lemme tell ya.
Alright, I will go marry the two parts together here in a few. The new carb came with another intake manifold, so I wonder if there's any hope of saving the first now broken carb via this same method.

I'll post back with results either tonight or tomorrow sometime.

On a side note, are boost bottles honestly a worthwhile upgrade? I mean I grasp the concept, I'm just not 100% convinced that it could make a noticeable increase in power. I guess the only surefire way would be to slap one on and test for myself.
 

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Already happened with the first carburetor like I said in my original post. I was so frustrated when that happened too, lemme tell ya.
Alright, I will go marry the two parts together here in a few. The new carb came with another intake manifold, so I wonder if there's any hope of saving the first now broken carb via this same method.

I'll post back with results either tonight or tomorrow sometime.

On a side note, are boost bottles honestly a worthwhile upgrade? I mean I grasp the concept, I'm just not 100% convinced that it could make a noticeable increase in power. I guess the only surefire way would be to slap one on and test for myself.
They help the Piston ported engine because it wants to spit but on the read inducted engine not so much.

It's better to get a small nitrous kit if you want to make more power. Even though people make fun of those small nitrous kits they do work hold on and lean forward so the bike doesn't shoot out from underneath you 😉
 

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Discussion Starter · #7 ·
Man, so I JB welded the broken carb to one of the intakes I have. It worked for about 3 blocks before it broke again..
The steel stick was crap. I tried it on the new carb and intake first and it didn't hold at all. First time I reved it blew the carb right off. So I tried putting another heavier layer on in hopes it would hold it. Same thing. I made it like one house down and "pop! MUHRRRRrrrr..."
I'm about fed up with this stupid "performance" carb business. If only I could use the stock crank with the big bore kit, in theory this issue would be resolved entirely.
I guess now I've got to chip all of the steel stick off of the new carb and intake and I'll try JB welding the ever living p!$$ out of it and see how long it holds.. I'll get back to the forum in a few days once I've gotten it completed. Again.
Man I miss my sport bike right about now..
 

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Discussion Starter · #8 ·
The first is the broken one I JB welded that worked for about 3 blocks.
The next 2 photos are the new carb that I used the steel stick BS on. The last pic you can see the 2 layers really well.
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Discussion Starter · #9 ·
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here is what the PITA looks like. I'm sure someone here will know what model it is. Not that it is super relevant to my issue though.
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here is the home made exhaust from a paint can. Sounds great too! Haha
 

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Just mod and put the stock carb back on you will need to order a jet kit so you can re jet the carburetor for your current setup you will need to do the high fuel flow aka petcock delete mod
 

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Discussion Starter · #12 ·
Would the jets that came with the pumper carb work to re jet the stock carb? I've got the pumper that isn't broken THUROUGHLY JB welded to the intake tube.. just about to go give it a whirl and see what happens! If it blows the carb off this time, I will follow your advice and go back to the stock carb without any doubt.

Best part about this bike is I got it for free. My neighbor at the time had it sitting in his backyard and knew I liked to tinker around the garage, so he asked me if I thought I could get it running again. Then told me if I could get it running I could keep it. It ran that same evening.
The guy couldn't believe it ran again, or that it only took me a few hours to get it running haha.

It was missing all of the exhaust from about even with the spark plug back, so it was LOUD af.
It has come a long way from when I first came to own it. Wish I had some before pictures, it was in rough rough shape in the beginning.

I'll post a picture of the red bike in a moment cause now I'm curious what model it is.
I've also got an upper/front fairing that I'm 99% sure is not for the red bike, but idk what it does go to. I'll post it also.
 

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Discussion Starter · #13 ·
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ignore the weird angle the exhaust is sticking out at, I need to cut it and re-weld it again.. When I cut it behind the expansion chamber to get rid of the inch of tubing that protrudes into the chamber, I didn't think to mark the original position, so I just guessed when i welded it back and wasn't quite there with where my guess was... oops! Haha
This bike is in time out, it has a gas leak and is making my garage smell so strongly of gas I can't work out there without getting a headache. Need to go to the store for some more fuel line hose.
 

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Discussion Starter · #14 ·
Well.... it worked. For about an hour and a half before the JB Weld gave up. My son and I tore up the neighborhood for a solid hour+. Then of course it broke nearly half a mile from the house, never fails 😆.
I've never actually experienced how huge of a difference all of the mods I've put on this bike have made. The damn thing does wheelies! It is down right stupid! Now if only I could keep the carburetor attached...

Mr Kitty, can you give me a quick walkthrough of how to make the stock carb setup work with the mods I've got installed now? Will the stock carb if rejetted and petcock moded, be able to match the pumper carb performance wise? Not that I really have much of a choice other than to go back to the stock at this point.
 

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What's your poison? Mine is 40:1
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So, a stock pumper carb for a true 49cc, not a goped, is 15mm intake. You can taper bore the stock round slide carb for 15mm, stock is 13mm. A rejet is needed, and the petcock mod is almost a necessity. Either will work with a stock engine or mildly modified, even a medium modified engine will benefit.
It is a half fairing MTA1 Chinese pocket bike. Looks clean. You could even chop off the muffler/stinger if noise is ok in your area.
 

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Definitely chop it off and only leave about an inch of stinger



I open up the back side of the carburetor just a little bit and match it to the intake manifold
 

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Discussion Starter · #18 ·
I ran the lucky 7 with open exhaust for awhile, like I said in an earlier post. It is too loud for my area though, I don't wanna have the cops posting up around the neighborhood trying to catch me again like they were back before I built the expansion chamber and muffler. Honestly I think it has more overall power afterwards anyways. Probably due to the expansion chamber if I had to guess hah.

I will watch the videos posted and see what I can get accomplished this afternoon before the wife gets home from work. 😆

Neither one of you answered if the jets for the pumper would work for a rejet on the stock carb or not. Guess I'll just have to tear it open and find out.
 

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Discussion Starter · #19 ·
I'm going to go with no on the pumper jets working. Where in the world am I going to find a jet kit for this stock carb? Preferably somewhere that I can get it in a day or 2. I guess worst case scenario is I have a very nice drill bit set that goes up by the thousandths so I could in theory rejet this stock jet that way too.. not that I really wanna try. Haha
I've also got an assortment of carb jets and misc parts in a drawer, I'll look through there and see what I can find here in a bit.

At least I've already got a good carbide burr! 😁
 

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Correct, the Jets are not interchangeable. I hand drill mine with a tiny drill set from Amazon. I know the Jets are on eBay, look up 47cc Jets
 
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