*new* Questions about raising performance

Bizare

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Jan 24, 2020
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Hello,
I enjoy cycling and all motorsports to begin with and thought that while I am in college, and since I am on a budget motorized bikes would be the easiest way to get my fix for danger and speed. I know they are not built for high speeds but I just want something to enjoy and practice my mechanic skills on for the next year or so.

Firstly,
I know the easiest way to really get more speed outta the bike is to mount a lower tooth count sprocket on it, I plan on doing this immediately after the break-in period is over. my question here is would a "performance" or "racing" carb actually increase the performance of the engine on the little 49cc bike.

Secondly, I plan on removing the pedals and plan on replacing them with foot pegs to make it into what my state calls a "motor scooter", given that I was wondering how effective or reliable the pull starters are or if in an emergency could you start it like an old board track racer. (ie, spinning the wheel on the back to start the engine.)

Finally, this is just an aesthetic question, can the gas tank fit inside the gap in the frame on a huffy Cranbrook, between the top bar and those two parallel curved bars? I feel like a smaller 1.5-liter tank could fit there with some modified mounting equipment.

Thank you all in advance for any and all input on my questions!
 
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indian22

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Welcome. The Cranbrook tanks been used by thousands of bike builders. Buy them or make them, lots of examples.

Carb by itself probably not unless your stock carb isn't set up correctly and you'd probably face the same problem with the new "performance" carb.

Smaller sprocket aids speed, but you'll end up pedaling more on hills. It's a trade off, but if you live in an area without many hills; it might be worth a try to go to a 40 or 38 tooth, but you'll end up pedaling to get started from stops. No free lunch with performance.

I'd say removing the pedal function on a 49cc engine the worst idea possible, the reasons are too numerous to go into but use your imagination. Starting from a dead stop and climbing hills are two big hints.

Good luck this is a great hobby and good way to get around on a budget.

Rick C.
Cranbrook fuel tank.jpg
 

Greg58

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May 1, 2011
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Welcome to the forum, Rick gave some good points. When you say you are building a 49cc I think of a four stroke, 48cc is the common two stroke. Which engine makes a big difference in what you can do to improve performance. I have been running 48cc engines from the start, tuned well with a good pipe a two stroke is a joy to ride. From my experience the 48cc needs higher rpm to get in the power band, on one of my bikes I changed from a 44 tooth to a 41 and lost top speed.
 
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Greg58

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With either engine removing the pedals is a bad idea, these engines are designed to start pulling from a roll not from a dead stop. To start without pedals will require a very large rear sprocket which will lower your top speed.
 

Bizare

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Jan 24, 2020
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Welcome to the forum, Rick gave some good points. When you say you are building a 49cc I think of a four stroke, 48cc is the common two stroke. Which engine makes a big difference in what you can do to improve performance. I have been running 48cc engines from the start, tuned well with a good pipe a two stroke is a joy to ride. From my experience the 48cc needs higher rpm to get in the power band, on one of my bikes I changed from a 44 tooth to a 41 and lost top speed.
I plan on using a 2 stroke engine, I also live in Florida so hills are not a major concern, I just want something to race around on. regarding the pull-start, i have read that there is a way to launch from a standstill by feathering the clutch or by giving a it a push forward.
 

indian22

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Now we see for certain you've a two stroke in mind and ride flat the mystery unfolds, but the results are the same. You need pedals, yes you can slip the clutch and push off at the same time, but you will burn the tiny clutch quickly, especially with a small speed sprocket, in doing so. If you come to a halt on slight inclines you are totally screwed going forward. To top it all off you become a road hazard to others and a danger to yourself. I know newbies think they got it figured, but brother you're dead wrong on this one. For your own safety buy a scooter if that's what you want 'cause a kit motor bicycle needs pedals to operate in the real world of riding.

That said do it any way you like 'cause it's still a free country.

Rick C.
 

Tristan Gillett

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Jan 31, 2019
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Another big reason you should keep the pedals is, it's so easy for these motors to break down. Something simple like a clogged jet or a blown gasket can leave you stranded on the side of the road, and if you don't have tools to fix it right then and there, having pedals are an absolute life saver. While you can start your bike like it's a board track racer, it's always great to be able to pedal up to speed and drop the clutch.

As far as performance upgrades go, from what I know, doing a good porting job is the best way to get more performance out of your bike. Only after that is when I would worry about getting a carb and a smaller sprocket. You can of course get a good pipe on there, but from my experience, they dont help too much unless you port the motor first. For now, I would suggest gutting the stock exhaust as those are very restrictive and limit bottom end a whole lot.
 

Bizare

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Jan 24, 2020
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Another big reason you should keep the pedals is, it's so easy for these motors to break down. Something simple like a clogged jet or a blown gasket can leave you stranded on the side of the road, and if you don't have tools to fix it right then and there, having pedals are an absolute life saver. While you can start your bike like it's a board track racer, it's always great to be able to pedal up to speed and drop the clutch.

As far as performance upgrades go, from what I know, doing a good porting job is the best way to get more performance out of your bike. Only after that is when I would worry about getting a carb and a smaller sprocket. You can of course get a good pipe on there, but from my experience, they dont help too much unless you port the motor first. For now, I would suggest gutting the stock exhaust as those are very restrictive and limit bottom end a whole lot.
I understand the concern with being stranded but. This is more of a closed circuit "speed machine" project for me. So reliability has never been a goal. Thank you for the advise on porting. I will look into do this after the break in period.
 
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Bizare

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Jan 24, 2020
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Now we see for certain you've a two stroke in mind and ride flat the mystery unfolds, but the results are the same. You need pedals, yes you can slip the clutch and push off at the same time, but you will burn the tiny clutch quickly, especially with a small speed sprocket, in doing so. If you come to a halt on slight inclines you are totally screwed going forward. To top it all off you become a road hazard to others and a danger to yourself. I know newbies think they got it figured, but brother you're dead wrong on this one. For your own safety buy a scooter if that's what you want 'cause a kit motor bicycle needs pedals to operate in the real world of riding.

That said do it any way you like 'cause it's still a free country.

Rick C.
I appreciate your advice and input, I know for a fact that i don't know a ton about these engines, and i respect your concern for the safety of the motorists in my area. But I plan not on using this as transportation but rather a performance machine hobby. Much like karting, but for probably about a grand less. I know that there are even races for these things and i was thinking about getting into some of those.
Hope you kinda get where i am coming from now, not trying to be a danger to society just a kid trying to better my wrenching skills.
(Also clutch pads on these things are replaceable right? Genuine question)
 
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Greg58

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The 48cc engine needs to operate at a higher rpm to make maximum power, they run pretty good but it's not as good as a 66cc or 69cc engine. The gt2b Grubee is the best 48cc I have found, the piston clears the intake completely, the ports and transfers are fairly clean and the head has a squish band. The generic no name engines from eBay will need a lot of work to get close to the Grubee. It may cost a little more for the Grubee but will be worth it.
 

NickJ

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Apr 16, 2020
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The 48cc engine needs to operate at a higher rpm to make maximum power, they run pretty good but it's not as good as a 66cc or 69cc engine. The gt2b Grubee is the best 48cc I have found, the piston clears the intake completely, the ports and transfers are fairly clean and the head has a squish band. The generic no name engines from eBay will need a lot of work to get close to the Grubee. It may cost a little more for the Grubee but will be worth it.
I bought the 48cc from monster scooter. The sales people could not tell me much about it. I want to get a new cylinder body to port out but don't know where to find one. Also I think a red valve would help but what do you think?
 

Greg58

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Nick after posting the link I thought of a couple of things you can do to help, if you are planning on porting you'll need to check the piston anyway. You will need to remove the intake to see the piston skirt at top dead cylinder looking into the intake port, I use a sharpie to mark the area of the piston skirt to Dremel off. Then remove the cylinder and piston and Dremel out the area marked rounding the edge slightly. I had to do this on one eBay engine that was down on performance, only trim what's needed, don't trim the exhaust side or you could get it out of balance. Clean any slag out of the ports and transfers and you should see a difference.
 
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domN8er

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Aug 16, 2016
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Hello,
I enjoy cycling and all motorsports to begin with and thought that while I am in college, and since I am on a budget motorized bikes would be the easiest way to get my fix for danger and speed. I know they are not built for high speeds but I just want something to enjoy and practice my mechanic skills on for the next year or so.

Firstly,
I know the easiest way to really get more speed outta the bike is to mount a lower tooth count sprocket on it, I plan on doing this immediately after the break-in period is over. my question here is would a "performance" or "racing" carb actually increase the performance of the engine on the little 49cc bike.

Secondly, I plan on removing the pedals and plan on replacing them with foot pegs to make it into what my state calls a "motor scooter", given that I was wondering how effective or reliable the pull starters are or if in an emergency could you start it like an old board track racer. (ie, spinning the wheel on the back to start the engine.)

Finally, this is just an aesthetic question, can the gas tank fit inside the gap in the frame on a huffy Cranbrook, between the top bar and those two parallel curved bars? I feel like a smaller 1.5-liter tank could fit there with some modified mounting equipment.

Thank you all in advance for any and all input on my questions!
on a 2-stroke it kinda requires a rolling start and for the 4-stroke if you dont help you engine your gonna pay about 20$ every couple months for a new centrifugal clutch
 
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