Help me hit 30mph.

3yt

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Sep 20, 2019
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22
I have 33cc 2 stroke bicycle, after tuning and tweaking im up to about 27mph. Its essentially a weed wacker motor with a stock butterfly carb and muffler. Im getting the best performance when the carb adjustment screw is nearly all the way screwed in, so i dont think fuel would be the limiting factor. Would a new carb, jetting, or new exhaust get me up to 30mph? Thanks!

Pictures
 


Frogslayer

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Jan 20, 2019
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27mph is sensational from a 33cc. I'm not sure which carb you have but isn't screwed in leaned way out? Do you have a tach or some way to see how fast the engine is spinning? Can you post a picture for us? A pipe may be a way to attain your goal.
 

3yt

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Sep 20, 2019
Messages
22
27mph is sensational from a 33cc. I'm not sure which carb you have but isn't screwed in leaned way out? Do you have a tach or some way to see how fast the engine is spinning? Can you post a picture for us? A pipe may be a way to attain your goal.
Thanks, Its pretty fun. Unfortunately no tach, ive been using gps for mph. posted a link to an album with a bunch of pictures in the main. As far as I know screwed in all the way is reducing the fuel flow as much as possible, so lean? yes. From the carb is a velocity stack and a 90deg radiator hose. Appreciate your response,



Ps, the flex pipe is gone, also the skateboard rain guard lol
 
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Pedroj

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Oct 13, 2019
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First things first make sure you have a helmet in order for you to reach the speed you want you need a bigger carburetor take your muffler remove the silencer going to your phone and get app with a speedometer
 

CrazyDan

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Jul 9, 2016
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Bigger carb, porting, expansion chamber. For more power you need more air/fuel to flow. The expansion chamber would act like a turbo at certain rpm, pretty sure a goped expansion chamber would work. Then you can run a smaller sprocket for a higher speed.
 

3yt

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Sep 20, 2019
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Bigger carb, porting, expansion chamber. For more power you need more air/fuel to flow. The expansion chamber would act like a turbo at certain rpm, pretty sure a goped expansion chamber would work. Then you can run a smaller sprocket for a higher speed.
Thanks for the response. When considering a new carb is there such thing as too big? Seems easier to restrict airflow than porting. What's the limiting factor, Intake port size?
 

CrazyDan

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Jul 9, 2016
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The intake port size is the bottleneck if you haven't done any port work. If you've opened up ports then the limiting factor is how much volume your engine can pump. That's where you can go too big on a carb.
You'll see instant gains with a proper pipe, after tuning the carb of course. Here's a nice carb and pipe combo, might be just what the doctor ordered. Make sure you choose the 33cc pack.

Edit: here's another combo pack.
 

RB55

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Sep 18, 2019
Messages
55
From my experience with a 66cc engine;
1. Sprocket makes a HUGE difference, it is easily the most important mod you can to with any of these motorized bikes. Looks like you are using a 44T, that’s too big. On my 66cc heavy hybrid bike build, I could only top 28mph with a 44T on a good day. I’m not sure how low you should go because your 33cc is probably not putting out that many HPs and torque, but at least drop down to a 40T (I use 38T). The switch from a 44T to 38T already made an enormous difference for me, top speed went from 28 to 35, RPM and vibrations significantly reduced (better for engine to run at low RPM) and better fuel economy.

2. Exhaust also determines top speed but mostly acceleration and torque. It’s the second most important mod. Stock muffler is nice and quiet but very restrictive with its baffling, I bought a 20$ straight through muffler from EBay (just look up 2 stroke muffler) and with a little exhaust cement and angle grinding it fit fine over the stock. My acceleration went from being dull to having to hold to stop myself from flying off! Also, it really improved low-end torque, meaning I could cruise around at low RPM and throttle, saving gas and making for a nice smooth ride. It did improve top speed a bit (few MPH). Just warning you though, it is louder than stock but much better than expansion chamber, which are stupidly loud and hurt my ears. An expansion chamber could boost a bit more, but the extra noise is a big turn off for me. If you want the best of both worlds, you could get an expansion chamber and attach a muffler :)

3. Carburetor adjustment - you can get better performance, but is a challenge. If you are willing to spend hours messing around with them, that’s fine, but I’m warning you they are a pain sometimes and can lead you in circles. Porting is simple and effective. I removed the stock air filter on mine and replaced with high flow custom filter I made, and that boosted my top speed by at least 5 mph or so. Restricting the carb’s air intake is easier way to kill performance; it will work fine at low RPM but once you rev up it will just suck. Wide open intake or high flow filter will let your carb reach max performance by allowing it to pump as much air/gas mix into the engine as possible.
 
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