Pocket Bike Engine Project 3 (V Belt)

lowracer

lowracer

New Member
This bike most recently was setup as a DIY rear rack friction drive. I didnt care for the friction drive w/ the high powered engine (bad tire wear) & changed it to a more efficient V-Belt drivetrain.
I mounting this pocket bike engine on a lightweight, strong, aluminum rear rack using 1/4" aluminum stock & some 1/2" thick rubber skateboard riser pads as motor mounts to absorb vibration. I'll probably need to flip the handlebars upside down to get more weight onto the front wheel for handling purposes. Here are some pics of the mostly completed project. Check out the cable connection I made using a brass spoke nipple & some silver/lead solder. Instead of having to solder a new end to fit into the throttle slide, I simply cut the too short 42" cable I had, cut a new cable to fit into the brake lever throttle controller & soldered the two cut ends into the brass spoke nipple. Works great.
-Lowracer-
 

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I've been having expansion chamber withdrawal syndrome (ECWS) since putting on the DAX canister muffler. The little can kills the power output of the 2 stroke engine in a big way & though I thought a little de-tuning would be a good thing for a no-suspension bike, I was wrong.
I had to do quite a bit of re-engineering to get the chamber onto this rig. The engine mounts had to be moved a few inches out & required a full day of re-work.
Got it done today & I like the power...
I also flipped the handlebars, slid the seat forward, & dropped it down for better center of gravity & handling.
Also added the skateboard wheel belt guide/tensioner.
-Lowracer-
 

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I havent done the rollout-test on this one yet, but the gear calculator suggests that I have a 17.1:1 ratio. The clutch pulley is 1.43", the rim pulley is 24.5" & the tire diameter is 27.5". My other pocket bike engines MB 'The Beast' has a 15.6:1 ratio.
Acceleration is brisk but I haven't dared attempt a top speed test (not on this no-suspension rig).
-Lowracer-
 
Lowracer doesn't the carburetor have to sit straight and not at an angle? Maybe that causes the power loss due to unregular float bowl position.
 
Gera,
May not look it in the pics but it sits almost straight & runs great.
I never mentioned a loss of power, just expansion chamber giving more power (compared to the Dax exhaust canister).
-lowracer-
 
I did the rollout test to confirm the gear ratio math & it worked out slightly different than the online gear calculator probably due to my discrepency w/ actual pulley measurements (v-belts sit within the pulleys).
I get 18.2:1 (rolling the back wheel one complete revolution turns the engine pulley 18.2 x's).
-Lowracer-
 
UnknownBMX,
The small 1.5" OD, 1/2" bore pulley I bought at ACE Hardware for a few bucks (also available @ Tractor Supply), the large pulley is another same size rim attached to the spoked wheel with JB weld, then a few carefully drilled holes to pop rivet or very thin bolts & nuts (made a few of these). Worked well on the rear, but better on the front wheel.
-Lowracer-
 
so it works better on the front? interesting. i saw how you attached the wheel. i was gonna weld mine if i can. but the pop rivits is a good idea too. im building a motorized bicycle for my brother and he gave me a nice little 31cc leaf blower engine. gonna end up spending like 20$ to get this one running lol
 
unknownbmx,
If you can weld, that would be better than glue, rivets or bolts. I don't weld so I have to make holes...lol
Good luck with the Brother`s motorized bicycle build.
-Low-
 
ill post it when i get done...gonna be a strange asortment of parts. right now its 26' wheels on a 27' frame with bmx handlebars and im going to mount the engine in the back
 
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