Here I go


Local time
2:37 AM
Sep 17, 2008
I finally managed to scrounge up most of my parts to get started. After trying to get a hold of several gas trimmer engines, a chainsaw engine, and a used pocket bike engine, I got a "new" 49cc cag style pocket bike engine. For whatever reason i went with a GEBE kit. Right now i have it all mounted up and the throttle plumbed with a spare brake lever.

I'm waiting on my gas tank and exhaust to arrive before I can fire it up. I'm also going to get a small toggle kill switch and drill a hole in the pull start housing to mount it.

The engine seemed to be quite a bit lighter than the trimmer engine, but that is before the exhaust is added.

As I noted in the new members area, the bike is a Mongoose XR-75. I finally gave it some love with new aluminum linear pull brakes, a new chain, lots of grease and a new shock spring.

Some things I'm noting is that with the current spring it squats quite a bit when I sit on it. I have a longer spring that is the same tension as my current short one. I was hoping to have a bit more suspension travel for the higher speeds.

The GEBE may not have been the best choice for the higher powered engine, but I got the stronger mount for the Tanaka 40cc engine. I'll just have to take it easy at first so i don't slip the belt. What fun would this be if i didn't have to tinker with it? :D I may end up having to detune it a bit to keep it quiet anyways, so starting with more power might be beneficial.

I was wondering what most people use for their control setup. I'm a motorcycle guy, but what I have on it seems goofy but usable. I have my front brake on the right, the rear brake on the left, and the throttle "backwards" on the left. My front derailer is toast, so that grip shifter is gone for that. I flipped the engine and carb around so the pullstart can be pulled from the seat.

On a side note.... flipping the engine also put the intake on the front and the exhaust up and rear..... it should be fun getting the exhaust routed with the port pointing straight up.

I'll post some pics here in a little bit once i get a chance to organize and upload them.
I snapped a few pics.

It looks really lopsided, but I pedaled it around and didn't notice any tendency to lean.

I'm really happy with the kill switch. it looks like it came that way from the factory. Just like the rest of the engine, it has no labels :eek:

After flipping the engine, the mounts point up and look like a decent place to put my gas tank. If not, i might try and make a cover out of aluminum or plastic. The engine does look nice naked though


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My exhaust and gas tank came earlier this week. I was very excited.

The ebay seller sent me the wrong gas tank, and the exhaust (different source)was absolutely terrible. It was just a regular pocket bike exhaust with a can on the end. The stinger was filled up with slag from welding and there were loose pieces of metal inside. I had to rip it apart just so air could come out the end.

The gas tank is forgivable as it is a larger and nicer tank, just not usable for my situation.

In the mean time I found the following link which has a calculator for tuned pipes

Towards the bottom of the page there is a link to a Silencer Application which lets you play with dimensions and see how much sound gets attenuated.

I'm going to try to make due with the exhaust i have, but any suggestions for something that's easy to make or premade would be great.
After some tinkering and a new exhaust, i got the beast outside and ran it a bit today.

My impressions are as follows

1. 1-2-3 pull 1-2-3 pull 1-2-3 pull blub blub blub
2. HEY this goes fast
3. shakes a lot

I still need a gas tank setup. I currently have it so the inlet is a hair above the carb inlet. It runs fine until it splashes all the gas away from the tube in the tank :( . This problem has been plaguing me since the beginning.

I only used 1 gear to pedal up to speed. Do ya'll use your derailers? I hate to remove stuff i don't feel like fixing, but I want to rip all that stuff out. Surprisingly I wasn't coordinated enough to pedal, steer, avoid bumps, and use the throttle at the same time.

My speedo wasn't setup correctly. Its set for a bigger wheel and it said 22 mph, so I think I'm way over my goal of 25. The brakes work fine at that speed, but the steering and suspension do not. I have a lot of wobble. I'm also used to motorcycle, so everything felt a bit on the gonna-fall-apart side.

I'm beginning to think I should use a newer bike that isn't as worn, switch to something like an EHO35, or figure out how to fix my bike the right way ;) I originally wanted to be able to use it to commute, but I feel that the high perf. bug bit me. With that new pipe on there it sounded really good. No weed wacker sound at all. Nice and even tone with no ringy dinging. It did sound like a larger dirtbike though.

On a very positive note, my neighbors had evidently been watching me fiddle with the critter every other week or so in the parking lot and gave me an applause once i got it down the road and back with the engine running. I had two guys on bikes stop by to ask me about it. I pointed them to this site :D

Chalk this one as a successful run.
An update would not be complete without pics!!!!

The 11-06 shot shows the gas tank and bracket i threw together with scrap from the engineering lab. It could be better, but I think its great for 5 minutes work and no measurements whatsoever :cool:

The other pictures show the exhaust and how ridiculous it looks :rolleyes:


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