20" Mongoose BMX Race Bike
- Thread starter Wild Bill
- Start date
d_gizzle
Active Member
Calhoun cycles. They also have a 20" multi speed rear wheel.
Umm..........the wheels are 12.5" front disc wheels for a scwhinn 1000 electric scooter (and similar models) but.......its gas powered. The thread is '5150-straight jacket sold separatly' in the non-kit section. I will eventually do the same to a Toucan20S
Umm..........the wheels are 12.5" front disc wheels for a scwhinn 1000 electric scooter (and similar models) but.......its gas powered. The thread is '5150-straight jacket sold separatly' in the non-kit section. I will eventually do the same to a Toucan20S
Wild Bill
New Member
Thanks to Norm at Venice Bikes and D Gizzle for the tips.
Well I have about 1/2 gallon break in fuel thru it and it started to suck air and I found the crank seal on the magneto side wasn't installed all the way in and was rubbing the magnet and damaged the seal. I decided to go ahead and port it and cut the piston skirt while I was doing engine repairs anyway.
After replacing the seal that problem went away and I changed the rear wheel to a disc brake hub and went with a 22t disc hub mounted sprocket ala D Gizzle's suggestion on the hub mounted sprockets. Im still breaking in the engine on 24:1 and Im about 4 jet sizes too big but I still went from about 28-30mph(without porting or cut skirt) on the 30t to 40mph on the new 22t(with porting and cut skirt)and its still 4 stroking because of the fat mixture. I think it will pull a taller gear yet and will pick up a 20t sprocket to try out later.
I am also gonna try out a HuffyDavidson ignition and put my Dellorto clone carb back on (Took it off when I had the vacuum leak to eliminate the carb as the prob). Also I just cut off the muffler because it was pretty restrictive and I welded on a 5" stinger that I will test out later on with the other changes to try to get more speed out of it. I will add on a removable muffler for street riding and run a straight stinger for the races.
I may also go to a rear disc brake since it now has the rear hub for it. I also may cut the head tube and give the forks a little more angle, this thing has very quick steering (Meant for usual bmx speed and handling). Its kinda frightening turning into a high speed corner although I kinda like it!!! I will need to go from a 16t freewheel to a 15t to bring up the pedal gearing, I run out of pedal gearing too quick getting off a turn and would like to be able to pedal farther off a turn.
At the point I decide I wont need to do anymore welding on it I will go ahead and paint it, Im thinking black with maybe some bright blue highlights.
Well I have about 1/2 gallon break in fuel thru it and it started to suck air and I found the crank seal on the magneto side wasn't installed all the way in and was rubbing the magnet and damaged the seal. I decided to go ahead and port it and cut the piston skirt while I was doing engine repairs anyway.
After replacing the seal that problem went away and I changed the rear wheel to a disc brake hub and went with a 22t disc hub mounted sprocket ala D Gizzle's suggestion on the hub mounted sprockets. Im still breaking in the engine on 24:1 and Im about 4 jet sizes too big but I still went from about 28-30mph(without porting or cut skirt) on the 30t to 40mph on the new 22t(with porting and cut skirt)and its still 4 stroking because of the fat mixture. I think it will pull a taller gear yet and will pick up a 20t sprocket to try out later.
I am also gonna try out a HuffyDavidson ignition and put my Dellorto clone carb back on (Took it off when I had the vacuum leak to eliminate the carb as the prob). Also I just cut off the muffler because it was pretty restrictive and I welded on a 5" stinger that I will test out later on with the other changes to try to get more speed out of it. I will add on a removable muffler for street riding and run a straight stinger for the races.
I may also go to a rear disc brake since it now has the rear hub for it. I also may cut the head tube and give the forks a little more angle, this thing has very quick steering (Meant for usual bmx speed and handling). Its kinda frightening turning into a high speed corner although I kinda like it!!! I will need to go from a 16t freewheel to a 15t to bring up the pedal gearing, I run out of pedal gearing too quick getting off a turn and would like to be able to pedal farther off a turn.
At the point I decide I wont need to do anymore welding on it I will go ahead and paint it, Im thinking black with maybe some bright blue highlights.
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Wild Bill
New Member
I just got a Fred Head and the Lightning CDI. I had to hack up the head to clear my fuel valve and frame, I could have moved the tank but I would have had to still hack it up to clear the frame so......
I went out for a test session today to my level marked off road, there was no wind and I went from the previous best on a 22t of 39-40mph to 45mph huge difference!!!! Since I changed the head and cdi at the same time I don't know what did what for sure but now I have much better bottom mid and top end! I can tell as quick as I get up to top speed it will pull more gear so Im sure theres more usable mph left in it and I just ordered a 20t. This bike is quicker and faster than the other China Girl bike I built and Im sure that there is something to the 20" bikes having more potential that a 26". I Know with more work I will find more speed out of this thing. I currently have a Speed carb on it and I should pick up a little by going back to the Delorto clone.
I believe the ignition is well worth the the money! And same goes for the head.
I went out for a test session today to my level marked off road, there was no wind and I went from the previous best on a 22t of 39-40mph to 45mph huge difference!!!! Since I changed the head and cdi at the same time I don't know what did what for sure but now I have much better bottom mid and top end! I can tell as quick as I get up to top speed it will pull more gear so Im sure theres more usable mph left in it and I just ordered a 20t. This bike is quicker and faster than the other China Girl bike I built and Im sure that there is something to the 20" bikes having more potential that a 26". I Know with more work I will find more speed out of this thing. I currently have a Speed carb on it and I should pick up a little by going back to the Delorto clone.
I believe the ignition is well worth the the money! And same goes for the head.
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Wild Bill
New Member
Thanks Theon, I wouldn't say its twitchy at speed, it doesn't get head shake like some motorcycles at high speed but it turns into a turn very, very quick and has got your attention at all times!
I tried some high speed slalom between the roadlines at speed like I do with my bigger bike and I wont be doing that anymore though! It feels good doing the sort of cornering it will be doing at the track. I am getting used to it but I still may cut the frame and reweld the head tube at a lesser head angle.
I tried some high speed slalom between the roadlines at speed like I do with my bigger bike and I wont be doing that anymore though! It feels good doing the sort of cornering it will be doing at the track. I am getting used to it but I still may cut the frame and reweld the head tube at a lesser head angle.
Going by the photo,
those front forks don't offer much caster/trail offset.
I'd be either increasing the rake of the head tube or increasing the trail offset(moving the front wheel back in the forks).
Increasing the rake has the bonus of lengthening the wheel base,
I'd start by trying a set of forks with the wheel closer to rear.
Get a straight edge, use it to follow your headtube to the ground, then use a roofing square to drop a vertical from your front axle to the ground, you want at least 40mm of trail in my experience.
those front forks don't offer much caster/trail offset.
I'd be either increasing the rake of the head tube or increasing the trail offset(moving the front wheel back in the forks).
Increasing the rake has the bonus of lengthening the wheel base,
I'd start by trying a set of forks with the wheel closer to rear.
Get a straight edge, use it to follow your headtube to the ground, then use a roofing square to drop a vertical from your front axle to the ground, you want at least 40mm of trail in my experience.
Wild Bill
New Member
I still have to try the Dellorto clone carb but I have to wail till the 2 jets I ordered come in since I suspect the Dellorto may need a jet that is still missing from my jet assortment. So as I wait I needed something to do on the Mongoof so I made a number plate. I also ordered two Hook Worm tires.
I tried to do a short test session yesterday but it was a windy day so no accurate speed testing was possible now I will just wait and go when I can also test the new carb.
I tried to do a short test session yesterday but it was a windy day so no accurate speed testing was possible now I will just wait and go when I can also test the new carb.
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Wild Bill
New Member
Well the Willow Springs race was a blast! ( I added a vid clip of my KTM Midrange heat race at the bottom, it was kinda a boring race since not everyone made the start. There were a few Motopeds in my race) But the Mongoose only got 2-3 practice runs. We had never been to Willow before and being a 6/10 mile it is shorter than the track we normally race on (The Grange 8/10) and it rides even tighter than it measures. That and since the Mongoose is the first single speed bike I have built(the 2 previous are both shifters), I had no idea what to gear it and what good bottom end acceleration should feel like on a single speed so it was way off! On the longest straight it didn't even really start to get on the pipe.
My Sons lap times on it were 2 seconds off what he was running on his other bike, so he raced the bike he normally rides instead. I think as far off as it was and the fact he ran within 2 seconds of his other bike says a lot about the potential of this bike but time will tell. I was very impressed that no matter what bike my Son rode his lap times were consistently within 1/10 second of each other in practice.
Now with what I learned at Willow Springs, I made a much longer header pipe to try to gain more bottom end and since both the tracks we race on I have found are too tight to use the 23t I had it geared at, I made up a 25t sprocket. I just test rode this morning and what a huge difference!!!!! The new Header pipe is about 8" longer.
It now gets up on the pipe way quicker and takes less than 1/2 the distance to get up to speed. With the 25t it doesn't hit the 42mph it did before the bigger gear and longer header, but now it hits 40mph in less than 1/2 the distance. I believe that with the 23t it will hit 44mph but I doubt the tracks have long enuff straights for that gear. I will take the 23t and 22t with me to the track the next time out just incase it can use it.
I cant wait until the next time out, this thing should be very fast as compared to my Sons current bike!
https://www.youtube.com/watch?v=Q2xOIWyfMjo&list=UUp2zIoY4JB6KWvEWedGWidg
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My Sons lap times on it were 2 seconds off what he was running on his other bike, so he raced the bike he normally rides instead. I think as far off as it was and the fact he ran within 2 seconds of his other bike says a lot about the potential of this bike but time will tell. I was very impressed that no matter what bike my Son rode his lap times were consistently within 1/10 second of each other in practice.
Now with what I learned at Willow Springs, I made a much longer header pipe to try to gain more bottom end and since both the tracks we race on I have found are too tight to use the 23t I had it geared at, I made up a 25t sprocket. I just test rode this morning and what a huge difference!!!!! The new Header pipe is about 8" longer.
It now gets up on the pipe way quicker and takes less than 1/2 the distance to get up to speed. With the 25t it doesn't hit the 42mph it did before the bigger gear and longer header, but now it hits 40mph in less than 1/2 the distance. I believe that with the 23t it will hit 44mph but I doubt the tracks have long enuff straights for that gear. I will take the 23t and 22t with me to the track the next time out just incase it can use it.
I cant wait until the next time out, this thing should be very fast as compared to my Sons current bike!
https://www.youtube.com/watch?v=Q2xOIWyfMjo&list=UUp2zIoY4JB6KWvEWedGWidg
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