Motorbike forks for a minibike

[r97]

hey, great job on the bike landuse!! From the start i knew that 3hp would be a little low but i didnt say anything. I think that you should invest in a new engine. Something over 5hp. And then remove the governor and you should be happy. That bike looks really cool and IMO the speed is dissapointing. Congrats on the build though!!!

3hp should be a decent amount to putt around on a mini bike with. in the video the performance is down because of an improper gear ratio, and an engine that wont rev up very much.

 

[landuse]

hey, great job on the bike landuse!! From the start i knew that 3hp would be a little low but i didnt say anything. I think that you should invest in a new engine. Something over 5hp. And then remove the governor and you should be happy. That bike looks really cool and IMO the speed is dissapointing. Congrats on the build though!!!

Thanks j.concepcion54321. I got up to 15MPH according to my GPS. It goes fast enough for me and my daughter, but I know what you mean about wanting more speed. I will look into another engine some time in the future.

Like r97 says though, the engine is not revving properly all the way, and I am thinking of removing the air vein governer, but I am not sure how. Could someone maybe show me how that is done using one of my engine pics that I posted previously. What would I connect my throttle to then?

 

[bighead]

Well I finally got the bike finished and took it for a spin. The torque is pretty low, but it moves me OK. Here is the vid of my running minibike. No build is complete without a vid.

http://www.youtube.com/watch?v=GhxsNNXaqXo

The engine is still giving me some problems, but I should sort that out soon though. As I give full throttle, the engine seems to want to die. If I let off the throttle it starts running again.

Tell me what you think.

I CANT BELIEVE THAT i MADE SOMETHING THAT ACTUALLY RUNS!!!

Freaking cool friend. Good job.

 

[landuse]

Heres another vid of my daughter riding something other than a bicycle for the first time in her life. I think she did pretty well considering.

We went out and rode on the road afterwards, and she was a whole lot better
http://www.youtube.com/watch?v=wKkWXBJzXKA

 

[HellSpawn]

I think your gear ratio is still really goofy or you have a goofed up clutch. It seems like its slipping really bad in those videos. Even with 3hp that thing should be able to scoot along pretty well. I'd swap out to an even lower ratio before you toast that clutch.

 

[landuse]

I might think of changing my 14 tooth JS out sprocket for a 12 or 10 tooth. I am also going to have the engine looked at again by the small engine repair shop that I originally took it to. This will happen at the beginning of next week.

I would definately prefer a bit more torque.

 

[Leftythenub]

Thanks j.concepcion54321. I got up to 15MPH according to my GPS. It goes fast enough for me and my daughter, but I know what you mean about wanting more speed. I will look into another engine some time in the future.

Like r97 says though, the engine is not revving properly all the way...

Try this:
Put the bike on a stand. Start the motor and let it warm up a bit. When it's warm, twist the throttle. If it revs higher with no load on the bike, you need a higher gear ratio. If it still doesn't rev any higher, it's an engine problem and not your gearing. You are currently at a 8.14:1 ratio. With that ratio, you should be able to pull the front tire off the ground.

If you want more power and speed, I highly recommend the HF 6.5HP. I have one on my heavy bonanza frame with 14.5" tall tires and my big a$$(280lbs) and I can go 40Mph all day long.

 

[landuse]

Thanks Leftythenub. I will give that a try as well. I would hate to change engines, cos I only have one size clutch, and all my other engines have larger shafts. Clutches here in South Africa are so expensive that you don't want to buy them. Thats why I am putting all my resources into this small Briggs.

 

[machinist@large]

Try this:
Put the bike on a stand. Start the motor and let it warm up a bit. When it's warm, twist the throttle. If it revs higher with no load on the bike, you need a higher gear ratio. If it still doesn't rev any higher, it's an engine problem and not your gearing. You are currently at a 8.14:1 ratio. With that ratio, you should be able to pull the front tire off the ground.

If you want more power and speed, I highly recommend the HF 6.5HP. I have one on my heavy bonanza frame with 14.5" tall tires and my big a$$(280lbs) and I can go 40Mph all day long.

I think you're going to have a new issue once you get past the teething pains; once your daughter learns how to ride it,your not going to get it back! Nice Build!

 

[jrmints1415]

really like it! Great Job!

 

[landuse]

I think you're going to have a new issue once you get past the teething pains; once your daughter learns how to ride it,your not going to get it back! Nice Build!

really like it! Great Job!

Thanks guys. I am definately in the teething pains phase. The engine now doesn't want to start, so I have called the shop who serviced it, and they are going to come out to my house for free and have a look at it. I have to wait till monday though.

My daughter has been trying to start it like crazy, so I definately think she is going to claim it as her own. She is also talking about the colour she wants it painted.

 

[Bluethunder3320]

NICE! the engine doesnt sound like its reaching 3600 rpm, tho. my guess is its in the gearing. too high.

i wouldnt drive like that or else the clutch will burn up!

 

[landuse]

My ratio at the moment is 8.14:1. Should I gear it for about 10:1, or somewhere there?

 

[Bluethunder3320]

whats your tire diameter, (sorry if you said it before and i didnt read)

my warrior mini bike has 10:1 gearing, with 19" tires, and i get to about 25... with the governor bypassed by my hand under the gas tank...

so about 9:1 is what you have. hmmm.... wont make much of a difference going 10:1.

does the wheel go alot faster raised off the ground?

ill go look at that governor thing now.

 

[Bluethunder3320]

ok heres the best i can explain how to do it, regarding removing governor.

there are 2 ways, in my head, that you can do it.

(1) take a picture of the air vein and the linkages. the way i am thinking of, is if you can hardwire the throttle to the air vane and carb, use it as a pivot point, and cut off the vane.

(2) remove the air vane and linkages, and wire it just like a 5hp briggs raptor.

this is a terrible pic, but maybe you get the idea....

the user kendelrk has an engine that is set up this way.. see what i mean about the throttle cable sleeve retainer bolted onto one of the headbolts.

so post a pic of that air vane, and ill get a better idea.

good luck!

 

[landuse]

I have 12" rims on my bike, and a 1:8.14 ratio [(38/16)*(48/14) = 8.14]. I was thinking of maybe going with a 12th instead of a 14th. That would give me 9.5:1.

Here are some pics of my throttle setup and the governer. I am still a bit confused as to where I should do the linkage if the governor is gone. My cable comes in from the back of the engine (as you can see in the pics), not the top like you suggested.

Maybe you can indicate on the pics as to what I should do. As you can see, the butterfly is also connected to the governor. If I have disconnected it from the governor, would it even work?

Thanks

 

[Bluethunder3320]

do you have a return spring?

from what i can see, you are already bypassing the governor.

does it move the throttle wide open when you pull back on your cable? i cant really see anything else happening if you removed this.

i would get rid of the air vane anyways, and make a hinge for the throttle to connect those 2 linkages. you could even just cut off the bottom part of the air vane... i just dont understand how the air vane would restrict the throttle as it is now if you can hold the throttle wide open.

 

[landuse]

do you have a return spring?

from what i can see, you are already bypassing the governor.

does it move the throttle wide open when you pull back on your cable? i cant really see anything else happening if you removed this.

i would get rid of the air vane anyways, and make a hinge for the throttle to connect those 2 linkages. you could even just cut off the bottom part of the air vane... i just dont understand how the air vane would restrict the throttle as it is now if you can hold the throttle wide open.

I installed a return spring after I had taken these pics. I was also thinking that at full throttle the air vane would not be able to move back cos I am holding it open. The throttle does open all the way. It cannot go any further.

I guess I am just going to have to wait and see what the small engine shop people say when they come look at the engine next week. I am sure they didn't fix it up properly, and it isn't hitting 3600rpm.

Here are the pics of the return spring. I also included some pics of my kill switch and how I attached the seat with saddles

 

[HellSpawn]

Can you take some pictures of your sprockets and jackshaft setup? and maybe a video of the thing up on stands.

 

[landuse]

I will do the vid next week when I get the engine running again, but here are the pics of jackshaft and sprockets. It has a 16T clutch, 38T in, 14T out and 48T on the wheel.

The jackshaft now has the two sprockets swapped around. I had stupidly given myself pretty much a 1:1 ratio before I realised I should have had them on the other way around. I will take better pics and post them over the weekend.