79cc powered bmx bike(mongoose)

[chancer]

So bottom line a fuel tank needs a 2 way breather valve. for expansion and contraction of the fuel.
So if you just put a barbed fitting in the top of the tank or in the cap and left some hose dangling... you would be fine? I am talking about on a DIY tank like the extinguisher etc.

 

[itsid]

well. "needs" is a bit much..
All that's needed is a tiny hole in the cap IMHO

'sid

 

[Poboy kartman]

Yeah...like I said...silly argument...BUT....regardless of which way you want to twist it...I made a valid statement that hasn't been disproved...

A Vent is only needed for fuel delivery. You could even expand that that to include removing the cap...because even accessing the fuel could be conceived as delivery.

 

[chancer]

well. "needs" is a bit much..
All that's needed is a tiny hole in the cap IMHO

This tank ventilation issue has got me thinking.
Remember the few threads that pop up where guys have a crankcase full of gas, cause they forgot to turn off the fuel? But most of us never need to worry about turning off the fuel.
I wonder if the fuel is leaking past the carb in those situations due to excess pressure in the fuel tank due to faulty ventilation.

Any thoughts?

 

[mckutzy]

I could see that happining...
In the cases I had the gas leaking in the motor.... I had keep filling the tank(thinking I had burned it and not payed attention).... but no gas hiss came when I cracked the gas cap...

 

[pearl111]

I am new to mini bike building have yet to finish mine ( almost done ) and it looks funny too. For the gas tank issue maybe you should put the pedals back on. All in good fun though that is something I always wanted to do when I was younger. To put a motor on my BMX bike.
I think when your done it will run down the rode just fine. Although I would get a stunt man to do the first act on that ride. Really though good luck with finished project. mike

 

[DeathMachine]

Having built something similar a long time ago (before digital cameras!) I can tell you that you definitely do not have enough gear reduction there.

For that to be able to get rolling, your sprocket on the rear wheel will need to be nearly the same diameter as the wheel, or you will need some gear reduction on the jackshaft as well.

Mine was even cruder, consisting of a second rim welded to the bike rim, and using a belt drive. I took the idea from very early Harleys.

The bicycle motor kits that use the sprocket you have use an internal gear reduction of around 5 to 1 (I think) or maybe more.

As that is set up currently, you will be duckpaddling like mad to get going and it will have a very high (theoretically) top speed.

 

[ironman]

That is a very nice build you got there that's next project belt driven for me.
Actually work on the mongoose over the weekend.got the hole drilled in the tank,ran fuel line,drilled out a hole in the cap for pressure,tighten some bolts and ran the throttle cable.with the 79cc had already the setup like the 212cc do so easy on throttle


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[ironman]

Throttle moves good.
No sticking nice and smooth.motor filled with oil,about cup load of gas in the tank.forgot about the header so either make one over the weekend or buy one from omb.

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[chancer]

Make a header! DIY.
OMB is for guys that cant remove Governors with buying expensive unneccessary parts. LOL

 

[ironman]

Make a header! DIY.
OMB is for guys that cant remove Governors with buying expensive unneccessary parts. LOL

You right..your right.so I get started on it tomorrow

 

[ironman]

The day has finally come it lives..first test run went good felt like a teenager again


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---------- Post added at 07:06 PM ---------- Previous post was at 07:03 PM ----------

https://vimeo.com/182940187


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[ironman]

Second test ride went good .back chain pop off once adjusted the wheel all good.i will say this a lot different riding a bicycle than a mini bike.


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[Flyinhillbilly]

How fast does your seatofthepantsometer say it goes?

 

[ironman]

Haven't went full throttle yet.Well I know I'm not going no way as fast as my mini bikes go but It felt way scarier sitting up higher.i had some real bad bmx bike wrecks when I was a teenager flash backs when going fast. and O yea forgot no brakes on bike yet!!


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[RobertD]

Cool build -- looks terrifying! Be safe!

 

[ultralight01]

Now this is something I have to build, only with a full sized bike. Man, motorized bicycles are so much lighter than dirt bikes, which makes them really fun, and easy to jump!