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Old 02-16-2010, 02:01 PM
Wood.Neely Wood.Neely is offline
Motorized Bicycle Member
Join Date: Feb 2010
Location: Auburn, AL
Posts: 31
Default another newbie

hey guys, i just joined the team today after ordering my new 80cc angle fire grubee skyhawk. i also picked up a used motobecane mt. bike to mount the moor to.

a couple of question....
1. i keep reading about gear ratio... do these things have seperate gears or does this change with the number of teeth on the rear sporcket??
2. i have been searching for an exhaust extension. i have been reading that messing with the stock mufflers can mess up the motor but i don't want the exhaust blowing all over my feet... any suggestions??

will take any advice,

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Old 02-16-2010, 02:41 PM
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MaxPower MaxPower is offline
Motorized Bicycle Elite Member
Join Date: Jul 2009
Location: Sierra Vista AZ
Posts: 555
Default Re: another newbie


I think what you are asking is if there are gears on the motor. the answer is no. you can buy a shift kit from but it's expensive. the internal gear ratio of the engine is 4.41:1. with a 44 tooth sprocket on the wheel (4.4:1) you get a final gear ratio of 19:1. If you get a smaller sprocket you will go faster but sacrafice acceleration.

as far as the muffler, you can get something called a Poo-Poo pipe. I think sells them. you can also buy an tuned exhaust. sells a really nice one.

good luck
Max Power is my hero
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Old 02-16-2010, 02:45 PM
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2door 2door is offline
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Join Date: Sep 2008
Location: Littleton, Colorado
Posts: 16,222
Default Re: another newbie

Welcome Wood,
We're glad you've joined us. Let's look at your questions:
1.Gearing. The drive ratio is determined by rear wheel sprocket size. The larger the sprocket (tooth count/diameter) the lower the rear gear ration. If you live in a hilly area you might want to stay with the middle of the road sizes such as a 44 to 48T. If you're looking for a better top speed on flat ground, go smaller; 41 to a 36T sprocket.
There are available so called, 'shift kits' which allow use of the bicycle rear gears through a jack shaft and a chain ring free wheel on the pedals.
2. Pipes and mufflers/extensions. Extending the pipe will not harm your engine but could rob a little power. A two stoke engine requires a certain degree of back pressure from the exhaust to function properly which is why we never recommend running an open exhaust system. Open or unrestricted exhaust can cause a lean condition which would be detrimental to the engine. Loud exhaust also can upset your neighbors and is not good for the hobby. Tuned exhaust, or expansion chambers help in the low and mid range power band but can be a little noisier than the kit supplied muffler. Many of us, me included have fabricated extensions which place the muffler aft of the rider and keeps exhaust and oil vapor from staining your pants and shoes.
Hope this helps a little and keep us informed on your build. We're always here to help when we can and you'll get several replies so keep reading.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"

Last edited by 2door; 02-16-2010 at 08:22 PM.
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Old 02-16-2010, 06:00 PM
Wood.Neely Wood.Neely is offline
Motorized Bicycle Member
Join Date: Feb 2010
Location: Auburn, AL
Posts: 31
Default Re: another newbie

thankyou both. you couldn't have answered my gear ratio any better. I thought that was the way it worked, but now realize how the sprocket size effects the speed. as far as the muffler, i think i may pass on the $50 dollar poo poo pipe although that's exactly what i was talking about. i may work on welding one myself. thanks again and will continue to read on.
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