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Old 02-13-2013, 12:33 AM
jeeperharmon09 jeeperharmon09 is offline
Motorized Bicycle Newbie
Join Date: Feb 2013
Location: IL
Posts: 1
Default Advice?

Hey there!
This bike of mine is my first build of my own. I first started with my friends bike. me being the one with all the tools and know how of mechanical parts. So he is my bike. Its a 29 inch Jeep mountain bike. front disc and rear v breaks. before I put the engine on it I road down the road a few times to see how it rode. Anyway. . .
Im trying to get a better understanding of my engine. I had ordered it of ebay, the listing said 80cc but i know that its only a 69cc as far as i can tell from reading around. What I am trying to figure out if my bike is running smooth enough. Its at its probably second tank of gas. and runs great when moving but its still hard to find that sweet spot for idle. I am going to post my youtube video (sorry for the bad video quality but audio sounds good). Can anyone tell me if it sounds like its 4 stroking? and I think I might need to do a better job on the sealing the intake bc it sounds like its idling to long after throttle is down. I have ported both the intake and exhuast to a good size. shortened the intake to fit the carb and just put on the speed carb.
She starts up good, im just trying to fine tune it. Being from Illinois its about 39 degrees so it takes a bit longer to warm it up. Let me know what you think!

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Old 02-13-2013, 01:28 AM
brown brown is offline
Motorized Bicycle Elite Member
Join Date: Feb 2013
Location: Bloomington IL
Posts: 216
Default Re: Advice?

All these little 2 strokes seem to have a sluggish throttle response when you left off them while not in gear. Maybe if you added one of the reed valve conversions it would help. It a little pricey in my opinion for something that is easy to get used to.

If the motors rotating mass weight was reduced I am sure that would help also.
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Old 02-13-2013, 01:29 AM
brown brown is offline
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Join Date: Feb 2013
Location: Bloomington IL
Posts: 216
Default Re: Advice?

It is not 4 cycling. it wont unless you hasve a main jet that is too large.
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Old 02-13-2013, 07:51 AM
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Dave31 Dave31 is offline
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Join Date: Mar 2008
Location: Old Pueblo,Arizona
Posts: 11,118
Default Re: Advice?

Hello jeeperharmon welcome to the forum.

I don't hear and wont any four stroking in your video. But I do agree, I'd check for vacuum leaks it does sound to me like you have a small air leak indicated by how your motor wont rev down after goosing the throttle.
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jeep, mountain bike

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