My build with a GT 90 Kit sputters until it's over ~15mph

Ryan843

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Sep 29, 2019
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Thanks, we will! I’ll upload finished pics of the whole bike and a video of me riding it when it has the x chamber on it
 
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Ryan843

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Sep 29, 2019
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I tried riding it today and man it sounds good. It’s grittier than the other two bikes we’ve built. It’s the first bike I can really tell the 44 tooth sprocket limits it, it accelerates so fast even near top speed. I love it
 
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Ryan843

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Sep 29, 2019
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So tonight my dad found the problem with the bike! One of the 3 wires going to the magneto was thought to be a ground wire, but it’s actually tied to a positive lead. It was touching the frame intermittently, shorting out the circuit. The wire is now insulated and the bike runs great at any speed!

Now all that’s left is adding the expansion chamber!
 
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Ryan843

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Sep 29, 2019
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https://imgur.com/a/v1xcP5b

I can’t figure out how to get it to upload with audio. There’s a bit of a metallic pinging/rattling sound when it reaches higher RPMs but I’m not sure why or if it’s even something to be concerned about. Is that normal? This thing is so much more fun to ride than either of our previous two builds. It’s addicting lol
 
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indian22

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Dec 31, 2014
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Glad to see an update & find out it's performing well Ryan. I'd not completely ignore anything that sounds, looks or feels strange. That said these little engines can make some strange vibes and sounds that are specific to "your" motor not "these" CG motors in general. I've one that makes a pinging sound from the clutch housing, but I've not been able to eliminate it after several years of trying this or that and it runs great...just sounds different to me.

Rick C.
 

James Thomas

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Dec 8, 2019
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Hey everyone! I'm new to the forum, but not exactly new to building motorized bikes.

This is my 3rd build. I kept wanting something faster after building the last two, so this time I went with a GT7 kit with the GT90 conversion kit. Rebuilt the engine, got it set up and all.

The problem I'm having is the bike sputters so badly it won't run on its own until it reaches about 15mph, then it's like a switch flips and it runs great and gets up to 30mph with a 44 tooth sprocket. But under 15mph it's useless.

Tried different spark plugs, a different voltage regulator that worked on another bike, and tried with the choke on and off. Only things I can think of are that the carb that came with the GT90 kit is too big to pull in enough air at low RPMs or something is wrong with the coil on the engine that generates the electricity for the spark plug.

Any ideas? Thanks
Jus the carb ..what jet ya got in it? And where are u located? Reason I ask location it altitude means everything to getting .. get back with me and let me know I'll tell ya what mm jet to run .. best to ya!
 

Jerdoggiedog

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Jun 3, 2021
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Jus the carb ..what jet ya got in it? And where are u located? Reason I ask location it altitude means everything to getting .. get back with me and let me know I'll tell ya what mm jet to run .. best to ya!
HEY GUYS, I BOUGHT A GT7 KHIEN REED MOTOR TOO, AND MINE IS DOING THE SAME THING BASICALLY. EXCEPT MINE DIDN'T COME WITH A WINDOWED PISTON, JUST THE REED TRANSFER PORT CYLINDER. SO SHOULD I ORDER A WINDOW PISTON?.
 
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indian22

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The window piston is necessary to make more power with the reed setup. Buying a widow piston is the cheapest way to make your reed engine work and carb for a novice engine tuner. The vendors should package the piston with the reed and carb or at least include good instructions on how the reed kit should be installed, but don't.

Rick C.
 

Jerdoggiedog

New Member
Jun 3, 2021
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The window piston is necessary to make more power with the reed setup. Buying a widow piston is the cheapest way to make your reed engine work and carb for a novice engine tuner. The vendors should package the piston with the reed and carb or at least include good instructions on how the reed kit should be installed, but don't.

Rick C.
I have a question will the GT90 Ported piston fit in my GT7 motor
 
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indian22

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Dec 31, 2014
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So Many GT this and that in the world, marketing & I don't pay much attention to any of it. I'll share some basic CG piston with you however. There are two common types the high wrist pin version and the low wrist pin version. I'm talking 66cc motors which . . are commonly sold as 80cc...again with the marketing stuff. If you have your piston out look and see if the pin runs across basically half way up the piston or if it is noticeably lower. Then compare to the photo of the window port piston if it's the same wrist pin location as yours your golden, if not plan on machining a port window in your old piston, easy job with basic hand tools and patience. Once you know what you got let us know if you need help with cutting the window. I cut round windows many cut more of a rectangle.

Good luck with this there are quite a few posts dealing with reed valves on the forum.

Rick C.