Gt90 Case Reed Keihin Clone Carb Info

Guy Marquette

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Local time
10:42 AM
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Aug 1, 2020
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I’m having a lot of trouble getting this motor to idle. The carb in the gt90 case reed kit from gasbike.net has no markings, I have no clue how to source jets, (the “gt80” jet kit they sell is not the correct jet type for this carb).

I think the pilot jet is in range because I can tune the idle/low throttle from pretty lean to pretty rich with the air screw. But no matter where I go, from lean to rich and in between, the idle kind of wanders from a high speed to a lower speed, and if that lower speed is enough to keep it running, the higher speed is screaming high.
The rest of the range runs fairly well.
There’s a vacuum port and hose from the engine side of carb throat...no clue what that’s supposed to do. It’s just open into the vacuum of the carb so I’ve plugged it.

I’m stumped, and out of money and generally ready to just sell this thing off. I’ve had dozens of motorcycles and cars and power equipment, I maintained a fleet of 30ish chainsaws, I ran lots of 2 stroke backcountry firefighting water pumps over many years. I can’t remember any engine that was so hard to get correctly running than this turd. My other bone-stock china-bike motor runs great with its tiny NT carb...but isn’t powerful enough to pull my fat ass up our steep hills without going with a 54 tooth rear sprocket, which makes riding anything but a steep hill ridiculous. I need the power of the gt90 but I’m getting to the point where I’m done trying to figure out how to make it idle. Trying to pedal start it at intersections while car people stare at me like I’m an idiot.

Any input? Is this a normal feature of this “gt90” heavily ported setup: that it won’t hold an idle...so you have to sit there revving it so it doesn’t die at an intersection?

Anybody want to buy this motor? I’ve got about $200 in it, and I’m pretty much ready to just go with a 4 stroke that isn’t so finicky.
 

Ooze

New Member
Local time
10:42 AM
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Mar 24, 2022
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You have probably already pondered this route but I put a “jack shaft” on mine so I can use the 6 rear gears to change speed like a transmission. About equivalent to the 200$motor.
I have been thinking about going to the reed for more power/speed. Your experience may have slowed my desire there :). Good luck
 
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