Engine Trouble GT90 Conversion Kit Won't Start

Phabbits

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Aug 7, 2017
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Hey all,
I am quite new to motorbiking scene, so my motor knowledge currently is quite limited.
I have been having trouble trying to get my GT90 conversion kit from GasBike.net, sketchy I know, to start. I have tightened all the bolts, ensured that theres is a spark, checked and rechecked the the head cylinder, probably ruining the gasket, and confirmed that there is fuel, from it dripping out of the muffler, and leaking out of the bottom of the motor :( Before I pull apart the motor again and redo the gaskets I would like to get your guys opinion on what might else be happening. When trying to start I can feel the compression, since I have the SickBikeParts gear kit and have to pedal to start it, and sometimes it will backfire. I have no idea if the fuel mixture is to rich or lean, because I have not been able to find any documentation on my new carburetor, and I am quite unsure of how it works. One wierd thing that I noticed was that with fuel petcock off, it would still backfire even more often, maybe something to do with it being a ported piston? Anyway I really appreciate and help and knowledge you guys can give. I am currently at college right now, so I wont be able to try anything for another two weeks, but I have a lot of pictures that I can upload that maybe will help.
Cheers,
Phabbits
 

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crassius

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I'd first check that rotor and stator of the mag are both on correctly, and then try a different CDI unit
 

Phabbits

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Thanks for the reply, I will be sure to check that first. Also I did replace my spark plug about halfway through the troubleshooting process, and it still looked perfectly clean when I checked it at the end. Is this normal if the bike never actually started?
 

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crassius

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can't see end of plug in pic, but if it is dry, then you have a fuel problem rather than ignition - unlikely if fuel is dripping from muffler
 

Phabbits

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Very true. Could the problem also be from a air leak, and if so would my using of gasket sealer on the bottom temporarily fix it?

Thanks
 

crassius

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you need to pay more attention to what you see - fuel dripping could mean motor is full of fuel - spark plug dry could be no fuel to cylinder - case leak should show low compression

each of these can cause no start condition, but fixes for them are in some ways opposite
 

Tyler6357

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That looks like a very nice reed valve and carb. If it's backfiring it could mean a carb or timing problem but I'm really not sure what kind of carb that is One thing you should do is rotate your head 90 degrees so that the fins are pointing front to back. These little engines are air cooled and the wind should flow between the fins.
 

Phabbits

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Thanks for the advice, I will definitely change that when I get home.

One thing that I did find with my mostly unsuccessful research was that when reassembling the motor it was possible that a key or something slipped, which would mess with the timing.
Is there any way to ensure that the timing is correct?

I attached a little better picture of the carb also.
 

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Street Ryderz

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One thing I noticed on the gt90 is that it has a windowed piston and trench port that are not needed for a case reed.You may want to try a reg (non windowed) piston also make sure that the piston crown doesn't come down below the intake at all.
 

crassius

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with piston at top, check that rotor of mag has its key slot at about 1 o'clock and the flats in the rotor are about level with the ground
 
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