New engine need info

Discussion in '2-Stroke Engines' started by SRPM, Apr 18, 2016.

  1. SRPM

    SRPM Member

    Just got the gt80 from gasbike.net and I'm having trouble finding any info on it.
    It has a Super Charge CDI for 48cc 66cc 80cc - High Performance
    - A Ported cylinder
    - High Performance Reed Valve
    - Balanced Crank
    - High Performance CNC Head
    - Keihin Carburetor clone
    The carb it the biggest mystery to me I'll include a pic. It's got three nipples for gas lines, obviously one is gas inlet one is the drain but what is the third one for? Fuel bowl vent?
    Also fired up for the first time and it would not rev up very high; but first time running, 38F out too. Smell fishy to anyone?
     

    Attached Files:

    Last edited: Apr 18, 2016

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  2. Comandoriv

    Comandoriv New Member

    Hi, being that it is a clone I cannot speak with 100% certainty.

    One of my motorcycles uses keihin carbs, so maybe this one may be the same. Yes, there is a gas inlet and a drain. The third one is something like a fuel tank vent - at least on my motorcycle. It attaches to a inlet on the gas tank and uses vacumm to suck gas through a seperate outlet.

    It could also be a possibility that this is an overflow tube. When you run your engine, cover the tube with your finger and see if it sucks it like a vacuum. Describe what happens also.

    Maybe someone familiar with the "clone" version can chime in.
     
  3. SRPM

    SRPM Member

    Nothing happens when I put my finger on it no vacuum or anything. I have just heard of some carbs taking a crankcase pulse so maybe it's for that? Also I've looked around a lot for info and the only thing I can figure out is that it might be a fuel bowl vent so if you leave your fuel on and the needle stop thing that connects to the float is worn out it will dripple out there instead of flooding the engine.
    Also I'm very curious about this extra jet it has and there is hole leading to the screw next to obviously this screw controls it or something (see pic) I've fiddled with it with the engine running and doesn't seem to do much. I'm thinking it's a idle jet...?or WOT jet..?

    There is a pic of what the carb says on it. Maybe you guy might be able to do more good with that info than I can.
     

    Attached Files:

    Last edited: Apr 19, 2016
  4. jaguar

    jaguar Well-Known Member

    It's got a high compression head. that is limiting to high revs due to pumping losses. also causes plating loss from the cylinder walls.
    get a pressure gauge that screws into the spark plug hole and see what the cranking pressure is. Above 140psi is bad. You can use a dremel to enlarge the combustion bowl for more head area which lowers the compression ratio.
    Also the Arrow reed valve increases the crank space which is the opposite of what you want to do for a high reving engine. Less crank space is what is needed. The Rock Solid Engines reed is better in that respect.
    I'm not familiar with that CDI. If you bought my CDI then you could rest assured that it's adjustability would enable you to have the best timing for high revs.
    Last but not least, it is a horrible idea to keep the stock piston if you want a high reving engine. The rings have too much end gap and the rings are too thick. Rings for high reving engines are thinner. Yours causes too much drag. On my engines I always used motorcycle piston/rings.

    It's just a plain ole scam, one of these engines like yours. everything's wrong. they sold you "bling", not true functionality.
     
  5. SRPM

    SRPM Member

    Revs fine now before it was like the choke was 3/4 of the way on but wasnt. I found the spark plug boot wasn't able to sit all the way down on the spark plug. Seems to run fine now doesn't have much in the top end right now but first ride and second time running not going to push it too hard yet. Ill check comprsion and let you know. It's mainly the carburetor that is a mystery to me now any ideas on that?
     
  6. Comandoriv

    Comandoriv New Member

    With no vacuum, then it must be an overflow tube. As you stated, fuel will trickle out of that tube instead of flooding the engine. The screw has to be an idle adjuster.

    Keihin carbs have different kinds of jets - these can be,

    Air jet, leak jet, main jet, needle jet, slow jet, and starter jet.

    Being that this is a clone, I cannot say what the jet is, but some research on these jets may help you out
     
  7. SRPM

    SRPM Member

    Thanks it looks like it is an idle jet it's just looks super different. So this carb has an idle jet, needle jet and main jet. What would happen if your where to put a crankcase pulse into the carb, is it even do-able not that I want to just wondering
     
  8. David Bogle

    David Bogle Member

    I'm so happy that I settled for their GT6! Good luck.
     
  9. 45u

    45u Active Member

    I have been making my living working on motorcycles for over 45 years. The 3 places you have for the hoses are bowl drain bottom on the side you have a vent with a hose to help keep dirt out and the 3rd is for the gas line from the tank. As far as plating on the cylinders I plane on having several nickle sealed that holds up much better then the plating on the stock cylinders but is not cheap but will out last stock may times over.
     
  10. SRPM

    SRPM Member

    Thanks? Are these type of carbs new to the market or what? I have found out it has an idle jet the one in the pic, a slow jet? And the main jet of course. I've spent hours looking for jets and info, but can't find anything still.
     
  11. 45u

    45u Active Member

    I do not know anything about these clones I know Keihin but have worked on many genuine Keihin s.
     
  12. Ron Smith

    Ron Smith New Member

    I have the Keihin clone carb and reed valve kit. I got the GT7 Pro Racing engine kit. Didn't read question and answer section before I ordered it. First thing mentioned by the seller is you need to change jets in carb. No info on Keihin clone carb anywhere. It runs nice and smooth idling but has little low in torque. Thinking about buying a different hi performance carb. Going to do some porting work on intake and exhaust first.
     
  13. jaguar

    jaguar Well-Known Member

  14. gary55

    gary55 Well-Known Member

    Google tuning keihin carbs.. The gt 80's form Kings/Gasbike come with two different heads. The one on the left with the fins angling inward towards the plug is a 6cc head. That means it has the same compression as a stock slant plug head. The one on the right with the straight fins is a 8cc head and has less compression than a stock slant plug head and requires decking the cyl. to have the same comp as a stock slant plug head. They do not have high compression heads on the gt80's.
     
  15. Ron Smith

    Ron Smith New Member

    Looks very similar. Air fuel mixture and idle screw are in same place. Float bowl looks different. Has a nipple with a hose at the bottom of float bowl pointing straight down and a brass screw right beside it, same side air fuel mixture and idle screw. Thought I had read somewhere that it is a 16mm Keihin clone. It is very similar to the GT80 add on carb and reed valve kit only screws are brass and choke lever is brass colored. I'll send a picture. Ordered a GT80 jet kit to experiment with. GT7 Pro Racing engine kit is supposed to be 4.5 horse. Maybe after re-jetting carb. Idles nice and smooth and revs up quick but hop on it and ride it and it's a pooch.
     
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