Gt80 junk?

Discussion in '2-Stroke Engines' started by 1max, Jul 19, 2016.

  1. 1max

    1max Member

    Just got gt80 a month ago nothing but problems right now I just replaced cylinder head and piston got rid of low compression head it had a ported cylinder I got a stock one kept reed and keihin carb . My o original head and piston are fried . This one is starting to do the same . Now the carb is leaking . The engine is smoking hot after about 2mins. Of running. Is a non ported cylinder an issue ? I'm t replacing the carb with a stock carb will that help ? It's getting way to much air.

  2. Steve Best

    Steve Best Well-Known Member

    Oh boy...
    So, I have run these 66cc and 48cc motors for hundreds of kms with no great problems since last summer.
    I started with a well worn stock 66cc motor I bought used. Repaired all the bad things as I found them.
    This is a mechanical maintenance principle know as "return to as designed state".
    It had many things wrong, but one by one, I repaired them and got a reliable bicycle.
    I took gradually longer trips with it, repairing anything wrong in the inspections when I returned.
    By then I had learned enough to make some mods, one by one, to see if they worked or not.

    So here is my seasoned advice to you. Return it to stock, as best you can. Repair what is wrong.
    Learn mechanical skills, using the right tools, torquing bolts properly, fitting gaskets, etc.
    Learn to read the plug. Look up "plug chop" so you can learn to jet.

  3. jaguar

    jaguar Well-Known Member

    ruining pistons can be due to 4 things:
    1. not using a good foam air filter that is well oiled
    2. having an air leak between carb and cylinder or at the crank seals
    3. having a bad seal at the head/cylinder junction. you need to plane the head surface flat using sandpaper on glass and make your own fiber gasket
    4. not using the correct oil/gas ratio. for standard mineral oil mix at 20:1, for semi-synthetic mix at 25:1, for full synthetic mix at 30:1
    Steve Best likes this.
  4. I've done everything you said yes but I have my own feul mixture un 32 to 1 93 octane. I use Liquid copper Gasket maker on the intake manifold for carburetor. As well as the exhaust
  5. Thanks Steve good advice for my archives
  6. Steve Best

    Steve Best Well-Known Member

    I think Jag got it nailed pretty good with more practical things to do.
  7. 1max

    1max Member

    Thanks guys I'll try out some of these things jaguar and thank you Steve I am going back to basics on this I do believe it was probably an air leak at my keihin carburetor where the fuel went in but it could be something else so I'm going to go over to the things the Jaguar put in and see if I can resolve this issue I'm going back to just a speed car and see how that works
  8. jaguar

    jaguar Well-Known Member

    also using a soft material between the cases and the frame allows the engine to vibrate too much which can froth the gasoline in the float bowl which can cause the fuel/air mixture to be lean and cause engine over-heating
  9. I have been considering putting on am expansion cahmber,from BikeBerry.
    NO MUFFLER NO SILENCER. My only concerned is,,,,,,,,,no silencer/Muffler, now this because it's high performance. O d
  10. Has anyone used thes do the rims or tires on the path that you're writing on the ground to making The roads slick as it spits out its exhaust onto the blacktop or concrete whatever you may be traveling on that is my concern where does the exhaust go to which direction does it spit out? I don't want to be having to clean my room at all the time again. Or clean the bottom of my frame in the Kranks and messing up my gym shoes. Because if I ask Mike Berry we order it from They are going to say( OH NO IT'LL BE JUST FINE)
    Then I will be stuck cleaning my cranks and idles sprockets and shoes. Being all fucked up again I just solved that problem and don't want to go back to it.

    Thank you sincerely
  11. Steve Best

    Steve Best Well-Known Member

    I do Bob, switch to a good quality synthetic and use less than 32:1 and you will not have oil spit out the pipe.
    32:1 is about the border line, I still get a tiny bit of oil. None at 40:1.

    I tried a similar pipe from

    I would not call it a "tuned pipe" or "expansion chamber" in the true sense of the name.
    Its power band was at mid to low rpm (better than stock) and it was actually noisier than stock.

  12. Thanks a bunch Steve. I was thinking of ordering that exact pipe? But, I got nervous when I seen that "BIG NUT" rite where the where the engine is. I guess it's no problem though.
    I was also gonna GET a Huffydavidson CDI/ignition set Up. But you can't take the plug wire out and replace it with an automotive plug wire so I don't need to "TAKE MY NIPPLES OFF!" I LIKE NIPPLES!!!
    ;-) that was the only deal breaker and jag's is just a bit too much $$$$$$ any suggestions? I'm also gonna port intake and output sooner or later hopefully sooner than later.
  13. I wanna have enough speed and confidence so when I go visit my daughter 20. Miles give or take, I can do it safely and be able to keep up when I need to I'm living in the burbs caring for handicaped family member rite now in the western subrubs. She's rite on the edge of the CITY. All my bearings are new I just need new retailers Wichita I got a line on and its all new accept the frame. AND THAT DIAMOND BACK IS SOLID!!!
  14. Your rite Jag, thanks for the good info. I will and have done all those things. However I did put a single inertube wrap around the seatpost when I mounted my Wichita is all but gone accept a little residue on the inside of the frame tube after taking IT out, I fihured WTH? Its not gonna hurt its such a minute amount of rubber. More like a stain. So thanks. A bunch.
  15. Steve Best

    Steve Best Well-Known Member

    Bob, I did some stock pipe testing this afternoon. This is a mostly copy and paste from another post:

    I have a recently abandoned runway in my backyard for testing.
    Level but strong winds, saw speeds of as low as 40 kph against the wind and then as high as 58 with it.
    48cc (stock cylinder, converted back to single speed 56T) and 66cc (44t stock cylinder), both with modded heads.
    48cc is in a lightweight 10spd frame (with shifter frame still in place), 66cc in a heavy MTB and big tires.

    Upwind/downwind, 48cc/66cc. speeds in Kph
    stock pipe= 44/52, 44/57,
    portmatched pipe= 46/52, 46/58
    Straight pipe= 40/42, 42/44
    Stock portmatched pipe, baffle removed= 42/48, 42/50

  16. thank you for sharing, i did some plug testing & short list ,,,E3-22 3rd/ NGK B7HS 2ND/ BEST PLUG IN 1ST PLACE 100 degrees 90% plus humidity .NGK IRIDIUM BPR7HIX 5944. tires were sticking to the pavement.

    thanks again

  17. Fabian

    Fabian Well-Known Member

    These engines are surprisingly reliable so long as 25:1 oil/fuel ratio is used, and there are no air leaks, and carburettor jetting is optimised, and they are not over revved.
    It is much better to add aftermarket accessories that boost torque; enabling you to use lower rpm to make the same horsepower. The engine will be in a lower state of stress, and provide significantly greater reliability, with reduced vibration.

    Excessively high compression cylinder heads, as well as not having large cooling surface area tend to cause detonation issues, which damages connecting rod bearings.

    My setup achieves exactly that. The top end is good for 2,500 miles, and the bottom end is good for 6,000 miles to "near failure" point.

  18. Frankfort MB's

    Frankfort MB's Well-Known Member

    Id think that low end torque would be harder on chains and the clutch.... It would also be harder to keep cool
  19. Not to sound harsh fabi. But its not a Lexus man. I'm not checking 2500 miles and stuff. Please slow down a.bit
  20. I'm sorry Fabian I thought. You were talking to me PLEASE DISREGARD.