Engine Trouble one jug gasket instead of two? timing issues?

Discussion in '2-Stroke Engines' started by jatgm1, Aug 6, 2016.

  1. jatgm1

    jatgm1 Member

    i have a 66cc grubee skyhawk engine, the jug crapped out, i swapped it with a new one, i put one gasket because i only had one, but originally it had two.
    at open throttle it seems like it bogs out, however i put a smaller jet, and then it died out when i revved it, or just used it at all after turning off the choke. i replaced the entire fuel hose, got a high flow petcock valve, and new fuel filter. (after having issues not before)
    ive tried jets from #80 to #55 in increments of 5. id rather not have to take the jug off, does it seem possible that a single gasket would make it bog like that? it almost sounds like its 4 stroking, if i apply the throttle fully(or more that 1/3 of the way on flat land) it starts firing weird. (with a size 60 jet)(dellorto sha carb) would that single gasket really cause this kind of problem? also, gas and oil keep winding up in the intake.
    I assume the ports are not lined up right or the timing is off or something. i have two gaskets now, i just dont want to go through the effort if im totally off base. or if i can just get a jaguar cdi and tune it to the way the piston and cylinder is now. (dont really care if theirs oil in the fuel filter to be honest, just want to go at a decent speed.)
     

  2. You're rite I'm sorry I created. Different post /thread my apoilogize
     
  3. butre

    butre Well-Known Member

    messing with the number of gaskets messes with compression and port timing, which messes with jetting. it should be making more power on the low end with only one gasket, as that's how many the engine is supposed to come with. I've run no base gaskets all the way to 3 base gaskets on different motors that needed to make their power at different rpms, it's a cheap and easy way to experiment with port timings. on piston port engines I generally don't use a base gasket at all, just throw a little bit of paint on the mating halves, let it tack up a bit, and put them together. on reed valved engines I'll usually run 2 or maybe even 3
     
    FurryOnTheInside likes this.
  4. jatgm1

    jatgm1 Member

    can you explain what port timing is and how it relates to ignition timing?
     
  5. crassius

    crassius Well-Known Member

    ports are opened/closed as the piston moves past them - with extra gasket, ports sit higher while piston is in same old place - wouldn't hurt to try to get them back where they were - but problem may be a slight diff in cylinder size since standards are loose in these factories
     
  6. jatgm1

    jatgm1 Member

    okay, added another gasket, (took forever to scrape the rest of the original gasket off) and now it does indeed perform better. i had no idea such a small thing could screw an engine up so much.
     
  7. butre

    butre Well-Known Member

    port timing doesn't relate to ignition timing. messing with port timing is the 2 stroke equivalent of messing with the cams
     
  8. jatgm1

    jatgm1 Member

    thank you, actually after i looked up a youtube video i figured it out. these little things are mind blowing to me. out of curiousity, is the grubee skyhawk engine design based on anything made by a reputable company? like an old honda or yamaha engine that they changed a bit?
     
  9. butre

    butre Well-Known Member

    it's a mostly original design, but it draws heavily from an old Latvian moped engine. you could call it a clone, but I'm hesitant on account of the fact that there's zero parts commonality.
     
  10. jatgm1

    jatgm1 Member

    do you happen to know what the name of the company that made the engine and the engine model is? or where info on it could be found?
     
  11. jatgm1

    jatgm1 Member

    http://motorbicycling.com/showthread.php?t=6820
    found something. this has side by side comparisons of the chinese and russian engines, by "riga" if im not mistaken, fantasticly similar, but obviously outdated, looks like it had some kind of manual ignition timing adjustment, and some other odd little features. never thought id be thanking the russians for any tech im running. retrofitting an old russian engine with modern parts could be quite interesting, everything would have to be custom machined though. i wonder how it would handle.
     
  12. FurryOnTheInside

    FurryOnTheInside Active Member

    I would have thought you would be more interested in the frames.
    Latvians BTW, are not Russians, lol. ;)
    Riga is the capital of Latvia. I guess after WWII the Soviets, like many of the allies needed to make super cheap transport for as many people as possible, with as little metal as possible and I think they got a great idea in the motorised bicycles, lightweight moped, whatever you'd call them.
    Google images of Riga motor museum, lots of really great very cool looking classic light motor bikes and motor bicycles with frames that were made specifically for the purpose of getting as much function as possible out of very little vehicle. An ethos I think is still at the centre of MB :)

    Oh and this:
     
    Last edited: Aug 9, 2016
  13. jatgm1

    jatgm1 Member

    your right about that, when my step dad saw my gas bicycle he said it reminded him of his old moped. quite nostalgic. especially the two stroke ones.
     
  14. jatgm1

    jatgm1 Member

    plus, apparently the d-8 and d-8e engines could use a normal bicycle frame. idk about the other models.
     
  15. Steve Best

    Steve Best Active Member

    No sealer is needed on these engine if you use a gasket. Makes part swapping easy.
    The beauty of these engines IS that small and easy changes make great power, if you know what you are doing.
    Port timing, squish, loop scavenging, exhaust tuning, and most of all Gordon Jennings Two-Stroke Tuner's Guide are your secrets to success.

    Steve
     
  16. jatgm1

    jatgm1 Member

    you know, thats what i figured, but while i was taking apart the cylinder, i realized that the head was leaking a little. thats why i sealed it and tightened it well.
     
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