Engine Trouble Engine bogging at low rpm then possibly runs lean at high rpm

Discussion in '2-Stroke Engines' started by P3_Takuto, Jun 23, 2016.

  1. P3_Takuto

    P3_Takuto New Member

    Alrighty where do I begin.
    I finally got my bike out of storage for the winter a month ago (it has a Grubee Skyhawk GT5A installed) after giving it the once-over twice I got it running nicely, no problems for the first couple of tanks running at a 25:1 ratio.
    After letting it sit for a couple days i start it up, the idle was acting weird so I tried adjusting it, giving the throttle a blip it responded quickly and went back to idle, just as it reached idle the engine seemed to rev back at me, staying at a higher rpm then the idle was set to for a while and then going back down. While riding it would bog a bit at high rpm's.
    I decided to check the carburetor thinking it was just running a little rich, then i found that the fuel was leaking out of the lower vent hose of the carb (I have a CNS gen one which had been running flawlessly up till now) checking the throttle slide needle and restricting it to the second most upper clip, and taking it apart, tuning the fuel pin to restrict the fuel level inside the carburetor a little, hoping to stop the leak. After a quick test I found I was still a little rich but it was running better. So another couple days pass and I decide to go out for a ride and seeing the idle was okay I started to get on the throttle, as I slowly increased the throttle It started to bog harder and harder to the point it couldn't fire anymore if I applied more than 1/3rd throttle, only being able to apply 1/6th throttle to slowly accelerate without bogging. When the engine finally reached a higher rpm the power came back quick, but it was constantly 2-stroking rarely ever 4-stroking, which I didn't think was normal, as if it were running a little too lean, i performed several plug chop tests at the low rpm bogging point and the high rpm, the spark plug was wet in the low rpm and became more grey at the high rpm as well as it was noticeably hotter. So I'm stumped on what's going on, running rich and lean at the same time just doesn't make sense to me, I'm going to try to revert the carb tuning to how it was before to correct the leaning out but I really have no clue why it decided to act like this all of a sudden. What do you guys think? If you have any suggestions for me please say so.

  2. skyash

    skyash Active Member

    Cdi an up an down spark ? Air leak? might have to look past the carby try a bigger gap or smaller? Idk
  3. gary55

    gary55 Well-Known Member

    I would be looking in the direction of what could have changed while sitting over the winter. The fuel system is where I would start. With new gas and a new in line filter I would disassemble carb, clean everything with carb cleaner, especially the fuel intake, float needle, and main jet. If I remember right the early CNS carbs had a secondary idle circuit with it's own air fuel adjustment needle. Probably need to get that cleaned out too. Sounds like air fuel issues especially with the rev up then dye back down, like when you turn your fuel off with the engine running as the bowl empties the engine revs up from sucking air into the jet then calms back down if you turn the fuel back on real quick.