Engine Trouble need advice on 66cc bog at high rpms

Discussion in '2-Stroke Engines' started by jonathan62019, Jul 11, 2015.

  1. jonathan62019

    jonathan62019 New Member

    my first post. i might be all over the place sorry in advanced.. ok so i got this bike used. put it all back together, started up great runs great at idle and even WOT until it gets to a certain RPM then it just bogs out, even if i give just a little gas. i thought i was running lean, so i checked for air leaks. found i was leaking air through the intake manifold.(would only run when choked) so fixed that air leak. no need to choke it now to run. idles smooth. has good power until that rpm gets a little high, its not starting at a real high RPM either i dont have a tach but id say 3/4 of what it should be doing. i moved the clip up a few notches each time it didnt fix the problem.. just messed with the lower end of the rpms. cleaned carb and jet all that good stuff. ....

    so this is where i am now. thanks for still reading if you are. this is my real question and situation,... i was running around right under the RPM where is starts to bog when all of a sudden i have a lot of power and this thing starts to move. hit about 35 mph i was moving and no BOG! i went to turn down my street and slowed down and it was running really bad now, i looked down and my intake manifold was broken... moved the choke up a little bit to keep it running and babied it home. SO any suggestions? am i starving for air at those high RPMS? or what? i dont know if the intake manifold broke before or during the burst of awesome power haha. the new intake manifold is in the mail so i cant ride it yet, any advice or feedback would be great. thanks for reading :)
     

  2. crassius

    crassius Well-Known Member

    could be you need a lower float level or smaller main jet
     
  3. jonathan62019

    jonathan62019 New Member

    Yeah I was thinking of just buying a new carb when i ordered the 40mm intake manifold. They are so cheap. I'm shocked how cool these engines run. I figured I couldn't touch the head after an hour ride. But I can put my hand on it for 4 seconds before I go OUCH!.
     
  4. KCvale

    KCvale Motorized Bicycle Vendor

    Put in an NGK 5944 (BPR7HIX) Iridium plug and a better air cleaner on.
     
  5. jonathan62019

    jonathan62019 New Member

    i had a NGK 5944 in it when i got it. i switched in a bosch platinum 2 and it didnt change anything. when i get the manifold in i will most def check into the air cleaner. it looked pretty bad. most likely going to just fab up a better set up. from what i have been reading. i think i might have been 4 stroking at the point of the bog down. so now i know where to start looking for answers. ( new to 2 stroke engines.)
     
  6. jonathan62019

    jonathan62019 New Member

    new manifold is out for delivery from local post office.. wow bikeberry outlet on ebay has some super fast delivery. i just ordered it Saturday. pretty excited.
     
  7. jonathan62019

    jonathan62019 New Member

    well i am an idiot i ordered a 40mm intake manifold.. sigh.. too wide for my cylinder head.
     
  8. Waxxumus

    Waxxumus Member

    BPR 6 HIX

    If you live anywhere where its hotter than 80 degrees and less than 1000 ft above sea level.

    The 7 Was running too rich for me. Then it looks like its running to lean. Idkwtf.

    I Have my fuel mix at roughly 32:1
     
  9. jonathan62019

    jonathan62019 New Member

    Lol yeah they seem to do what they want when they want
     
  10. KCvale

    KCvale Motorized Bicycle Vendor

    The higher the number, the cooler your engine runs.
    Too cold and you foul plugs.
    Too hot and well, anything can happen.

    The coldest (highest number) you can run without fouling is best but your carb plays a big part in this too.
     
  11. Waxxumus

    Waxxumus Member

    Wellll, Im jetted with a rt dax carb at a #70. i should be theoretically at a 68. so its running a tad rich. but when i put 32:1 in it, my already fowled plug comes out with a white tinge on it, as if it is running too lean. Still need to try and put that third hole in for better fuel atomization. i d k. its been hard to tune perfectly. and right after I had the nt carb running perfectly choco brown XD
     
  12. KCvale

    KCvale Motorized Bicycle Vendor

    I'm not familiar with that carb but you'll figure it out ;-}
     
  13. jonathan62019

    jonathan62019 New Member

    well i stripped my threads out lol i dont know how i was barely! twisting it with a tiny little wrench. going to tap it out today. i did run it with no air filter on and at high rpms i could feel gas coming out the back of the carb.. Do not know if that is usual or not. after i tap the hole and get it back on. ill mess with the float and see if that fixes. it.
     
  14. KCvale

    KCvale Motorized Bicycle Vendor

    It can be normal if you have an expansion chamber exhaust as it is forcing unburnt fuel against the incoming fuel mix.
    Otherwise you have carb float problem would be my guess.

    An intake reed between the carb and cylinder can help with that but they have their disadvantages too, a restriction of the incoming fuel/air flow.

    In short no, you should never have fuel spitting out anywhere on any engine build bud.
     
  15. crassius

    crassius Well-Known Member

    on an unmodified standard motor, when the piston comes down to compress the charge in bottom end, you may get a bit of back pressure out the carb just before piston closes intake port, also, when piston starts back up, there may be a bit of back pressure when the intake port first opens - if your air filter is on the carb, this shouldn't even be enough to see a drip there
     
  16. Waxxumus

    Waxxumus Member

    So do intake leaks, and throttle control and sparkplug gap.

    Recently I put my gap from .024 to .028 and the engine responded better.

    Said what the hell and gapped it to .031

    Now she purrs down the street without any sign of 4 stroking, aside from the normal "Im at my max rpm im not going to do this forever" 4 stroking.
     
  17. Waxxumus

    Waxxumus Member

    Spray some carb cleaner or starter fluid on the intake port while the engine is running. You have a leak? Carb cleaner instantly choked mine to death. So I fastened the bolts down tighter, and the engine started running richer. I thought i couldnt go any leaner on these jets. But we might be going down to a .67~.68 soon
     
  18. KCvale

    KCvale Motorized Bicycle Vendor

    Hehehe ;-}
    Kind of like a long tailed cat in room full of rocking chairs ;-}
     
Loading...