42 miles of He.....

Discussion in 'Motorized Bicycle General Discussion' started by junked, Jun 1, 2010.

  1. junked

    junked New Member

    Joined:
    May 2, 2010
    Messages:
    65
    Likes Received:
    0
    I put together a Grubee Skyhawk about a month ago on my old Columbia mountain bike. I did all the basic mods, cut piston skirt, intake and exhaust manifolds were opened up etc, along with a 41 chain as the kit came with the worthless bicycle chain.

    Up until yesterday, I just went on 1-5 mile rides trying to determine whether or not it was dependable and what tools and parts I should carry. Got 38 mph out of it once. On these short rides the only problem I had was four stroking almost all the time except when there was sufficient drag on the engine, inclines, hills. I adjusted and shimmed the needle so many times I could do it blind folded. Never did get it dialed in. It was either too rich, plenty of torque for hills but 4 stroked on the flats, or too lean better on flats with less 4 stroking but no torque for hills. Well, chose a happy medium and decided yesterday to go on a long ride, 42 miles round trip.

    It really was no fun. The further I went the more i began to hate it. This engine sounds like it gonna blow at any moment. I averaged about 15 mph on this trip due to the 4 stroking and fear that it was going to throw the rod. Downhill is agony trying to keep fuel flow so it doesn't lean out too much and a reasonable speed so it doesn't blow up. This engine makes some very scary noises for a 2 stroke and it is unsettling.

    The bottom line for me is this, yes the 4 stroking can be dealt with, and the engine is what it is, a cheap Chinese engine put together with kitchen cabinet hardware, and measured with a yard stick. To get my moneys worth I am going to set the bike up on a home made (Chinese like dyno) and see what it takes to blow it up. I will post a video as long as the shrapnel doesn't hit the camera. I am done with this engine. I am looking at the Harbor Freight 2-1/2 HP 4 stroke. Film at 11:00.
     
  2. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    1
    Well, a grubby skyhog....all the hype and fancy stickers didn't make it a better engine did it?

    Here's how much it will take, run it without the chain with the throttle wide open....it will run for about a half hour before something gives, and then you'll wish you just sorted it out instead of throwing away a fist full of dollars.
     
  3. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    1
    Don't learn to hate it, learn about it.
     
  4. junked

    junked New Member

    Joined:
    May 2, 2010
    Messages:
    65
    Likes Received:
    0
    The four stroking, I have shimmed to half way between notches and it still does it.
     
  5. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    1
    Some four stroking especially when not under load is normal. These are ancient tech cross ported two strokes, it's sorta the way they are.

    Have you tried re-drilling to a smaller jet size, or changing the float level?
     
  6. junked

    junked New Member

    Joined:
    May 2, 2010
    Messages:
    65
    Likes Received:
    0
    No, I haven't. I suppose I should at least start with the float level. I don't have the right size bit for re drilling.
     
  7. dag_29307

    dag_29307 New Member

    Joined:
    Jul 1, 2009
    Messages:
    296
    Likes Received:
    0
    Take a deep breath and count to ten. Now start with the basics. You said it yourself you did all the mods yourself, Think about what you have done to this little engine. Give it some TLC and it will all work out. Four stroking is normal at some point in your ride. Check out your chain tension and also look closely at your exhaust gasket too. these are the problems I had with mine when it was doing the same thing. found the exhaust gasket had a hole and tore open on bottom. made it sound as though the motor was gonna run off the bike. If you are having problems just ask us we will help out as much as we can. Also what is your fuel mix ratio? that could be a factor in the four stroking too.
     
  8. drhofferber

    drhofferber New Member

    Joined:
    Jun 22, 2008
    Messages:
    307
    Likes Received:
    0
    which carb do you have on it???i had one with those symtems and went to the old carb i bought from dax and things fell in place...Dennis
     
  9. BarelyAWake

    BarelyAWake New Member

    Joined:
    Jul 21, 2009
    Messages:
    7,209
    Likes Received:
    4
    42 miles?

    It's not even broken in yet... *shrug*
     
  10. junked

    junked New Member

    Joined:
    May 2, 2010
    Messages:
    65
    Likes Received:
    0
    It was broken in prior to yesterday. I have the carb with the red filter housing if that means anything. The exhaust is good, no leaks, and I am running 32-1 mixture.
     
  11. drhofferber

    drhofferber New Member

    Joined:
    Jun 22, 2008
    Messages:
    307
    Likes Received:
    0
    had 2 of them....never did get them working right....like i said the old style carb...dax...14.95....or keep tring to fix the carb you have...by the way how many miles do you have on your bike...???sorry just read the other post,,,,barely awake is right...its not broken in yet...
     
    #11 drhofferber, Jun 1, 2010
    Last edited: Jun 1, 2010
  12. junked

    junked New Member

    Joined:
    May 2, 2010
    Messages:
    65
    Likes Received:
    0
    okay, okay, I will give this engine a reprieve. I will get to the bottom of the 4 stroking and share my efforts with those that are interested.
     
  13. drhofferber

    drhofferber New Member

    Joined:
    Jun 22, 2008
    Messages:
    307
    Likes Received:
    0
    when breaking in...spike the trottle on a continuos basis....some of best advise i got was from spooky tooth mechanics...after riding around the block 2 or 3 times. i would let it idle 10 minutes...slow but it has worked and the other way, driving them hard blew 3 of my engines up...Dennis
     
  14. omegaunderground

    omegaunderground New Member

    Joined:
    Sep 16, 2009
    Messages:
    98
    Likes Received:
    0
    Junked, my skyhawk was doing similar to yours at the beginning of the year (around its 500th mile) I was stumped on how to fix it as well. I rode across town probably about 10 miles and on my way home the motor would not rev fully, and at every stop light it 4 stroked like crazy. My top speed went from 32MPH to 18MPH, and it began leaking oil from the magneto case. I went home checked my seals on the head, replaced the bottom jug gasket and head gasket, exhaust and intake gasket. Cleaned the carb, and even checked all of my wiring. After nearly a full day of work I test rode it, same thing it ran horribly barely pulled me. I went back in the shop and thought it could be clogged catalytic converter. I only thought of this because my impala the same week had a bad catalytic converter, it only drove 20MPH tops for 3 days before I took it to the shop. Anyways I drilled a hole in the tip of the muffler to bypass the catalytic converter, and went for a test ride. It was a bit louder but it ran like a brand new engine I was very surprised. Just make sure you have or know somebody that has a welder you can plug the hole up with if this does not fix your problem. Good luck!
     
  15. camlifter

    camlifter Active Member

    Joined:
    May 4, 2009
    Messages:
    1,034
    Likes Received:
    0
    i've had 4 of the skyjunk kits, never had a problem with the carb but they all have made horrible rattling noise's. worst kit on the market imho. in comparison the jet kits seem like a BMW
     
  16. oldtimer54

    oldtimer54 Member

    Joined:
    May 15, 2010
    Messages:
    539
    Likes Received:
    0
    Iam having ALL the same problems with my skyhawk. I paid extra for it as I was told it was the best motor? Seems like the only motor having all these problems. I cant trash mine I need to fix it. I cant afford a new one and I need to get to town with it. I need to buy food and check mail. This one is brand new sooo how do you fix a brand new motor? I dont understand why I should have to fix a NEW motor? If you get it sorted out youll be helping an ever growing number of members with the great skyrock motor!
     
    #16 oldtimer54, Jun 1, 2010
    Last edited: Jun 1, 2010
  17. charles.paskell

    charles.paskell New Member

    Joined:
    Feb 25, 2010
    Messages:
    201
    Likes Received:
    0
    hey if you do decide to blow it up can you send me whats leftover cause I sure could use some of those screws that are on it and I need a bucking bar also.
    Ps I have a Grubee skyhawk too
     
    #17 charles.paskell, Jun 1, 2010
    Last edited: Jun 1, 2010
  18. bairdco

    bairdco a guy who makes cool bikes

    Joined:
    Aug 18, 2009
    Messages:
    6,333
    Likes Received:
    19
    everytime someone has a problem with their kit, everyone else jumps in with their problems, and then they decide that it's the kit, and not the installer.

    now, i'm not saying it isn't the kit, but i've seen these exact posts no matter what engine they're talking about.

    i've also seen a lot of people who have the same kit and have nothing but praise for it.

    as for the original poster's problems, sounds like all the "mods" you've done to your motor are the problem. it's really easy to get carried away, especially if you don't know what you're doing, or haven't done it before.

    there's is such a thing as "too much" when it comes to porting, where a few millimeters too far could give some bad results, or it could be that you made your motor need more that the carb allows.

    once you get into "performance" mods, one step at a time is the way to go. if you did everything you said at one time, for the first time, without knowing what works and what doesn't, then you'll have no idea what's causing things to go wrong.

    it could also be a simple as bad fuel, wrong float level, airleak, crappy plug and/or wire, loose connections at the terminals...

    finally, even if it's a bad motor right from the start, since you modded it out, you'll never know, and your warranty is void.

    next time, assuming you don't give up on these motors, i suggest running it bone stock for a month till it's broken in, then start tricking it out, one step at a time.
     
  19. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    1
    Best advice yet.
     
  20. junked

    junked New Member

    Joined:
    May 2, 2010
    Messages:
    65
    Likes Received:
    0
    Here is some of the work I did. The engine was broken in when this was done. It ran much better after this work. I think I am expecting to much in terms of engine noise. I wear a half helmet, and it scoops the sounds from the engine in ways that allow you to hear things in a more amplified way. If I turn my head the sound changes and is more tolerable.

    I will keep working on it.
     

    Attached Files:

Share This Page