Starfire GT50 engine fires up but stalls prematurely

Discussion in '2-Stroke Engines' started by Hajuu, Jan 9, 2010.

  1. Hajuu

    Hajuu Member

    Hey guys!

    I used to have an account here a few months ago and I was pretty sure this was the nick name I used, but I had just bought a Starfire GT50 and was having great problems with the clutch.

    Now it's all done! Looking very tidy if I do say so myself, however just now when I tried to fire it up it stalled.. I rode down a very small incline, pedalling as fast as I could ( I havent fitted new bike gears yet), let the clutch out gently, and it fired up, I even felt it give a tiny little kick at the back wheel. But then after about 2 meters or so it just started to stall.

    The choke is all the way up, the arrow on the tank petcock is facing downwards (down towards the carb but the actual lever is pointed up).

    The only fuel adjustment I could see was the idle screw, could this be the issue? I turned it about 3.5 turns out from seated.

    Mmm apart from that it seems to be working ok so im anxious to get it fired up :p.

    I've never ridden a motorbike or anything like that so i'm totally noob at starting anything, let alone a friction starter.

    Any ideas are appreciated.

  2. Hajuu

    Hajuu Member

    Oh, and obviously I tried it 3-4 times.. still no luck.
  3. give me vtec

    give me vtec Active Member

    sounds like a bad carb... I have had two of them with my grubee engines. Does it leak gas when you lean the bike over on its side with the petcock open???? Did you get the engine from bikeberry???

    Dont worry... these carbs are cheap.... has them.
  4. spunout

    spunout Member

    before you go looking to spend money on new carbs or anything :ack2:, try turning the choke down to the "off" position (down) after trying to start once with it in the "on" (up). it will pop and sputter with full choke. pedal again and let out clutch with the choke off. should fire right up. it will NOT run on full choke :cool2:
  5. Hajuu

    Hajuu Member

    haha yeah that problem seems to have been the choke. I got it fired up for a minute or two before but it still cuts out very very easilly.

    Like any time I slow down it will just cut out. Could this happen if the fuel mixture is very slightly too rich? Or possibly to do with the idle screw? Someone also mentioned fuel mixture but I dont think these have settings for that?

    Also, on a fairly unrelated note, does anyone know how to hard-set a shimano gear changer to a different gear? I've currently got my front derailer off. I just want it in a fairly easy gear to help start it, unlike now where its stuck in quite a hard gear combo. then later ill fit a new set of gears.

    I've posted this question in the general bicycle repairs and modifications forum so if anyone knows head on over. ( ).

    Thanks so much, sounds beautiful.. When I heard the pistons moving when I was making it I thought itd be very high pitch and annoying, but its actually quite pleasant and quiet. Bound to not annoy any cops.

    Now if I can just get her running smooth, and easier to start, ill be a very happy man.
  6. Hajuu

    Hajuu Member

    Finishing tips and final notes on my first build :)

    Got it running smooth, got the gears working good enough to get it started even on a slight uphill (going to install a whole new bike gear system tomorrow), so it's all good now I guess..

    Last thing is to ride it down to pump up the tyres cause they're definately feeling the added weight.

    I just had a few final tweaking questions.

    1. Is it worthwhile buying reinforced inner tubes
    2. Is it worth it to get kevlar tyres
    3. Is it worth it to get both 1 and 2 done on the back AND front
    4. What is the best sprayable chain lube
    5. Loctite *all* threads? Is loctite easilly breakable with a wrench?
    6. Anything else you can think of! :)
  7. spunout

    spunout Member

    a "very slightly too rich" oil mix isnt going to hurt. FYI for the first two tanks, i run 7oz 2stroke oil per gallon. after two tanks, drop the oil down to 6oz per gallon.
    did you dope-up those pesky slots on the carb inlet? air gets in thru those slots frequently.
    remember its a new engine, rings havent seated and everything is tight. sometimes, they dont run very well until theyve been run awhile. but why it stalls out....? hmmm.

    try turning the idle screw up, yes. but also check all electrical connections. ive seen more than a few bad kill switches. guys have had to disconnect the killswitch wire completely, for the bike to run as it should.
    edit: and make sure the carb is tight on the intake
    Last edited: Jan 10, 2010
  8. Hajuu

    Hajuu Member

  9. Al.Fisherman

    Al.Fisherman Active Member

    I believe the tires and tubs front and rear are worth it. A safety pin or sorts went through and out a tube on my son's on the way to work...sealed itself.
    Chain lube...I use bar chain oil dispensed from a squeeze container you might see in restaurants.
    Locktite...I use nothing but needs heat to I hear can be removed with a wrench. I only do it to the studs to the engine. I use nylon locking nuts on everything I can.
  10. GearNut

    GearNut Active Member

    Under most circumstances #242Blue loc-tite holds up very well. With any loc-tite product only a drop is needed, you don't need to liberally coat the threads as some folks think. Doing so is just a waste.
    #271Red loc-tite does need heat to remove, and under hot situations will hold up much better than 242Blue. #277Red is much stronger than #271Red. It may get you into trouble if you ever need to remove a fastner in the future. Use it with caution.
    These observations are based on me wrenching on Harley-Davidsons for 16 years at various dealerships and independant shops. Harleys are notorious for vibrating and shaking darn near everything loose, especially Panheads, Shovelheads, and Ironhead Sportsters.
  11. Al.Fisherman

    Al.Fisherman Active Member

    98% of all Harleys are on the road...the other 2% made it home.
  12. professor

    professor Active Member

    Al- that remark was really good!
    Not true but funny. ( I don't have a Harley- rode by buddy's reworked 1200 Sportster and was shocked at how fast it is, and mimimal vib.)
  13. GearNut

    GearNut Active Member

    You should stop wrenching on other people's Harleys then! :jester:

    They really are not that bad at all. Yes, they do need more maintenance then metric bikes.

    Ok, I am done. Thread hi-jack over.
    Last edited: Jan 11, 2010
  14. Hajuu

    Hajuu Member

    Reguarding probable too rich fuel mix

    Hey guys,

    Just been running my first build trying to get it finished however in my efforts to be better safe than sorry, combined with my first time fuel mixing, I think i've most likely quite richly overmixed my oil to fuel.

    Seems to me that this is now causing some real problems with starting the engine, I removed the spark plug and it was covered in a thick black carbon.

    I cleaned it off and reinstalled it but upon removing it again it had black rings on the outer casing of the spark plug.

    It also seems possible that dispite my best efforts washing out the fuel tank, from some collected particles in the fuel line, maybe some small particles got in there?

    Anyway. As far as I can tell I just need a way to clean it out, as it still seems to be trying to turn over just fine.

    Thanks peeps
  15. ToeCutter66

    ToeCutter66 New Member

    I am kind of a newb around here, but I believe that too much oil in the fuel will cause a lean running condition. Try re-mixing the fuel at a recommended ratio and running it again. It might be extra oil fouling the spark plug, not too much fuel in relation to fuel/air ratio.

    Try one of those cheap plastic fuel filters, and pop off the carb bowl and see if it is full of crud.

    You might also want to try a slightly hotter plug.

    With this being said, I have yet to ride a HT bike, I am still working on mine, but I have experience with 4 stroke air cooled bikes.

    Good luck, let us know how it goes.
  16. Pablo

    Pablo Motored Bikes Sponsor

    For sure get a good small external fuel filter and remove the in-tank filter before you do anything.

    Just get a new plug at this point.

    Mix up a 25:1 fuel to oil mixture, which is 5.1 fl oz (5 oz is fine) oil to 1 gallon (128 fl oz) of fuel. Use a good oil.

    You may need to clean the carb.

    Give it a go.
  17. HoughMade

    HoughMade Guest

    Lets be clear...and this is a bit of a hobbyhorse issue for me. Too much oil is simply too much oil. It is not "rich". Save the terms "rich" and "lean" for describing the ratio of fuel to air...and nothing else.

    When speaking about gas and oil, state the ratio of use the terms "more oil" or "less oil" or some such...this helps us to keep from getting 2 issues confused.

    It is true that too much oil causes a lean fuel condition because if there is more oil in the mix, there is less gas and therefore less gas to mix with the air.

    I agree with Pablo and Toe- mix up some fresh gas, drain out the fuel, and give it another shot.
  18. Hajuu

    Hajuu Member

    Thanks for the vocabulary lesson....

    So black unburned oil in the cylander isn't a problem? Sorry if unburned isn't the right word.
  19. Mountainman

    Mountainman Active Member

    sounds like too much oil

    sounds like too much oil

    maybe we may try a visit to the local auto store
    buy a -- 2 cycle measuring cup makes it so very easy

    there has been so much said regarding proper mixture around site ??

    25 to 1 while brake in ??
    32 to 1 after break in ??

    I like mine a little rich ---------- sorry for using the wrong term
    just a little smokey -- seems to keep that THING running okee dokee

  20. Hajuu

    Hajuu Member

    heh yeah probably the oil but still surely now I need to clean it out, if its invariably filled with black sooty stuff..