So, I'm running a 1mm jet and think I may need to go bigger....

Discussion in '2-Stroke Engines' started by EnFlaMEd, Sep 26, 2009.

  1. EnFlaMEd

    EnFlaMEd Member

    When I upgraded my air filter to a velocity stack + UFO style the other day I found that my bike ran a bit ****house. So I dropped the clip on the needle and found that it ran better slightly richer however at WOT the engine would die. There were no weird noises or anything associated with this, the engine simply cut out until I backed off the throttle. In order to cure this I hunted around for some larger jets but didn't really have much luck in finding anything so being the impatient ******* I am I found a 1.0mm drill bit and ran it through the jet with my fingers.
    I figured that was probably going to be way to big and cause problems however that was not the case. The engine is running great now and is pretty good at WOT but it still feels like it is running a little lean. A check of the plug after a good 20km or so thrash has revealed it to be a bordering on a light tan colour whereas with my old setup it was always a dark grey. Is it possible I need to go larger again? I only doubt myself because everyone else seems to be running such smaller jets in their engines even with setups like mine. What do you guys/girls think?


  2. Hawaii_Ed

    Hawaii_Ed Member

    That really does look just like my setup LOL! Suprised to see the stock wire though, easy to upgrade! I even used the same tailpipe hanger as you!

    The WOT bog is a sure sign you are in the danger zone lean and closed to melting the piston. Ask me how I know :)

    If you motor likes it where you are, go with it! You could tune the pipe by adjusting the length though.

  3. EnFlaMEd

    EnFlaMEd Member

    Yes I know, thats why its good comparing notes with you and I've seen your piston with its speed hole lol :D

    There is a new plug wire on its way to me from sbp. I had to order some other parts so thought I may as well get that while im paying for shipping. I hadnt really bothered to upgrade it before as I don't think I have had any spark problems. I wonder if there will be any further improvement with it. Notice anything on yours Ed?

    I have thought about mucking around with the pipe some more. I trimmed it a bit when I first installed it but I can't remember how much. An inch perhaps.
  4. Hawaii_Ed

    Hawaii_Ed Member

    Had the wire on my old bike, so I just moved it over when I built this one. Never tried without it, but can not hurt. I'd see what Pablo thinks on the pipe tuning, they are really sharp with this stuff!
  5. arceeguy

    arceeguy Active Member

    WOW - 1mm? You must be getting some great power out of that combo to effectively utilize that large jet!

    I usually need to go up to .82 - .85 from the stock .78, but then again, this is with a stock exhaust and intake.
  6. Pablo

    Pablo Motored Bikes Sponsor

    Sounds huge.

    Tell us about your other mods. What about oil and oil ratio?
  7. Foximus

    Foximus Member

    The IDEAL color for spark plug tuning is HERSHEYS MILK CHOCOLATE.

    And if your playing with advancing your timing you want the heat band parallel with the inner edge of your earth diode.
  8. EnFlaMEd

    EnFlaMEd Member

    Acreeguy: It is definitely making good power but I still feel it should be doing more in the higher RPMs. It just doesn't rev like it used to at WOT but I think its very close to perfect. I can just feel it struggling with fuel supply. Loads of grunt throughout the rest of the range though.

    Pablo: The engine is a Skyhawk GT5 badboy 66cc/"80cc"

    Apart from your shift kit it has the following...

    -Velocity stack and UFO style filter
    -Boost Bottle
    -Rocksolidengines Billet Head
    -Your expansion chamber exhaust
    -Shaved and side cut BPH6s

    Fuel is BP Ultimate 98 RON mixed at 30:1 with FUCHS Silkolene Comp 2 Pre-Mix Synthetic Ester.

    Other than that it is still wired the way described in the supplied instructions using the crappy little bullet connectors and standard plug wire. When I initially assembled the motor I cleaned up the manifolds and also the expansion chamber with my dremel to try and match the ports as much as possible without actually touching the jug itself.

    I should mention that when I rode the bike the other day it was only about 13 degrees Celsius outside.
  9. Foximus

    Foximus Member

    Do you know your RPMs when your hitting this bog?

    You could be going to rich, or on the bad side if you have a big sprocket you really could be over revving and getting ring flutter.

    If you really want to see whats going on in your engine get a harbor frieght laser thermometer. get readings at sustained riding rpms, slowly going up. See what happens to your motor.

    Oooooorr... If you want to get even more fancy, get something called a (if i remember correctly, its been a while since ive had one) ColorTune Spark plug.
    Last edited: Sep 27, 2009
  10. EnFlaMEd

    EnFlaMEd Member

    It doesn't really happen at any particular RPM its just when Ive got the taps opened right up. Like I can still rev the engine out with less throttle but it just takes longer and is harder to do in higher gears.

    Gearing wise its all standard SBP Shift kit with a 11t-32t 9spd rear cassette.

    I don't think I am running too rich because what I am experiencing now was far far worse before I increased the jet size.That is my reasoning anyway lol. It is now almost at the sweet spot but just not quite.
  11. Foximus

    Foximus Member

    put a piece of tape on your air filter. If you improve performance where you describe having a problem, then you need to go to a larger jet.
  12. EnFlaMEd

    EnFlaMEd Member

    Might give that a crack tomorrow Foximus. I picked up a few extra drill bits today including one that 0.8mm and another which is 1.2mm. I can move either way with a bit of solder :p
  13. EnFlaMEd

    EnFlaMEd Member

    Today I drilled the jet out to 1.2mm. She's a real screamer now. After raising the clip a notch I would say the bike is running perfectly. Seems to be reving out absolutely no worries at all and the acceleration it has now compared to before I had the new head and air filter is astounding. I can't wait till I take it back into the suburbs on some smooth roads to give it a power run and see what speed I can manage. PB so far is 63kmh and that was before I changed the jet and filter. I will take some footage of the computer in next few days so I can depict how she accelerates.

    Just for reference this is some footage I took not long after I set the bike up and had it run in.
  14. Foximus

    Foximus Member


    Shift kit sounds really appitizing... might actually have to put one on my first or second bike.

    Sounds like you could get some more revs out of that though....

    You could try shortening your head pipe a bit, get your chamber tucked in real close to the frame. The shorter your exhaust track the higher your powerband will be.
  15. EnFlaMEd

    EnFlaMEd Member

    Took this video this afternoon. I tried beating my top speed of 63kmh but ran out of road. I need to take it out on the long flat stretch in the suburbs that I hit 63kmh on last time.

    Just now I have shortened the head pipe about another 10mm and removed the extra lawn mower muffler from the expansion pipe to see if it goes any better but that will have to wait till the morning. Unfortunately the silicone rubbers supplied with the exhaust don't seem to have coped very well as they basically crumbled when I took them off. Hopefully the high temp copper silicone I used instead will hold up.
  16. tacoshell4

    tacoshell4 Member

    silkolene is grade a oil comp 2 is good stuff
  17. tacoshell4

    tacoshell4 Member

    what do the actual jets look like pics? anybody? I have a bunch of dynojet jets from many kits when i worked in bike shops. round head with flat slot?
  18. EnFlaMEd

    EnFlaMEd Member

    hex head but I think there are a few different styles that fit. When I went looking around at carbuettor shops they showed me ones like you described that came from a webber carb I think. These fit but their smallest was way too big but I can't remember what size exactly.
  19. EnFlaMEd

    EnFlaMEd Member

    Hey people. After running the bike for a few weeks with the 1.2mm jet I decided I still wasn't happy with it as it was still bogging at WOT. So I am now running a 1.5mm jet! Bike seems almost perfect now and I have hit 66kmh or around 41mph! Fuel economy isn't that much worse either :D
  20. flashstar

    flashstar Member

    I love these bikes. Upgrading the fuel supply is a simple matter of getting drill bits instead of shelling over hundreds for new injectors on a car!

    Nice setup. It looks like a shift kit is worth it. Are you thinking about adding some NOS for a boost? You might be able to reach 50 mph on a suicide run!