(chinese 2-stroke) Mixture Adjustment - needle - pic

Discussion in '2-Stroke Engines' started by gone_fishin, Apr 26, 2007.

  1. gone_fishin

    gone_fishin Guest

    there are 4 slots on the needle, these are used to adjust mixture

    by putting the circlip in a different slot, you're changing the position of the needle (gas) in relation to the slide (air)

    1st (top) = leanest setting, not used by many
    2nd = common setting for shipping & initial start-up
    3rd = seems to be applicable to sea-level or high-flow setups, a pretty rich mixture
    4th (bottom) = not used much, but some burn it fine at sea-level

  2. spad4me

    spad4me Member

    Question where is the needle to adjust the fuel to air ratio

    I believe I left it at the factory setting when I installed the throttle slide assembly.

    But I don't remember (recognizing) seeing it as an adjustable item.
    A small black circlip attached to a brass needle on the slide assembly, Not the larger silver circlip that holds the throttle assembly together.
    Please describe in detail where the E-clip fuel mixture adjustment is?
    I have seen the pictures of the adjustment at this site using the search function.
    Way too close up .
    Thanks in advance.
    Too windy now but riding soon.
  3. eltatertoto

    eltatertoto Guest

    it is the brass pin that is in the throttle assembly, you have to remnove it to set up the throttle cable, it you look VERY close there are notches for the c clip..
  4. gone_fishin

    gone_fishin Guest

    Last edited by a moderator: Jan 21, 2008
  5. Instantbacon

    Instantbacon New Member

    I am wondering if I need to readjust my needle. it was working fine, and then I cut the baffle one inch from the exhaust tip to improve performance and now im having problems with my bike. here are the symptoms. with the choke off, the bike will only go if you hold it full throttle, but when its there it cruises around 30 and it doesnt sound bad at all, but the downside is that if you left off it wont go it will just coast to a stop untill you full throttle again.

    The only other things I have done is remove the engine (rather lifted it up) so that I could reduce vibration via tubing (it was actually pretty difficult to size the tubing to get the bolts to get past it while still covering the mount bracket).

    One more thing, if the choke is fully on it will only go on the lower side of the throttle, and the more throttle you give it the more it bogs down, and then when you let go it revs up even if your hand is off the throttle (kinda scary).

    If anyone has any advice I would appreciate it, I dont know if its the bowl, or the needle that needs adjustment.
  6. mickey

    mickey Guest

    With the baffle cut to reduce backpressure, you could well be running lean. Have you read your spark plug?

    If that's all that changed (no sudden air leak in the intake), it would be no big deal to move your carb needle up by moving the C-clip down a notch. Try it and see if it helps. If it gets better, try another notch.
  7. Instantbacon

    Instantbacon New Member

    I had a feeling it had something to do with back pressure, and I also thought maybe changing the needle position would help, but I really dont know why I thought that, so I wanted to ask before I adjusted it (Its just kind of a hassle because my bicycle frame has such a small frame triangle that I have to take the carb off because it touches the top). gonna see if it helps!
  8. Skyliner70cc

    Skyliner70cc Active Member

    Tip: do not adjust your mixture while on a ride. You are guaranteed for that little e-clip to pop off never to be found again.

    I keep my clip on the top notch and use miniature washers to adjust my mixture. It gives me a little more flexibility and allows me to adjust on those long rides if needed. I found it often necessary to fine tune the needle height during break in.
  9. mickey

    mickey Guest

    Now thats clever. Where do you find washers small and thin enough? The would have to be as thin as gear box shims to be equal to moving notch by notch. Do you cut them yourself?
  10. Skyliner70cc

    Skyliner70cc Active Member

    I don't know. I've got tons of tiny parts from tearing and repairing electronic items over the years I want to say that the tiny washers cam off of casette tape recorders/players.
    Last edited: Mar 17, 2008
  11. Instantbacon

    Instantbacon New Member

    okay I took the needle out, was busy last night, and I noticed that the clip is nearest the sharp end of the needle, so its already running as rich as possible. I dont have time to put it in because I am about to leave the house but I was curious if you think running leaner would help, im really confused. thanks!
  12. mickey

    mickey Guest

    How does your plug look? Black & sooty, black & shiny, brown & dry? the blacker it is the more rich you're running and wet is the richest of all. Checking the plug is a great diagnostic tool when you're worried about the mixture. (really the only tool that a home builder is likely to have)

    You could go leaner and try it. I just reread you initial comments and I may have mislead you with the leaned-out speculation. I just based that on the drop in back pressure from removing the baffle.

    Really, I think the state of your plug will be the tell. If its good and black, I don't think that you will hurt anything by moving the clip up and rereading the plug after a middlin length ride.
    Last edited by a moderator: Mar 18, 2008
  13. Instantbacon

    Instantbacon New Member

    Okay, I tried different settings running it leaner by moving it up one notch, didnt seem to change anything, except maybe less co-operative. I moved it up again, and it it acted like it was running the same was as the richest setting. I dont feel like running it on the leanest setting, cause I dont think thats helping at all. I dont know what to do, kinda out of ideas. im wondering if it was a bad idea to cut the baffle, on thatsdax.com it didnt say anything about backpressure or anything. oh well. Oh, and I cant see the plug at the moment, I only have an adjustable wrench and two screw drivers, so I cant look at the spark plug at the moment.
  14. mickey

    mickey Guest

    How's the plug? I still think that's the best tell. Get the bike to normal operating temp, when you're about 50 or 60 yards from home, run it wide open for most of those yards, then hit the kill switch and disengage the clutch so the motor dies and stops turning near simultaneously . Roll home and when the plug is cool enough to handle, take it out and look at it.

    (thats my technique anyway, others may jump in if they have a different method)

    Edit: I see you said that you didn't have the spark plug tool, my bad. Still, take a look when you can.
    Last edited by a moderator: Mar 18, 2008
  15. Skyliner70cc

    Skyliner70cc Active Member

    Pull the plug and check gap. If gap is acceptable then find and address the airleak you have in your engine.

    If you are using stock intake gasket, chuck it. Go to Napa and buy a sheet of their thinest gasket material (about 4 times thicker than stock **** gasket) and cut your own intake gasket. See if this works.
  16. Instantbacon

    Instantbacon New Member

    Okay, went to work today (we repair bikes so I have all the tools I need), checked the plug, it was darkish but didnt look obstructed. I used a plug cleaning machine and got it looking brand new, then tried it out.
    didnt notice any difference.
    I went to this place called redline cycle center and let this guy look at it (who knows alittle bit about these bikes) and we adjusted the needle again and nothing seemed to help. he suggested that because of the lack of backpressure it may be running lean, he says that because it runs the lower rpm with the choke on then it needs more fuel so its lean. I dont know what else to do, since we put the needle back on the richest setting (which originally worked great before I modified the exhaust). I am thinking of making it run richer, maybe this will work, by putting less oil in the fuel mix? I was on a 20:1 but im going to switch to a 50:1, dont know if it will make a difference. I might try the air gasket thing in a day or so, he said he doesnt think it is affecting it currently.
  17. mickey

    mickey Guest

    How about packing a bit of steel wool into the muffler to up the back pressure and see if the problem goes away. Vary the amount and feel for differences. That might tell you if it really is the muffler mod that caused it, and not something on the intake side of the engine.
  18. Marktur

    Marktur Member

    I was going to suggest some chewing gum! :)

    I'm not sure we're going in the right direction here...most motors will run without backpressure. Maybe not the best, but should run. There actually is some back pressure from the header and the expansion chamber.

    You mentioned that the choke is making it leaner...and I think it's the opposite - doesn't the choke limit the air?

    Also - nobody really mentions this, but the carb is "keyed"...it should slide all the way in (the needle assembly) flush with the carb top - if it's higher, and you can see it, it's not in right, but be aware that it will drop in flush in 2 positions...If it's in correctly your throttle will move full range, and if it's wrong, it still sits well in the carb, but you get minimal throw to move the throttle (on the handlebars). If that happens, you're pretty much set with an open throttle, which will **** off a lot of engines when trying to start them. If you look down into the carb (with the assembly out) you'll see a little pimple on the cylinder wall...The part where you insert the cable into the brass part - that channel should also be where the little "pimple" is.

    Jeez, I hope this is clear and I don't sound like an idiot! :)

    Go back to basics when in doubt: set the needle to factory (second slot from the end), reseat the throttle assembly, put in a brand new plug - not a clean, used one, and go from there.
  19. rumme

    rumme Member

    Just for reference....

    I did the muffler mod 1st and then assembled my motor on my bike..

    it wouldnt run correctly { had to keep the choke 1/2- 3/4 on }

    I redrilled my main jet bigger.....runs great now
  20. HERPER

    HERPER Member

    this might sound trivial, but have you checked your idler pin? it could have popped off, loosened up or anything. this could affect how it idles which could explain things?