Carby Easy way to tell if you are running engine too lean

Discussion in '2-Stroke Engines' started by rcjunkie, May 13, 2007.

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  1. rcjunkie

    rcjunkie Guest

    A too lean mixture setting will eventually damage your engine. An easy way to check if you are too lean is warm your engine up fully and then ride it at full throttle for a little bit. Immediately cut throttle and pull clutch lever in. Engine should immediately drop to idle. If engine speed remains high and takes a second or two to drop to idle, it means your mixture is too lean and you should lower your needle clip by one position and repeat as necessary. If dropping clip doesn't help then check for airleaks.

  2. Patch

    Patch Guest

    So when you say drop...which way would that be? so with the pointy end down...move the clip toward the pointy end? right-

    thanks junky
  3. Guest

    Guest Guest

    Alternately and much less harmful to a potentially lean running engine is warm it up and as you are accelerating, slowly pull up the choke. If you get better throttle response and smoother running, you're too lean.

    Beats running a lean running engine wide open. :shock:
  4. gone_fishin

    gone_fishin Guest

    this should help:
  5. thatsdax

    thatsdax Guest

    and Remember.....

    Dropping Clip means raising the needle.
  6. rcjunkie

    rcjunkie Guest

    Yep, choke tip is also very good if you suspect a lean run. The problem is recognizing a lean situation that that occurs while riding and wasn't there previously. It can happen (a lean run) when blow an intake gasket or carb loosens and develops an airleak and then notice it taking a while to drop to idle speed.

    Its happened a few times that engine had more pickup than usual and as soon as I pulled throttle and clutch it revved a little more than it should before it settled to an idle....bummer! Using choke on return trip home kept engine damage from occuring and richened the mixture a bit.
  7. Werdna

    Werdna Guest

    Hmm...I've always run my bike with the choke slightly up because I get better throttle respones ect... So do you think I'm running it to lean? I haven't checked rcjunkie's method yet....
  8. rcjunkie

    rcjunkie Guest

    Yes, if you need choke, it means you are too lean.
  9. jol

    jol Guest

  10. Patch

    Patch Guest

    Now..In augi's referal to the post on adjusting, I moved my clip down one notch. But still I need to run it with about 3/4 or more choke.

    If I move it down to were Augi says its rediculusly rich (the last notch), would I get better performance on my engine? I replaced my intake gasket before I even fired it up with high temp material and permatex 1a (hardening sealer). So what do you guys think?
  11. Guest

    Guest Guest

    Patch, how long do you have to run it with the choke like that?

    I have mine on the third from the top, and I have to run the choke at 1/2 for the first several minutes (10-15) especially when it's cooler outside (60 degrees F).

    I'm at 1000' elevation above sea level.
  12. Guest

    Guest Guest

    Yes jol, I've read my plug several times, it always looks perfectly brown like it should.

    To further this, I have made numerous runs with the choke/throttle in various places. What is perfect (choke setting 1/2, clip second from bottom) for cruise is too rich for WOT. If i set the clip at the bottom, it's just too rich. If I set the clip second from the top, it's too lean. I've become quite good at using the choke as a "mixture control".

    Summary- these one jet carbs are not the best by any stretch. Either we have to live with them, vary the choke to "optimize", or buy a better "regular" carb.

    In the near future, I'm going to do some "adjusting" of the needle taper, I will be sure to report my findings.
  13. Guest

    Guest Guest

    O.K. folks, here are the final results.

    I took my needle out and chucked it up in a drill. I used some 240 wet or dry (the black stuff). I pinched the end of the needle lightly and ran the drill while keeping the paper moving and changing the paper position every several seconds. The brass needle started leaving some grey residue so I kept at it for about ten minutes. I then "dressed" the needle the same way with some 320 wet or dry and reinstalled the needle clip where it had been- third slot from the top.

    I ran the bike and now it was so rich I flooded it with full choke. Once I got it started and tried to clear it out, it still ran in a rich four cycle. I pulled over and changed the clip to the second from the top, fired it up and the dang thing ran better than ever. I don't need partial choke for 1/2 throttle cruise as I did before, and it runs clean and even at WOT.

    I've been running this bike for close to 400 miles with a uneven misfire at part throttle and in fact the only time it ran really smooth and clean was with a pretty good load on it. As soon as I reached cruise, it would go back to the misfire. Now it runs smooooth at part throttle, accelerates well at full throttle.

    Disclaimer here- I got lucky, and the taper was good the first time out. If you are going to try this, do it when you have some time, and do it a little at a time. If you take too much material off the needle, you can't get it back and I don't know if raising the clip to the first slot is going to help if you do.

    Take your time, test run it, take a little more off, test until it's good.
  14. cooltoy

    cooltoy Member

    Very interesting read everyone. I've noticed that if I give full throttle, it just boggs out but if I pull choke up for a second or two,it winds out. I will try the above.
  15. Mogyver69

    Mogyver69 Guest

    Im having the same problem. I have to run my choke 3/4 closed in order for my engine to run. Did you ever get yours fixed? Im getting ready to move my click one space down on the needle valve and possibly check for a vacumn leak. Any suggestions.
  16. gone_fishin

    gone_fishin Guest

    if you have a richer slot left, definitely try that first. noted in many places, but again: a good intake seal can be checked by going full-choke with the engine warmed should kill it on the spot.
  17. Mogyver69

    Mogyver69 Guest

    Hi Augie, Ya I just pulled the carb back apart it was set at the # 2 spot on the pin. I moved it down to the # 3 slot. Also i noticed alot of people talking about placing a seal between the carb and intake. I noticed when I did that it moved my carb out further exposing the groves on the outside area where the clamp goes. I figured I could try finding a skinnier seal or. See if the intake was actually going all the way inside the carb. I noticed that the carb bottomed out on the intake and really gave me no way of knowing weather I had more area to push the intake in and give me more seal on the carb and intake. So what I did was machined off a bit of the clamping area on the carb. I was able to push the carb on to the intake almost another 1/8 inch which gave me alot more sealing area. Ive got it all back together and ready for a run. Yes I completely disassembled the carb and cleaned it out to be sure there where no metal chavings left inside. Its late almost 11 pm and the roads are icy now so Ill try tomorrow and see what happens. Thanks
  18. nik

    nik Member

    interesting thread.

    so.. i just switched my dax 65cc throttle needle to the 3rd slot from the top.. to richen up the mix (fuel intake ;). I was getting the feeling i was running lean (although i get little drips from the exhaust now and then <normal i suppose) The engine seemed to need choke about 1/2 half way to be at its sweetest running spot...

    i also was noticing some misfire at a mid throttle that never let up in that "spot" when you get going...

    after reading this thread i decided to switch my needle adjustment and i am pleased with the results after that ride. I seemed to be less backfire-y and need less choke!

    I just put the choke right near the bottom (open) and it seemed to run better ;)

    I wondered how the needle moving up (allowing more fuel in) and leaving more choke open would be a good thing.. then i thought about it .. and decided... maybe.. just maybe.. more air and more fuel will allow this sucker to kick butt.. so far i think so.

    keep tweaking those bikes.. they need you, like you need them! ;)

    oh, and one more side note.. i noticed that one full tank of gas (1/2gallon) only seemed to get me around 15 miles maybe 30 tops! That doesnt seem right does it? I still am breaking in on my now 3rd tank of gas and driving it at a moderate speed most of the time.. i may need a speedometer to track miles traveled but oh well.. ill look around for mpg threads now.. later gang. -nik in NC
    Last edited: Mar 28, 2008
  19. KiDD

    KiDD Member

    I just adjusted my needle to the very bottom notch (super rich) and now I can run it with the choke off fully, it idles smooth, seems to run fine...

    How long can you run in a lean condition before it hurts your engine? And how does it hurt your engine?
  20. stude13

    stude13 Active Member

    one way to check if you have a vac leak at carb is to spray wd40 or starting fluid at connection, be very careful as both are highly flammanle