strange problem with carb

Discussion in '2-Stroke Engines' started by back2theborstal, Feb 8, 2011.

  1. i have a regular NT carb on a sd stinger 66 cc engine, with about 25 miles on it. the problem is i have had a very hard time getting the thing to start. and i have to first warm it up with a hair dryer. but last night i figured out what was going on. i had the needle clip on the second from top notch (5 notch needle). and the bike would run good, when i could get it to start. but i decided to put the clip back down on the 3rd notch (where it was when i got it new) i closed the choke almost all the way. AND IT STARTED! so for what ever reason the engine wont start when the clip is on the 2nd notch, but the 3rd notch it will. the only problem, and the reason i put it on thr 2nd notch in the first place, the 3rd notch makes the engine run much too rich. and it will "4 stroke" almost the whole time except wide open throttle. so now its really annoying. i have to put the clip on the 3rd notch, start the engine. then take it apart and put the needle on the 2nd notch after the engine warms up. then i can drive it and have it run pretty good. but it seems very dumb i have to do this. i have tried the "tickle botton" but that seems to only make the thing get flooded and then never wanna start. so im now thinking maybe i should try going with 1 size smaller jet. does anyone think that would help? or does anyone have any other sugguestions... i do have a set of jets i ordered from sick bike parts. i have 60-78 (60-62-64...) ???? whats do you guys think?

  2. wbuttry

    wbuttry Member

    sounds like you are trying to get a real low idle i have never got a real low idle with mine . mine hits on fully closed choke starts on half closed chike runs best inbetween half closed and fully open it bogs on fully open so i closed it back just a bit and perfect for me it will idle kinda fast i can idle down till it acts like it wants to die and then i idle up about 1/4 to 1/2 a turn faster try that and i keep my motor bike in my storage unit down the road rite now in 20 ft it will start and run and it is 12degrees out side and gonna be -5 tonite gotta video i'll show you
    Last edited: Feb 8, 2011
  3. no im not trying to do anything with the idle. only the air/fuel mixture. it runs too rich with the needle clip on the 3rd notch, but it wont start unless its on the 3rd notch. it needs to be on the 2nd notch to run right and have the right air/fuel mixture. but on the 2nd notch it wont start. so i have to put the clip on the 3rd notch, start the bike and let it warm up. then i have to take the needle back out and put the clip on the 2nd notch to drive it around. i can drive it around on the 3rd notch, but it runs way too rich and 4 strokes the entire time. unless i keep it at WOT for a few seconds. then it will stop 4 stroking. but since its a new engine with only about 25 miles i hate to keep it wide open too long. im afraid ill sieze the engine or something. so what i was thinking is if i put 1 size smaller jet in it would run leaner at wide open throttle, but at idle and for start up it might still be rich enough. thats what i was wondering about. if anyone thought that would fix the problem? and i also wonder if anyone else has had anything like this. where they cant start the engine unless the mixture is set way too rich?

    its also funny too. because when the needle clip is set on the 3rd notch, and its too rich. the engine is much more quiet. and on the 2nd notch when running leaner (and i think where it should be), its alot louder. does this make sense to anyone??
  4. a/c man

    a/c man Member

    Are you using the choke?
    Also what carb are you using?
    I've never heard of your situation before, something doesn't sound right.
  5. yeah i have tried all different things with the choke. but it doesnt seem to matter. if the needle isnt on the 3rd notch. it will not start. period. i am using the regular stock NT carb. i think i am going to order a new carb though. im trying to decide if i want a SPEED or CNS v1 - v2. what would you guys recomend between those 3? but i still wish i could figure out why that problem is happening!
  6. GearNut

    GearNut Active Member

    Tune in the needle clip position and jet size for running.
    Learn what particular choke position it wants for starting. Slowly reduce the choke position towards full open as the engine warms up, do not simply flip it open as soon as the engine starts.
    The symptoms you are describing indicate a tuning/ choke error. The NT carburetor is the simplest of any carburetor I have ever seen. Trail and error will eventually get one tuned up.
  7. well like i said. if the needle clip isnt set on the 3rd notch it wont start. but when its on the 3rd notch its too rich. if i have the clip on the 2nd notch (where it should be) the bike will never start. it doesnt matter what the choke position is. if its on the 2nd notch i cant do anything to get it to start besides sometimes if i heat the engine with the a hair dyer it might start on the 2nd notch. but not always. and no matter if i hit the tickle botton 1 time or 5. it seems if i push it more than 1-2 times it floods. im thinking about putting 1 size smaller jet in and then keeping the clip on the 3rd notch. it seems like this might be the solution. but i havent tried it yet. i bought 10 different jet sizes from sick bike parts. i guess they are dellorto jets. im a little confused though. i have 60,62,64,66,68,70,72,74,76,78. i cant figure out which are the bigger and which are smaller. from what i have read the stock NT carb comes with a 70 jet. then when i try to read up on which is smaller they say the smaller the number, the bigger the jet. so you would then think the 60 is bigger than the 70. but when i compared the 60 to the 78. the 78 looked to the the bigger one. so whats the deal?
  8. Dave C

    Dave C Member

    As far as a new carb goes most are saying the SPEED carb is the best thing going until you get to a 18mm Mukuni. I have the CNS from BGF and I have no complaints. It has worked great right from the box so I feel no need to try a SPEED. The reason I'd say get the SPEED is others smarter than me say so and I'd get one, too, except I like my carb. It's like a $25 price difference, too. Can't ignore that.
  9. i have a little money to throw around so i was thinking of ordering both the SPEED and CNS carbs. also maybe another engine kit(grubee skyhawk). i want to start a second build, maybe let my friend drive it so we can go riding together:D and also maybe even race each other :helmet: haha. i was going to order some stuff from spooky tooth but it looks like they arent taking orderes right now because they are in the process of getting a new owner or something. i really want the pinneapple mount they sell. ive been having a hard time keeping my sprocket aligned right. whats the deal with the dellorto and mukuni carbs? how do you know which one will work? i have a 66cc sd stinger engine. so what dellorto/mukuni carbs will work for that? what ones do people like the best? and what do people feel is better, mukuni or dellorto??

    i also wish someone would comment on weather they think changing my jet size to a smaller jet might solve the problem i am having now. and also i have the jets. but dont know which are smaller. is a 60 smaller than a 78, or vise versa? constantly changing the needle adjustment is annoying!

    another problem i am having is i have stripped almost every bolt that came with the kit just tightening things down. its really ridiculous! i have bought and repalced everything i stripped with new high quality stuff from a local hardware. but the other night i stripped a rear engine mount stud. are these very hard to replace? and can i just go to a hardware store and buy a stud that will fit? dont they just twist out counter closkwise?
  10. a/c man

    a/c man Member

    Let's see if we can get you running so you can end your torture.

    The stock NT carb is the simplest, easiest carb to tune and most guys here will tell you to stick with it. Until you do some major engine modifications it will serve you well. Save your money. Learn on this one first.

    Jet size.....smaller number= smaller hole (measured in millimeters)
    example...70 jet is .7 mm 68 jet is .68 millimeters and so on.

    Stock #70 jet is usually slightly too big from my experience, and believe me I've fooled with mine plenty.

    Let's start at the beginning.
    Choke lever up ...full choke
    choke lever down... choke off

    What type of spark plug are you using?
    Did you gap your plug correctly? Try .024 inches with a feeler gauge
    Get rid of the stock plug and go get an NGK B6HS or B5HS
    Any motorcycle shop stocks these for about $3

    Make sure your gas to oil mix is correct..
    What ratio have you been using? Try 24 to1 since your engine is new.

    Since you have a terrific selection of jets on hand try the #68 jet
    Put the needle on the second down from the top notch.

    Usually a cold engine needs choking just long enough to get it started, I leave it on for about 3 seconds and take off the choke. (lever down is off)

    Go ride the thing and get it good and warmed up. It takes mine about 15 minutes. 2 strokes are moody s.o.b.'s when they're cold

    Take note of how it's sounding..When running right it should 4 stroke a little ,
    until you open it up, then it should smooth out and 2 stroke. Pulling a hill will always 2 stroke.

    Do a long wide open throttle run, making sure the engine's good and hot.
    Pull in the clutch and kill the engine immediately.
    Let it cool down for at least 15 minutes and pull the spark plug out and take a picture if you can and post it.

    Black and wet too rich
    White or light tan..too lean
    Light brown to chocolate brown just right.

    You are overtightening the hardware if you are snapping bolts and studs.
    Yes the studs do twist out counter clockwise like any standard bolt.
    Everything is metric.
    I use short metric open end or box end wrenches.A ratchet wrench will over do it really quick if you aren't carefull.
    The alloy used on these these is really soft.
    Obviously you need to back off some. Use blue locktight on the threads.
    Don't use red you'll never get stuff apart again.

    Don't try to ride with bad motor mounts. You'll rip the motor out while you're riding and get hurt.

    Get back and post your findings, don't give up you'll get it..

    I hope you didn't strip the hole into the crankcase. That's a big problem
  11. GearNut

    GearNut Active Member

    A possibility to ponder: The taper of the needle may not be enough. I have heard of folks comparing the needles out of 2 or more stock carburetors and the tapers are different between them. You may need to lightly sand the needle with 300 grit or so sand paper to thin it out a little. Doing so will allow more fuel to enter the carburetor respective to the throttle slide position. Initially sand only the portion of the needle that is immediately above the jet protruding out of the floor of the carburetor throat when the clip is in the second position. I recommend assembling the carburetor with the needle clip in the 2nd notch and, considering how little the slide opening will be at the closed/ idle position, marking the needle carefully with a mechanical pencil with the lead waaaay out to be able to reach into the carb and actually reach the needle.

    Sand the needle by spinning the needle with your fingertips on one hand while pinching the sand paper around the needle with the other hand. Go a little at a time and sneak up on the right needle diameter rather than sanding a whole bunch right from the get-go. Patience will be your friend.
  12. i am using an NGK spark plug. right now i have a B6HS in there. but i also have B5HS, B7HS and B-4L (i think thats what its called. i havent heard anyone say they use these but its what napa told me was replacement for stock plug) and i believe i have it gapped right now at .022 . i also replaced the plug wire with an 8mm wire. although i am going to try something different because i tested the wire and it has twice the ohm's of the stock wire. so that means it has more resistance and not transfering as much spark. i have a wire i ordered from sick bike parts. and it has metal coil rapped in it. so im going to try that next. since everyone says its best to use a plug wire that has actual metal wire in it. i think its a "magnecor" wire.

    i know the choke positions

    i am mixing the fuel at 16:1 as that is what the directions that came with the engine said to use. then it said after break in (150 miles) to switch to 20:1 i am using regular 87 octane gas, even though the directions said to use 91 octane. but i dont see how with a low compression engine this makes sense. **** i dont even have to use 91 octane in my 74 chrysler newport with 400ci 2bbl

    see whats funny is i feel like the engine is running to rich but when i look at the plug it will almost look too lean. i havent done the full throttle then shut off thing. but ill try it and see what happeneds.

    and when i say it 4 strokes all the time i mean it 4 strokes unless i am doing hard acceleration.. if i stay at a steady speed it will start 4 stroking within 2-3 seconds. but if i turn it to wide open it will stop. but only if im pushing it real hard will it stop 4 stroking. i was riding some this morning and after it warmed up i put the clip back on the 2nd notch. and it seemed to 4 stroke alot then too almost just as much as on the 3rd notch. i also put an after market air filter i got from sick bike parts on. its the one they have for $17. when i put that on i noticed it wanted to bog down some times. and it never did that before. and when i would hold the throttle all the way open it wouldnt have as much power as before. then if i would let off of it just a little it would get going. not sure what to make of that my guess is it would do something like that if it was running too lean. but i dont know...

    it also seems like it might have more power with the clip on the 3rd notch but i have to keep varying the throttle back and forth to get it to take off good. with it on the second notch it wants to bog down and i have to go wide open, then back off a little for it to get good speed.

    as far as the bolts go. i really didnt tighten anything very hard. just tried to snug things down. its like you have to keep everything loose unless you want to stip it. i dont think i stripped the threads in the engine. just the left rear mount stud it self, from the nut.

    ill try and post pictures but im not really sure how. but im sure i can figure it out...
  13. and as far as trying to sand down the needle. i dont know if that is something i would want to try. especially since i cant seem to find anywhere that sells new needles... but i guess if i cant seem to get things figured out by trying everything else. it might be a last resort. does anyone know if anyone sells new needles, springs, clips... i havent seen them anywhere