Mixture question...

Discussion in '2-Stroke Engines' started by Molotov256, Jun 15, 2009.

  1. Molotov256

    Molotov256 Member

    Hey all, and thanks again for your help with my last post, "Hi Rev Bog Down". This is kind of a follow up post to that thread which is located here:


    I'd been having trouble with the engine bogging at high RPM, and Enflamed pointed out the notches on the carb needle and how moving the e clip could change the mixture. He suggested leaning out the mixture by moving it to a higher setting. I did that, and at first, it made a world of difference, but after taking it for a good 15 mile ride, it started bogging again.

    Eventually, it started revving really high when I pulled in the clutch. When I pedaled to get moving again and engaged the clutch, it strained and sputtered at really low rpm and barely propelled me along. I tried to do a field adjustment on the clutch, but no problem there. I killed the engine and pedaled the rest of the way home.

    Anyhow, I messed with the e clip a bit, and got the bike running again at a richer setting, but I'm back at square one with the bogging at high RPM. I've read in other posts that the position of the needle will only effect the mixture at 0%-70% throttle, but the really high end throttle depends on the main jet. According to a knowledgeable coworker, he says it sounds like the bike is running lean at high revs.

    That being said, if it is running lean at high RPM, I'd need to widen the main jet, right? I read a great post about making the jet SMALLER here, but nobody seems to be interested in making it bigger. Am I on the right track, or am I being insanely stupid about this? I'm a bit gunshy about drilling the main jet until I know what I'm up against.

    Here's a pic of my spark plug - it's light grey and dull, which leads me to believe it's running lean as well.

    <a href="http://s6.photobucket.com/albums/y208/Molotov256/?action=view&current=Plug.jpg" target="_blank"><img src="http://i6.photobucket.com/albums/y208/Molotov256/th_Plug.jpg" border="0" alt="Lean Plug Jun 09" ></a>

    Thanks in advance for any advice!

  2. put the c-clip second from the top.
    get a performance aircleaner or clean the stock one.
    clean out your muffler
    replace the sparkplug(same as stock but new)
  3. Skyliner70cc

    Skyliner70cc Active Member

    fix the airleak first, don't use chinese spark plug, no need to mess with jetting.
  4. Molotov256

    Molotov256 Member

    Air leak?

    Skyliner - Air leak you say? I noticed when I went to pull the carb off the bike that the engine had settled back a little bit and was placing pressure on the airbox. Seems like that could well have been causing air to leak into the manifold at one of the seams. I'ma try and shim the back mount of the engine a bit and see if I can't get some more clearance for the carb. I'm getting tired of messing with the motor mounts, but that'd be good news if I don't have to jack with the jet.

    CabinFever... how does one go about cleaning out the muffler? Bottle brush?
  5. Molotov256

    Molotov256 Member

    Okay... it's been a few days and I've found time to make a few adjustments.

    I've followed some of the fore mentioned advice from Skyliner and CabinFever... I cleaned out the stock air filter (couldn't find a link to the performance one from sickbikeparts) and remounted the engine so there's no more pressure on the carb and o-ringed the intake manifold in case there was an air leak there. That didn't seem to help much, if at all, so I tested further for air leaks. I've basically got decent low end power, but mid range and high end is bad.

    Things I self admittedly have not done yet:
    • Clean Muffler - (I don't get it)
    • Adjust carb E clip (I've tried that before and have it set to a position that seems to work best.)
    • Replace spark plug

    From what I've gathered through research of previous threads, the preferred method of searching for air leaks is to spray starting fluid around the various joints of the engine as it idles and see if it idles higher. I did this, but I had the opposite result. None of the joints produced any result until I sprayed around the head gasket and the spark plug. When I did that, it bogged down. It didn't die, but it noticeably bogged. I can't tell for sure if it's the head gasket or the spark plug hole, but I've narrowed it down to two possible culprits.

    That being said, how does one go about sealing these potential leaks? I've read about using RTV sealant, but that's gotta make a F*ing mess of things. Any other suggestions? And, as always, am I chasing the right gremlin?
  6. Molotov256

    Molotov256 Member

    @!#$! *&#$#!!!! ONEONEOoneone!111!!! aAARH!

    I replaced the spark plug and tightened up the rear engine mount a bit, and i ended up breaking a bolt on the rear mount. Now I've gotta go get some tools to extract the bolt nub stuck in the $!#%ing mount, and of course, I used threadlocker on it so it didn't back out like the last one did. This bike will be the death of me... I'll get back to y'all once I figure this mess out... if I figure this mess out.
  7. fourfeathers

    fourfeathers Member

    Hi Molotov 256
    Chuck that awfull Chinese plug away and get yourself an NGK B6HS or slightly cooler B5HS and set the gap at .025 thou. these Chinese plugs don't like compression.
  8. A slightly "cooler" plug would be a higher number like B7HS. NGK the higher the number the COOLER the plug..... I run the NGK B6HS gapped at .036 for optimal performance on my engine.......
  9. Molotov256

    Molotov256 Member


    I've got the engine mounted again and I've changed the spark plug. I had an Autolite "U25" laying around which I believe I'd ordered from Dax, but I figured anything was better than the stock plug based on the responses I've had, so I popped that it. I also raised the E clip to the second notch from the top and tightened down the bolts holding the engine head on.

    End result is poo... the bike starts up fine and idles okay, but once I take it out and warm up the motor, it dies every time I pull in the clutch and come to a stop. It's got pretty minimal torque once it warms up and can't hardly accelerate except on downhill slopes.

    Does this still sound like an air leak?
  10. Molotov256

    Molotov256 Member

    I swapped carbs with my other bike, and it fired up and ran okay. Rode around the neighborhood and down to the store, and it didn't bog like before. It still didn't run as good as the other bike, but this engine usually doesn't.

    So, this is obviously a carb related problem, possibly with other underlying gremlins.
  11. fourfeathers

    fourfeathers Member

    My appologies ; yes you're right Misteright1 99; the B5hs is the hotter one.

    Excuse my momentary lapse of reason.
    Last edited: Jun 26, 2009
  12. Mountainman

    Mountainman Active Member

    those darn things

    have been known to fall apart and into top end of engine

    that's all that most need to hear

  13. solitus3989

    solitus3989 Member

    Try reattaching your old carb, making sure to seat it properly, and see if you have the same problems.

    This will factor out the idea that your first carb was not seated properly, creating an air leak.

    Good luck and watch out for gremlins. i got bit once...
  14. Molotov256

    Molotov256 Member

    Alright... here's what I did tonight:

    • RTV sealant on head gasket
    • RTV on exhaust gasket
    • RTV on carb manifold gasket
    • O-ringed carb
    • Removed boost bottle and associated carb manifold and replaced with stock manifold to eliminate boost bottle from the equation
    I also checked the cylinder for scoring since the engine had been running so lean, but it didn't have any markings worthy of mentioning, as far as I can tell.

    The bike fired up and idled REAAAAAAAAALY high without the boost bottle on, but once I adjusted the idle screw on the stock cab, it ran better... it still didn't pull up hills too well, but it was an improvement overall. As a matter of fact, the improvement almost felt like I eliminated an air leak :shifty2:.

    That being said, I brought it back to the garage and reinstalled the boost bottle, and it really picked back up then. Still not a whole ton of torque up hills, but this engine always pulled best at top end, and it was FLYING on even slight downhill inclines. I'm running it on a 32T sprocket now, but I think I may need to step it back up to a 36 or so now that it seems to be running proper.

    Thanks to all for your input... Methinks y'all were right about the air leak, it was just buried under a bigger problem with a clogged carb. I gave that carb to a coworker to clean over the weekend. I'll have to buy him a bottle of scotch if he actually does it, lol...

    In conclusion, my best advice to newcomers like me who suspect an air leak:

    Don't waste your time looking for the leak, because there's not that many holes in a HT engine!! RTV Gasket Sealer works wonders, so just take all the pieces off , seal 'em up, and hopefully your experience is a positive one.

    If you try this method and it doesn't work, my apologies :).
    Last edited: Jun 26, 2009
  15. MikeJ

    MikeJ Member

    I also had carb problems this past weekend. Maybe someone will find some use for my observations:

    At first, could not start. Clear fuel line would not clear itself of air. Fuel starvation? Fuel valve lever was parallel to the fuel line, pointed toward tank. I removed fuel line; no outpouring of gas. I moved lever 180 degrees to point toward carb. Gas started pouring out (slowly). It appears on my setup, the fuel valve has only one position out of four that will pour gas. Tapping gas line after reconnecting helped clear line of air.

    Cold engine would start, but run for only a few seconds at above-idle rpm's. Solution: Backed idle adjustment screw outward a full turn plus a little more to factory-recommended position. The last time I touched that idle screw was on a hot day on a hot engine. Yesterday was a cool day and a cool engine. Memo to self: Be ready to adjust idle screw if you tinkered with it on the previous ride.

    Noted filings, dirt, paint threads in pleats of clear-case fuel filter. That stuff will not make it to the carb's main jet!