Rich? Lean? Leaking? What's going on?

Discussion in '2-Stroke Engines' started by angryteabag, Jul 28, 2014.

  1. angryteabag

    angryteabag New Member

    Hey guys, first post and i'm scratching my head on this issue.
    Got my first moto bike the other day, second hand.
    The bike didn't come with a carb, but with fuel in the intake, it turned over so I got it.

    Replaced the spark plug and it fires fine.

    Bought a carb the next day, attached it and it wouldn't start.
    Moved the needle up one, nothing, down one, nothing.

    eventually, I took the air filter off. Using a spray bottle, sprayed fuel/oil into the carb intake and started it (Pin in the middle).
    The bike fired up with the throttle open, ran rough and would eventually just die. Tried to fire it up again and it didn't work.
    Sprayed into the carb intake again and it worked so long as the throttle was open. As soon as I let go, the bike wouldn't idle and just die right away.

    I have tried an O-ring on the carb. It is covered in silicon gasket goo. The intake manifold - the engine has fresh gasket goo. Exhaust has fresh cb gasket + goo.

    Why won't it start/idle?

    as it stands - Also, Hi from New Zealand

  2. HeadSmess

    HeadSmess Well-Known Member

    you didnt mention pulling the new carb apart and giving it a clean because thats the one part they seem to skimp on at the factory...gfetting the gunk out.

    if you cant see light through the jet...fuel wont have much chance of getting through it either.

    anyway. its to do with the new carb ;)
    angryteabag likes this.
  3. angryteabag

    angryteabag New Member

    Hey thanks for the reply. Yeah, took the carb apart. Can see through the fuel jet no problem, even blew through it for good measure. I'll try run a pin through it in an effort to clear it out incase though.

    Does the float level have any effect on how much fuel the jet picks up, or is it just a marker that tells the carb how much fuel to store in it's float area?
  4. HeadSmess

    HeadSmess Well-Known Member

    marginal effect on the amount it picks up. think of it as a straw. its hard to suck anything through a two metre straw!

    so, if the fuel level is high, it will tend to be rich, if its low, it tends to be lean, as its only the venturi effect sucking it up.

    could just be blocked needle valve... is the bowl actually filling up?

    go back to the carb that worked ;) after yay many years, im still using the plain old stock carbs, and trust me...ive done some fiddling with alternative carbs over the years ;)
    angryteabag likes this.
  5. angryteabag

    angryteabag New Member

    Yeah, no problem with the bowl filling up. I'm using a new stock NT carb, just trying to get the thing running before I play with alternative carby combinations haha.
    When you say marginal effect, would you go so far as to say that the effect is significant enough to prevent the bike from running?

    Maybe I should try bending the float levers to raise the level of fuel in the carb
  6. HeadSmess

    HeadSmess Well-Known Member

    by marginal i mean its a good fine tune when the jets are right, but thats it.

    unless it is SO low the jet isnt submerged, in which case...its excessive :jester: so no, not critical.

    pop carb, hold at same angle as its fitted, turn on tap... close, remove bowl carefully...and the fuel should be at least halfway up, a bit more with the float in there. most people say a few mm from the top, they just dont say how to measure it when you cant see it! (think about drilling a hole in a small screw, attaching some hose, and screwing it in where the drain normally goes ;))


    just a i read your first post closely...has the previous owner tried any home porting? like, chop the piston skirt?

    cus that will make em really hard to start, if done wrong.

    at TDC, you should normally see some of the piston skirt through the intake. can trim it away til its "just" flush with top of port, but anymore...oh dear.

    if you have to rotate it a fair bit before seeing piston...its been overdone, and it will need a new piston. shoving fuel down the intake will get it going, but it doesnt produce enough suck for a carb to work.

    thats a (really) messy silicone job there!
  7. HeadSmess

    HeadSmess Well-Known Member

    and pop the magneto cover/gear cover and just check for any suspicious looking oil/fuel around the crankshaft... if its got a leaky seal, once might start with a load of fuel, but not with a carb.
  8. angryteabag

    angryteabag New Member

    Piston is fine, no suspicious oil. that being said, the gasket in the clutch cover is destroyed and the cardboard the previous owner used for sound deadining was 100% saturated. Looks like gas that has leaked in from when my carb was leaking, there is no oil around/under the crank gear and no oil at the magnito side.
  9. butre

    butre Well-Known Member

    blown crank seals will make hard starts, usually it blows on the magneto side though
  10. angryteabag

    angryteabag New Member

    Here's a video with me getting it to run.
    It will only start when the throttle is open, and I have sprayed fuel in the intake. However occasionally it will turn over and draw fuel from the carb.

    Got it running indefinitely (like crap) and it wouldn't idle.

    Could one of the bearings or something have blown causing too much resistance?
    I don't have the space or tools to feel confident enough to take the whole engine apart. plus the bolts that hold the engine to the frame have been bent outwards because the bar is too big....

    Dr can you please look at my piston?
  11. HeadSmess

    HeadSmess Well-Known Member

    put that cylinder back on! thats the issue!

    lol, nah, it just pays to not remove cylinders unless replacing rings etc...naughty!

    um. im starting to think...go back to the beginning.

    a new carb, normal piston, etc should start, easily. and rev.

    so, something else is suspect, in my opinion.

    the oil can get into the clutch side by fuel sitting in that lil hollow just under the carb, seeps into the clutch mechanism, and other than getting oil on the pads, isnt a major issue. could just be previous owner tried putting oil in there... and yeah, normally the magneto side is the weak one.

    shame its 2nd hand because then you dont get the gear puller so you can actually LOOK at the crank seal. sometimes they just work their way out and rub through. maybe try filling the case up full with fuel? kero is less dangerous, but any fluid will make any leaks obvious, and water is obviously not really suitable... just drain it before trying to start it again, or you WILL pop a seal :jester:

    the thing turns over easy enough to kick start with no real hassles... oh dear... way too easy from my experience!

    might be new rings and cylinder stage. usual cause for starting, but with absolutely no get up and go. you also have no real idea how long the guy used it for?

    hows the cylinder look, inside the bore? any gouges, chrome missing, etc? rings? are they smooth and shiny or can you see lil ridges, grooves in them? newish rings have lil grooves. well worn rings go smooth and shiny.

    erm. get a cable on it. could just be a simple air leak because theres no outer cable to seal it up.

    but...when you remove carb, and dump fuel down the intake...does it do exactly what its doing on the video, run, but only just? (bad)

    or does it start, and then really rev up and die after a few seconds? (good) you only said it fires...not that it revs its **** off briefly!

    if it does peak out no worries...then its the carb at fault, and i have no idea why if its clean!

    otherwise... rebuild kit :( meh, a whole engine doesnt really cost that much more. then if its fresh in a box you know that no idiot has been at it, as disheartening as it is... and have some spare parts, to boot!

    well...just the rings alone are cheap, but youll need to hone the cylinder still. sandpaper on a stick, held in a drill doesnt really do quite the same job...
  12. angryteabag

    angryteabag New Member

    the rings were pretty smooth, but they were quite thick. Do you think worn piston rings can do that?
    When I got it running, I could rev it when I pulled the throttle up, I just had to be careful not to drop it too low or it would just cut out.

    I'll try put petrol in the intake tomorrow. (when the noise won't annoy everyone sleeping)

    The previous guy said "A few years"
  13. HeadSmess

    HeadSmess Well-Known Member

  14. HeadSmess

    HeadSmess Well-Known Member

    grrr. doing a kiwi accent on a keyboard is virtually impossible, ey bro!

    if you paid more than a hundred or so... i think you may have been ripped...
  15. angryteabag

    angryteabag New Member

    oh bro... paid $160
  16. HeadSmess

    HeadSmess Well-Known Member

    aw, not tooo bad. but still, it starts adding up when something is wrong... as long as he wasnt asking something really ridiculous...

    you got a frame already set up. spare parts. meh. rings and hone. should be right...should be :)
  17. butre

    butre Well-Known Member

    new engine only is like $90 usd on ebay last I checked. might be worth just eliminating the headache and buying a fresh engine