over revving when hot / locked up happy time / --CAUTION

Discussion in '2-Stroke Engines' started by Chris Crew, Aug 3, 2009.

  1. Chris Crew

    Chris Crew Member

    I've picked through all of the carb adjustment threads I can find, and I see similar issues, but none exactly like what I have experienced. I went on my first longish ride yesterday (maybe 20 miles) and about half way through, whenever I stopped for a light the engine would race to the point where raw fuel was dripping out of the air filter. When I gave a little tug on the throttle cable, it would rev back down, and I could also slow it by opening the choke.

    I have occasionally experienced this on shorter rides, particularly when it is very hot out, but it has been the exceptionn, not the rule.

    Any advice or ideas? It just takes something away from the elan to stop for traffic and have the motor run wild.

  2. arceeguy

    arceeguy Active Member

    There you go, sounds like the throttle is sticking when it gets hot.

    As far as the gas coming out of the intake, check the float level and condition of the float.
  3. Chris Crew

    Chris Crew Member

    uh huh. How do I make it STOP sticking when it is hot?

    It seems a little odd that pulling up on the cable calms it down unless that is just flooding it out.

    Any suggestions?
  4. arceeguy

    arceeguy Active Member

    Either the cable is sticking, or the slide valve is sticking in the carb. Tugging on the cable is freeing it up and letting the throttle close all the way.

    You can get a can of cable grease from a powersports dealer, and inject some into the cable. (do the clutch cable while you are at it, helps a lot)

    To troubleshoot the carb slide, unscrew the cap and remove it. Then use a sharpie to cover the slide with black ink. Screw it back in, then twist the throttle open and closed a few times. Take it apart again, and make note of where the marker has been rubbed off. You'll want to lightly sand and polish the areas where it is tight.
  5. Chris Crew

    Chris Crew Member

    Air Leak!

    took the carb off, checked the guts in the throttle

    put in an o-ring between the carb and manifold, added a strip of epdm rubber under the clamp and torqued it down tight

    problem seems cured

    thanks for the suggestions
  6. Chris Crew

    Chris Crew Member

    locked up happy time please help!

    I'm bummed because it is a beautiful summer evening in the Tarheel state and the road is calling. BUT

    On the way to work this morning, cruising along thinking things are fine, there was a SNAP (not too loud, no jolting, no vibration, vile smoke or other signs of disintegration) and the back wheel locked up tight.

    With the clutch disengaged, it rolls just fine. No odd tension in the clutch.

    I've taken off all of the covers, the exhaust manifold and the head.

    No bent, broken, scored, burned, missing, or messed-up looking parts; no shavings, no filings anywhere, nothing but some clean oil and grease and a small spot of carbon on the top of the piston right under the spark.

    The piston is stuck about .125 inch below the top of the exhaust port and I can see part of both rings--both look good. There is a little bit of a burr around the inside of the exhaust port on the cylinder end of the manifold. The burr points into the manifold, not into the cylinder.

    While there are some visible vertical lines in the cylinder walls, they are smooth to the touch and do not seem to be scored into the surface.

    If you turn the rear wheel, there is no play beyond that allowed by the spacing of the teeth on the clutch side gears.

    I don't see anything else I can take off or open up without removing either the clutch assembly or the flywheel in the magneto.

    The exploded view drawing of the HT on Zoombicycles.com shows some sort of woodruff key on the clutch side of the shaft, but I just don't quite see how to get in and check it.

    The situation reminds me very much of a lawn mower that has run over a big rock and busted the key---no play at all.

    Can anyone give me a clue where to go from here?
  7. srdavo

    srdavo Active Member

    Either the piston is seized to the cylinder, or the bottom end bearings are locked up.

    Double check the small & larger gears under the right side (clutch) cover.

    It doesn't sound good.

  8. Chris Crew

    Chris Crew Member

    so what do I do next?

    Do I have to take both the clutch and the magneto out to split the case and see which it is?

    Did I kill it by running without enough oil? I've been following the instructions in that regard--20:1 first tank 35:1 thereafter.
  9. Just_Gasit

    Just_Gasit Member

    +1 srdavo

    I doubt your mix ratio killed it. It may have been too lean though (air/fuel not oil/gas)

    Sounds like failure in a bad way, broken piston skirt etc. I've seen rings break and jamb things up tight, perhaps they are broken where you can't see them. Pull the jug off it you can. If the piston isn't the problem, it should come off easy. If the piston is the problem, it will lift the jug off the case when you try to crank the engine over.

    You will need to dis-assemble everything to split the cases.
  10. Chris Crew

    Chris Crew Member

    I think I might be a little slow . . .

    I've stripped the motor of the head and all covers and attachments and removed it from the bike.

    Given that the drive sproket will turn with the clutch disengaged, I'm pretty sure the problem is either a stuck piston, or a broken key.

    SO here are the questions:

    1) With the cylinder studs completely removed, if my piston and rings are ok, should I be able to just slip the jug off over the piston?

    2) If the piston is stuck, is my engine junk and better off being replaced, or can I knock the piston out and replace it and the rings?

    3) Per your advice below, I've rocked it back and forth with the chain and there is no play at all in the piston, crank or drive gear. Since the jug is not being pushed up, I'm assuming that a broken key is my problem.

    3) Can I split the case by just removing the magneto flywheel and drive sprocket, or do I have to take everything off of both sides of both the shaft and the clutch?

    4) How do I get the magneto flywheel off of its shaft? (I've taken the nut off already)

    5) Once I get the nut out of the middle of chain sproket, will the sprocket come right off, or is it pressed or splined on?

    6) If I take the drive sprocket off, do I need to mess with the right side of the clutch to pull the case apart, or can I now just pull it all through the case from the right?

    Thanks for helping a noob out. When I get it all broken down, I'll try and post some pictures for future reference. Given the quality of the drawings I have been able to find, couldn't hurt to have some on the board.
  11. srdavo

    srdavo Active Member

    1) = yes

    2) = It depends on what caused the piston to stick. If the rings seized to the cylinder wall, the top end is probably toast.
    If the lower bearings failed, there might have been loose metal fragments floating around in there.

    I'd start with trying to get the piston out of the jug. You'll know more then.

    good luck
  12. Chris Crew

    Chris Crew Member

    Stuck Piston

    Thanks, Dave.

    After contemplation, a few sips of my favorite barley pop (the one that made Milwaukee famous) and a few judicious taps with a rubber mallet, the jug popped right off---cylinder firmly seized.

    I found a couple of small metal shavings below the piston in the crankcase, but there were none on top when I removed the head.

    I can now rotate the crank in both directions and nothing seems either loose or binding in there, so I'm counting on the bottom end being ok. The piston however, is stuck fast.

    Is it prudent to try and drive the piston out with a drift at this point, or do I risk damaging the crank componenets?

    I feel a little better now---looks like I need some rings and possibly a piston and cylinder, but I don't think it's a total loss at this point. I've added a wrinkle or two to the old grey matter to boot.

    BTW, answer to question 4, below, the flywhell comes out of the magneto by tugging with slip joint pliers---there is a half moon key in the shaft.
  13. srdavo

    srdavo Active Member

    Schlitz?? i have become reaquainted, as of late. :grin5:

    what's a drift?

    not sure on this one???

    If you can get the piston to move down far enough to get the wrist pin out, you can remove the jug & piston.... and really wail on it!!:devilish:

    hopefully, one of the real mechanics, here, will have some advice for you.
  14. HoughMade

    HoughMade Guest

    Have you checked to see if the chain is bound up under the sprocket cover? Sounds more like that to me than a piston or crank issue.
  15. arceeguy

    arceeguy Active Member

    If that was the problem, he wouldn't be able to pedal with the clutch disengaged.

    I'm thinking something is jammed in the gears or magneto?

    Usually a piston seizure has some warning signs before they go.
  16. HoughMade

    HoughMade Guest

    Good point- missed that
  17. srdavo

    srdavo Active Member

    sounds seized to me......?
  18. Chris Crew

    Chris Crew Member

    What is a drift

    Dave, a drift is a fancy name for a block of wood, or a chunk of brass or some other material that is softer than the material you are getting ready to smack on with a hammer. It keeps the part from getting tool marks in it.

    Hough, I've got the chain out and the motor off and all opened up---definitely a stuck piston.

    Arcee, now that I have the "jug" loose from the crankcase, I can work the crank back and forth with no problem.

    And, yep---proud to be a Schlitz man.
  19. arceeguy

    arceeguy Active Member

    Yep - stuck piston for sure!

    After you get it knocked out, let us know what the post mortem diagnosis is!
  20. Just_Gasit

    Just_Gasit Member

    Okay, seized up.

    Lift the jug at high as you can and hold it up with blocks of wood between the edge of the cylinder and the case so you can tap the piston down with a hammer and a piece of wood, as it moves, add more wood as needed. You don't want to pound the piston into the case, flywheels etc. You could also clamp the cylinder in a vise and support the case as it drops down with the pounding. The idea is to only pound on the piston and not damage the rod or rod bearings, crank, etc. Your cyinder and piston is going to be junk, don't worry about damaging them now. Once the piston pin is visable, remove the clip on one side (or both if you wish) and drive out the wrist pin. You should then have a "good" bottom end to work with. Flush the bottom end out with something to get any metal junk out of there before you replace the piston/cylinder assembly. You can use gas mix or brake clean to flush it. Be sure to oil the bearings good after that and before re-assembly. Any loose metal down there will damage the new parts, get it all out if even if you see none. Check your rod good too, it will wiggle side to side some but should NOT have any up and down play when you hold the crank and pull up and down on the rod If there is up and down play, the bottom end has damage too. Likely, you will just need a new top end and some gaskets. Check for air leaks at your carb, manifold and possibly the case gasket and crank seals, you could have had a leak and it was too lean causing the siezure. Is the clip set too high on the needle? Has the main jet been resized too small? are you at or near sea level? Maybe you just had a junk top end? Just pointing out that if your too lean, this could happen again after you replace the bad parts.