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

[Chris Crew]

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.

 

[arceeguy]

.... When I gave a little tug on the throttle cable, it would rev back down, ......

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.

 

[Chris Crew]

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?

 

[arceeguy]

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.

 

[Chris Crew]

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

 

[Chris Crew]

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?

 

[srdavo]

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.



The piston is stuck about

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.

Sorry

 

[Chris Crew]

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.

 

[Just_Gasit]

+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.

 

[Chris Crew]

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.