Any 2 stroke experts around please?

[1198]

Hi. I've got a elderly Yamaha Yb100, as a project. It's in a pretty grotty state, and its more a nostalgia driven thing than a genuine good idea. I was amazed when I connected it to a small header tank of fuel with the ease it ran, and ran well, ticking over like a sewing machine, pulling as well as I'd expect, stopping on the key, restarting first or second kick. . Then it stopped, and hasn't run since.
Ive checked the spark, which is very good. I've checked the fuel pipe, and checked the carb. I whipped the plug out and squirted fuel down the hole, then replaced the plug, and on kicking it over it fired then stopped, presumably as it used the fuel in the cylinder. Figuring it to be a carb snag, I've had the carb in bits looking for grime and dirt, found none and rebuilt it. Still nothing.
Had I not had it running I'd have lost my patience by now and stripped it for spares, but I've heard it run, and actually ridden the thing. It was run on premix, as the oil tank is disconnected at present.
Thanks,
Ian.

[Timmeh]

are you sure you're getting a spark?
____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[1198]

[Timmeh]

hmm... although I will say that just because a plug sparks in the air it might not do so in the head.

Have you done a compression check?
____________________
GSXR400 x2 | '94 RVF400 | '93 TZR125 4DL (again)
20:22:30 BLUEX5: i would love to be forced to undergo a**l plugging with different sizes
20:48:18 Temeluchus: comp you hunk of smouldering homos3x you

[andy_uk]

What's the compression like?
When you try to start it with the plug in, is the plug wet when you take it out?
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Aprilia Classic 125, GS500E, ER5-A1, ER5-C4, ER6 & an XJ6 project frame...

[1198]

[27cows]

It's sparking...but is it sparking at the right time? Have you checked the points? After a long time laid up, it's entirely possible something has gone slightly out of whack. Possibly a loose contact breaker screw.
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The RXS100: vehicle of choice for Chuck Norris

[Ichy]

remove the air filter and spray easy start in to the carb. If then bike starts then the carb is not supplying fuel. either one of the jets is blocked or the needle valve is sticking. Is there a drain plug on the bottom of the carb you can undo a little to check there is fuel in the bowl?
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https://www.metacafe.com/watch/1972097/how_to_behave_on_a_forum/

[sidewinder]

fuel mixture ratio right for the bike?