Cascade Crew

[popballz]

I've been working on my dad's old like 70's or 80's dirt-bike.

It is a 250 Yamaha

I can feel the spark when I touch the spark plug.

I cleaned the carb twice, I cleaned the main jet and the idle jet and all the little tubes
The bottom of the carb also fills up with gas

And it has compression. I am thinking it is getting everything it needs to start, but it wont??

Any advice of what to try??

[flea]

fuel, air, and spark is all it should need to start. It won't even pop? What kind of bike is it YZ 250? two stroke I assume.

[aaron_sK]

Timing off?

[flea]

for that matter are you 100% positive it is getting gas? I used to mess with chainsaws some, and a common problem in older saws is the pickup line in the tank goes to crap. Funny how bad they run when the fuel line goes to crap. Even if the lines look good there could and likely is some degradation on the inside walls causing crap to plug it up. Chainsaws and old two stroke dirt bikes aren't very different.

Try a teaspoon of gas straight in the cylinder through the spark plug hole.

[popballz]

[flea]

well you don't want to make it vapor lock on you for sure, put a little in and kick it over a couple of times slowly with the plug out to move the gas through the whole cycle, putt he plug back in and kick it through gently as you can to make sure it will go through then give it real shot, it may kick back, it will probably try to kick you over the bars, but if it does pop or even run for a second then you know it must be fuel delivery. If you can't get it to pop on gas right in the cylinder then spark must be the problem.
fuel mixture, timing and all that will affect how it runs or even if it will run, but any simple motor like this should fire this way.

[popballz]

Well then spark must be the problem....

Can I have too weak of a spark? I mean, I don't know what a good spark feels like, but it shocks my finger.. new spark plug too.

[flea]

it could be too weak of a spark, make sure the magneto is clean and free of rust. It could also simply be shot.

if its not magneto related then all my ideas are shot and you might want to try these guys. But these engines are really simple Gas+spark=fire. If your not getting fire then it points to either your not using gas (I won't insult you that way) or no/not enough spark. The spark comes from a simple magneto ignition. Check your magnets, for that matter even improper plug gap could be the problem. Clean magneto and try hotter plug.

http://forums.dirtrider.com/index.html

[redlava]

Take the spark plug out of the head and leave it attached to the wire. Make the metal of the spark plug touch the metal of the head. Now have someone push the kick starter over and watch for your spark.

[chevymad]

Does it just shock your finger or make you jump? The spark should bridge a pretty good gap. Even cranking with the plug out won't tell you really if its strong enough, because you need more voltage to fire the plug under pressure/compression. If its a good white/blue spark though thats a good indicator. I know its hard to test with everything wiggling around, but if you could hold the wire 1/4" away from a ground and kick it over, that would tell you more.

[popballz]

[chevymad]

LMAO! I think we've just come up with a redneck spark tester..

Ya, bob.. just how far did he jump when ya kicked her over?

Oh, only twitched a little..

K, ya better take an fix that spark then.

[Al Hasse]

[aaron_sK]

[IROCDave]

Is the plug new? Those old bikes were hard on plugs, not unheard of to have to replace a plug every ride.

It is a two stroke so make sure your adding premix to the gas.

[popballz]

[aaron_sK]

[popballz]

[izcain]

Have you actually performed a compression test or just used a finger over the hole? Also have you taken a touch of fuel and squirted it into the cylinder then screwed the plug in and tryed it to see if it will spit and sputter or if it is totally dead even with that?

[popballz]