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Old 04-27-2004, 11:14 PM
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Motorcycle ignition problem. help!

It's my neighbor's 79 Yamaha 50cc put put. It gets fuel, has 120 psi compression, and it has fire, but it won't run???

We have tried everything we can think of but we can not get it to run. I had it crank off twice today but it didn't do anything after that. All I can think of is the timing could be out 180*, but the flywheel key is not sheared.
It has electronic ignition, so it has a pick up coil and a "magic box" or "black box" and I am wondering if the black box or the pick up coil could be messing up the timing, but still getting fire to the plug?

We are going to a swap meet this weekend and he needs it to ride around on.


Thanks in advance!

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Old 04-28-2004, 10:25 AM
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Anyone know how that "black box" works?
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Old 04-28-2004, 11:27 AM
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If its firing at the plug the box is good is it a 2 stroke or 4 stroke?
if its 2 I bet you have a carb problem. or--- a timing prob and 2 strokes are (fuel timed) by the piston skirts passing the ports.
if its a 4 stroke pull the stator off and sand the crap out of it, and check valve adjustments.
hope that helps some
Ed
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Old 04-28-2004, 12:14 PM
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"It has fuel"
To where? The carb inlet? Is it getting into the fuel bowl? Is it getting into the intake manifold?
Pull the plug and squirt a little fuel into the cyl. Install the plug and crank it to see if it starts and dies. Carburetors plug up in those things if they sit too long.
Its possible that the plug isnt firing under pressure in the cyl. Try a known good plug.
If ya wanna get on TVs *******, put a rope around the handlebars and pull it with a car up and down the street with the bike in 3rd gear to see if it starts, or if ya dont wanna go to the hospital have someone just push it. (but thats very tiring)
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Old 04-28-2004, 05:33 PM
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Quote:
Originally posted by 2-manytoyzs
"It has fuel"
To where? The carb inlet? Is it getting into the fuel bowl? Is it getting into the intake manifold?
Pull the plug and squirt a little fuel into the cyl. Install the plug and crank it to see if it starts and dies. Carburetors plug up in those things if they sit too long.
Its possible that the plug isnt firing under pressure in the cyl. Try a known good plug.
If ya wanna get on TVs *******, put a rope around the handlebars and pull it with a car up and down the street with the bike in 3rd gear to see if it starts, or if ya dont wanna go to the hospital have someone just push it. (but thats very tiring)
Funny you say that, the old man (70s) down the street had a 90 that wouldn't start, and he got another neighbor to tow it with his truck with the old man on it, to try and get it started, from what my buddy Jeff said (lives 3 doors down) they had the rope tied around the handle bars, and when the old man let out the clutch the bike dumped him off and the old man did a couple of cart wheels.

Around here, if you want to see a show, just walk outside.
I've had a few of my own neighborhood spectacles too.


Any way I could make a whole thread about that, but I'll get back to the point.
It is a 2 stroke, and we have sprayed starter fluid in the cyl.
And the carb has been cleaned twice, and gas will come out of it if I choke it with my hand.
It is not flooded either.

I have worked on those 50cc motorcycles many times in the past,
and I have never had a problem like this.
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Old 04-28-2004, 05:38 PM
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Put a new plug on it.
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Old 04-28-2004, 05:57 PM
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Replace the condenser. There will be no spark or weak spark if the condenser is bad.

If there is a "kill" switch, check to see that it isn't grounded.
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Old 04-28-2004, 05:59 PM
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Quote:
Originally posted by 4 Jaw Chuck
Put a new plug on it.
He has two new plugs, Captain Underpants.

I tried the Champion he got and the spark wasn't very strong, no matter how I gaped it, but the Bosch plug had a nice blue spark no matter how wide I set the gap at.
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Old 04-28-2004, 06:09 PM
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Does it have reed valves? If so, check to see that they are not cracked or broken and close completely. They are located under the carb into the cylinder.

Last edited by Frisco; 04-29-2004 at 04:06 AM.
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Old 04-28-2004, 06:26 PM
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Quote:
Originally posted by Frisco
Does it have reed valves? If so, check to see that they are not cracked or broken and close completely. They are located under the carb into the head.
No reeds, and we sprayed starter fluid in the cyl and nothing happened. He even cranked it with a drill and nothing.

We couldn't get the flywheel off, we used a puller too. And there is no reason I can think of why the key would be sheared, and it sure doesn't look sheared.
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Old 05-01-2004, 01:08 AM
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go buy 3 or 4 more spark plugs because you have most likely already fowled both of the new ones you have (just because it sparks, doesn't mean that it is NOT fowled).
then take the carb off and pull it completely apart.
looking at the bottom of the carb with the bowl and floats off, you will see a brass screw with a flat head slot on it, remove that, but DO NOT DUMP IT OUT IN TO YOUR HAND, there might be a small ball in there that you may loose.
when you have it out, you will notice that it is a sleve looking "thing" with a few holes in it, CLEAN THE **** OUT OF THAT, then reinstall it. then clean all of the other parts with carb cleaner as best as possible.
now the air/fuel mix screw,.......... turn it all the way in until it just starts to get tight (but NOT tight). then back it out 1 and 1/2 turns.
reinstall the carb and install NEW spark plug.

NOTE: use as little as possible of starting fluid, it will fowl your plugs, and i don't give a crap what anyone says, THEY ONLY FOWL ONCE.

hope this helps, late' Aaron

Last edited by akm; 05-01-2004 at 01:13 AM.
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Old 05-02-2004, 09:37 PM
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We havn't messed with it. Someone else told us it had a reed valve, hell I don't know, I just figured spraying starter fluid in the cyl would give it no choice but to run, or at least pop.

And the plug was not fouled out, it has to run to do that. And I had a bike just like it and it had a lawnmower plug in it, never changed it and I've poured gas in the carb to get it started, and I never had this much problem with that engine.
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Old 05-02-2004, 10:00 PM
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i would look up the correct (factory) spark plug number. you could have the wrong one in there.
then try what i just said. it wouldn't cost anything and those steps have fixed about 85% of all of our motorcycle problems, on many different makes and models of 2 strokers.............or don't
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Old 05-02-2004, 11:23 PM
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Quote:
Originally posted by akm
i would look up the correct (factory) spark plug number. you could have the wrong one in there.
then try what i just said. it wouldn't cost anything and those steps have fixed about 85% of all of our motorcycle problems, on many different makes and models of 2 strokers.............or don't

That's it, you just talked yourself into coming over here and helping out.
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Old 05-03-2004, 10:40 AM
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