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2003 GasGas MC125

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My son just recently bought a 2003 MC125 it runs great but two days ago he was going up the hill and it back fired and quit. He kicked it and it sputtered three times and quit and hasn't started since. There is fir to the plug the air filter is clean I think it is getting fuel I put a new plug and kill switch on it as he broke the one that came on it and still nothing. Any ideas on what I can try next.

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Does it still have compression / resistance to kicking it over?  Ask your son how the bike was acting before it died.  Was it normal and just stopped or did it start to run strange before it died?  How does the spark plug look?  Can you post a photo of the plug.

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Bike was running great. It feels like there is still a lot of compression. I bought a brand new plug. He did ride through a mud puddle about 200 ft before the bike backfired and quit I am stumped. I am going to get a compression test kit today. I also put a brand new kill switch on it because he wrecked and broke his. I have cleaned the air filter and carb I don't know what else to do.

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I did a compression test it is 130-135 psi, I checked the flywheel it is in good shape, I checked the coil it is putting out the way it should. I got air and gas I don't know what else to check. Anyone ant to buy a nice clean MC125 that doesn't start...

 

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yes, I'll buy it. :naughty:

 

I doubt its the carb because it stopped running.  I doubt it's the ignition because it has spark.

 

Did you check the reeds when you cleaned it?

 

I'm guessing the fix is easy and a shot in the dark is that it's bad gas.  Did you add gas to it.  Ride a while and then it died.  Often a bike will run on bad gas but once you give it full throttle it will sputter, backfire and die.  Once it died it was flooded.  I'd drain the carb and tank, kick it over a few times with out the sparkplug.  Put a new plug and gas/oil in and see if it starts.  I've argued with people who insist gas is only two weeks old and is not bad, but after changing gas....

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Taking the exhaust pipe off is an easy way to look inside the cylinder.  I don't know if 130 is good or not.

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I had gas mixed 40:1 in it and it ran terrible. I took it out drained the tank put new gas mixed 50:1 in it, put a new plug in it, and fixed a little hole he poked in the tank. it was running great then he ran through a puddle but was going fast and not a big puddle about 200 ft up the hill after the puddle it backfired and quit. I have not checked the reeds to be honest I don't really know how I was going to tackle that today. I read that 90-150 is good for compression on a 125 and a couple people said 130 or above is good. If the reeds are bad would it not at least start.

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90PSI  is not good.  You want over 150 for sure.  Open throttle, kill switch depressed,  kick hard untill gauge stops rising.  These bikes are prone to exhaust bridge and powervalve failure, but the loss of compression in that case would be obvious. I would upgrade to the newer steel PV flaps though, if your bike has the alloy ones. MCs and SMs got them before the ECs so you might be good.  I built one of these bikes  for my nephew from the ground up and it ran really well, but you have to go over the details.

 

Just pull the carb and look in the manifold it will be obvious if you lost a reed petal. 

 

Also check the HV coil wire where it enters the coil body.  Tends to come loose on GGs and then water enters easily and causes all sorts of problems. 

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That's actually part of the reeds.  It's known as a two stage reed.  The look like they've been leaking, but I don't think it's enough to make it not start, just not run as good as it should.  I'd replace them.  I always replace what I know is bad when trying to diagnose a problem.  Seems obvious but...

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I am at a loss. I will replace the reeds since I have them off and that one is bad. How is it possible to have spark and fuel and air and not even try to fire. Could the coil just be weak.

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I doubt it's the coil.  You said in the first post that it runs great.  Later you said that it didn't run well when you had 40:1 gas in it.  You switched gas and it ran well for a short period that now won't start.  When did you buy the 50:1 gas?  How do you know it's getting gas?

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Make sure your electrical connections(CDI) are not wet & dirty. You did say he rode through water, just prior to malfunction.

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I checked all the connections they are clean now and good still nothing. I think its getting gas because the plug is wet after I try starting it. Its not soaked but it is wet

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Check that HV wire on the coil body and cap.  If its not perfectly tight with the adhesive bond intact, unscrew it, cut it back, clean up the stud and coil body, rethread and bond with sealer of grip glue.  If you see a spark at the plug that does not mean it will fire under compression if its weak.  I've had my 250 GG go from running perfect to bogging and dying intermittantly on the same ride.  Touched the coil body and got a good shock while it was running.  Moisture is a good alternate path to ground for HV.  The only GG I've had WITHOUT this happening was my '12.  On the older bikes I think its because when you remove the plug cap you place a rotational force on the wire at the coil due to its location and it eventually loosens.

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I got it fixed last night!! It was the key way on the fly wheel. Believe it or not I made one to fit because no one wanted to work and sale me one yesterday.

IMG_20140613_110506_809.jpg

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Congratulations.  I'm sure your son is happy you didn't sell the bike.  My uncle did the same thing to my boat motor when he ran over a waterski rope.

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As good as this bike runs for a 125 I still think I am going to sell it. We like it but it is not easy getting parts for it I like to be able to walk into a local shop and ask questions and the minute they find out you have a GasGas they act like I'm stupid. It is a strong little bike my son said it is running better now than it ever has since he has owned it. I was going to buy a brand new KTM yesterday and the local dealer acted so stupid about my GasGas I forgot all about it. I may keep it and just buy him another bike to run in addition to the GasGas.

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