Elblado Posted April 2, 2015 Share Posted April 2, 2015 I'm trying to get an old mx running for my 12yr old to use. Picked it up as a non runner. Was told it was running then it sat for ages. I've got it running but it's cutting out after 5 secs or so. Things I've done: -Clean carby. Main jets ok pilot jet was a mess. -Replace spark plug, ignition coil- spark is now good -Bypassed autolube to run on premix from tank -Repaired some burnt wiring from stator to CDI. Wiring had cooked sitting next to exhaust -Checked petcock- good flow -Replaced air filter The only current thought that is the exhaust needs decarbonising. Otherwise I'm short on ideas. Any other tips would be appreciated. Posted a video on youtube:http://youtu.be/RbtAoiKkUEk Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 2, 2015 Moderator Share Posted April 2, 2015 I don't think it runs long enough to be an exhaust issue, I stick with carb and fuel delivery to the carb myself Link to comment Share on other sites More sharing options...
blackhat250 Posted April 2, 2015 Share Posted April 2, 2015 Yip, sounds like pilot jet, or you"ve not got a air filter on, is it on choke in video,? Link to comment Share on other sites More sharing options...
KevtheRev Posted April 3, 2015 Share Posted April 3, 2015 Try running it with the filler cap off to see if the fuel tank breather is blocked and go over the carb again to check the float height and float valve/seat for wear . Best o' luck . Link to comment Share on other sites More sharing options...
Elblado Posted April 3, 2015 Author Share Posted April 3, 2015 Pilot jet was cleaned. It was pretty bad when removed. Think I'll clean the carby again and soak the entire body overnight. Tank vents ok. Did the same thing with the filler cap removed. Going to decarbonise the exhaust today and see how it goes. From the rear with baffle out it looks pretty bad in there. At least I know it runs.... Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
YPVS TONE Posted April 4, 2015 Share Posted April 4, 2015 If you're sure the carb/jets are clear and there is a good fuel flow to the carb I think I would double check the electrics. You say you repaired some burn't wiring from the stator. Is the wiring ok now and insulated and not shorting to the exhaust or frame? Is there a kill switch on the bars? you should be able to unplug it from the main loom to eliminate this. Does the spark plug come out oiley? I Know you said you replaced it but have you got another to try incase the other one is oiled up. What is the plug cap like and is it screwed into the HT lead fully. If the coil is under the tank a good idea is to remove the tank and try starting the bike in the dark to see if you can see anything shorting out to the frame. You should have enough fuel left in the carb to try this. Tony Link to comment Share on other sites More sharing options...
Elblado Posted April 9, 2015 Author Share Posted April 9, 2015 Thanks. Electrics is my next area to check. Stator to CDI and kill switch is probably the first point. Coil to plug has all been replaced with new stuff. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Elblado Posted April 9, 2015 Author Share Posted April 9, 2015 Cleaned out the exhaust. Soaked for a few hrs in oven cleaner. Actually then ran better than before, idled nicely. Grabbed a helmet to go for a quick spin and it cut out. So it had idled for about 2 or 3 minutes. Then went back to starting easily but cutting out after 5 secs. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Moderator Airhead Posted April 9, 2015 Moderator Share Posted April 9, 2015 Try a different spark plug Link to comment Share on other sites More sharing options...
fabiostar Posted April 11, 2015 Share Posted April 11, 2015 has it got reed valves? could be a weak or broken one. plus if you have changed from autolube to premix it will now be running petrol and oil through the jets instead of petrol as normally the oil is injected after the carb jets.. what states the plug in? oily,dry? wet with petrol? Link to comment Share on other sites More sharing options...
Elblado Posted May 2, 2015 Author Share Posted May 2, 2015 Plug is oil fouled. Top end rebuild? Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Moderator Airhead Posted May 2, 2015 Moderator Share Posted May 2, 2015 just change the plug and give it a good tonking, isn't it obvious? Link to comment Share on other sites More sharing options...
Elblado Posted May 13, 2015 Author Share Posted May 13, 2015 Compression test shows 80psi. Time for a rebuild. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
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