Kayla Posted May 11, 2011 Report Share Posted May 11, 2011 I got an SR125 cheap that has a starting issue. It turns over ok on the starter motor and we've had it running and have ridden it up and down the street, but the starting is very hit and miss, and it'll cut out occasionally. We checked for a spark and there's a good spark initially but as you turn the engine over the spark gets more and more faint. There's fresh fuel and we've checked the valve clearances (just to rule them out). Any ideas? Please? I'm going to give it a thorough going over today but a pointer would be lovely. Link to comment Share on other sites More sharing options...
lorenzo Posted May 11, 2011 Report Share Posted May 11, 2011 I'd clean up all the contacts, especially any earths. Link to comment Share on other sites More sharing options...
BudgetBoy Posted May 11, 2011 Report Share Posted May 11, 2011 We checked for a spark and there's a good spark initially but as you turn the engine over the spark gets more and more faint. Battery. Charge it fully before you do anything. Then move on to carbs.. but try the battery first if i were you. Link to comment Share on other sites More sharing options...
Kayla Posted May 11, 2011 Author Report Share Posted May 11, 2011 I had a bit of a prod at it this afternoon, cleaned up the connections to the coil and it started up a few times and then cut out after running for what seemed like the same length of time each time. I've got the battery on charge now. I am puzzled. Is it possible to wire up a coil back to front? It's not the standard coil and the connectors are horrible bullet jobs. There are two wires to the coil, brown and orange, and two wires in the loom that are standard Yam colours- red/white and orange/white. Would it hurt anything if I tried swapping the wires over? They're currently connected up orange-orange/white and brown-red/white and I reconnected stuff how I found it. Link to comment Share on other sites More sharing options...
BudgetBoy Posted May 11, 2011 Report Share Posted May 11, 2011 I had a bit of a prod at it this afternoon, cleaned up the connections to the coil and it started up a few times and then cut out after running for what seemed like the same length of time each time. I've got the battery on charge now. I am puzzled. Is it possible to wire up a coil back to front? It's not the standard coil and the connectors are horrible bullet jobs. There are two wires to the coil, brown and orange, and two wires in the loom that are standard Yam colours- red/white and orange/white. Would it hurt anything if I tried swapping the wires over? They're currently connected up orange-orange/white and brown-red/white and I reconnected stuff how I found it. I would not change any wires about if i were you. I doubt it is your wiring or it would not run at all mate, so leave it all be. Charge up the battery 1st and see how that goes. Is it just dying or is it a splutter then dying? If you ride it down the road and open the taps does it pick up easily or is it struggling? It could/sounds likely to be electrical.. As the bike heats up things expand, and this could cause a wire to come away.And the bike dies. Have you checked the battery charge rate when the bike is running? Is it pumping more than 13volts into the battery at about 3000rpm or 1/4 throttle? If not stator is naffed. You could also have a faulty coil mate.. this would make it die when its warm.. but hard to know/diagnose over net.. Charge battery and try it again..But check the charge rate with a multimeter while battery is fully charged.let me know how you get on. Link to comment Share on other sites More sharing options...
monkeystew0 Posted May 12, 2011 Report Share Posted May 12, 2011 Four stroke single with one carb shouldn't be too hard to trouble shoot. First thing thst springs to mind...why has the coil been changed? Have you tried swapping it out for a spare? Check resistance and grab something of the same value and swap them over. Might be worth trying a new plug and plug cap too just to be sure. Wiring sounds like usual Yamaha colours. Red/ white would be the 12v feed and orange the trigger feed from the points or CDI. You could always check you have 12V at the red/white to make sure you will get a good spark. Other than that ,as already mentioned, check and clean all the harness connection you can get at.. Checked points and condensor if you have them? Clean the carb out, especially the pilot circuit which tends to gum up first. See if it works then.....Good luck!! Link to comment Share on other sites More sharing options...
Kayla Posted May 12, 2011 Author Report Share Posted May 12, 2011 Four stroke single with one carb shouldn't be too hard to trouble shoot. First thing thst springs to mind...why has the coil been changed? Have you tried swapping it out for a spare? Check resistance and grab something of the same value and swap them over. Might be worth trying a new plug and plug cap too just to be sure. Wiring sounds like usual Yamaha colours. Red/ white would be the 12v feed and orange the trigger feed from the points or CDI. You could always check you have 12V at the red/white to make sure you will get a good spark. Other than that ,as already mentioned, check and clean all the harness connection you can get at.. Checked points and condensor if you have them? Clean the carb out, especially the pilot circuit which tends to gum up first. See if it works then.....Good luck!! We've cleaned the carb a couple of times, it may be that it needs to be done again though. We don't have a spare single coil It's a CDI, not points, would it matter which way round the red/white and orange wires were on the coil? Anyway, thanks for the extra pointers, I'll have a look in a bit Link to comment Share on other sites More sharing options...
monkeystew0 Posted May 13, 2011 Report Share Posted May 13, 2011 Without getting into the fine detail of how coils work YES, switching the wires would make a difference. The Red and white provides 12v to the primary windings in the coil this creates a magnetic field which the secondary windings boost into a high voltage which passes through to the spark plug when the signal from the orange wire collapses the magnetic field. Reverse the wires and I can't see how you would induce the voltage to create the spark. On both the Yamaha single and the RG125 I have in the garage the trigger and power terminals are a different size spade connection so you can't physially connect them the wrong way round. The fact that you have a spark would suggest its wired up right ,its just not creating a strong consistant spark. Could be: 1.The wrong type of coil has been fitted (wrong resistance rating), poor Ht lead, cap or plug. 2. Its not getting 12v to the coil due to a bad battery or wiring, (Check all connection from battery to ignition switch , coil and check Kill switch is clean too) 3.The signal from the CDI is no good (wiring connection) 4.Something else thats effects the CDI........(Earthing, signal from pick up on rotor) Do you have a starter interlock circuit (sidestand switch, clutch switch) etc? If the connection from one of these to the CDI is a bit duff it could be killing the ignition at the CDI. Sidestand switches are notorious for this sort of fun and games due to thier location...... Good luck!! Link to comment Share on other sites More sharing options...
Kayla Posted May 13, 2011 Author Report Share Posted May 13, 2011 Without getting into the fine detail of how coils work YES, switching the wires would make a difference. The Red and white provides 12v to the primary windings in the coil this creates a magnetic field which the secondary windings boost into a high voltage which passes through to the spark plug when the signal from the orange wire collapses the magnetic field. Reverse the wires and I can't see how you would induce the voltage to create the spark. On both the Yamaha single and the RG125 I have in the garage the trigger and power terminals are a different size spade connection so you can't physially connect them the wrong way round. The fact that you have a spark would suggest its wired up right ,its just not creating a strong consistant spark. Could be: 1.The wrong type of coil has been fitted (wrong resistance rating), poor Ht lead, cap or plug. 2. Its not getting 12v to the coil due to a bad battery or wiring, (Check all connection from battery to ignition switch , coil and check Kill switch is clean too) 3.The signal from the CDI is no good (wiring connection) 4.Something else thats effects the CDI........(Earthing, signal from pick up on rotor) Do you have a starter interlock circuit (sidestand switch, clutch switch) etc? If the connection from one of these to the CDI is a bit duff it could be killing the ignition at the CDI. Sidestand switches are notorious for this sort of fun and games due to thier location...... Good luck!! Thanks for that! The non-standard coil is wired in with bullet connectors, so they are interchangeable. We're going to try a fresh plug, new HT lead and a different cap. It does run, just not for very long Link to comment Share on other sites More sharing options...
bignige Posted May 13, 2011 Report Share Posted May 13, 2011 fuel breather? Link to comment Share on other sites More sharing options...
Kayla Posted May 14, 2011 Author Report Share Posted May 14, 2011 fuel breather? No, there's fuel getting through but the spark isn't strong enough to make it burn. It's very frustrating. Link to comment Share on other sites More sharing options...
jaycee Posted May 14, 2011 Report Share Posted May 14, 2011 I'd go along with the coil breaking down under heat as well Kayla. Link to comment Share on other sites More sharing options...
Kayla Posted May 18, 2011 Author Report Share Posted May 18, 2011 I think I've sorted this now I think it was just crap wiring. I think. I'm also sort of thinking 'can we keep it please' It'd make a brill bobber or baby flat tracker- Link to comment Share on other sites More sharing options...
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