bo dawg 473 #1 Posted June 3, 2018 (edited) Ok, tractor was starting and running before I took top of carburetor off to clean. Put back together and try to start and got nothing. Everything has power, ign, starter, etc, all except the coil. So...does the relays have anything to do with it? Funny thing before working on carb, i had key turned on to test headlights and when I turned key off I got a loud bang which sounded like backfire out of carb. Scared the dog out of me. So did it again and same thing. I was afraid that blew something up so I tested coil then and I had power, all was good and I believe I started it up after that too before opening carb up. But now no power to coil. Edited June 3, 2018 by bo dawg Share this post Link to post Share on other sites
muz123 1,182 #2 Posted June 3, 2018 (edited) Was the engine running the first time you heard the bang? Edited June 3, 2018 by muz123 Share this post Link to post Share on other sites
bo dawg 473 #3 Posted June 3, 2018 No just the key was on and it happens right after I turn the key off. 3 different times. Share this post Link to post Share on other sites
muz123 1,182 #4 Posted June 3, 2018 7 minutes ago, bo dawg said: No just the key was on and it happens right after I turn the key off. 3 different times. I have to ask what was the tractor doing that made you feel that you needed to clean the carburetor? Share this post Link to post Share on other sites
bo dawg 473 #5 Posted June 3, 2018 (edited) Running like crap. Adjusting choke to make run. Carb was full of junk. Edited June 3, 2018 by bo dawg Share this post Link to post Share on other sites
953 nut 51,017 #6 Posted June 3, 2018 4 hours ago, bo dawg said: I turned key off I got a loud bang which sounded like backfire out of carb. Scared the dog out of me. So did it again and same thing. I have never experienced this and the likelihood of it ever happening again are slim, but here goes! If your ignition points were open at the time you turned the key on and off without cranking the engine over there is a possibility the condenser (capacitor) was charged and when the key was turned off it discharged through the coil creating a spark to both spark plugs and one of the intake valves was open enough to backfire through the carburetor. I can't prove this theory, but that could be what you heard. As far as not having 12 volts to the coil now, you may have unhooked a wire by accident while working on the carb. Share this post Link to post Share on other sites
bo dawg 473 #7 Posted June 4, 2018 No wire that I can see any where close to carb. Share this post Link to post Share on other sites
cleat 4,895 #8 Posted June 4, 2018 Here is the wire diagram. Later model 520 wire diagram.pdf If you trace the coil wire back, you will likely find your fault. Cleat Share this post Link to post Share on other sites
bo dawg 473 #9 Posted June 4, 2018 Thanks Cleat for the chart, that's my main question, could it be one of the relays. Cause its hot everywhere else except the coil. Share this post Link to post Share on other sites
gwest_ca-(File Mod) 10,442 #10 Posted June 4, 2018 1 Share this post Link to post Share on other sites
lynnmor 6,702 #11 Posted June 4, 2018 24 minutes ago, bo dawg said: Thanks Cleat for the chart, that's my main question, could it be one of the relays. Cause its hot everywhere else except the coil. Look at the kill relay, it might be bad. They can be found at many auto parts stores and don't cost much. You should have a spare anyway. Your system has no points, so that theory mentioned above doesn't apply. To get that backfire, if that is what you are hearing, would take an ignition source. 1 Share this post Link to post Share on other sites
cleat 4,895 #12 Posted June 4, 2018 (edited) Also, don't forget the simple things, Like is the PTO fully disengaged, motion lever firmly in neutral, your butt on the seat. I would also check to be sure you did not inadvertently bump a connector to the PTO safety switches or bump a fuse causing it to lose connection. Wiggle the relays to be sure they are fully seated, you can also swap them around I believe. Cleat Edited June 4, 2018 by cleat 1 Share this post Link to post Share on other sites
Skipper 1,788 #13 Posted June 4, 2018 (edited) The bang must be electrical IMO. Be carefull, those coils pack a punch, and a fully charged condenser has enough juice to do nasty things. Remember that it is DC, and it does not take that much DC to flat line you. If applied correctly ..... Edited June 4, 2018 by Skipper 2 Share this post Link to post Share on other sites
ericj 1,576 #14 Posted June 11, 2018 an onan will fire the coil when the switch is turned off or on, it fires with an interruption to the 12 volts. if the motor wasn't running correct and dumping raw gas into the muffler when you turn the switch off and on causing the coil to fire it will back fire. I've had this happen to me, generally only after running tractor and restarting right away. Did you get it figured out yet, good luck eric j Share this post Link to post Share on other sites