oe espo 32 #1 Posted July 7, 2018 Wife was mowing grass the other day. Said it was running when shut off. Drug it up to the garage. Really didn't want to crank, ran the battery dead several times. took the battery to the store to get a new one, and they said nothing wrong with it. so back on the charger. took a batter out another horse. cranked better but still no start. have spark both cylinders. dumped a little gas in carb, nothing, shot a little ether, nothing wouldnt even try to hit on a cylinder. ended up changing a bunch of parts from the running mower. still nothing. swapped battery, ign. coil, condenser, voltage reg. put new plugs in gapped at 0.025, new fuel filter. seems like it has compression. pulled the intake, exhaust just to get the valves, everything in tack and moving, did not check the clearance yet. when cranking a lot of oil spattering up the right cylinder. ended up pulling the head. and looked fine. im at a total loss. if the crank trigger wasn't working i would't get any spark right at all right? could valve timing be off enough to not start, or some other timing failure issue? any help appreciated. thanks. Share this post Link to post Share on other sites
oe espo 32 #2 Posted July 8, 2018 With the cranking drawing the supposedly good battery, I'm wondering about a valve timing issue, but never dug into an Onan Share this post Link to post Share on other sites
lynnmor 6,796 #3 Posted July 8, 2018 Open the gap on a spark plug to about .040" and watch for spark while cranking. If a spark is very weak, it can jump the normal gap outside the engine but not under compression. It still might be mechanical, but my bet is the trigger module. Mine just did the same thing, replaced the module and it never started better. manual 1 Share this post Link to post Share on other sites
oe espo 32 #4 Posted July 8, 2018 So even though I have spark, it could still be the ignition module Share this post Link to post Share on other sites
boovuc 1,090 #5 Posted July 8, 2018 I would do a compression check of both cyl before moving on to other presumptions. If you have decent compression in both cyl, look at the ignition module and the coil. If you go to our friends in the electrical section, search and ye shall find the numbers a good coil will have when checked on a VOM meter available at Walmart, Harber "Fright", Lowes, etc. I watched my #1 520-8 with the FEL go from a go-to machine to a "wonder if it will start" machine as the coil degraded. If you have a combo problem with some diminished compression and a weak coil, it will not start. It's hard to look at a sparking plug and determine if it's a "hot" spark or a weak spark if you never looked at a healthy spark on that machine. (We always look when there is a problem). Most Onan starting problems that are not fuel related are compression and ignition related. You determined it is probably not a fuel problem. If you need a coil, look at a 60's, 70's or 80's Harley Davidson Sportster coil. Share this post Link to post Share on other sites
oe espo 32 #6 Posted July 8, 2018 (edited) Update: Appears to be weak spark at 0.040 gap. Wires are original circa 1989. 1,009 hrs on the clock. Compression on one cylinder is 75psi. head not back on the other side yet. I tried coil, condenser, voltage reg from running machine. l typically don't throw parts at the problem but frustrated This is on my old 724Z mower. Power to pumps comes out the front to a an intermediate shaft with U joints. looks like iol have to take jackshaft out and mesh cover off to check the crank trigger Edited July 8, 2018 by oe espo Share this post Link to post Share on other sites
oe espo 32 #7 Posted July 8, 2018 Current status. I think I should adjust the valves (or check them?) button back up and try it before digging into the ign coil. I have to put it back together anyway Thoughts? Share this post Link to post Share on other sites