HokieAg07 129 #1 Posted June 9, 2013 96' 520H, 451 hours, the heads were decarboned, valves adjusted, general service at 435 hours. Engine was very clean and nothing noted out of the ordinary during that service. I noticed a slight stumble at idle and a intermittent miss under load while mowing last week. Figured Id take the top of the carb off and check/clean it yesterday, ran smooth at idle after this. Today went to mow grass, engaged the 60" deck and started moving and the stumble is even worse now. Vacuum gauge normally at 50% while mowing prior to this issue. When engine stumbles it jumps up between 75 and 100. It almost sounds like a coil or plug wire breaking down under load to me but I am not as well versed with these Onans. The issue while under load and mowing is intermittent, when it runs good it runs like usual. Of course my brain immediately goes to valve issues with these Onans but 15 hours ago the engine was apart and looking great! Carb issue? Ignition component going? Catastrophic failure!??! I am about dumb when it comes to carburetors, other than that I can do anything. I have a few videos as well. Share this post Link to post Share on other sites
WH nut 553 #2 Posted June 9, 2013 Take a spray bottle of water and spay the ignition and see if you can create the stumble Share this post Link to post Share on other sites
woodchuckfarmer 333 #3 Posted June 14, 2013 Take it out when its dark and see if there is spark jumping around on the ignition wires. Share this post Link to post Share on other sites
MalMac 1,332 #4 Posted June 14, 2013 Could be a number of things, like you I am not very well versed in the Onan and it's problems. Just last week I had something very similar happen. I traced it down to a bad spark plug. Got up in the high RPMs and started the same symptoms you are describing. Change out the plugs and it went away. I would tend to say that it is a ignition problem somewhere. There is enough wiring on that machine to drive Thomas Edison to the nut house. Share this post Link to post Share on other sites
leeave96 490 #5 Posted June 14, 2013 Could be plug wires - certainly check all of that, but could be a fuel issue. Is it possible you've got some water in the gas? Share this post Link to post Share on other sites
JackC 617 #6 Posted June 14, 2013 Carburetor issues are responsible for a lot of poor running conditions on the ONANs. A thorough cleaning or total replacement of the emissions carburetor on the 96 with an older non emissions carburetor should be considered. Wire terminal corrosion somewhere could also be a contributor. Share this post Link to post Share on other sites
HokieAg07 129 #7 Posted June 18, 2013 Carburetor issues are responsible for a lot of poor running conditions on the ONANs. A thorough cleaning or total replacement of the emissions carburetor on the 96 with an older non emissions carburetor should be considered. Wire terminal corrosion somewhere could also be a contributor. I have a brand new non emissions carb on the way. Even if its not the root cause, it will be less hassle down the road! Share this post Link to post Share on other sites
WH nut 553 #8 Posted June 18, 2013 Carburetor issues are responsible for a lot of poor running conditions on the ONANs. A thorough cleaning or total replacement of the emissions carburetor on the 96 with an older non emissions carburetor should be considered. Wire terminal corrosion somewhere could also be a contributor. I have a brand new non emissions carb on the way. Even if its not the root cause, it will be less hassle down the road! What was the outcome of the plug wire test? Share this post Link to post Share on other sites
HokieAg07 129 #9 Posted June 23, 2013 After a busy week, I finally got back in the garage today to work on the this tractor. I couldnt find anything wrong with the ignition system before I tore into the carburetor two weeks ago. My hunch was towards the carb so I went ahead and picked up a new non-emissions carb. To me there was no sense in spending 60-70 bucks on rebuilding the emissions carb when I could procure a new non emissions for $150. Got the tractor buttoned back up today and it seems to run great. Was cutting it close on on having to get to an event so my test cut didnt last more than 10 minutes but it runs smooth throughout the entire RPM range and no stumbles. Will spend a few hours on it tomorrow cutting and will really know then. My question is, although it seems to be fine are there any adjustments I need to make to the new carburetor or are they good out of the box? Share this post Link to post Share on other sites
