JeffreyLKY 43 #1 Posted October 14, 2015 Shocking to hear this, I'm sure. Anyway...490 hours, and has always run fine. I did get a momentary engine temp light yesterday as I was mowing, and I had to clean the flywheel screen like every 60 feet of the two acres I mowed. Terrible that you cannot keep this thing clean. Regardless, the light came on and I immediately cooled the engine with a gas blower, and the light went off. I shut off the mower and waited for 30 minutes with a huge fan blowing across the Onan. I figured it was the valve seat issue, so I ran a compression test. 125 on both cylinders. Changed fuel filters, both spark plugs, and ran an entire can of carb cleaner through the carb. Started the machine, and I immediately get a horrible surge at all RPM ranges. Ironically, it tends to "smooth out" when I am at WOT with the deck engaged. ANY advice on how to pursue this would be most appreciated. This is my first ONAN, and likely my one and only. In love with all my old Kohlers that haven't let me down. Thank you in advance! Share this post Link to post Share on other sites
KC9KAS 4,741 #2 Posted October 14, 2015 My Onan on my 520 seems to surge some at lower RPM's too. It seems much better at almost WOT.I think I have read that this is "normal" or anyway, common, but I would definitely check further into the (over) heating issue. Share this post Link to post Share on other sites
nylyon-(Admin) 7,120 #3 Posted October 14, 2015 Usually cleaning the inside of the carb will work. You can take the top off and clean it out, or on so,e there's a plug on the bowl which can be removed and you can spray carb cleaner directly into the jet. That'll usually help or resolve the surge. Share this post Link to post Share on other sites
JeffreyLKY 43 #4 Posted October 14, 2015 KC9, my Onan always runs extremely smooth until this occured. I don't mean a little fluctuation at times...surge in the sense that it cannot be operated. Complete cut out of engine power. Nylon, I appreciate the advice. I did take the top of the carb off last night after posting this, and if you are talking about the long brass tube that goes down into the carb, I can see through all (five??) holes. The bowl has zero sediment in it and the choke moves freely. Am I talking about the correct jet? Thanks again guys. Share this post Link to post Share on other sites
JackC 616 #5 Posted October 14, 2015 "125 on both cylinders."That is one healthy ONAN although carbon build up may increase compression.Often cleaning the carb on the tractor will work. The particles from the Ethanol can prevent the float needle from working properly causing surging.Last one I cleaned had a tablespoon full of particles in the float bowl.The Ethanol absorbs moisture from the air and then particles precipitate out and monkeys up the carb.I would recommend getting a replacement carburetor so you can simply swap and go.You can remove the carburetor with a crows foot wrench.Then learn how to clean the carb or take it to a shop.Those carbs hate Ethanol.Use only pure gas if you can find it.Stabilizers or additives do not not seem to cure the Ethanol disease for my ONANs.I only use pure gas and I do add some SeaFoam (a/k/a snake oil) just in case. 1 Share this post Link to post Share on other sites
KC9KAS 4,741 #6 Posted October 14, 2015 @JeffreyLKY, I would also suggest SEA FOAM.....snake oil as JackC called it! Share this post Link to post Share on other sites
nylyon-(Admin) 7,120 #7 Posted October 14, 2015 Just get that main jet good should fix ya right up 1 Share this post Link to post Share on other sites
JeffreyLKY 43 #8 Posted October 15, 2015 Guys, I appreciate all the helpful tips and advice, and I think I have finally gotten the Onan a bit happy again. I was able to run those jet cleaner wires through the main jet a bit earlier today as suggested, and quite a bit of gunk came out. I actually went ahead and flushed the fuel line from the carb inlet to the tank, and thoroughly drained the tank and "sponged" it out a bit. Installed yet another fuel filter and wham...just as Nylon said...that fixed me right up. I guess carb cleaner didn't clear it completely the first time, but the wires surely did. Thanks JackC for the awesome fuel analysis and explanation, and thanks to everyone for your timely response to this issue. I sincerely appreciate all of you taking time to both reply and educate me on taking care of my 520 issues. I feel much more confident in taking care of the issue if or when it arises. Thanks again, and have a great evening! 3 Share this post Link to post Share on other sites
JERSEYHAWG / Glenn 4,487 #9 Posted October 15, 2015 If you have a small airport near you, get 5 gallons of aviation fuel. As pure as it gets. My buddy runs nothing but that in his tractors. I bet that will give it the burp it needs. Its pricey but, results are what your looking for. Best of luck Jeff.Glenn 1 Share this post Link to post Share on other sites
AMC RULES 36,945 #10 Posted October 15, 2015 http://www.wheelhorseforum.com/store/ Share this post Link to post Share on other sites
bmsgaffer 2,043 #11 Posted October 15, 2015 Jet cleaner wires? Never heard of those before.I might have to find me some of them... Share this post Link to post Share on other sites
