Operator 7 #1 Posted July 22, 2012 Thoughts needed on my problem, 20 HP Onan , Start it to go mow and after about 10 minutes stops! Let it sit and come back in 10 minutes starts right up and runs great the rest of the time. What I've done trying to figure this out, changed ign switch , unplugged heat sensor on front , pushed pulled moved wires . can't be wireing because letting it sit and not touching anything will start. I took gas tank off and cleaned crap out, blew out gas line , cleaned the gas filter , Still does it!! When I'm on the road the wife will mow and when it happens to her she gets p#@%d! says she is going to sell it! Not good. As it dies it gives off a pop , there is fuel in carb I can see it "wet" in the throat. Gas line up to carb is "cool" so can't be vapor locking as it is just is getting going. I can let it high idle and it does it. I was thinking yesterday after it did i , sticking float - runs fuel out of bowl then dies, float drops more fuel ? Counting on you all here .. Randy Share this post Link to post Share on other sites
joel_400 59 #2 Posted July 22, 2012 Have you ran a compression test when it stops? Onans had valve seat problems. The seats would fall out of th block. Maybe when its getting hot the seats are popping loose and its causing issues like valves hanging open? Joel Share this post Link to post Share on other sites
Rooster 192 #3 Posted July 22, 2012 Have you checked for spark? Share this post Link to post Share on other sites
smoreau 658 #4 Posted July 22, 2012 Sounds like your losing spark. not to familiar with the onen ignition system and the little plastic spark thingy behind the flywheel. Share this post Link to post Share on other sites
CRE1992 135 #5 Posted July 22, 2012 Onans have a coil. It is possible yours is going bad. Sometimes when coils are going bad, after a little while of running the heat causes them to stop working. Share this post Link to post Share on other sites
ericj 1,579 #6 Posted July 22, 2012 onan manual goes through step by step on how to check out their motors. sound like it is either the coil or the ignition module but the manual take you through it step by step eric Share this post Link to post Share on other sites
.5racer 14 #7 Posted July 22, 2012 take a look at points and condenser . my 16 had a run problem on the D , but with new points runs great ! Share this post Link to post Share on other sites
JackC 617 #8 Posted July 22, 2012 My 20 hp ONAN ran fine and then didn't. I took the carburetor off and cleaned it. I could not believe the crud that was in it. Some of the crud was interfering with fuel flow into the bowl by clogging the fuel inlet. It starts and runs fine now. If you have not cleaned the carburetor that is the first thing i would do. Ethanol is bad news for carburetors. The gasoline evaporates faster than the Ethanol leaving the crud behind. That may not be your problem but it should be eliminated as a possibility. I also started using clear fuel line between the fuel pump and carburetor so I can see if there are any fuel delivery issues on my engines. Share this post Link to post Share on other sites
546cowboy 302 #9 Posted July 22, 2012 I assume you have a 520 with a P-220 and they do not have points or condenser. I have had that problem in the past and like yours when you let it cool down some it may run the rest of the day but it can also run for 15 minutes and die again. The suggestion above about checking for spark is what you need to do when it dies like that and is still warm. If you have no spark it will most likely be the ignition control behind the flywheel by the crankshaft. I have owned 5-520's and have had to replace a couple of those. Do not go cheap and buy a used one. Buy a new one and solve the problem. Share this post Link to post Share on other sites
Operator 7 #10 Posted July 22, 2012 All good suggestions , No points and condensers on Onans. Lynn I hear you on don't go cheap! buy new. This 520 is my baby and gets treated like that, I've had like five come and go and also another here that is on garden duty. But this is the first time for this problem. I got done mowing around 7:30 last nite and went out this morning around 8 and started him and let it high idle and sure enough stopped after about 5 to 10 minutes! Not enough time to get the engine hot let alone really warmed up good. Let him sit about 5 minutes and started right up and ran good to finish up mowing. Stumper I'll tell ya. Going into carb next and check for "crud". Thanks all! Share this post Link to post Share on other sites
6wheeler 669 #11 Posted July 23, 2012 Instead of dealing with all this stress Randy, I could just come and get it. Problem solved . I would check the carb too. I've replaced the spark plug wires on mine but not the coil as of yet. But that is a real possibility. It doesn't take much heat to make a coil fail if its already bad. Good luck Pat Share this post Link to post Share on other sites
546cowboy 302 #12 Posted July 23, 2012 Like I said operator I have been there and done that and it like to drove me crazy that first time. I have to admit I did try a used one once and the problem started again about 6 months later so I always bite the bullet and buy a new one. Seems like the last one was about $80 but well worth it. Share this post Link to post Share on other sites
gomer gump 8 #13 Posted July 24, 2012 bet if you take the miserable engine shroud off and pull the flywheel off ,inside the flywheel will be a full of dirt and crud clean it out then check your contact area on the flywheel where it meets the ignition module probably all rusted over wire wheel it clean then check the ign module gap should be about .012 or so also wire wheel the ign mod contact surface . put all back together start motor get the motor to normal running temp pour sea foam in carb till it stalls motor it will smoke you out ok let it set for half hr start again bet you it will run like a dream after you restart it try an see biggest problem you got is ign mod not makeing contact with flywheel and carb gunked up inside you can get sea foam at any auto store i had done this to 3 onans off of 520h i bought guys said motor,s bad all i did was clean them up an the run beautiful just takes a little elbow grease . biggest headache is getting the onan shrouds of what a head ache rest is easy good luck Share this post Link to post Share on other sites
HorseFixer 2,013 #14 Posted July 24, 2012 I assume you have a 520 with a P-220 and they do not have points or condenser. Well your half right..... They dont have points but they do have a condesor. at least mine does its located on the blower shroud cover next to carb and yellow wire hooks to + coil. You need to get a Spark Checker and at the moment when this happens check for spark. if no spark II would then get a VOM and see If I have voltage to the coil If I had voltage at the coil and no spark I would suspect the coil. If no voltage at the coil take the VOM and trace back through all safetys Untill you find the culprit. If I had spark I would then look at the fuel system for problems. Good luck! ~Duke Below is a manual go to page 65-3 Onan_16_18_20_241.pdf Share this post Link to post Share on other sites
MalMac 1,332 #15 Posted July 24, 2012 Gotta love them Onan's Great to see your still out there Duke. Share this post Link to post Share on other sites
wh416lbz 1 #16 Posted July 24, 2012 I like onan's but when they don't run right, they are miserable :) Share this post Link to post Share on other sites
gomer gump 8 #17 Posted July 25, 2012 horse fixer is correct i was thinking about the kohler motor,s the onans have an electronic unit can,t clean them off . just have to replace them when they go bad . as for the safety switches well some people like them i prefer to eliminate them . i,ve found that most electrical problems can be found by just useing a simple test light and just traceing each wire . it does help to clean all the motor componets with electrical contact cleaner . onans a good motor but a head ache to work on i prefer kohler or new briggs vanguard replacement motor which will give you alot of room to work around when installed in a w. horse their easier to work on . takeing the onan shroud off is enough to try all your patience,, and the ignition spk mod is alot of fun to get to also good luck sorry got my kohlers mixed up with my onans thats why they call me gomer check out the b&s vanguard replacement motors for w ..horse at small eng warehouse on line their a good replacement motor Share this post Link to post Share on other sites
Operator 7 #18 Posted July 30, 2012 Well guys I didn't get a chance to play/check my probems out, spent sat. helping my son and daughter in law move then today sunday the wife decided we needed a bigger frig! Then a last haul of sons stuff. Wanted to get some mowing done but just ran out of time. Back on the road monday. I'll try it next weekend. I'll have my spark checker in hand too! Thanks all! Share this post Link to post Share on other sites
smoke171 0 #19 Posted August 2, 2012 I had the exact same problem with my 416-8 Onan. It would run anywhere from 15 min to 30 min then just shut down and not restart for a while. I found it happened mostly in the heat of the summer while mowing and almost never in the winter while plowing. I replaced the condenser, coil pack, checked all safety switches and tested everything. Still kept happening. Someone on this board suggested the IGNITION MODULE (control- ignition according to RCPW). and sure as sh?t that was it. Going on 2 years and works great. Very easy fix just need to remove the flywheel (need a flywheel puller) Unfortunately the MODULE costs about $150! also make sure you replace the insulator as well (that only costs about $2 and is worth it it.) Good luck. Keep us posted. John Share this post Link to post Share on other sites
clyde 5 #20 Posted August 2, 2012 hi!had the same trouble with a customers 520 change the ign. module no more troubles.but check with a cummins dealer the module is alot cheaper than going to a toro dealer.go figure :) Share this post Link to post Share on other sites
Operator 7 #21 Posted August 13, 2012 Well here is what has happened. Tried to get on here last weekend and the forum wouldn't take my password, worked this time first try! Anyway last sunday got on my trusty 520 with spark tester in hand and ready, started it up and mowed for 3 hours! No shutdown! During the week my son got on it with spark tester in hand and mowed , no shutdown! I got on it today to mow ditches, with spark tester in hand, no problems no shutdown!! Now our outside temps aren't as high as before if that might have anything to do with it. I don't know but just maybe after I cleaned fuel tank any final water maybe left in carb bowl passed through ? I'll just have to try spark tester if it starts giving me trouble in the future. I did put tester away, remember Murphy' Law? Thanks for all the suggestions, Randy Share this post Link to post Share on other sites
