Strokerace2639 2 #1 Posted June 6 Yes I understand there are many threads about this. As they as a few years old, and I just picked up this machine I am starting a new. 1988 Wheel Horse 520-H bought from original owner. only parts I have replaced to this point are the Fuel Filter and the starter solenoid. Runs great on start up and until its good and warm ( 15 minutes or so), then it starts surging/hunting. The engine speed goes up and down, the vacuum goes from like 2 to 15 very rapidly, under load. As soon as I stop the mower deck it settles right back to what I would consider normal. Sets already done. used propane and starter fluid around the intake and carb. found no noticeable changes. i did notice the fuel filter never seems FULL. is this normal? What are the things I should look at and in what order? Thank You, StrokerA Share this post Link to post Share on other sites
sqrlgtr 3,031 #2 Posted June 6 (edited) just acquired a 520H a few months ago same symptoms and the 2 piece manifold was leaking/sucking air. Replaced manifold and runs like a champ now. I did clean/rebuild carb while I had it apart also dun a good cleaning of engine cooling fins whist I was in tare down mode...Oh yeah had a bad oil leak at oil drain where it goes into block. Just some well needed love and ready for another 30 years A few pictures for encouragement/courage Edited June 6 by sqrlgtr 1 Share this post Link to post Share on other sites
sqrlgtr 3,031 #3 Posted June 6 Almost forgot Welcome to Share this post Link to post Share on other sites
Ed Kennell 46,203 #4 Posted June 6 (edited) 1. clean the carb 2. clean the carb 3. clean the carb to the Edited June 6 by Ed Kennell 1 2 1 Share this post Link to post Share on other sites
953 nut 66,572 #5 Posted June 6 Perhaps a vacuum hose has a small crack which is aggravated by the vibration of the mower deck. 1 Share this post Link to post Share on other sites
Strokerace2639 2 #6 Posted June 7 2 hours ago, Ed Kennell said: 1. clean the carb 2. clean the carb 3. clean the carb to the Yeah thats what I was thinking.. best way to do that? can I get away with just removing the 4 screw from the top of the carb? then use something like permatex orange on reassembly? I normally remove gaskets and use stuff like Sillycone or TheRightStuff. Never had anything leak yet. Thank You! Share this post Link to post Share on other sites
Strokerace2639 2 #7 Posted June 7 2 hours ago, 953 nut said: Perhaps a vacuum hose has a small crack which is aggravated by the vibration of the mower deck. Thank you and your Family for your Service. 1 Share this post Link to post Share on other sites
Bill D 2,881 #8 Posted June 7 5 minutes ago, Strokerace2639 said: Yeah thats what I was thinking.. best way to do that? can I get away with just removing the 4 screw from the top of the carb? then use something like permatex orange on reassembly? I normally remove gaskets and use stuff like Sillycone or TheRightStuff. Never had anything leak yet. Thank You! Take the top off the carb. Clean the bowl and main jet with cleaner and compressed air. Be careful not to lose any small parts, or drop them down the intake. Do not use sealant on the gasket when reassembling. You may have to clean it several times. 2 Share this post Link to post Share on other sites
kpinnc 18,403 #9 Posted June 7 1 hour ago, Strokerace2639 said: Yeah thats what I was thinking.. best way to do that? can I get away with just removing the 4 screw from the top of the carb? then use something like permatex orange on reassembly? I normally remove gaskets and use stuff like Sillycone or TheRightStuff. Never had anything leak yet. I would also run a fine bead of silicone or similar on the seam of the two piece intake manifold. All the way down the seam on both sides. That, along with cleaning the carb worked wonders for my 520-H. Share this post Link to post Share on other sites
parsonsponyz 346 #10 Posted June 7 to Red Square. Pull the carb off and do a thorough cleaning. Share this post Link to post Share on other sites
lynnmor 8,845 #11 Posted June 7 It is best to pull the intake in order to remove the carburetor for proper cleaning. It makes sense to do a valve adjustment at the same time since the intake needs removed to do that. Before doing any of that, check the compression to see if there may be other problems. Use only genuine Onan gaskets for the intake, valve covers and exhaust and torque to specs found in the Onan Service Manual that can be downloaded in the Manuals section. The cheap kits found on the auction site are rather poor quality but some of the parts are OK, I use the carburetor bowl gaskets without issue but the manifold gaskets and needle are junk. Use no goop on the carburetor, check the intake manifold for leaks while off by blocking the carb port and filling it with gas, kerosene or diesel fuel, if a leak is found come back for guidance on that repair. Follow the manual and do nothing that you aren't sure of, return here for advice. 2 Share this post Link to post Share on other sites
sqrlgtr 3,031 #12 Posted June 7 I forgot that I did that also here is a link where I found a lot of my parts and easy to deal with Engine Related Parts & Kits | Case Ingersoll Tractors Northeast | Connecticut 1 Share this post Link to post Share on other sites
Strokerace2639 2 #13 Posted June 7 7 hours ago, lynnmor said: It is best to pull the intake in order to remove the carburetor for proper cleaning. It makes sense to do a valve adjustment at the same time since the intake needs removed to do that. Before doing any of that, check the compression to see if there may be other problems. Use only genuine Onan gaskets for the intake, valve covers and exhaust and torque to specs found in the Onan Service Manual that can be downloaded in the Manuals section. The cheap kits found on the auction site are rather poor quality but some of the parts are OK, I use the carburetor bowl gaskets without issue but the manifold gaskets and needle are junk. Use no goop on the carburetor, check the intake manifold for leaks while off by blocking the carb port and filling it with gas, kerosene or diesel fuel, if a leak is found come back for guidance on that repair. Follow the manual and do nothing that you aren't sure of, return here for advice. I think the following are the correct but feel free to correct me if I am mistaken, ( these are from ONANPARTS.com intake manifold gaskets- 154-2495 carb gasket - 146-0657 valve cover gasket - unknown to me Thank You. 1 Share this post Link to post Share on other sites
lynnmor 8,845 #14 Posted June 8 4 hours ago, Strokerace2639 said: I think the following are the correct but feel free to correct me if I am mistaken, ( these are from ONANPARTS.com intake manifold gaskets- 154-2495 carb gasket - 146-0657 valve cover gasket - unknown to me Thank You. If the listings say the parts are for an Onan P220G, they would be correct. Download the Onan Service Manual to see what you need, all of the 20 HP Onans are about the same, one exception is the valve cover gaskets where the breather design changed and the old style with the breather in a valve cover took 3 gaskets instead of 2. Onanparts sells good parts but he appears to be having difficulty getting some parts, lay in spares that you might need in the future. 1 Share this post Link to post Share on other sites
Strokerace2639 2 #15 Posted 17 hours ago update: While I wait for parts to arrive. as suggested by another forum member I, choose to do a compression test. I got the following. Front Back Dry 110 120 Wet 120 120 I am also adding a pic of the plugs. As the problem is far worse with mower deck engaged I think I am also going to add new vacuum hoses just to be safe... Keep wishing me luck. Thank You. Share this post Link to post Share on other sites
oliver2-44 11,529 #16 Posted 16 hours ago The plug on the left has a nice tank color which they say is good. The plug on the right is white which I think means it is operating on the lean side. dirty carb, carb adjustment or air lean could make it lean. Better to have it rich than a little lean. Share this post Link to post Share on other sites
Strokerace2639 2 #17 Posted 13 hours ago 3 hours ago, oliver2-44 said: The plug on the left has a nice tank color which they say is good. The plug on the right is white which I think means it is operating on the lean side. dirty carb, carb adjustment or air lean could make it lean. Better to have it rich than a little lean. AGREED! Share this post Link to post Share on other sites
Strokerace2639 2 #18 Posted 13 hours ago update: update: so to this point I have only done the fuel filter and seafoam in the gas.. Day 1- surging on start up. Day 2- Surging after about 7 minutes of use Day 3- Surging after about 10 min of use Day 4- (really a few days later) got a good 15 min out of it before the surging Day ??- about the same as last time Day TODAY- 2 runs at over 30 minutes and 1 little hick-up other than this it seems good..... now to decide if I work on my 312-H or let it go to someone else that wants to work on it... THANK YOU EVERYONE. Share this post Link to post Share on other sites
