SPINJIM 1,978 #1 Posted September 1, 2018 I have a 520H with an Onan engine that was in parts when I received it. I did a partial overhaul, and have it running now. Final step is the air filter assembly. There are 3 tubes going into the bottom of the air filter housing: the large one from the flywheel shroud, the medium size one from the breather, and a small one connected to a stainless steel nipple on the bottom of the housing. I can't figure out where that small tube is supposed to go. Any help would be appreciated. Jim Share this post Link to post Share on other sites
daveoman1966 3,611 #2 Posted September 1, 2018 (edited) Gwest has the answer...my post was wrong... Edited September 1, 2018 by daveoman1966 1 1 Share this post Link to post Share on other sites
SPINJIM 1,978 #4 Posted September 1, 2018 (edited) The vacuum gauge is connected to a larger diameter line that comes off of the Intake manifold. That is connected. This is smaller 1/8" I.D. tubing. Daveoman1966, if you see the small stainless steel fitting just to the right of the carburetor throat in your picture, please look underneath the housing to see where that tube goes. Edited September 1, 2018 by SPINJIM Share this post Link to post Share on other sites
gwest_ca-(File Mod) 10,499 #5 Posted September 1, 2018 The small air cleaner tube goes to a sensor item #15 on this page right below the light switch in the illustration. Controls an air filter restricted dash light. https://www.partstree.com/parts/toro/mowers-lawn-garden-tractor/73501-520-h-toro-520-h-garden-tractor-sn-59002869-59002946-1995/electrical-system/ Garry 1 Share this post Link to post Share on other sites
daveoman1966 3,611 #6 Posted September 1, 2018 5 hours ago, SPINJIM said: The vacuum gauge is connected to a larger diameter line that comes off of the Intake manifold. That is connected. This is smaller 1/8" I.D. tubing. Daveoman1966, if you see the small stainless steel fitting just to the right of the carburetor throat in your picture, please look underneath the housing to see where that tube goes. I don't have that tractor anymore...this is just a file pic of years gone by. Now knowing it is wrong, per Gwest, I've deleted the post... 1 Share this post Link to post Share on other sites
SPINJIM 1,978 #7 Posted September 1, 2018 5 hours ago, gwest_ca said: The small air cleaner tube goes to a sensor item #15 on this page right below the light switch in the illustration. Controls an air filter restricted dash light. https://www.partstree.com/parts/toro/mowers-lawn-garden-tractor/73501-520-h-toro-520-h-garden-tractor-sn-59002869-59002946-1995/electrical-system/ Garry Thanks Garry for the valuable info. Once you gave me the description and item number, I was able to find a couple of threads here that describe it as a very common problem, and not a critical component. The nipple is broke off of the sensor. I found one on ebay for $80, which means that I'm going to use the same solution that many have used. I'm going to plug the tube, and ignore it. I check the air filter annually anyway. Thanks, Jim Share this post Link to post Share on other sites
gwest_ca-(File Mod) 10,499 #8 Posted September 1, 2018 You could JB weld a short metal tube to the sensor for a repair. Brake line is 3/16" or 1/4". Sand it first so the JB has a surface it will stick to. Garry Share this post Link to post Share on other sites