WickedGame 0 #1 Posted October 18, 2013 I have a 518-H that runs nicely, except for one problem that I can not figure out. Here's what happens: Start the engine - runs normally for half an hour or so. On flat ground or on a hill, while mowing, at full throttle, the engine maintains a constant speed for the first half an hour. Then it begins... On flat ground, all is fine, but as soon as I start uphill the engine, as it should, slows slightly. That's when the governor starts pulling the carb open for more gas. The problem is the governor goes way past a normal speed, then swings back to a lower speed. Speed up. Slow down. Speed up. Slow down. Maddening! I have to let the tractor sit for a while before I can continue mowing. Then, all is well for a half an hour or so, and it begins again. I have no idea what the top RPM is when it happens, but it is way past the normal speed. Scary fast. It begins with a sudden added engine load. It happens with a used air filter and with a new air filter. It happens after a half an hour or so no matter what the ambient temperature is. Disengaging the mower deck allows the engine to settle down to normal, but that's useless. I'm trying to mow here. Carb problem? Governor problem? Vacuum leak? Bad deck? Please help! I have five acres to mow one last time before winter. Share this post Link to post Share on other sites
JackC 616 #2 Posted October 19, 2013 The ONAN P Series engines are notorious for needing their carburetors cleaned. Surging or surging under load is one of the common symptoms. If you use fuel with ethanol then all the more reason to clean the carburetor. I have spare carburetors so I can swap and keep going and clean later when I get to it. I use ethanol free gas in my tractors. Share this post Link to post Share on other sites
WickedGame 0 #3 Posted October 19, 2013 Thanks, Jack. Come on over and you can help with the cleaning. How does one remove the carb from an Onan Performer? Looks like the mounting screws are well hidden. Gaskets? Should I order gaskets before I begin the job? Share this post Link to post Share on other sites
WickedGame 0 #4 Posted October 19, 2013 (edited) Is this the correct gasket kit? http://www.amazon.com/Stens-part-520-690-Carburetor-Gasket/dp/B001OK6PLS/ref=pd_sim_sbs_hi_2 EDIT ----- Answer: NOPE. See post below Edited October 19, 2013 by WickedGame Share this post Link to post Share on other sites
Martin 2,130 #5 Posted October 19, 2013 i would think this kit would be correct. there are different specs on these onan engines, so make sure you check the spec number on the engine....... http://onanparts.com/index.php?main_page=product_info&cPath=1_12&products_id=262 they also have a more comprehensive carb kit........ http://onanparts.com/index.php?main_page=product_info&cPath=1_12&products_id=54 Share this post Link to post Share on other sites
WickedGame 0 #6 Posted October 19, 2013 Thanks, Martin. 146-0650/146-0657 looks to be a basic kit. The 146-0500 (more comprehensive) seems to have more and different parts. No float, for one. Any reason to choose one over the other? Share this post Link to post Share on other sites
Martin 2,130 #7 Posted October 19, 2013 i would probably just use the basic kit. sounds like your carb is basically working how it should, just have some junk in there making things difficult. i have a rough running p216 right now and need to maybe do a simple rebuild too. i would feel happier if you could just get a couple gaskets and forget about the float as these kits are expensive enough. i think this is the most basic kit available though. i currently have tried cleaning out the tank, replacing gas line from tank to carb and filter, and have a decent amount of seafoam in ethanol free gas in there. will be running a full tank or two through there first before messing with the carb. i wouldnt be surprised if you have other fuel related problems though...... have you looked inside the gas tank? you may have some junk in there moving around, this would make sense seeing you have problems as you start going up hills. gravity and levelling of the gas in the tank make the fuel move to the rear as you go uphill and with it could be any other junk in there moving rearward as well. the pickup is at the bottom rear of the tank and it could be getting covered in junk, blocking the pickup momentarily. it would take a small amount of time to feel the effects, but it could be something to look at....... also make sure the pickup has the screen sock filter intact as well. if this is damaged that would be allowing crap to get sucked up. if it was me dealing with your problem, i would start at the tank, clean it out, if the shutoff valve/ pickup filter sock is damaged-replace it and install with a good tank bung or buy a new one they are cheap. then look at the gas lines, replace if old or questionable, if you have found junk in the tank you need to at least flush them if not replacing. then a new filter is in order. do you have one now that is clear? if so how does it look? flush the fuel pump too or at least run some gas through it before connecting up to the lines. this is all stuff that needs looking at even if it is not the cause of your problems. take a look and let us know how you go...... Share this post Link to post Share on other sites
JackC 616 #8 Posted October 19, 2013 To remove and clean the carburetor there is the long way and there are shortcuts. I remove everything from the top of the engine including the intake manifold and the exhaust in order to clean the top of the engine and check the valves. Short cuts include using a crow's foot wrench to undo the bolts holding the carburetor to the intake manifold. The heads of the bolts are under the intake manifold. Not sure if there is enough clearance to remove the bolts but the John Deere manual recommends that for the ONAN engines on their tractors. Some also get away with just taking the top of the carburetor off and cleaning what they can that way. If you take the long way be sure to use a torque wrench when reassembling because the block is aluminum and you can easily strip threads if you are not careful. You will also need gaskets for the intake and exhaust. I also use clear fuel line for the section of line just before the carburetor. If I have a no start situation I can at least see if fuel is getting to the carburetor or not. On the older machines you can have a bad fuel pump gasket or a blockage in the fuel tank or lines. With carburetor cleaning becoming more of an issue due to the ethanol in fuel and absorption of water, a back up carburetor is a good idea and you can buy new ones for around $160 on eBay. I am able to buy ethanol free gas in NY state and that is all I use now for my tractors and yard tools. Share this post Link to post Share on other sites
ericj 1,576 #9 Posted October 19, 2013 i use a shorter short cut than pulling the carb off. i just take the top off and clean the carb that way i have never bought a rebuild kit just be careful taking the gasket off. make sure you take the big nut off on the side of the carb and get access to the main jet and clean it , that sound like your main problem area. the main jet will cause the surging but i agree with at least checking the tank and fuel line. one other thing some my onans will rev fine when cold but when warm will tend to over rev when hot i just back off the throttle some and it take care of the problem. i still have to figure out why it does this though eric j Share this post Link to post Share on other sites
