herbinohio 0 #1 Posted September 4, 2009 I have a 1988 518-H that i just rebuilt the motor on. Everything runs great except the motor seems to have a surge to it. At low idle and high idle. I also have a 520-H that has a spring over the linkage between the carb and the governor arm. My 518 does not have that spring. My question is, Should i have a spring around that linkage ? Thanks Shane Share this post Link to post Share on other sites
hummod 0 #2 Posted September 4, 2009 Most of the Onan powered tractors I own would surge until I cleaned the carb. Have you done that yet? I have been amazed by how much junk I have found inside some of them. Larry (hummod) Share this post Link to post Share on other sites
herbinohio 0 #3 Posted September 4, 2009 Larry, Thanks for the reply. I have taken the carb and fuel pump apart and cleaned both. Neither was all to bad considering it is 21 yrs old. I have made several adjustments with the linkages and it seems to be better. However, the governor still seems to have some movement. In comparison to my 20hp onan the spring around the linkage seems to make things much move stiff. My 520 is a 1990 so there is only 2yrs difference, I was hoping someone out here might have a 18hp like mine that they can compare to see if the linkage has a spring or not ? After all the hard work of putting this motor back together, this is the last piece.....l just hope i can get it fixed. Thanks shane Share this post Link to post Share on other sites
kpinnc 10,981 #4 Posted September 4, 2009 Shane, if you'll get a pic of the spring you're talking about- I'll look at my 518-h for comparison. I would also agree with the previous post on cleaning the carb. Even when they look nice, the jets are notorious for getting gummed up over time. That is sure to cause the engine to surge. I just did the same thing with the 518-H, and it now purrs like a kitten at idle and roars like a lion at WOT. It really made a tremendous difference. Applying a bit of choke will probably make the surging subside, but it is NOT a fix. It will make the engine run hotter, which is a very bad thing to do to an Onan... Kevin Share this post Link to post Share on other sites
herbinohio 0 #5 Posted September 4, 2009 Kevin, I thought i did a pretty thorough job of cleaning the carb with Carb and Choke Cleaner. i did not let the carb soak over night though ? The engine does exactly what you stated at low idle. If i choke it a bit, everything smooths out. hmmm.....? here are some pics of the 2 different linkages. the 518 being the one without the spring. thanks shane Attached Image Share this post Link to post Share on other sites
Herbl 10 #6 Posted September 4, 2009 I have a 520-H also with the same problem and I also cleaned the carb or so I thought. After my first cleaning it was doing the exact same thing, surging and the choke would smooth it out. I'm into Classic Cars and one of my car friends is a Toro Tech and he told me what to do. Take the top of the carb off and use carb cleaner and squirt it down every hole you see, if you look down the ventura you can see 3 tiny holes above where the idle screw comes out, they are air bleed valves and they are tiny and they get clogged. Just keep squirting carb cleaner till you see it coming out of these 3 holes and your surging will be gone, I hope this helps it sure did me... Share this post Link to post Share on other sites
kpinnc 10,981 #7 Posted September 4, 2009 Shane, my 518 does NOT have a spring. Looks just like yours, but a whole lot dirtier! With the top of the carb off, I agree with the spraying everything idea. But, if you look at the top of the jet, you'll see it is slotted for a screwdriver. You can carefully (use the proper size blade on the screwdriver) remove the jet and check visually for any gunk. It's part number 5 below: You should be able to see light through the main bore and the inlets on the sides. There are 4 total. DO NOT use anything to "rod" the jet, as you can damage it- but spraying carb cleaner and compressed air will open it up. The removable jet is directly above the fixed jet, which exits the bottom right-hand side of the sediment bowl. With the upper jet removed, spray cleaner through the fixed jet until it appears to be opened up. If there is ANY gunk in the sediment bowl, I would advise a good soaking in carb cleaner. Just remember to remove any gaskets, as the cleaner will damage them. When re-installing the jet, GENTLY seat it, as with any other carburetor. Lightly snug is all you need here. If you over tighten it, you'll have to buy that lovely $80 kit to make it right... I would also recommend using a VERY small amount of gasket sealer when putting it all back together again. It should be so little that nothing squeezes out when it's assembled, but it will eliminate any vacuum leaks you may cause opening it up- providing you don't destroy the gasket. It would also be a good time to replace the in-line fuel filter upon reassembly. Just my $.02... Good luck! Kevin Share this post Link to post Share on other sites
nylyon-(Admin) 7,130 #8 Posted September 4, 2009 I have a 520-H also with the same problem and I also cleaned the carb or so I thought. After my first cleaning it was doing the exact same thing, surging and the choke would smooth it out. I'm into Classic Cars and one of my car friends is a Toro Tech and he told me what to do. Take the top of the carb off and use carb cleaner and squirt it down every hole you see, if you look down the ventura you can see 3 tiny holes above where the idle screw comes out, they are air bleed valves and they are tiny and they get clogged. Just keep squirting carb cleaner till you see it coming out of these 3 holes and your surging will be gone, I hope this helps it sure did me... x2 that's how I fixed the surge on my 416 :scratchead: Share this post Link to post Share on other sites
