tsmall07 49 #1 Posted September 22, 2016 (edited) My engine has always surged some, but it's getting worse, particularly at lower rpm. Any ideas what could be causing this? The air filter is fairly clean. Also, I lost my dash panel this winter. Anyone have a spare? Edited September 22, 2016 by tsmall07 Share this post Link to post Share on other sites
lynnmor 6,706 #2 Posted September 22, 2016 Sounds like the governor to me. Look at the manuals on this site for adjustment procedures. The voltage regulator appears to not be working as well, aftermarket regulators are available for far less than oem. 1 Share this post Link to post Share on other sites
Pollack Pete 2,273 #3 Posted September 22, 2016 Every Onan twin that I have,and I have several,that had a surging problem was a plugged carb.Engine surges.........clean carb.........surge gone. 2 Share this post Link to post Share on other sites
608KEB 794 #4 Posted September 22, 2016 (edited) Common problem, take the top of the carburetor off. Clean the float area and especially the needle. It's usually the needle. Use carburetor cleaner. Also use unleaded premium with no ethanol. This will reduce the problem. Edited September 22, 2016 by 608KEB 1 Share this post Link to post Share on other sites
tsmall07 49 #5 Posted September 22, 2016 Is it a paper gasket or can you reuse it sometimes? I have no idea where to buy a gasket for the carb on this thing. Maybe I can make one with RTV. Share this post Link to post Share on other sites
WHX?? 46,404 #6 Posted September 22, 2016 @boomers_influence has parts for Onans maybe he can help you out. There is another member here as well that has Onan stuff but don't remember his name, he does have a regular website he sells parts through tho. Check the vendors section for other possibilities. 1 Share this post Link to post Share on other sites
Ed Kennell 35,146 #7 Posted September 22, 2016 The three things you need to do to stop the surging.....Clean the carb X3. 1 Share this post Link to post Share on other sites
boomers_influence 106 #8 Posted September 22, 2016 tsmall most likely the idle jet tube is the problem. it can be reached with the top of the carb removed. e/mail me and i will send you a parts manual page showing the location of the tube. boomers_influence@yahoo.com 651 437 2826 M-F 10-7 S-S 12-6 cent time. thank you. boomer ( the used onan engine parts guy,also NOS and new ) 1 Share this post Link to post Share on other sites
fireman 1,021 #9 Posted September 22, 2016 The intake manifold on the Onan engines is of a two piece aluminum design. The sealant they used to seal the two halves becomes brittle over the years. This causes extra air to be sucked into the mixture giving an erratic surge and incorrect fuel to air ratio. I had the same exact problem on my John Deere 318 which has the same engine and the 520. On the recommendation from a thread on a JD forum I took the intake manifold apart, cleaned and re-sealed it. The surging problem was gone. Also the carburetors are known for gunking up. Take that apart and clean out the jets and passages. Last thing is the fuel lines. Ethanol in todays fuels breaks down the inside of older fuel lines which also clogs up the little passages and jets in the carb. I highly recommend replacing them with new high quality fuel line. I had the same issue as you and after doing all of these things my Onan runs excellent! As a note make sure the fins on the heads are clear of grass clippings etc. The Onans are notorious for loose valve seats due to over heating. 4 Share this post Link to post Share on other sites
WHX?? 46,404 #10 Posted September 23, 2016 Another member said to spray WD-40 around the manifold seam Fireman mentioned while running, if the motor changes pitch it is leaking. 2 Share this post Link to post Share on other sites
HokieAg07 129 #11 Posted September 24, 2016 Its easy, Tyler. Give me a call if you want. 1 Share this post Link to post Share on other sites