Bigt31 8 #1 Posted April 30, 2016 Hello,all.I'm working on a 520-H I bought a few weeks ago.The engine is running rough,and surging.I noticed there is very little fuel in the fuel filter.Okay,do here's what I've done so far.I put a new fuel filter on it,blew out all the lines,drained and cleaned out the tank.I also cleaned the carb,and put a new fuel pump on it.There is still just a little bit of fuel in the filter.I was reading that it could be the pulse line.I havnt taken the shroud off yet,but I just wondered if anybody here would have any insight on the matter.Thanks for reading my post,and any help would be appreciated. 1 Share this post Link to post Share on other sites
newtowheel 6 #2 Posted April 30, 2016 Check to see if your mower has a shut off valve below the tank I'm not that knowledged about the 520s but some of them have a screen in the valve it may be clogging when the gas is flowing into the line. Also a good idea to make sure there is no problem with the pulse line. Good luck and hope it goes well for you. 1 Share this post Link to post Share on other sites
Pollack Pete 2,273 #3 Posted April 30, 2016 Every Onan that I've owned that had a surging problems was crap in the carburetor.I pull the top off the carb and soak all obvious places with carb cleaner.I've had good luck doing it this way so far. 1 Share this post Link to post Share on other sites
Tankman 3,514 #4 Posted April 30, 2016 Ethanol gas gums up the works. Carb cleaner, fuel additive, 100 octane low lead, non-ethanol gas keeps my '90 520-8 purring. Grandsons love visiting our local airport while I pick up 5 gallons of the non-ethanol fuel. Hear tell most marinas have non-ethanol gas too. 1 Share this post Link to post Share on other sites
Bigt31 8 #5 Posted April 30, 2016 ThanksThanks for all of the input guys.I appreciate it.Other than the surging,the engine also seem to be running rough. It dosen't just sound like the typical surging.I did take the valve off the bottom of the gas tank, and cleaned it too.I guess I'll take the carb apart again, and try another cleaning.Maybe I missed something when I cleaned it.Thanks again for the input.I appreciate it. Share this post Link to post Share on other sites
farmer 1,075 #6 Posted April 30, 2016 Another check (sometimes overlooked) is the fuel tank filler cap, make sure it's clear and venting. Share this post Link to post Share on other sites
312Hydro 473 #7 Posted April 30, 2016 (edited) Check the plug wires too. I had a bad coil and I found out by switching the wires . Only one cylinder was firing. Edited April 30, 2016 by 312Hydro Share this post Link to post Share on other sites
lynnmor 6,706 #8 Posted April 30, 2016 13 hours ago, Bigt31 said: I noticed there is very little fuel in the fuel filter. They all do that, it looks like it can't work, but it is just a big air bubble. If you are still having problems, check the compression. Share this post Link to post Share on other sites
whman01 15 #9 Posted April 30, 2016 I use my 416 for blowing snow and usually have to pull the choke out a little to get it to stop surging. It may need to have a larger main jet. However for the running rough, check the compression and the condition of the spark plugs. Compression should be within 10% of each other. Share this post Link to post Share on other sites
Bigt31 8 #10 Posted April 30, 2016 Okay,I forgot to mention I did check the fuel filler cap as well.I havnt checked the plug wires yet though.I'll check them next.I thought there should be more fuel in it.I have another 520-H,and a 520-8,and both of the filters on them are about 1/2 full. Share this post Link to post Share on other sites
elliot ness 1,916 #11 Posted April 30, 2016 It might just be the heads on the Onan need to come off and clean the carbon off of them I have had to do this on a few 20hp Onans, for some reason they get gummed up. Take a [soft] stainless brush on your grinder and it works good to remove the crap. taking the shrouding off is the only ruff thing. I have seen them so carboned up you could hardly see the spark plug. Share this post Link to post Share on other sites
Bigt31 8 #12 Posted April 30, 2016 Well,thanks everybody for all the ideas.I think I found the problem. I went to remove the plugs and I only had to use my hand to remove the rear one.I didn't mention before that I've also had a starter issue.It would only do it some times.I would go to start it,and it would just grind.Well,today I havnt been able to get it to turn over at all.I'm gonna take the starter off of the 520-8,and give it a try.Thanks again to everyone for your input.Hope everyone has a good weekend. 1 Share this post Link to post Share on other sites