520H Engine Issues

[Coors 0]

I have a '95 520H with an Onan 20hp engine with about 434 hours on it. I was plowing snow the other day and it started to run rough after about 15 minutes of running. The engine would rev up then down, then up, then down over and over again. I finally used the choke and it puffed a little black smoke and it was fine. I started plowing again, and about 5 minutes later the engine did the same thing. Choked it a few times and then it ran fine. It was like it wasn't getting gas then it wasn't or was just running on one cylinder. I recently cleaned out the fuel tank and blew out the lines and bought a new fuel filter.

Any ideas??

Thanks,

[Operator 7]

Sounds like water in your gas. See what the other fellers think.

Randy

[MalMac 1,328]

I agree with Operator plus the Onans are famous for any small particle in the carb causing the same problem your having. Try taking the top off the carb and cleaning out all the ports, holes everything. This time of year it would not be out of the question to get condensation in the tank or the carb itself. Like Operator said you could be getting water in it.

[Shuboxlover 474]

Yep, that's the first thing I thought, carb is icing up, gotta keep that thing warm

[rickv1957 70]

Carb might need a good cleaning also.........

[Brandonsj04 0]

I have to agree with everyone else that it probably just needs a carb cleaning but from my experience, check everything else before you decide to pull the carb as it is no easy(maybe I should say quick) task with the onan engine.

Case in point. 2 months ago I go to start up the 520 and started her up with the choke on, ran good, but once I took her off choke she started to surge. Everything pointed to a dirty carb, so armed with a box full of tools, some seafoam, and gummout I started off with the easiest line of defense and just pulled the top of the carb off. Removed the gas in the bowl, sprayed gummout in all the right areas, primed the bowl with gas and some seafoam for good measure bolted everything back up but to no avail. Well went back and repeated step 1, this time pulled off the muffler tin to get at the bowl drain plug. Removed that to get at the main jet. Contorted a screwdriver to get the jet out. Cleaned that, bolted everything back up, but once again to no avail. Pulling out the big guns I then removed muffler, dropped the pto bracket, removed all choke and throttle linkages, disconnected fuel and vacuum lines, removed all tins in the way, I was finally able to remove the intake manifold. Submerged the carburetor in some gunk (1 gallon stuff) for 24 hrs, bolted everything back on and no change Now I am believing that I have an intake leak so spraying carb cleaner around intake manifold, I finally get a bite. Welch plug decided to jump ship causing the engine to run lean. Run to Toro with the once again dismounted carb to get a welch plug and some new intake gaskets for sanity. Got parts, installed, bolted everything back together, crossed fingers, hit the key, and vroom prr prr prr.

Gotta love a good running onan, but boy are they time consuming to service

[Operator 7]

Start with the simple things first, add some "Heet". I have had the same problem too. The one time I did have to do like Brandon and pull just the top off carb and get down in there, small something or other was in there and that took care of it.

It i just one more of those "learning experiences".

Randy

[Coors 0]

Thanks for all of the responses. I will try to add some heet the next time I use it. Hopefully it is that simple.

Thanks everyone.