520H engine problem

[papasan1 4]

I just purchased a 520H. 

First day I replaced all fluids and filters.  Still running fine.  Second day I replaced the plugs.  Now it won't idle, rpms fluctuate and will only run full throtle with the choke 1/4 closed.  To be sure, I put the old plugs back in....same thing.  What could I possibly have screwed up?

Thanks,

Frank

[richmondred01 2,237]

Check the plug wires to make sure there no issues with the actual wires and make sure they are on the plug and coil

[boovuc 1,090]

Otherwise, as Richmond stated, it could just be a coincidence and you need to clean out that carburetor as choking on idle is a common theme when you have some debris in them.

[papasan1 4]

Thanks, I'll look into yhe carb.  I'll let you know in a fewq days

[MalMac 1,331]

We need a whole topic Pinned at the top " Onan surging problems" or Onan carb cleaning. Maybe it's just me but anytime you see the words 520h or Onan, it's connected to a surging dirty carburetor.

[papasan1 4]

Hopefully I can find some instruction for cleaning the carb.  Anyone seen a link for this procedure?

Thanks

[MalMac 1,331]

Just take the top of the carb off. Pull out the floats and get all the gunk out of the bottom of the carb. Get some good carb cleaner and spray all the nooks and crannies. Get some thin wire and poke and probe all the orifice's. That should do it. If not you can take the carb off and soak it in some carb cleaner overnight the blow it off with compressed air. Make sure your tank is clean and your fuel line is in good shape and not deteriorating. Try and use a non-ethanol gas. If you can't find it use a higher octane. This is just what I have done. I am sure there are others on RS that have different and better ways. The carb on the Onan is  very temperamental to any kind of containments and can cause a whole host of problems. Oh yeah when you get it back together run some SeaFoam in your gas for a tank or two. That's some good stuff just don't over use it, because it is very hard on rubber gas lines.

[boovuc 1,090]

Papasan, if you do a search of the site, in particular, the engines forum, you'll find some detailed instructions members posted on removing the top of that carb and spraying it with Seafoam cleaner. (Seafoam is what I recommend using). Also details for things to watch out for and places to really get the spray into. 

Here is one of the posts and I know there are a few more that show you how to do this cleanout without removing the intake manifold and carb from the engine.

 

[papasan1 4]

Thanks for the link and for all responses. Once the holiday visitors are gone, I'm on it.

[boovuc 1,090]

Enjoy the holiday weekend. Even the inlaws! 

[richmondred01 2,237]

Seem very strange that the same time you removed the plugs you also got a carb problem. Once again I would check the wires and connections prior to getting into the carb. Once I've certain it's a carb issue I won't do a half smacked job on the carb. Pull the intake, reseal the intake, soak the carb on cleaner over night, get a new rebuild kit, new intake to block gaskets and do it correct one time. While the Carb and intake are off I would pull the exhaust, reset the valves too. For that you will need to valve cover gaskets and the exhaust to block gasket.

I can almost guarantee that the fin in the back cylinder are full of years on crud just waiting to pop a valve seat that why on Every wheel horse onan I have had I always pull the engine and clean the heads within the first hour or two. This way I know what I have. That's just me. Do it once, you know what you have then use it.

[papasan1 4]

Thanks again for all the input.  I took off the top of the carb, removed the float and needle valve, used carb cleaner in every orifice, blew out with compressed air....PROBLEM SOLVED1111

I have a hydro question but I'm sure it goes in transmissions.

Thanks again to everyone.