520H won't idle up, black smoke. Help!

[Rusty_Tractor 0]

Hey guys,

I just bought a nice 1990 520H but it doesn't run quite right. I know it has potential because I mowed with it 2 weeks in a row. It ran strong and did not smoke then.

When I met the seller, it would start but only run at low rpm. It would not idle up when the throttle was increased. Any choke would stall it and there were puffs of black smoke. After a while it just started to run normally.

Well I bought it anyway because otherwise it is in really nice shape. Today it was doing the same thing. I could not get it to run right. I thought it was running on one cylinder so I cleaned the plugs and wire terminals, no real change. It seems to be running very rich but I don't know why. I have spark on both plugs. The fuel filter is clean and I can see gas pulsing into the filter. The plugs had dry, black soot on them when I cleaned them. No oil or gas.

Anyone have any ideas?

Thank you,

Jamie

[CRE1992 135]

It definitely sounds as if it is running rich, could be a problem with the float in the carburetor, or the needle is not seating and it is letting the fuel keep pouring on in. Did you see if it ran any better with the air filter off? I have a 1995 520H and I love it. So goodluck

[Rusty_Tractor 0]

Diagnosis!!!

Hey guys, I wanted to close out this thread with a diagnosis of the issue.

Today I fired up the 520 for the first time in over a week, it ran OK but would not get to 3500 RPM and sounded rough. Removing the rear plug wire did almost nothing, removing the front shut it down. We concentrated on the rear cylinder. I noticed that it would shoot gas out of the carb while running. A friend of mine who is really slick with engines said "the valve isn't closing all the way." I said OK, how do you know that?

Anyway, we tore the intake and exhaust off, adjusted all 4 valves, and now it runs like a new tractor. I am amazed at how easy that was.

Jamie