Surging/Hunting

[Strokerace2639 1]

 Yes I understand there are many threads about this. As they as a few years old, and I just picked up this machine I am starting a new. 

  1988 Wheel Horse 520-H bought from original owner.

  only parts I have replaced to this point are the Fuel Filter and the starter solenoid.

 Runs great on start up and until its good and warm ( 15 minutes or so), then  it starts surging/hunting. The engine speed goes up and down, the vacuum goes from like 2 to 15 very rapidly, under load. As

soon as I stop the mower deck it settles right back to what I would consider normal. 

  Sets already  done.   used propane and starter fluid around the intake and carb. found no noticeable changes. 

i did notice the fuel filter never seems FULL. is this normal? 

What are the things I should look at and in what order?

 

Thank You, StrokerA

[sqrlgtr 2,990]

just acquired a 520H a few months ago same symptoms and the 2 piece manifold was leaking/sucking air. Replaced manifold and runs like a champ now. I did clean/rebuild carb while I had it apart also dun  a good cleaning of engine cooling fins whist I was in tare down mode...Oh yeah had a bad oil leak at oil drain where it goes into block. Just some well needed love and ready for another 30 years

A few pictures for encouragement/courage 

Edited 21 hours ago by sqrlgtr

[sqrlgtr 2,990]

Almost forgot Welcome to 

[Ed Kennell 46,161]

1. clean the carb

2. clean the carb

3. clean the carb

 

 

                     to the 

Edited 20 hours ago by Ed Kennell

[953 nut 66,400]

                Perhaps a vacuum hose has a small crack which is aggravated by the vibration of the mower deck.

[Strokerace2639 1]

2 hours ago, Ed Kennell said:

1. clean the carb

2. clean the carb

3. clean the carb

 

 

                     to the 

 Yeah thats what  I was thinking..  best way to do that? can I get away with just removing the 4 screw from the top of the carb? then use something like permatex orange on reassembly? I normally remove gaskets and use stuff like Sillycone or TheRightStuff. Never had anything leak yet.

Thank You!

[Strokerace2639 1]

2 hours ago, 953 nut said:

                Perhaps a vacuum hose has a small crack which is aggravated by the vibration of the mower deck.

Thank you and your Family for your Service.

 

[Bill D 2,873]

5 minutes ago, Strokerace2639 said:

 Yeah thats what  I was thinking..  best way to do that? can I get away with just removing the 4 screw from the top of the carb? then use something like permatex orange on reassembly? I normally remove gaskets and use stuff like Sillycone or TheRightStuff. Never had anything leak yet.

Thank You!

Take the top off the carb.   Clean the bowl and main jet with cleaner and compressed air.  Be careful not to lose any small parts, or drop them down the intake.   Do not use sealant on the gasket when reassembling.   You may have to clean it several times.  

[kpinnc 18,325]

1 hour ago, Strokerace2639 said:

Yeah thats what  I was thinking..  best way to do that? can I get away with just removing the 4 screw from the top of the carb? then use something like permatex orange on reassembly? I normally remove gaskets and use stuff like Sillycone or TheRightStuff. Never had anything leak yet.

 

I would also run a fine bead of silicone or similar on the seam of the two piece intake manifold. All the way down the seam on both sides. 

 

That, along with cleaning the carb worked wonders for my 520-H. 

[parsonsponyz 341]

to Red Square.

 

Pull the carb off and do a thorough cleaning.

[lynnmor 8,833]

It is best to pull the intake in order to remove the carburetor for proper cleaning.  It makes sense to do a valve adjustment at the same time since the intake needs removed to do that.  Before doing any of that, check the compression to see if there may be other problems.  Use only genuine Onan gaskets for the intake, valve covers and exhaust and torque to specs found in the Onan Service Manual that can be downloaded in the Manuals section.  The cheap kits found on the auction site are rather poor quality but some of the parts are OK, I use the carburetor bowl gaskets without issue but the manifold gaskets and needle are junk.  Use no goop on the carburetor, check the intake manifold for leaks while off by blocking the carb port and filling it with gas, kerosene or diesel fuel, if a leak is found come back for guidance on that repair.  Follow the manual and do nothing that you aren't sure of, return here for advice.