520 HC Onan 20 HP Governor issue?

[westkane 1]

I am new to the site and am looking for info on how to fix my 520 hc.  If the tractor is under load, such as mowing, it seems to run OK at a steady rpm, but if it isn't under load, the engine "cycles" speeds up, then slows down repeatedly, engage the mower and it settles down, I think it is related to governor function, but don't know for certain.  Anybody tell me what may be the problem and how to repair it?  Thanks for any input

[stevebo-(Moderator) 8,409]

From one 520HC owner to another... you have a dirty carb.

[Rock farmer 41]

You may have a dirty carborater. Does it run good at higher RPM's but, surge at lower RPM's

Joe

[JackC 617]

From one 520HC owner to another... you have a dirty carb.

From a second 520HC owner to another... you have a dirty carb.

[MalMac 1,332]

• Yep dirty carb, eventually it will even get to doing it at High RPM. Onan carbs famous for being sensitive to dirt, even microscopical particles of dirt.

[AMC RULES 37,153]

You need a bath...err...I mean, at least your carb does.     

[ben06351 19]

Yup sounds like a dirty carb. My 520 HC did the same thing.

[westkane 1]

THANK YOU!  for all the replies and quick responses, great forum and super members

[woodchuckfarmer 333]

Yep , Dirty carb.   Mine did it too

[zenithradio 1]

 

I belived problem was a lean idle mixture problem. Problem has mostly gone at high

speed and better with choke on. Looking at Onan engine manual (on16_24h.pdf) page 7-4-2

figure 4a Carburetor middle drawing it shows a TAMPER-RESISTANT PLUG OVER

IDLE MIXTURE NEEDLE. I was sure the problem was with this covered idle needle

value.

 

The engine slows down do to lean mixture, then governor speeds engine up

so engine does not stop, then this repeats.

 

The fix is to remove idle needle value, clean, re-assemble and adjust.

 

Remove the muffler to gain access to the right side of carburetor. 

 

Looking at right side of carb on lower left is accelerator pump. Pump is round

and held on with 3 screws. To right of pump there is 2 temper resistant soft metal

round plugs. A larger one above a smaller one. The lower smaller plug is the

one we want to remove.

I used a small nail. Tap the nail into center of small plug making hole. Using nail,

bend to side and pull plug out. In my case plug was very soft and came right out.

 

Remove idle needle valve with small flat screwdriver. Using small spray tube on can of

carburetor cleaned spray cleaner into needle valve hole. Give valve hole several

good shots of cleaner.

 

Clean idle needle valve and re-install. Very lightly turn needle until it bottoms

in hole. Now turn back out (counter-clockwise) 2 turns.

 

The muffler has a bracket on bottom. The bolts for bracket go through part number

113874 Engine bracket (3318-524 Parts Catalog sheet 24). Install muffler, leaving off

the 113874 engine bracket.

 

With engine bracket removed we can run engine and still get to idle needle value

and make idle adjustment. 

 

Start engine. In my case idle was about 2200 RPM with NO hunting.

Let engine warm up. Using a long small blade flat screwdriver turn needle valve clockwise

slowly until idle is about 1400/1600 RPM.

 

Re-install 113874 engine bracket. 

 

I have made this repair on 2 model 520H Wheel Horse tractors, fixed both.

[WH nut 553]

Clean the carb and everything will be fine.

[lippy-01 0]

Hello, Sorry I'm new to the forum just like the original posting member. I just got a steal on a 518h 42" deck had a flat front tire and flat rear tire and 473 hours on the meter and with a little wax would honestly look new paid 300$ for it oh I also put a new seat on it other has a slight tare and a new battery.. However, I come to find out though I'm currently having the same problem with the 18HP onan that is on it, it is searching for the right rpm for its self would this most likely be the same issue? the air filter was plugged solid with crap so I also replaced it and the pre filter and cleaned out the gas tank.. If anyone is interested I have a 244H for sale that looks good and clean it is what the 518h replaced..

[WH nut 553]

Hello, Sorry I'm new to the forum just like the original posting member. I just got a steal on a 518h 42" deck had a flat front tire and flat rear tire and 473 hours on the meter and with a little wax would honestly look new paid 300$ for it oh I also put a new seat on it other has a slight tare and a new battery.. However, I come to find out though I'm currently having the same problem with the 18HP onan that is on it, it is searching for the right rpm for its self would this most likely be the same issue? the air filter was plugged solid with crap so I also replaced it and the pre filter and cleaned out the gas tank.. If anyone is interested I have a 244H for sale that looks good and clean it is what the 518h replaced..

How long has it been sitting, you should clean the carb but youmay get lucky by putting some sea foam in the tank and running it.

[lippy-01 0]

Honestly I have no Idea how long it has been sitting see I work at a tractor dealer and this one the guy kinda just wanted rid of so we took it in on trade and I picked it up cause my boss didn't want to put any money into it.. Which his loss my gain cause it is prob worth a grand I would imagine.. like I said other then no general care of  the machine it is in great shape I put some sea foam in it and drove it for 20min or so and now it has been sitting for a week so I'm hoping that the foam will take care of it but if not then I will clean the carb.  Thank for your reply