520-H Garden Tractor (Model: 73501) Engine Issue

[PAguy 8]

Good Evening, 

 

I just bought a 1993 520-H Toro Wheel Horse in relatively great condition. The problem that it has though is that it will not run if the throttle is to low. It runs with the throttle on high and seems to work fine other then an occasional sputter but if you lower the throttle it will sputter and if you put it all the way down it turns off. 
 

At this point I have replaced the battery, the spark plugs, and gas filter. I have to replace the air filter still but I am having a hard time finding one at the moment. I was trying to trouble shoot the best I could without having to take it into the shop. 

 

Any thoughts would be greatly appreciated. 

[AMC RULES 37,130]

Along with the dirty air filter, I'm sure you'll find your carburetor is in need of a good thorough cleaning.

[Handy Don 12,227]

Welcome to the forum.

Distance diagnoses are always tricky, but to me, as well, this is a carburetor issue.

A fresh air filter isn't a bad idea, but if the one you're running were really bad, you'd have poor performance at the higher revs as well.

How are your mechanical skills? Are you able to get in, remove the carburetor and give it a really thorough cleaning?

[lynnmor 7,306]

I too will bet that the idle circuits in the carburetor are blocked.

[PAguy 8]

30 minutes ago, Handy Don said:

Welcome to the forum.

Distance diagnoses are always tricky, but to me, as well, this is a carburetor issue.

A fresh air filter isn't a bad idea, but if the one you're running were really bad, you'd have poor performance at the higher revs as well.

How are your mechanical skills? Are you able to get in, remove the carburetor and give it a really thorough cleaning?

 

Thank you! Appreciate the responses. I was afraid that it was the carburetor in need of a clean. I have not taken a carburetor apart before but am pretty good at learning as I go along. Have been successful at working on the 314 I inherited from my grandfather. Is there a manual that I could reference? Any assistance would be greatly appreciate. Would like to save myself the house call from the mechanic if I can. 

[Handy Don 12,227]

There are some very useful documents in the forum's "manual" section (under Browse on the home page). It's best to use the search to find them.

The one I find most useful is this one:

 

I also have a parts manual that I think I got from the Onan site. Be careful with this to make sure you are referencing the correct model/serial from your engine.

Onan P216G P218G P220G OL16 OL18 OL20 LX720 LX770 LX790 Parts Manual 965-0268B.pdf

 

A few things to start you off:

1. READ the Service Manual several times before starting so you develop a familiarity with how its written and the job you are tackling

2. Take lots of pictures as you work--especially to see where you are removing screws and bolts so you know what goes back where

3. Patience is your friend. If you are stumped or confused, put down your tools and post some questions here along with pictures. There are some amazing resources here!

4. A two-cylinder, 20hp engine is not a toy. It can be a bit tricky to work on it but on the other hand, it is not rocket science!

5. Use new gaskets! One source I've used successfully is onanparts.com

6. Browse the forum. Practice searching so you can find some of the several recent threads here where members have tackled refurbishing Onan's from 520's. Read them over, they'll likely answer some questions you haven't even thought to ask!

 

As you browse the forum, you'll notice that not all members are fans of Onan's but there are a lot of us who respect and appreciate these engines. That yours is running reasonably well at high RPM tells us that it isn't a major issue. Good luck!

 

 

 

 

 

Edited September 5, 2021 by Handy Don

[roadapples 6,983]

I'd replace fuel lines also, so your time cleaning the carb isn't wasted...

  And 

[PAguy 8]

29 minutes ago, Handy Don said:

There are some very useful documents in the forum's "manual" section (under Browse on the home page). It's best to use the search to find them.

The one I find most useful is this one:

 

I also have a parts manual that I think I got from the Onan site. Be careful with this to make sure you are referencing the correct model/serial from your engine.

Onan P216G P218G P220G OL16 OL18 OL20 LX720 LX770 LX790 Parts Manual 965-0268B.pdf 1.07 MB · 0 downloads

 

A few things to start you off:

1. READ the Service Manual several times before starting so you develop a familiarity with how its written and the job you are tackling

2. Take lots of pictures as you work--especially to see where you are removing screws and bolts so you know what goes back where

3. Patience is your friend. If you are stumped or confused, put down your tools and post some questions here along with pictures. There are some amazing resources here!

4. A two-cylinder, 20hp engine is not a toy. It can be a bit tricky to work on it but on the other hand, it is not rocket science!

5. Use new gaskets! One source I've used successfully is onanparts.com

6. Browse the forum. Practice searching so you can find some of the several recent threads here where members have tackled refurbishing Onan's from 520's. Read them over, they'll likely answer some questions you haven't even thought to ask!

 

As you browse the forum, you'll notice that not all members are fans of Onan's but there are a lot of us who respect and appreciate these engines. That yours is running reasonably well at high RPM tells us that it isn't a major issue. Good luck!

 

 

 

 

 

 

THANK YOU! This is very helpful. Might be a next weekend project for me but in the meantime I will look for the gaskets to replace them when I take this apart and study the manual. 

 

Appreciate the encouraging words regarding the Onan, I was concerned I might have made a mistake reading some of the other feeds on them. The previous owner garage kept the tractor but it had not really been used much in the past three years. It is hard to find a well maintained wheel horse and I snatched it up as I was looking for something with a bit more power then the 314 that I have. Hope that cleaning the carb does the trick and it will run smooth again. 

 

Thanks again for all the help and I will check back in as I have additional questions and move forward. 

[kpinnc 12,049]

Just in case- make sure you're running ethanol- free fuel.

 

Carburetors don't do well with ethanol. 

[lynnmor 7,306]

5 hours ago, PAguy said:

 

The previous owner garage kept the tractor but it had not really been used much in the past three years.  It is hard to find a well maintained wheel horse and I snatched it up as I was looking for something with a bit more power then the 314 that I have. Hope that cleaning the carb does the trick and it will run smooth again. 

 

 

The words "it had not really been used much in the past three years" is likely the issue.  Ethanol in gasoline causes moisture to be absorbed and quickly degrades the fuel.  Use fresh fuel and run it often or buy ethanol free gasoline if available.

 

How many hours on the engine?  If it has 750 hours or more, it is time to adjust the valves.  Since you may be pulling the intake to remove the carburetor this would be a good time for that maintenance.  I have a few more chores for you to get it right, so report back the number of hours, also include some photos if you can.

 

NAPA always had air filters and pre-filters.

Edited September 5, 2021 by lynnmor

[oliver2-44 9,750]

Welcome. Looks like they have you headed in the right direction on the Oman. There a great engine, just a little more involved to work on. 
once you have the engine running good you might consider doing some transmission maintenance. Remove the cover over the tunnel between the dash and seat pan also remove the seat and seat pan. Then give that Eaton 1100 transmission and linkage a good cleaning. Keeping those hydro fins clean helps cooling it. Also gently clean the hydro linkage from the dash to the tunnel to the hydro. if you find any worn/lose/sloppy linkage post pictures and these guys can help you with it.  Then change the transmission fluid and filter.  

[lynnmor 7,306]

In addition to what oliver2-44 said, go a bit farther and pull the fuel tank, debris collects under there and lays wet causing rust.  The tank is easy to pull with the hydro filter off and not hiding that bolt.  Flush the tank and inspect or replace the petcock and its grommet.  Oil all moving linkage with the exception of the friction washer on the cam plate.  I do this service every fall after mowing and before snow removal to get the grass out of there and prevent the rust problem.

[PAguy 8]

On 9/5/2021 at 4:18 AM, lynnmor said:

 

The words "it had not really been used much in the past three years" is likely the issue.  Ethanol in gasoline causes moisture to be absorbed and quickly degrades the fuel.  Use fresh fuel and run it often or buy ethanol free gasoline if available.

 

How many hours on the engine?  If it has 750 hours or more, it is time to adjust the valves.  Since you may be pulling the intake to remove the carburetor this would be a good time for that maintenance.  I have a few more chores for you to get it right, so report back the number of hours, also include some photos if you can.

 

NAPA always had air filters and pre-filters.

So it has 1100 hours on it. I have included some photos. At this point I have just took the top of the carb off and cleared all that and checked the float with new gaskets. Did not completely take the carb off at this point. I also took the gas can off cleaned it out and replaced all the fuel lines as they looked in need of replacing. I have to order a replacement valve and grommet for the tank. It's not dirty but it looked a little bent. Also was able to determine the gas gage issue was the float was full of gas.

 

Did try it again with just having done all that and still having the same issue. Though it will run on low throttle if the choke is slightly engaged. 

 

Here is a link to photos waiser to share through Google. https://photos.app.goo.gl/uu57RNqYPJffvTFBA

 

Thanks again for all your help! 

[lynnmor 7,306]

2 hours ago, PAguy said:

So it has 1100 hours on it. I have included some photos. At this point I have just took the top of the carb off and cleared all that and checked the float with new gaskets. Did not completely take the carb off at this point. I also took the gas can off cleaned it out and replaced all the fuel lines as they looked in need of replacing. I have to order a replacement valve and grommet for the tank. It's not dirty but it looked a little bent. Also was able to determine the gas gage issue was the float was full of gas.

 

Did try it again with just having done all that and still having the same issue. Though it will run on low throttle if the choke is slightly engaged. 

 

Here is a link to photos waiser to share through Google. https://photos.app.goo.gl/uu57RNqYPJffvTFBA

 

Thanks again for all your help! 

 

It sounds like you need to do a more thorough cleaning of the carburetor, if choking it helps that means it could be a fuel restriction.  The intake manifold is made in two pieces and an air leak between them can cause the same symptoms at low speed.

 

Since there is 1100 hours, it is overdue for a valve adjustment and a de-carbon, the intake and exhaust needs to come off to do that maintenance.  While the valve adjustment won't cure the current condition, it would be a good time to do a number of things so that work isn't repeated.

 

The fuel valve with screen and the grommet are available from Amazon and eBay.  These are generic parts so you don't have to pay Toro prices.

 

Dorman makes a sending unit that works well to replace your defective one, the information is on this site somewhere.

 

That breather hose next to the carburetor should be replaced to keep dirt out.  Dielectric grease on it makes assembly easy.

 

The three screws holding the air filter box to the carburetor should have blue thread locker to prevent them from falling into the engine.

 

Ask questions here as you progress, I have more suggestions when I have more time.

 

Always keep the choke closed while the air box is off to keep things out of the engine.