520H starting issues

[Junkyard_sal 8]

I have a relatively new to me 520H. I noticed when I got it that it would surge at full throttle until it warmed up. 
 

it ran fine once warm. I let it sit for a week and it was super hard to start. Like it fired but it didn’t want to take throttle or release the choke. It died and then would not retire. 
 

I used carb cleaner and got it fired but it wouldn’t run on its own. I let it sit gave it full choke and half throttle and got it fired and it ran fine.

 

it sat another couple of weeks and now I can’t get it to fire except with carb cleaner. I removed the fuel pump and tried to gravity feed the fuel filter. Still no fire. 
 

if anyone is near Waterbury VT. I have a new fuel pump coming.
 

 I am open to paying for a pro to sort it out if you know one near me or I will pay for your time to come to me, some I would have to rent a trailer to move the mower and winch it onto a trailer. 
 

I am not a small engine guy at heart. Give me a BMW or Chevy big or small block and I will fix it but small engines are not my bag! 

[953 nut 55,393]

Since you don't know the maintenance history on this I would suggest you begin by checking fuel flow from the tank, replace the fuel line and add d fuel filter. An old fuel hose could be cracked allowing air in ant the fuel pump won't pump air.

Be sure to use non-ethanol gas https://www.pure-gas.org/

[Junkyard_sal 8]

Hi 953

 

i got it running on a gravity feed and it runs smoothly (thirsty though) 

 

I inspected all fuel lines and pressure tested them this afternoon. 
 

primer bulb pulls fuel from tank smoothly and cleanly. No hissing. Fuel line closed will hold negative pressure without leaking. 
 

The lines are old but in good condition this is a 255 hour machine! So that is good and bad rubber likes to be kept moist! 
 

 

[Junkyard_sal 8]

48 minutes ago, 953 nut said:

Since you don't know the maintenance history on this I would suggest you begin by checking fuel flow from the tank, replace the fuel line and add d fuel filter. An old fuel hose could be cracked allowing air in ant the fuel pump won't pump air.

Be sure to use non-ethanol gas https://www.pure-gas.org/

We have ethanol free in Waitsfield VT and that is what is in the tank. 

[WHX?? 48,853]

53 minutes ago, Junkyard_sal said:

255 hour machine! 

Really... any pics? 

[BBQVultureWings 104]

    Every Single Small Engine I buy or aquire Always gets the fuel tank cleaned, New Fuel lines & a New Filter even if they "look" new. I do not believe most previous owners stories, descriptions or historical accounts as they are just wanting rid of what is a problem for them anyway & will say whatever it takes to get it sold....  Fuel lines are primarily rubber & Petroleum products decay rubber. For that reason alone I change fuel lines & filters every year (or 2 if it is a light use machine) Bulk fuel line is cheap & Fuel filters are cheap too, cheap enough that I just make it a habbit to give the new to Moo-Wah Engine the best chance at running strong without problems. This also gives me a place to start from when diagnosing future problems without frustration    . I already know The Fuel system is good & clean Fuel pumps get a good cleaning as well if it has 1 that is..... This Practice eliminates a possibility when diagnosing issues. Not Everyone does this. After fixing enough small engines I just made this a standard practice.& it has made the other things easier to find.

[Junkyard_sal 8]

1 hour ago, WHX?? said:

Really... any pics? 

Will get some tomorrow 

[peter lena 8,653]

@BBQVultureWings   just a brain fart , reading your fuel hose reply , been there done that , since adding an ounce and a half of STA BIL  to all my tank top offs ,  made for storage , there is ZERO FUEL HOSE / FILTER DEBRIS , have 2 filters on my horses , one large / clear close to tank , another close to carb , clean / clear , carb bowels , clean clear , alsi only use regular ethanol  gas , been doing this for years now , and it consistently  is clean / clear  in all my fuels    had replaced all my fuel hoses , clean carb bowl , tank since STA/ BIL  there has been ZERO DEBRIS IN MY FILTERS , what is that telling you ?  regularly experiment with a  repetitive problem  to improve / eliminate it , my generator  sits for months , fuel filters are clean / clear , tank is also clean clear , STA BIL  in the gas , starts  right up , used to have , mower deck spindle / noise / failures , lucas hi temp re grease , eliminated that , no whyining noise , failures , make a change ,  pete    

[Handy Don 12,281]

On 10/22/2024 at 8:20 PM, Junkyard_sal said:

this is a 255 hour machine!

Primer bulbs were not a factory option, so someone has been in there & probably replaced the lines when the bulb got added.

Hours on the machine is essential for mechanical parts, but AGE is a big factor for other stuff like fuel lines and fuel pump diaphrams & check valves.

 

Onan’s can be cranky, especially if their maintenance is ignored and they are stored unprotected. You may need a thorough carb cleaning (I recommend an ultrasonic bath with the proper solution). With no fire on carb cleaner, though, I’d start with checking for power at the ignition coil and for spark. This could be a simple wiring problem.

Edited October 25 by Handy Don

[Junkyard_sal 8]

On 10/22/2024 at 9:14 PM, WHX?? said:

Really... any pics? 

 

[Junkyard_sal 8]

So I solved the hard starting issue 

 

but the tractor hunts on start-up until it gets fully hot.

 

i wonder if I have a leak in the vacuum hose to the fuel pump or in another vacuum hose. 
 

I should clean the carb as that upper needle is probably part of the problem for a tractor that has mostly sat for 20+ years 
 

anyone else have a 520H that hunts on startup until fully warm? 
 

she looks good though doesn’t she 

Edited October 25 by Junkyard_sal

[Junkyard_sal 8]

On 10/23/2024 at 5:17 PM, Handy Don said:

Primer bulbs were not a factor option, so someone has been in there & probably replaced the lines when the bulb got added.

Hours on the machine is essential for mechanical parts, but AGE is a big factor for other stuff like fuel lines and fuel pump diaphrams & check valves.

 

Onan’s can be cranky, especially if their maintenance is ignored and they are stored unprotected. You may need a thorough carb cleaning (I recommend an ultrasonic bath with the proper solution). With no fire on carb cleaner, though, I’d start with checking for power at the ignition coil and for spark. This could be a simple wiring problem.

I put the primer bulb on for my diagnosis and then used a motorcycle gravity feed tank. 
 

I might put the gravity feed tank back on to try and diagnosis the issue with the tractor’s throttle hunting on startup until it is warm 

[lynnmor 7,321]

18 minutes ago, Junkyard_sal said:

So I solved the hard starting issue 

 

but the tractor hunts on start-up until it gets fully hot.

 

i wonder if I have a leak in the vacuum hose to the fuel pump or in another vacuum hose. 
 

anyone else have a 520H that hunts on startup until fully warm? 

The line to the fuel pump is a pulse hose from the crankcase so not a vacuum problem.

 

Check the intake manifold gaskets at each end and under the carburetor, spraying carb cleaner at those while running might help find a leak but it is a fire hazard.

 

Sometime around the time yours was made carburetors with an accelerator pump were installed so that the mixture could be leaner for emissions purposes, that pump can fail.  onanparts.com had those pumps.

pump

 

I would pull the intake manifold and clean the carburetor properly.  Use new genuine Onan intake and exhaust gaskets, cheap ones fail.  Cheap carburetor kits with 3/8" aluminum welch plugs might be available on eBay but I am not seeing one right now, they will give you a backup plan if you tear a gasket but be aware that some of the parts are junk.

 

The intake manifold is in two pieces and the seam can leak, instructions on how to repair is on this site.  If you suspect a leak and want to repair, get back for even more instruction.  Also, heat shields often cut into the edge of the intake so check that and cut a bit clearance so they cannot touch. intake

 

A torque wrench will be needed to install the intake and exhaust.  Download the Onan engine manual for torque values and instructions. Onan Manual

[Junkyard_sal 8]

50 minutes ago, lynnmor said:

The line to the fuel pump is a pulse hose from the crankcase so not a vacuum problem.

 

Check the intake manifold gaskets at each end and under the carburetor, spraying carb cleaner at those while running might help find a leak but it is a fire hazard.

 

Sometime around the time yours was made carburetors with an accelerator pump were installed so that the mixture could be leaner for emissions purposes, that pump can fail.  onanparts.com had those pumps.

pump

 

My Stihl 200t had an accelerator pump and when it failed the saw ran like ****. Some people fill the accel pump with JB weld. I installed an 020 carb and she runs like a scalded dog! 
 

 

[Handy Don 12,281]

2 hours ago, lynnmor said:

The line to the fuel pump is a pulse hose from the crankcase so not a vacuum problem.

 

Check the intake manifold gaskets at each end and under the carburetor, spraying carb cleaner at those while running might help find a leak but it is a fire hazard.

 

Sometime around the time yours was made carburetors with an accelerator pump were installed so that the mixture could be leaner for emissions purposes, that pump can fail.  onanparts.com had those pumps.

pump

 

I would pull the intake manifold and clean the carburetor properly.  Use new genuine Onan intake and exhaust gaskets, cheap ones fail.  Cheap carburetor kits with 3/8" aluminum welch plugs might be available on eBay but I am not seeing one right now, they will give you a backup plan if you tear a gasket but be aware that some of the parts are junk.

 

The intake manifold is in two pieces and the seam can leak, instructions on how to repair is on this site.  If you suspect a leak and want to repair, get back for even more instruction.  Also, heat shields often cut into the edge of the intake so check that and cut a bit clearance so they cannot touch. intake

 

A torque wrench will be needed to install the intake and exhaust.  Download the Onan engine manual for torque values and instructions. Onan Manual

 

, since you are now getting fire and it’s running....

Edited October 25 by Handy Don

[Junkyard_sal 8]

4 hours ago, lynnmor said:

The line to the fuel pump is a pulse hose from the crankcase so not a vacuum problem.

 

Check the intake manifold gaskets at each end and under the carburetor, spraying carb cleaner at those while running might help find a leak but it is a fire hazard.

 

Sometime around the time yours was made carburetors with an accelerator pump were installed so that the mixture could be leaner for emissions purposes, that pump can fail.  onanparts.com had those pumps.

pump

 

 

I will start the diagnosis of the intake and the carb.

 

she is doing work now but will be better soon.

 

mixing two great makers. That gravely cart is pretty handy! 
 

 

[WHX?? 48,853]

9 hours ago, Junkyard_sal said:

she looks good though doesn’t she 

 

Got that right!!!!! 

 

Try sea foam in the gas ... might not help but sure won't hurt.