Fuel pump issue

[Brad520H 17]

Currently working on 1991 520H. Fuel pump isn’t getting gas to it at all. Lines are clean, valve under tank is clean and in opened position. First time trying to start since restored. Any way to test pump without fuel ever making it to it? I’ve read vacuum hose could be cracked but not sure how big a job that’d be to replace. Looks like a lot of shrouds would have to come back off 

[ri702bill 8,327]

I'm sure some folks will chime in - there is a great photo of Eric @ebinmaine manually "presurizing" a rear tank prior to start-up.

Tractors like the 520 and the C series with the tank below the seat can be difficult to prime. Some have added a hand bulb primer like on an outboard motor, others ditched the OE pump for an electric one...

[lynnmor 7,307]

First, it is not a vacuum fuel pump, it uses pulses caused by changes in crankcase pressure as the pistons move.

 

The pulse hose is indeed difficult to replace with the shroud in place, but a brain surgeon may be able to do it thru the opening for the oil filter.  Get extra length of hose and don’t cut it till you are fastening the pump.

 

Remove the fuel hose at the pump and lower it to see if there is a flow.  If that checks out, reconnect and remove the hose at the top of the pump and add a hose to direct fuel into a container, then run the starter to check for flow.  
 

No priming is necessary, but it takes awhile to get fuel to the carburetor if the tank was ran dry or the engine sat for many days.  A leak in the fuel hose will allow air to be drawn in and prevent pumping, so be sure you have good hose and spring clamps.

[Handy Don 12,233]

I agree with @lynnmor on testing for fuel availability and pumping action at the pump before looking deeper. When I overhauled my 518 I found that a PO had routed the supply line awkwardly and it was pinched behind the side tin against a hydro line so that only dribbles of fuel were coming through. New supply line and better routing and then delivery was fine.

 

Also be careful, many of those pump bodies are plastic and the nipples can be broken off with rough handing--experience speaking. Nor can I see a way that to replace the pulse pump hose without removing the tins, but I’m no brain surgeon!  

 

BTW, that pulse pump hose is the only heavy ¼” fuel line on my 518 and I replaced it when I had the tins off a couple years ago just on principle. Since it doesn’t carry fuel I don’t worry about ethanol and its thick sidewalls (vs. the relatively thin Stens TruBlu tubing I use as fuel line) won’t flex. Of course that stiffness also gave me some resistance when I installed it! 

Edited February 9, 2023 by Handy Don

[Brad520H 17]

15 minutes ago, lynnmor said:

First, it is not a vacuum fuel pump, it uses pulses caused by changes in crankcase pressure as the pistons move.

 

The pulse hose is indeed difficult to replace with the shroud in place, but a brain surgeon may be able to do it thru the opening for the oil filter.  Get extra length of hose and don’t cut it till you are fastening the pump.

 

Remove the fuel hose at the pump and lower it to see if there is a flow.  If that checks out, reconnect and remove the hose at the top of the pump and add a hose to direct fuel into a container, then run the starter to check for flow.  
 

No priming is necessary, but it takes awhile to get fuel to the carburetor if the tank was ran dry or the engine sat for many days.  A leak in the fuel hose will allow air to be drawn in and prevent pumping, so be sure you have good hose and spring clamps.

Sorry correct, pulse hose. I was able to take it off and it does in fact still have pulse so doesn’t seem to be cracked/ disconnected thankfully, but gonna be a little tough to get back on the pump with basically no extra. I cranked for awhile with nothing. Going to replace long fuel line from tank to pump since it’s definitely old. Didn’t see leaks but definitely chance of air getting in from some places. Had been out in the sun for awhile so some very small rot areas by the pump may be the problem. Thanks for the help!

[lynnmor 7,307]

1 hour ago, Brad520H said:

Sorry correct, pulse hose. I was able to take it off and it does in fact still have pulse so doesn’t seem to be cracked/ disconnected thankfully, but gonna be a little tough to get back on the pump with basically no extra. I cranked for awhile with nothing. Going to replace long fuel line from tank to pump since it’s definitely old. Didn’t see leaks but definitely chance of air getting in from some places. Had been out in the sun for awhile so some very small rot areas by the pump may be the problem. Thanks for the help!

Did you try pulling the line that goes back to the tank to see if fuel will flow?

You usually can hold the pulse hose with skinny long needle nose pliers while installing it on the pump.

Your pump might be bad, you can buy cheap aftermarket for about $15.

 

Here is a photo, the black hose above the blue oil filter is the pulse hose, as you can see there is a path to the hose nipple with the oil filter off.

 

[Achto 27,594]

16 hours ago, Brad520H said:

Fuel pump isn’t getting gas to it at all. Lines are clean, valve under tank is clean and in opened position. First time trying to start since restored.

 

You can try to dribble a little gas in the carb to get the engine running. This will cause a better pulse for the pump. I have to do this to my 520 every spring to get gas up to the carb. As I run the carb out of gas before storing for the winter. Some times I have to repeat the process 2 or 3 times. One other option would be to hook a line to the pump from an IV bottle to get fuel into it to prime it.

 

Many members here have switched to an electric fuel pump on their 520's as well, faster start up's, less hassle.

Edited February 10, 2023 by Achto

[Brad520H 17]

19 hours ago, lynnmor said:

Did you try pulling the line that goes back to the tank to see if fuel will flow?

You usually can hold the pulse hose with skinny long needle nose pliers while installing it on the pump.

Your pump might be bad, you can buy cheap aftermarket for about $15.

 

Here is a photo, the black hose above the blue oil filter is the pulse hose, as you can see there is a path to the hose nipple with the oil filter off.

 

Thanks this helps for sure seeing where it goes. Thankfully that line happened to still be good but gonna save this for reference if needed in the future

[Brad520H 17]

17 hours ago, Achto said:

 

You can try to dribble a little gas in the carb to get the engine running. This will cause a better pulse for the pump. I have to do this to my 520 every spring to get gas up to the carb. As I run the carb out of gas before storing for the winter. Some times I have to repeat the process 2 or 3 times. One other option would be to hook a line to the pump from an IV bottle to get fuel into it to prime it.

 

Many members here have switched to an electric fuel pump on their 520's as well, faster start up's, less hassle.

This happened to be the winning solution. Thank you. It eventually pulled all the way through and ran on its own. Going to still replace the long fuel line going to tank as it’s seen better days so may have to repeat this process after. Thanks again !

[Tonytoro416 1,034]

3 hours ago, Brad520H said:

This happened to be the winning solution. Thank you. It eventually pulled all the way through and ran on its own. Going to still replace the long fuel line going to tank as it’s seen better days so may have to repeat this process after. Thanks again !

I installed a check valve in the fuel line to keep it from losing its prime.  Works great.  Also before I did the check valve I would blow air into the fuel tank to help prime