Weird surging problems with 520H

[lynnmor 6,775]

There is a welch plug on the carb above the idle mixture screw, is it intact?  Did you remove that plug, clean behind it and replace with a new one?

[TC10284 109]

1 hour ago, lynnmor said:

There is a welch plug on the carb above the idle mixture screw, is it intact?  Did you remove that plug, clean behind it and replace with a new one?

I looked at that when it was taken apart. It is intact as far as being in place and not loose. I did not clean behind it. 

[cleat 4,983]

I have not had the issue on any of mine but possibly your intake manifold is leaking.

 

Not sure of any other reasons for your lean running.

[TC10284 109]

12 hours ago, cleat said:

I have not had the issue on any of mine but possibly your intake manifold is leaking.

 

Not sure of any other reasons for your lean running.

I'll likely end up taking the carb/intake back off and try to see if anything is leaking there too. 

[Kurt-NEPA 755]

22 minutes ago, TC10284 said:

I'll likely end up taking the carb/intake back off and try to see if anything is leaking there too. 

 

A quick check to see if you have an intake leak.

 

Start Engine.

Take a propane torch and open the propane but do not light it.

Move the torch around the intake and carb.  If the engine changes (speeds up or slows down) you have an intake leak.

 

You can try the same thing with a can of carb cleaner, but its not quite as good.

 

 

Edited May 15, 2018 by Kurt-NEPA

[TC10284 109]

13 hours ago, Kurt-NEPA said:

 

A quick check to see if you have an intake leak.

 

Start Engine.

Take a propane torch and open the propane but do not light it.

Move the torch around the intake and carb.  If the engine changes (speeds up or slows down) you have an intake leak.

 

You can try the same thing with a can of carb cleaner, but its not quite as good.

 

 

 

Could I do the same with a can of starter fluid (ether)? 

[Kurt-NEPA 755]

6 hours ago, TC10284 said:

 

Could I do the same with a can of starter fluid (ether)? 

 

Yes, be careful.  You don't need much, starting fluid can flash easily.

[cleat 4,983]

You could, just be careful of fire.

[TC10284 109]

Yesterday evening I replaced the vacuum fuel pump, the fuel shut off valve, and blew out the fuel lines (I don't have new ones right now to install, but will be getting some). It seemed to run immediately better. More fuel in the filter closest to the carb. 

However, it still sputters/stalls when you rev it up quickly without the choke about 1/4 of the way up. Keep in mind I didn't have time to let it fully warm up and test it then. 

 

I noticed when I took the valve covers off again to make sure all the new gaskets were good, that the front exhaust valve stem was white, meaning running lean. The rear exhaust valve stem looked regular black. Dunno if that helps. 

 

I didn't have time to run it for 15min to see if it would still surge/hunt though. It got dark. 

Edited May 18, 2018 by TC10284

[TC10284 109]

Update:

Put heat sheilds and air filter/cover back on. Was hard to start. Real hard. I must've choked it too much and flooded it since it was ran the night before. 

 

Anyway, I let it sit for a bit and came back to it. Finally started running. Rough at first and then a lot better. 

Sudden throttle up now results in much less of a hesitation and sputter or outright dying. It's a a lot shorter hesitation. 

 

Took it for a test drive. Tried mowing the very back yard. 

Ran as pretty as you've ever seen. RPM stayed right at 3500, until...

 

The ol' hunting and surging issue popped up a little over half way through the back yard, which is about 20 minute of run time. Starts slowly at first, then gets worse and worse. It will spike to 3800 RPM then go back down. In the past, if I let it go on, it will eventually run as hard as it can go at 4000RPM or so. 

 

I stopped the mower and let it sit wide open and put my finger on the governor control arm and when I held it, the hunting/surging would mostly stop. 

 

To recap, I have: 

• Removed carb, took out all parts/jets, cleaned and soaked
• Adjusted intake and exhaust valves to spec
• Installed all new intake and exhaust gaskets
• Installed all new valve cover gaskets
• Checked compression on both cyl - 115PSI
• Replaced vacuum fuel pump with a new one
• Replaced the fuel filter closest to the carb
• Replaced the fuel shut off
• Blew out the fuel lines 
• Tried a governor control rod from a newer Nikki carb with spring

This is so frustrating and a huge let down when I almost expect the problem to be gone.

It CAN run smooth. But why does it STOP running smooth? 

 

 

Edited May 19, 2018 by TC10284

[cleat 4,983]

One of mine did that and in my case the fix was simple.

 

Fuel line was resting on the engine oil filter causing it to eventually get hot and start to vapour lock.

 

This is the line from the tank to the pump so a slight vacuum on this line likely was not helping either.

 

Moved the line over to the other side of the negative battery cable to hold it away from the hot filter and problem went away.

 

 

On 5/14/2018 at 1:22 PM, lynnmor said:

There is a welch plug on the carb above the idle mixture screw, is it intact?  Did you remove that plug, clean behind it and replace with a new one?

 

Where can these small welch plugs be purchased ?

 

They do not even show up in the parts manual.

 

Cleat

[cleat 4,983]

18 minutes ago, TC10284 said:

it will eventually run as hard as it can go at 4000RPM or so.

 

 

 

Holy, engine must sound like a jet at that RPM.

I have never seen mine go that fast.

 

[lynnmor 6,775]

21 minutes ago, cleat said:

 

Where can these small welch plugs be purchased ?

 

They do not even show up in the parts manual.

 

Cleat

 

I bought cheap imported carb kits on eBay that had the plugs.  Doing a quick check just now, I couldn't find the cheap kits, just the high priced OEM.  You might measure the hole and try NAPA or other auto store.  Real hardware stores had them, but few exist today.   If you find a number that fits, perhaps you could post it and we all can lay in a supply.

[TC10284 109]

Update #2 today:

So, I did a little more Googling and happened to read this thread:

I took a chance and said "WTH..." and tried the old gas cap from my flawless running 416H. 

 

Do you know this 520H ran almost flawlessly this time around? I mowed the front with it, which takes an hour or so to do. It stayed right at 3500RPM, right under it actually.

At one point, it did surge ever so slightly. So I throttled down, took off the gas cap, then put back on, not as tight. Ran great still.

 

Now keep in mind, this is just a cap, that even has a small crack in it, no fuel level gauge like the fancier ones. 

 

Unless you guys think there's something else wrong, I'm pretty satisfied with how it did.  

 

[TC10284 109]

1 hour ago, cleat said:

 

Holy, engine must sound like a jet at that RPM.

I have never seen mine go that fast.

 

 

When that happened, it actually was smoking a little and very hot when I shut it down. This was BEFORE I did all the maintenance mentioned above. 

Edited May 19, 2018 by TC10284

[DerekN 5]

You need to replace your fuel line with new. Blowing out old fuel line may only temporarily fix a problem with fuel line.You may also need to flush your fuel tank. I had one tractor that I replaced everything and cleaned the carb. Ran great for 1/2 hour and started surging again. The culprit was a clear jelly like substance in the fuel tank. Once I flushed the tank and cleaned everything again it has been running great for the last 3 years.

[TC10284 109]

Just an update to this:

Still seems to be running well after this post also:

 

I used it to mow yesterday and it did start to surge some, but it seemed like every time it wanted to, there was a build-up of grass clippings on the flywheel cover. I don't know if that is the actual cause, but each time it got built up, I would throttle down and clean it off. That seemed to take care of it each time. 

 

But again, nowhere near as bad surging as it was before. 

[TC10284 109]

An update for anyone else that may have this problem:

 

I'm pretty sure I finally fixed this for good. 

 

I went out the other week to start it up and saw that there wasn't any fuel in the filter and turning it over didn't pump any into it. Started to get frustrated again since I've dealt with fuel problems on this one so often. 

I somehow, by luck, started squeezing the fuel line and felt a crack about three inches form the the fuel pump and when I squeezed it, gas got on my hand. You couldn't see it with your eyes if you didn't squeeze it. 

When I took it off fully, I saw that it had three cracks total. Two were about 2" long and one further down was 1" long.  

Replaced and so far, so good...