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TC10284

Weird surging problems with 520H

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TC10284

I have a 3120OE01 model Wheel Horse 520H with original Onan 20HP. 

After running a few minutes it runs fine. But after running it wide open for about 10 to 15min, such as when mowing, it starts surging. It's odd because it seems like the surging stops momentarily when I turn to the left or right, but then goes right back to surging. It also seems to stop when I push the stick forward. 

When it happens, I can see the vacuum pressure gauge go from "5" to "20" repeatedly. 

I stopped the tractor and let it sit, but wide open. It took about a minute, but after stopping, the surging seemed to die down and run stable. 

 

Also, the oil stick said to add a pint of oil, so I added some. I may have added a bit too much, because when I was on a hill leaning to the left, I would occasionally see a quick puff of white smoke. And when I parked and turned it off, it seemed like it was burning off some oil (I could see it smoking). That's the first time I've noticed this, so that's why I think I may have put in a tad too much oil. 

 

And lastly, the headlight toggle switch is finicky. Works rarely, most of the time doesn't. The test switch is similar, but works more often that not. 

 

I am not having much luck with my two 520H's...

:-( 

 

Any ideas? 

Edited by TC10284

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cleat

Clean the carb to fix the surge. Also replace the fuel filter if it is not fairly new.

 

Fuel pump may be weak but that would likely cause hard starting as well.

 

Yours is just starting to plug so that is why it only does it under different loads.

 

Switches also need cleaning and relubing. The grease is old and hard inside causing your issues.

 

They come apart for this. Not really difficult, just don't lose any parts.

 

I have cleaned up all of mine.

 

Not really a defect, just dealing with an old machine.

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Cvans

Turning left to right and getting that much change in your vacuum could indicate a vacuum leak. Your throttle cable could be moving the carb. Check to see if your carb mounting bolts are loose. Generally surging is an indication of improper fuel metering in the carb. Flooding will be indicated by black smoke and surging with no smoke usually means a lean situation. If it gets too lean it will start popping back through the carb. 

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moe1965

There should be a filter in the tank as well even if you have a external filter. I just bought one that goes in the tank off eBay. It was about 10 bucks with the shipping.

Screenshot_20180407-084630.png

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TC10284

Update:

Took off air filter, plate, and the housing for the air filter. Sprayed it out pretty well with some Carb Cleaner. Also took off the main fuel line coming into the carb and sprayed out the connector for it. I sprayed what I thought was the main jet near the top under the choke plate. I know that wasn't a thorough clean, like taking off the whole carb...

 

Put it all back together, started it up. Took a while of turning it over to fire up. Started up and ran pretty good. Decided to test it by mowing the back yard. It mowed great for about 10 to 15 minutes. The RPM stayed right at "35". Then as I was almost about to call it fixed, I seemed to hit a small dip and it started surging like before. The RPM would fluctuate anywhere from 25 and go above the 40 mark.

 

I don't get it why it takes 10 to 15min of running for it to start doing that. I compared the throttle under the carb housing to my newer 520H and 416H and they have a spring that connects the two. 

 

I've noticed that when I disengage the hydrostatic drive, it runs smoother, but that could be due to load on the engine (even when stopped though?). I also noticed a chunk missing out of the V-Belt so that has me thinking that might have something to do with it. 

 

Here's two pics of the throttle under the air filter housing:

(newer 520H)
FqqPsm7.jpg

 

(Older 520H)

XWCulce.jpg

Edited by TC10284

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gwest_ca

Don't know if this fits your problem or not but it must have been significant to generate a service bulletin. Click on the fuzzy picture

Garry

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TC10284

Hmmm that does sound similar. I may look into these and try a spring if I have one. 

"Governor spring needs relocation to "less-sensitive" hole in governor arm" 

"Looseness in governor linkage"

"If looseness is noted in the governor linkage, check for free play at the carburetor end of the governor rod. Play can be eliminated by removing the governor rod clip and bending it as illustrated below."

 

I don't quite understand their graphic yet, but I may try that. 

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TC10284

I did a little Googling and found this one - very similar problems to mine:

http://www.wheelhorsestables.com/forum/tractors/1067-my-520h-has-gone-hunting-needs-some-help

 

Page 2 shows that he seemed to resolve it by moving the governor linkage to different holes. Although my other 520H and 416H are both in the middle holes (like the pics above). 

 

And this:

 

Edited by TC10284

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WVHillbilly520H

Depending on year of production and how many operating hours if your Onan has the plastic governor flyweights (balls) they could be broken and need replacing/upgrading to the better steel style, check with @boomers_influence or @onanparts.com, Jeff.

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Kurt-NEPA
6 hours ago, TC10284 said:

I did a little Googling and found this one - very similar problems to mine:

http://www.wheelhorsestables.com/forum/tractors/1067-my-520h-has-gone-hunting-needs-some-help

 

Page 2 shows that he seemed to resolve it by moving the governor linkage to different holes. Although my other 520H and 416H are both in the middle holes (like the pics above). 

 

And this:

 

 

That was my post.  My 89 520H did some really strange surging. I did the quick carb clean and then removed the carb and soaked in a can of carb cleaner for two days.  No help.  I removed the governor and inspected it.  Everything was fine.  So I tried different positions on the governor linkage and that really helped.  Never did understand what happened or why.

 

Strange thing is that about a year later, I put the governor linkage back where the manual says it should be and that big Onan ran just fine.

 

Good luck with yours. If it were mine, I would try a really good carb cleaning next.

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TC10284
8 hours ago, Kurt-NEPA said:

 

That was my post.  My 89 520H did some really strange surging. I did the quick carb clean and then removed the carb and soaked in a can of carb cleaner for two days.  No help.  I removed the governor and inspected it.  Everything was fine.  So I tried different positions on the governor linkage and that really helped.  Never did understand what happened or why.

 

Strange thing is that about a year later, I put the governor linkage back where the manual says it should be and that big Onan ran just fine.

 

Good luck with yours. If it were mine, I would try a really good carb cleaning next.

 

Did you ever determine what the root cause was? Such as the plastic governor flyweights? 

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TC10284

Update:

Tried moving the linkage of the governor to the further out hole, seemed to help at first until it hit the magic 15min mark. Shut it off, moved to the closest hole to the carb. Ran ok for a few minutes, then the RPM slowly crept up to 4000RPM, then over 4000 RPM a few minutes later. Acting like the governor wasn't even working. 

 

Don't get it...

 

I guess next step is taking off the carb and soaking/cleaning. 

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Kurt-NEPA
6 hours ago, TC10284 said:

 

Did you ever determine what the root cause was? Such as the plastic governor flyweights? 

 

I got the governor apart and everything looked good. The plastic governor ball spacer looked like new. I put it back together and changed nothing.

 

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CTBT&D

This may not be entirely on point of this post but is related. I worked on my 1995 520H snow machine once (don't remember why though) and took the governor linkage off. When I put it back together it would not run correctly (over revved) no matter what I did. So with close inspection I found the linkage rod end with the u-shaped end was ever so lightly worn. Looked at my other Onan P220's (1990-1992) and the linkage had a 90 degree bend on that end, so swapped one out and it ran like it supposed to. The over all length from the connection ends were exactly the same. I figured the worn area wasn't seating exactly the same when reassembled causing some type of miniscule binding. Bought another linkage off Ebay to replace the one I had pilfered from the donor machine. Sorry no picture of the original problem linkage.

Craig

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TC10284

Update: I was finally able to pull the carb/intake/exhaust off this 520H.

I noticed there was quite a build up of sticky dirt on top. 

When I took off the intake, I noticed there was kind of a large pool of gas in the front intake valve. 

 

Is there anything else I should look for/do while I have it off and cleaning the carb? 

Edited by TC10284

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TC10284
On 4/14/2018 at 9:49 AM, CTBT&D said:

This may not be entirely on point of this post but is related. I worked on my 1995 520H snow machine once (don't remember why though) and took the governor linkage off. When I put it back together it would not run correctly (over revved) no matter what I did. So with close inspection I found the linkage rod end with the u-shaped end was ever so lightly worn. Looked at my other Onan P220's (1990-1992) and the linkage had a 90 degree bend on that end, so swapped one out and it ran like it supposed to. The over all length from the connection ends were exactly the same. I figured the worn area wasn't seating exactly the same when reassembled causing some type of miniscule binding. Bought another linkage off Ebay to replace the one I had pilfered from the donor machine. Sorry no picture of the original problem linkage.

Craig

 

Thanks for that. I may look into that, even though I pulled off the carb/intake already. 

 

Edit: I don't have my newer 520H here at home to compare exactly. But I just looked at the difference between the governor linkage rod on my older 520H vs a newer 416H and I see what you mean. 

Edited by TC10284

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lynnmor

Check the part line of the intake for leaks.  Check that the welch plug above the idle mixture screw is there.  If the carb has dirt, remove welch plug, clean behind it and replace with a new one.  Check the engine compression.  Adjust the valves.  Optional, but easy now; glass bead and paint the exhaust.  Replace the fuel lines and filter.  Check the float and float needle.  Report your findings.

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TC10284

Update:

I was finally able to get the carb cleaned and soaked. Bought new intake/exhaust gaskets, as well as valve cover gaskets. Cleaned off the built up crud on top. Adjusted the valves according to spec. 

Put it all back together and it is harder to start. When I finally get it running, as before, it runs for 15 to 20min pretty well, and then starts surging. Just like clockwork. Ugh! 

This is a very aggravating and annoying problem. It runs so smooth and then all of a sudden...rev up, come down, rev up, come down, and so on...

 

Even bought and put on a new governor control arm from eBay that goes on a newer model Nikki carb (the kind with the u-shaped end and spring). 

 

I haven't tried a new fuel line/filter yet. I'm almost thinking of trying a new fuel pump since they are so cheap. 

 

I noticed when putting things back on that the valve covers looked like they were previously tightened a little too much to where they seemed to be a little sunk down where the bolt tightens down (wasn't done by me). The front valve cover seemed worse. I don't think it's causing a leak, but I can't be for certain. 

 

I tested compression prior to putting it all back together and am getting 115 psi on both cyl. 

 

Last possibly important bit of info: 

When I throttle up quick, it dies unless I throttle down really quickly. If I choke it a little less than half way, or maybe 1/4 of the way, I can throttle up quicker better. This tells me there's too much air and not enough fuel. 

 

What should I look at next? 

New fuel pump/lines/filter? 

New valve covers?

New carb? 

New fuel tank filter/shut off?

Edited by TC10284

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lynnmor

Disassemble the carb completely and clean it right.  Soaking a carb that is still partially or completely assembled will do nothing useful.

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TC10284
4 hours ago, lynnmor said:

Disassemble the carb completely and clean it right.  Soaking a carb that is still partially or completely assembled will do nothing useful.

 

This was already done. Taken apart, cleaned, then soaked. 

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Kurt-NEPA

I've been thinking about this since you posted yesterday.  Its been nagging at me.  You've done a lot of good work and have nothing to show for it, in fact you made things worse.  Time to step back and re-think this.

 

Now you seem to have three problems

1.  Surging

2.  Hard Starting

3.  Lean running.  When you pull out the choke and its runs better, the engine is running lean.

 

These three can come from the same source.  It could be a dirty carb or poor fuel delivery.  Another way to think of this is that gas is not getting into the engine properly.

 

I think I would pull off both filters (at the engine and at the bottom of tank - screen on top of the shut off valve) and replace them.  Then replace the fuel line.  This modern ethanol gas is really hard on old rubber fuel lines.  They deteriorate and small particles break loose and lodge in the carb. See if that helps.

 

Nothing wrong with trying a new electric fuel pump.  Small money and it might help.  It sure will help the engine start faster.  Well worth the investment of about $25

 

Beyond that, I'm thinking valve clearance (but you checked that) and maybe checking the governor.

 

Best of Luck

 

Kurt

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Kurt-NEPA

Another thought,  When you cleaned the carb did you remove the main jet?  I had one that I cleaned without taking that out.  I sprayed carb cleaner though all the passages, ran a copper wire through the passages and used carb cleaner again, then blew all the passages clear with compressed air.  Put the carb back on and it still didn't run right.  So I took it off again, this time I removed the jet and found a small piece of black rubber under it that was blocking the passage.  I got it out and cleaned everything up.  Put the carb back on and it ran perfectly.  That little black particle was really hard to see, I assume it was a piece of the fuel line.

 

Hope that helps,

 

Kurt

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boomers_influence

club

i also had a P 220 main jet the was partially blocked.

 

you MUST remove them to clean them.

if you use a tip cleaner, without removing the jet

you will just push the debris into the body of the carb.

 

thank you. boomer ( the used onan engine parts guy, also NOS and new )

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TC10284
On 5/12/2018 at 3:58 PM, Kurt-NEPA said:

I've been thinking about this since you posted yesterday.  Its been nagging at me.  You've done a lot of good work and have nothing to show for it, in fact you made things worse.  Time to step back and re-think this.

 

Now you seem to have three problems

1.  Surging

2.  Hard Starting

3.  Lean running.  When you pull out the choke and its runs better, the engine is running lean.

 

These three can come from the same source.  It could be a dirty carb or poor fuel delivery.  Another way to think of this is that gas is not getting into the engine properly.

 

I think I would pull off both filters (at the engine and at the bottom of tank - screen on top of the shut off valve) and replace them.  Then replace the fuel line.  This modern ethanol gas is really hard on old rubber fuel lines.  They deteriorate and small particles break loose and lodge in the carb. See if that helps.

 

Nothing wrong with trying a new electric fuel pump.  Small money and it might help.  It sure will help the engine start faster.  Well worth the investment of about $25

 

Beyond that, I'm thinking valve clearance (but you checked that) and maybe checking the governor.

 

Best of Luck

 

Kurt

 

I am going to try replacing the vacuum fuel pump since it's only $20, the fuel filter closest to the fuel pump/carb, and the fuel filter in the tank/shut off valve, as well as try to replace and/or blow out all the fuel lines. All of these are pretty cheap replacements to test. 

 

My last concern would be the governor, as that might take tearing down the motor (AFAIK). 

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TC10284
On 5/12/2018 at 4:07 PM, Kurt-NEPA said:

Another thought,  When you cleaned the carb did you remove the main jet?  I had one that I cleaned without taking that out.  I sprayed carb cleaner though all the passages, ran a copper wire through the passages and used carb cleaner again, then blew all the passages clear with compressed air.  Put the carb back on and it still didn't run right.  So I took it off again, this time I removed the jet and found a small piece of black rubber under it that was blocking the passage.  I got it out and cleaned everything up.  Put the carb back on and it ran perfectly.  That little black particle was really hard to see, I assume it was a piece of the fuel line.

 

Hope that helps,

 

Kurt

Yes, the main jet was removed. Anything that is able to be removed, and supposed to be removed, was taken apart and cleaned then soaked. 

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