518H - Random, mild surging at WOT

[TC10284 109]

I have a 518H with a P218g. I used it today to mow the yard (probably the last time for the season).

I have had trouble with this thing surging before, and have soaked the carb for a week. Recently found water in the gas. Drained all gas, blew out the line, took off carb, took apart the carb, had a lot of corrosion from water/gas. Used Carb cleaner on corrosion and all openings in carb. Used air to blow out holes as well.

Put all back together. Ran well at idle and WOT. Engage mower deck. Mild surging after engaging. Eases off and runs smooth. Start moving and get random mild surging. Seems to be very random. Only time it seems to run the smoothest is when on a flat surface. Seems like as soon as I start hitting small bumps, or going up a slight incline, that's when I notice it. 

Closing the choke makes no difference, only makes it run worse (about half choke). 

 

Could this be a carb issue still, such as a failing float or something? Or is it something else such as extra air being sucked in intermittently somewhere? 

[WHX?? 46,678]

3 minutes ago, TC10284 said:

Could this be a carb issue still

Could be .. some of the fellas report having to clean the carb multiple times. Did you change fuel filter/lines while you were at it?  Try some seafoam just for grins??? 

[TC10284 109]

22 minutes ago, WHX24 said:

Could be .. some of the fellas report having to clean the carb multiple times. Did you change fuel filter/lines while you were at it?  Try some seafoam just for grins??? 

I replaced the fuel filter with a new one, yes. Fuel line no. I see the fuel filter constantly 75 to 85% full with fuel. New fuel pump as well. 

 

As for seafoam, I got fed up with it surging and put half a can in the full fuel tank and ran it for maybe 1hr to 1.5hr after. No change. 

Edited November 11, 2019 by TC10284

[gwest_ca-(File Mod) 10,478]

Worth reading

Garry

[lynnmor 6,762]

The last of the Onans had carbs with accelerator pumps that were finicky, what year is the tractor?

 

The symptoms sound like a bad or maladjusted float, set to specification.

 

Your carb should have a 3/8" welch plug near the idle mixture screw, make sure it is intact.  If it is and the problem continues, remove the plug and clean out in there.  You will need a new plug, NAPA might have one.

[TC10284 109]

1 hour ago, lynnmor said:

The last of the Onans had carbs with accelerator pumps that were finicky, what year is the tractor?

 

The symptoms sound like a bad or maladjusted float, set to specification.

 

Your carb should have a 3/8" welch plug near the idle mixture screw, make sure it is intact.  If it is and the problem continues, remove the plug and clean out in there.  You will need a new plug, NAPA might have one.

 

I'll have to get you the model number a bit later, but I know that it is NOT a Toro branded WH. 

[Stepney 2,314]

I had a 516h that ran well till one day I washed it.. you read that right. Started surging and couldn't get it to stop. Started studying the linkage and the grit must have been holding the throttle rod to governor lever 'tight' and when it got wet, it became loose. Check the linkage for any slop at all.. it doesn't take much. 

[TC10284 109]

10 hours ago, Stepney said:

I had a 516h that ran well till one day I washed it.. you read that right. Started surging and couldn't get it to stop. Started studying the linkage and the grit must have been holding the throttle rod to governor lever 'tight' and when it got wet, it became loose. Check the linkage for any slop at all.. it doesn't take much. 

 

So I should be looking at the governor arm to see if there is any play in it where I can move it freely with little force? If it does, bend the linkage rod according the linked pdf file above so there is less play? 

Edited November 13, 2019 by TC10284

[Stepney 2,314]

Honestly I never even questioned anything, and just added a little spring from the lever to the rod to compensate for the slop. Mine was loose where the throttle fits into the lever. Just barely, but visible. 

[WVHillbilly520H 10,369]

On 11/11/2019 at 1:38 PM, TC10284 said:

 Or is it something else such as extra air being sucked in intermittently somewhere? 

Its easy to check for that... With engine running using a can of carb/choke cleaner spray around intake manifold and carb base if engine RPMs speed up you have a "vacuum" leak and will need to reseal the problem area if it doesn't speed up then no vacuum leak.

[Mudrig150 298]

Onans with the 2 piece intake are notorious for the seal going bad. If you have an intake leak, here's what you do: 

There should be a bunch of mushroomed pins that hold the halves together, they need to be drilled out.

Reseal the halves with a new gasket and silicone.

Drill and tap new holes, put in some screws.

That should fix any intake leaks.

[WVHillbilly520H 10,369]

5 hours ago, Mudrig150 said:

Onans with the 2 piece intake are notorious for the seal going bad. 

That depends I have owned 3 (now 2) all original and "run hard and put up wet" and haven't had an intake seal issue in 20 plus years with Onan power...

[Mudrig150 298]

14 hours ago, WVHillbilly520H said:

That depends I have owned 3 (now 2) all original and "run hard and put up wet" and haven't had an intake seal issue in 20 plus years with Onan power...

What models and years? Early B series engines and some early P series had the intake seal problems. On later P series engines they actually sealed it with a gasket AND sealer instead of just sealer.

[lynnmor 6,762]

2 hours ago, Mudrig150 said:

What models and years? Early B series engines and some early P series had the intake seal problems. On later P series engines they actually sealed it with a gasket AND sealer instead of just sealer.

I've not seen a gasket for between the two halves of an Onan intake.  Do you know of a source?

[Mudrig150 298]

21 minutes ago, lynnmor said:

I've not seen a gasket for between the two halves of an Onan intake.  Do you know of a source?

Well usually they just tell you to slap some gasket maker on it and apply liberally. The gasket is not really made by anyone, so you'd have to make it yourself.

[WVHillbilly520H 10,369]

3 hours ago, Mudrig150 said:

What models and years? Early B series engines and some early P series had the intake seal problems. On later P series engines they actually sealed it with a gasket AND sealer instead of just sealer.

I know you are a young man wanting to help out here on the forum but just because someone has said this or that about a certain product doesn't mean it's notorious... I for one could say Kohlers are notoriously famous for scoring cranks,  throwing rods and busting pistons from reading some of your very own posts but without actually having physically spent many years around all the various brands (engines tractors cars ect) and seen the pros and cons of each I wouldn't say any one is any more notorious than the other as maintenance or lack thereof is usually more the culprit than the brand.

[Mudrig150 298]

16 minutes ago, WVHillbilly520H said:

I know you are a young man wanting to help out here on the forum but just because someone has said this or that about a certain product doesn't mean it's notorious... I for one could say Kohlers are notoriously famous for scoring cranks,  throwing rods and busting pistons from reading some of your very own posts but without actually having physically spent many years around all the various brands (engines tractors cars ect) and seen the pros and cons of each I wouldn't say any one is any more notorious than the other as maintenance or lack thereof is usually more the culprit than the brand.

 

The Onan intakes are overall a bad design, a 2 piece intake with what are essentially rivets holding it together and only a thin bead of sealant keeping it from leaking. A one piece intake or even an intake with bolts holding the halves together would have been a much better idea. The design is like putting a head gasket in something then not torqueing the head bolts. Overheating makes leaks even worse, causing the halves of the intake to expand and contract differently, which makes the sealant break its seal. It's an inherent design flaw that a lot of the time is unnoticed, misdiagnosed, or just has already been fixed.

Onans are torquey, but they have some...questionable design. Even Kohler and briggs have some wierd design. 

In my opinion, no one was at the top of their game with the opposed twins at all. Briggs was the definite leader, then Kohler and then Onan.

 

A simple google search and out of the first 5 results, 3 are how to fix the leaking seal. Searches on some forums brings up even more, on one Deere forum, there are over 70 threads talking about the leaking seal. And that doesn't even count archived posts from 2014 and before.

[WVHillbilly520H 10,369]

1 hour ago, Mudrig150 said:

 

The Onan intakes are overall a bad design, a 2 piece intake with what are essentially rivets holding it together and only a thin bead of sealant keeping it from leaking. A one piece intake or even an intake with bolts holding the halves together would have been a much better idea. The design is like putting a head gasket in something then not torqueing the head bolts. Overheating makes leaks even worse, causing the halves of the intake to expand and contract differently, which makes the sealant break its seal. It's an inherent design flaw that a lot of the time is unnoticed, misdiagnosed, or just has already been fixed.

Onans are torquey, but they have some...questionable design. Even Kohler and briggs have some wierd design. 

In my opinion, no one was at the top of their game with the opposed twins at all. Briggs was the definite leader, then Kohler and then Onan.

 

A simple google search and out of the first 5 results, 3 are how to fix the leaking seal. Searches on some forums brings up even more, on one Deere forum, there are over 70 threads talking about the leaking seal. And that doesn't even count archived posts from 2014 and before.

I'm not going argue with some 3 times less my age over something as trivial as an intake seal that obviously YOU have had more personal experience with than myself... The internet is full of keystroke mechanics.

[Bill D 1,595]

Every engine has its issues and design flaws.  It just comes down to what you like, why you like it and what you are willing to deal with on your favorite engine.  Bill

[TC10284 109]

I believe the issue has been resolved. I applied a spring to the throttle to governor linkage and that seemed to resolve the issue. I also found a hard/broken seal on the front valves that I replaced, but that didn't resolve anything than an oil leak. 

 

Videos below.

In the first video, you can see it hunting even before the mower deck is engaged and lots after.

In the second video you might can see some of the free play in the linkage.

In the third video, I found a spring that I was able to connect between the linkage and the throttle, and that it appears to work well.

 

https://photos.google.com/share/AF1QipP4r6sAdyMvwcitDjWXMXChVZ4X1aT1vaxQ_RZ7premSmefWXvwMFTusKRXYWNlCA?key=ZUxuRzl1ckRCUXRYLW9OQTFuNWN0SmF5RmZ3eTV3

Edited November 20, 2019 by TC10284