Onan P220 surging/hunting at operate

[WheelHorse520H 708]

Hi all,

I have a 1988 520-H and I got it running again recently, but when I move the throttle to operate it does this odd surging/hunting where I have to operate often around half choke. Thank you all for your help,

Andrew

P.S. I am so glad I got this running again, I have a dirt driveway and used the plow/dozer blade to clean up after my plow guy this winter.

[lynnmor 7,313]

Most likely a very dirty carburetor.  Take photos of the linkage, then remove the intake and carburetor together.  Separate the carburetor from the intake, disassemble and clean properly.  Check the intake seam for leaks.  Use new genuine Onan gaskets when you assemble, and use a torque wrench to carefully tighten the intake bolts.  If you are lucky and careful, you won't need any carburetor parts.

[Ed Kennell 38,244]

8 minutes ago, lynnmor said:

Most likely a very dirty carburetor.

Absolutely ,  even a slightly dirty carb will cause the Onan 220s to surge.   I cleaned my '88 three times before the surging stopped.

[WheelHorse520H 708]

Thank you for the help, I will try this out, can you give me a manual or step by step, this is the first time I have rebuilt a carb and I do not want to make a mistake. Also, I read on another threat that the seals on the intake could be brittle, should I try to reseal them with RYV? Thanks again.

[lynnmor 7,313]

7 minutes ago, WheelHorse520H said:

Thank you for the help, I will try this out, can you give me a manual or step by step, this is the first time I have rebuilt a carb and I do not want to make a mistake. Also, I read on another threat that the seals on the intake could be brittle, should I try to reseal them with RYV? Thanks again.

You are not "rebuilding" a carb, simply opening it up and cleaning it out.  The information is in the manual I linked to in one of your other posts.  The intake can be tested by blocking off the hole where the carb mounts and then turned upside down so you can fill it with a liquid.

[WheelHorse520H 708]

Ok thank you for the help, I will look at that

[Tuneup 1,433]

Good morning!   Since you'll be in there, why not order the genuine intake and exhaust gaskets and give it a good inspection? You can just seal the intake seam with a good RTV like gray or black (I did). Get rid of that possible leak source. The simplest route if you're in a hurry is to remove the main (large plug on side of carb), unscrew the main jet and clean it. Remove the top of the carb and clean the bowl and set the float. My rebuilt P216 ran fine for 5 hours and then began surging. The carb top removal and main inspections cleaned solved it. Dang, it was spotless when I buttoned it up!

[Handy Don 12,243]

43 minutes ago, Tuneup said:

good RTV like gray or black

Make sure to read the labels on these sealants. Only a very few of them are formulated to work in contact with gasoline. Others will work for a while but then deteriorate.

[WheelHorse520H 708]

I will see how the gaskets look, probably not a bad idea those gaskets are 30+ years old. Not a bad idea to double check that too, I don’t need to go through this twice!

Edited April 24, 2021 by WheelHorse520H

[WheelHorse520H 708]

So, I have not had a chance to look at the gaskets yet, but a few weeks ago I noticed the more it ran the less I needed the choke, I had to keep lowering it otherwise it would die. Before I knew it I was running it at no choke. This would mean I need new gaskets correct? I only say this because the more the engine warms up the more the metal expands, thus the more the seams on the intake manifold seal. Correct?

Thanks,

Andrew

[lynnmor 7,313]

3 hours ago, WheelHorse520H said:

So, I have not had a chance to look at the gaskets yet, but a few weeks ago I noticed the more it ran the less I needed the choke, I had to keep lowering it otherwise it would die. Before I knew it I was running it at no choke. This would mean I need new gaskets correct? I only say this because the more the engine warms up the more the metal expands, thus the more the seams on the intake manifold seal. Correct?

 

No way of knowing what is inside the carburetor till you take it apart.  There is no way to know if the intake is leaking at the seam until you test it or take it apart, most are just fine.  The fact that performance improved with use, may mean that crud is being dissolved or flushed thru.  You really need to pull the intake, disassemble the carburetor, inspect the intake, adjust the valves and do it right and completely.  You will need genuine Onan intake, valve cover and exhaust gaskets.  The carburetor may or may not need gaskets, the cheap ones are likely OK. 

[WheelHorse520H 708]

1 hour ago, lynnmor said:

There is no way to know if the intake is leaking at the seam until you test it or take it apart, most are just fine.  The fact that performance improved with use, may mean that crud is being dissolved or flushed thru.  You really need to pull the intake, disassemble the carburetor, inspect the intake, adjust the valves and do it right and completely.  You will need genuine Onan intake, valve cover and exhaust gaskets.  The carburetor may or may not need gaskets, the cheap ones are likely OK. 

Ok, I will start on that tomorrow. I know that it is tough to get to the mounting bolts for the intake, do you have a particular order that you disassemble it?

Thank you again for the help,

Andrew

[lynnmor 7,313]

1 hour ago, WheelHorse520H said:

Ok, I will start on that tomorrow. I know that it is tough to get to the mounting bolts for the intake, do you have a particular order that you disassemble it?

Thank you again for the help,

Andrew

I remove the exhaust, then the intake, followed by removing the carburetor from the intake.  Do a good cleanup, then remove the valve covers, a shop vacuum is your friend.  I paint the valve covers, glass bead and paint the exhaust and shields.  I run a tap in all bolt holes and use a torque wrench to prevent over-tightening.  Yes, there are many details that I left out, ask as you go along.  If you do this right you will only be doing the maintenance that needs performed anyway and the result should be a good performing engine for years to come.

[WheelHorse520H 708]

Ok, thank you I will start taking the exhaust off this afternoon.

[WheelHorse520H 708]

On 5/13/2021 at 9:31 PM, lynnmor said:

glass bead and paint the exhaust and shields.

I do not think so, but can you use glass beads on chrome? 

 

On 5/13/2021 at 9:31 PM, lynnmor said:

Do a good cleanup, then remove the valve covers, a shop vacuum is your friend. 

Is there any way to decarbon the piston and head/valve cover other than a shop vac?

[lynnmor 7,313]

59 minutes ago, WheelHorse520H said:

I do not think so, but can you use glass beads on chrome? 

 

Is there any way to decarbon the piston and head/valve cover other than a shop vac?

 

If you want to preserve the expensive exhaust, then all rust should be removed.  Glass beading is the most thorough without doing too much damage to the thin metal.  I use Rust-Oleum High Heat paint to finish.  The muffler shield is stainless steel and is removed by taking out the 10-24 screws, of course you have been soaking all fasteners with penetrating oil for weeks now.

 

After removing the head, turn the engine till the piston is all the way up, then apply some grease to seal the gap where the piston meets the cylinder wall, this will hold debris as you scrape the carbon with a plastic scraper.  After scraping, move the piston down and up a small amount while wiping things clean.  The cylinder head can be cleaned using oven cleaner.

 

There is no good way to remove the debris in the valve cover area besides a vacuum.  Blowing will force debris into areas that you want to protect.  You must block drain-back holes in the valve box area to keep debris and small parts out.

[WheelHorse520H 708]

42 minutes ago, lynnmor said:

 

If you want to preserve the expensive exhaust, then all rust should be removed.  Glass beading is the most thorough without doing too much damage to the thin metal.  I use Rust-Oleum High Heat paint to finish.  The muffler shield is stainless steel and is removed by taking out the 10-24 screws, of course you have been soaking all fasteners with penetrating oil for weeks now.

I just wasn’t sure about the stainless steel shield, on the topic of soaking the muffler for weeks I used some good ol’ WD-40 and they all came right out.

 

50 minutes ago, lynnmor said:

 

After removing the head, turn the engine till the piston is all the way up, then apply some grease to seal the gap where the piston meets the cylinder wall, this will hold debris as you scrape the carbon with a plastic scraper.  After scraping, move the piston down and up a small amount while wiping things clean.  The cylinder head can be cleaned using oven cleaner.

Contrary to my expectation of the inside of the cylinder, it was actually kind of shiny, not like anything was scraping but it was good and clean. Guess what, I HAVE PICTURES!!! Could I use a wire brush to clean the piston and valve cover? 

 

55 minutes ago, lynnmor said:

 

There is no good way to remove the debris in the valve cover area besides a vacuum.

Are you referring to where the valves are or on the actual cover?

Thanks for the help,

Andrew

P.S. I apologize for the poor quality in some of the photos, there are a lot of tight spaces.

[lynnmor 7,313]

While some do use a wire wheel or wire brush, I do not.  There is risk of scratching surfaces and rounding edges.  After going to the trouble of removing the exhaust and intake, it only makes sense to adjust the valves at this time.  Cleaning and vacuuming before and after removing the valve covers will keep debris from falling inside the engine.

 

It appears that there is a dark stain on the cylinder wall that is not normal, the rings should have kept the cylinder walls shiny.   Perhaps wiping it clean and using a different camera angle will show if there is a real problem.

Edited May 16, 2021 by lynnmor

[WheelHorse520H 708]

53 minutes ago, lynnmor said:

 

It appears that there is a dark stain on the cylinder wall that is not normal, the rings should have kept the cylinder walls shiny.   Perhaps wiping it clean and using a different camera angle will show if there is a real problem.

Wiping the stain on the cylinder wall correct? I will send along more pictures later

[WheelHorse520H 708]

No stain. Bad camera angle/bad lighting, had me fooled for a second, I wiped it out and it was still there. Then brought over a light and moved it around, I can make the “stain” appear anywhere on the cylinder wall.

[lynnmor 7,313]

Looks good, it was the lighting.  The hone marks indicate little wear, but there are some straight lines that suggest that oil changes and air filter maintenance was not the best.

[WheelHorse520H 708]

Agreed, it was sitting for about 5 years outside so I will do better now that it runs. Also, I am trying to remove the hood for better lighting, and cannot get the headlight connector off, anyone on here know how?

Thanks,

Andrew

Edited May 16, 2021 by WheelHorse520H

[WheelHorse520H 708]

New update: the intake manifold does not leak, holds the water just fine. The gasket between the carb and the intake was crushed one heck of a lot, could air get in that way? I do need new head gaskets and new intake and exhaust gaskets, should I just get one for the seam on the intake manifold since I have it all apart?

 

Andrew

[lynnmor 7,313]

The tab on the bottom right in your photo is preventing the plug from being pulled apart, pry it out a bit.  If it still is stuck, spray WD-40 in and try again.

 

You need a new carburetor gasket, there is no gasket between the manifold halves, just sealant.  There is a sticky showing the repair process of the intake manifold, but apparently you don’t need a repair.

[WheelHorse520H 708]

11 hours ago, lynnmor said:

 

The tab on the bottom right in your photo is preventing the plug from being pulled apart, pry it out a bit.  If it still is stuck, spray WD-40 in and try again.

 

I thought that’s where it separated, but I didn’t want to break it.

 

11 hours ago, lynnmor said:

You need a new carburetor gasket, there is no gasket between the manifold halves, just sealant.  There is a sticky showing the repair process of the intake manifold, but apparently you don’t need a repair.

Ok, so new carb to intake gasket, new intake gaskets, new exhaust gaskets, and new head/valve cover gaskets... got it. I will see about ordering those tonight, thanks again for all the help.

 

Andrew