520-8 Onan surges

[davem1111 1,943]

Some of you have seen and commented on the 520-8 I picked up recently in this thread:  https://www.wheelhorseforum.com/topic/73681-what-have-you-done-to-your-wheel-horse-today/?page=768

Most of it is on that page. So far I haven't had much time to mess with it, but I've done this:  Pulled top of carb, removed float and float valve, cleaned it as good as possible when only going that far, and put it back together. Drained all gas, replaced tank valve and put a new filter on up by the pump.  Replaced spark plugs. (Old ones seemed to have a significant amount of oil on them...).  So, now it still does the same thing.  Governor just keeps surging. It fires a few times, then drops off for a few rounds. If I hold the governor arm, it seems to run okay, but it does put out some white smoke. I tried adjusting the screw on the side of the carb without looking up the prescribed number of turns - took it all the way in and back out 2-3 turns and nothing seems to change.  Leaks in the intake manifold were mentioned as a known possible culprit, so I'll need some time to diagnose that and more time to repair it if that's the problem.  Even really dirty used replacements are quite expensive.

 

I took this video so the engine could be heard running - do you all think this is indicative of the intake manifold, a valve or carb problem, or something else?
 

 

[ri702bill 7,482]

We find those pesky intake leaks on a cold engine using a light spray of WD-40 with the engine running. Spray it at the intake to engine joint - if the RPM's improve - there's the leak!!

Any hydrocarcon spray would work - carb cleaner, etc. , but WD is the least volatile.

[Ed Kennell 36,112]

When I got my free badly abused '88 520H , it surged just like that.       I cleaned the carb three times to get the surging to stop.    It's been running great for 15 years.

[lynnmor 6,868]

There should be a welch plug covering the hole just above the idle mixture screw, I can't determine if it is there but it kind of appears it is missing.  Also, if you have a HP gauge does it work?  I don't see the hose that runs from the fitting on the intake manifold just in front of the carburetor to the gauge, but again you likely don't have one.  If it is there, make sure it is in good condition.  If all of this checks out, it is time to pull the carburetor and manifold to do a proper repair and cleaning.

 

[TJ5208 1,823]

19 hours ago, davem1111 said:

Some of you have seen and commented on the 520-8 I picked up recently in this thread:  https://www.wheelhorseforum.com/topic/73681-what-have-you-done-to-your-wheel-horse-today/?page=768

Most of it is on that page. So far I haven't had much time to mess with it, but I've done this:  Pulled top of carb, removed float and float valve, cleaned it as good as possible when only going that far, and put it back together. Drained all gas, replaced tank valve and put a new filter on up by the pump.  Replaced spark plugs. (Old ones seemed to have a significant amount of oil on them...).  So, now it still does the same thing.  Governor just keeps surging. It fires a few times, then drops off for a few rounds. If I hold the governor arm, it seems to run okay, but it does put out some white smoke. I tried adjusting the screw on the side of the carb without looking up the prescribed number of turns - took it all the way in and back out 2-3 turns and nothing seems to change.  Leaks in the intake manifold were mentioned as a known possible culprit, so I'll need some time to diagnose that and more time to repair it if that's the problem.  Even really dirty used replacements are quite expensive.

 

I took this video so the engine could be heard running - do you all think this is indicative of the intake manifold, a valve or carb problem, or something else?
 

IMG_0856.MOV 24.62 MB · 2 downloads

 

I know how to fix the problem just give it to me

[lynnmor 6,868]

I did see that your voltage regulator isn't mounted down in the hole where it would get cooling air, maybe it isn't the correct one.

[ebinmaine 63,567]

Old saying from the retail auto parts industry. 

You need to do ALL maintenance before doing ANY diagnostics.  

 

Nowadays the list of parts and procedures on the "maintenance" list is growing with the lack of PO repairs and maintenance along with the poor quality fuels we're using as a mass society. 

 

Combine that with the age of the machines. 

 

I agree with the above mentioned removal of the intake and carb for a proper complete cleaning and rebuild.  

Following that, if the surging is still there... More diagnosis.  

 

IMHO you shouldn't be too concerned about getting a used intake manifold unless you find a specific reason to replace your own. 

 

[davem1111 1,943]

17 hours ago, TJ5208 said:

I know how to fix the problem just give it to me

 

Well, I didn't get it for free, so I can't afford to "give" it to you.  Plus, since one of the front tires was completely shot, I put new tires on it so I'm in a little deeper already.  That said, I still am not sure I want to try to tackle a proper restoration of this rare piece, so I may decide to sell it (but would like to get it running right first).  Since you're in Indiana (don't know how far away from me though), you might be in a good position to be the next owner if I decide to sell and you're interested. 

[Horse Newbie 6,953]

As mentioned, a good carb cleaning(or 2-3) may produce good results.

Also if you get far enough into it and decide to take a close look at the intake manifold, check on the sides of the manifold where the heat shields for the exhaust pipes may be rubbing a hole in the manifold.

You don’t have to split the manifold to repair it. I don’t remember the name of the brand sealer I used on mine. Seal where the two halves join all the way around. Someone on here may have a recommendation as what would be a good sealer.

If you find holes where the heat shields have rubbed the intake and repair it, trim the heat shields a little with tin snips so it won’t happen again.

Edited June 18, 2023 by Horse Newbie

[TJ5208 1,823]

1 hour ago, davem1111 said:

 

Well, I didn't get it for free, so I can't afford to "give" it to you.  Plus, since one of the front tires was completely shot, I put new tires on it so I'm in a little deeper already.  That said, I still am not sure I want to try to tackle a proper restoration of this rare piece, so I may decide to sell it (but would like to get it running right first).  Since you're in Indiana (don't know how far away from me though), you might be in a good position to be the next owner if I decide to sell and you're interested. 

I'm about 80 miles from you. 

[davem1111 1,943]

15 hours ago, lynnmor said:

I did see that your voltage regulator isn't mounted down in the hole where it would get cooling air, maybe it isn't the correct one.

 

I do think the regulator has been replaced, and it may not be the correct one but so far it seems to do its job. If it's not the right one, could that have something to do with the surging?   Doesn't seem like that would be an electrical problem.

 

23 hours ago, lynnmor said:

There should be a welch plug covering the hole just above the idle mixture screw, I can't determine if it is there but it kind of appears it is missing.  Also, if you have a HP gauge does it work?  I don't see the hose that runs from the fitting on the intake manifold just in front of the carburetor to the gauge, but again you likely don't have one.  If it is there, make sure it is in good condition.  If all of this checks out, it is time to pull the carburetor and manifold to do a proper repair and cleaning.

 

 

BTW, the welch plug is still on the carb, and I don't see any HP gauge or hose. The place that would come out of on the manifold looks to just be plugged.

 

When I can get this tractor back outside for a bit, I'll test the manifold with some carb cleaner or WD-40.  Running it in the garage is not a good idea - it's smoking too much. Guess I should get a compression tester. 

[Handy Don 10,759]

20 minutes ago, davem1111 said:

 

I do think the regulator has been replaced, and it may not be the correct one but so far it seems to do its job. If it's not the right one, could that have something to do with the surging?   Doesn't seem like that would be an electrical problem.

 

 

BTW, the welch plug is still on the carb, and I don't see any HP gauge or hose. The place that would come out of on the manifold looks to just be plugged.

 

When I can get this tractor back outside for a bit, I'll test the manifold with some carb cleaner or WD-40.  Running it in the garage is not a good idea - it's smoking too much. Guess I should get a compression tester. 

Bad voltage regulator will not cause surge--only a dead battery. They do get hot though, so they must have a way to dump the heat--either a substantial finned heat sink or else being placed in the airflow of the engine cooling air. There is a hole in the Onan shroud where the correct regulator goes. And, btw, leaving that hole open for air to escape robs the rear cylinder of essential cooling airflow.

The manifold port for the HP gauge is cast into all the manifolds but is only drilled out for engine builds that need it.

[lynnmor 6,868]

It might even be the correct voltage regulator, some people don’t know how to put it in.  Don gave you some good information above.

If the engine is smoking badly, first make sure that there is fresh 30 weight and it is at the correct level on the dipstick, engines that have been running with problems might dilute the oil with gas.

[ri702bill 7,482]

3 hours ago, lynnmor said:

engines that have been running with problems might dilute the oil with gas.

And that gas dilutes the oil and THAT runs into money...

[Phil_free_horse 3]

If you are looking for a possible simple fix, there is one.
My guess would be a blocked low idle jet, as i can see you are running her on low throttle.

Then the governor speeds up as no fuel can’t get in but after that the revs are too high so it cuts and then so again in a loop.

Nothing new, someone told about that here:

 

Being new in this forum I’d like to Thank everybody helping others as I have myself found invaluable information sorting out a non running 518he (E=Europa)

 

[davem1111 1,943]

I finally had some time to mess around with this again.  It stopped raining for a while so I pushed the tractor outside and started it. It seemed to be fine for a minute, then started surging. It was better at about 1/2 choke, which makes more sense if there is an air leak somewhere.  I tried spraying some carb cleaner around the intake seam, but only noticed a minor change here and there.

 

But, no matter. I have some great news - the previous owner forgot to tell me (or I didn't catch what he was saying) when I picked up the tractor, that he had some "other parts" for the tractor. I actually did a computer repair for him as partial barter, and when I took the computer back fixed, he gave me two boxes. One is a brand new carb, and the other is a full set of gaskets and a tune-up kit.  Since I already now have a new carb, I took the intake and carb off, and this is what I saw:

 

 

Sure looked bad.  So I went ahead and split it, and yep, it was bad.  I have it mostly cleaned up - need to hit with some acetone first. I have some blue gasket maker but it's old, and I need to run out for some other things this morning (unimportant stuff, like food)   so I'm going to buy a new tube of that to use on here.  I didn't notice the manufacturer of the carb but most likely it's cheap Chinese, but we'll see how it goes. I have moderately high hopes that this will be the end of the surging problem.

[ebinmaine 63,567]

1 hour ago, davem1111 said:

(unimportant stuff, like food) 

 

 

Excellent news.  

 

[Jon Paulsen 282]

You might even try full on high hopes 

 

Whatever sealant you might use, you need it to be fuel safe. I don't recall for sure, but Permatex Aviation comes to mind. There were two types when I last used it, A and B. For the life of me, I can't remember which is best for fuel systems. 

 

You probably don't need to go to this extreme, but the images might help:

 

318 Intake.pdf

 

I think there's a thread on this PDF. If I can find it, I will post the link. 

[davem1111 1,943]

6 hours ago, Jon Paulsen said:

You might even try full on high hopes 

 

Whatever sealant you might use, you need it to be fuel safe. I don't recall for sure, but Permatex Aviation comes to mind. There were two types when I last used it, A and B. For the life of me, I can't remember which is best for fuel systems. 

 

What I had on hand is Permatex Ultra Blue, and part of the tube has gone solid so I'd have to cut it open for usable stuff, and not sure I want to trust that with something I'd rather not have to take apart again.

 

I bought a tube of J-B Weld Blue RTV, which "The manufacturer claims that this product can withstand temperatures of up to 550 degrees Fahrenheit and exposure to different types of fuels, including gasoline, diesel fuel, propane, and natural gas."

 

Just finished doing some mowing but it started raining (again) so I think I'm going to see if I can put this together.  Will give it plenty of time to cure with clamps on before testing it.

 

[davem1111 1,943]

The new carb IS Chinese, but I'm going to give it a try.  Oddly, it has an adjustment screw above the fuel inlet that the old one didn't have. Anyone know what that's for?

 

[ebinmaine 63,567]

I can't speak for the extra screw but if the intake was clearly leaking I'd be prone to reinstalling the old carb after a quick cleanup.   

[davem1111 1,943]

3 hours ago, ebinmaine said:

I can't speak for the extra screw but if the intake was clearly leaking I'd be prone to reinstalling the old carb after a quick cleanup.   

 

Well.... I already have the new carb mounted on the intake, but I'm going to set the valve clearance before putting that back in. It really wasn't that hard to get the intake/carb assembly out, so I'm not too worried about having to do that part again. I just don't want to have to split the intake again. But obviously I will if it leaks. 

 

Hope to finish the valves tomorrow and get the intake & carb assembly back in to see how she runs. We shall see. Wishing I had an ultrasonic (?) cleaner like you have - I'd pop the old one in there. Calling it a day for now. Thunderstorms have rolled through about 5-6 times today, and the power has flickered off but is still on.  Hoping I'm not back into generator mode again soon. Internet was out for a while, and just came back on. 

[lynnmor 6,868]

3 hours ago, davem1111 said:

The new carb IS Chinese, but I'm going to give it a try.  Oddly, it has an adjustment screw above the fuel inlet that the old one didn't have. Anyone know what that's for?

 

Just a guess, it is right above the float pivot so maybe an adjustment for float level.

[ebinmaine 63,567]

10 minutes ago, davem1111 said:

Wishing I had an ultrasonic (?) cleaner like you have - I'd pop the old one in there

Send yours out to me. 

I'll rebuild it for ya. 

[davem1111 1,943]

Valves set, re-sealed intake and new carb installed - she runs pretty good now. Only a little surging while warming up but changing the choke level straightened it out. I also found that the vacuum hose for the air filter was not connected to the sensor behind the dash. Hose was there but was actually too short. Luckily I have a variety of hoses on hand and had a proper piece to put in.

 

Now I have another problem. The starter relay was pulled apart (could see the coil) when I got it, and I had to squeeze it to kick in the starter. No big deal, right?  I ordered a new relay, and after the above work was done I put in the new relay. 

 

...turn the key and nothing happens.   Put the old one back in, same thing. So something else must be keeping the relay from kicking in. I'll have some more troubleshooting to do when I get time. But probably not tomorrow, too much going on and too much grass left to mow. I think I need to re-sharpen the blades on 2 decks already, grass and weeds have gotten tough after being let grow too tall. Sigh...