520H/P220 - Carb/Governor Proplems

[Kurt-NEPA 755]

New member here.  A 1988 520H followed me home last week. In general I'm very happy with the tractor.  It came with a 42in rear discharge mower and a snow plow.  Most of it is in decent condition.

 

When I first looked at it I noticed several things.  The mower lift did not work and the brakes grabbed badly.  But what got my attention was the throttle.  It only moved about 1/4 of the travel and varied the engine speed between about 3000 and 3400 rpm (my best guess).  When I got the tractor home, I power washed it and started looking it over.   I found a broken lift bracket and bent and loose brake actuator.  Simple fixes.

 

I started checking out the throttle problem.  I found the cable adjusted keep the carburetor partially open.  So I adjusted the cable and set the idle.  That is when the fun began.  Below about 2000 rpm the engine runs rough.  When I advanced the throttle, the engine surges a bit but comes up to about 2500 rpm where the governor fights the throttle and keeps it there.  I can force the throttle against the governor spring and get the engine speed up to 3000 rpm but that is it. When I release the throttle, the governor pushes the throttle lever back and drops the engine speed to about 2500 rpm.

What I've done so far.

1.  I disconnected the carb linkage. The throttle plate moves normally and the engine runs across the RPM range.  Below 2000 rpm the engine runs rough.

2.  I tried all the governor spring positions with little success, but I did get a bit more throttle response.

3.  Checked for a vacuum leak with propane and found a fairly serious leak on top of the rear cylinder.  I assume that is a blown intake gasket, but I'm not sure yet. The vacuum gauge confirms the leak with only about 10-15 inches of vacuum at 2000 rpm.

 

I'm going to pull the intake manifold, check it over and reinstall with fresh gaskets.  I'll also clean the carb.  But I'm concerned about that governor limiting the engine speed so aggressively.  In my mind, I can't connect the intake leak with the governor problem

Anyone have any thoughts?

[ericj 1,576]

when you say the governor limiting the rpm do you mean that the engine is surging high then low and back en forth? if that is what its doing the vacuum leak and dirty carb should fix it. down load the onan manual and it will tell you how to set the governor. good luck  welcome to red square

 

 

 

eric j

[Kurt-NEPA 755]

Thanks for the welcome and the response Eric,

 

The surging is minor, I'm sure fixing the leak and cleaning the carb will deal with that.

 

The real problem is the throttle.  Its hard to put into words.  When I advance the throttle, all is well up to 2500 rpm.  If I push the throttle further the governor pulls it back to 2500 rpm.  If I hold the throttle higher, I'm pulling against the spring.  I can get the rpms to about 3000 but I have to hold the throttle there. If I release it, it returns the engine back to 2500 rpm.  Sure sounds like the governor is working.  But........

 

I have the Onan manual, I'll check out the governor section.  Thanks,

[Martin 2,130]

sounds to me like the governor itself (inside the engine) is limiting the rpm. maybe you have some governor flyballs stuck or something in there isn't allowing the governor to move its full travel. to check that out it would involve pulling the timing gear cover and investigating. if you look in the manual it explains how the governor/flyballs/spacer/cup all work to provide in and out travel than in turn moves the external arm to control engine speed. 

one thing to look at is the travel of the external arm. does it move the full extent of its travel? i could go and measure one of mine. the tip of the governor arm should move a certain amount. does the carb throttle plate move from fully closed to fully open if the throttle position screw is adjusted out with all the control linkage intact?

another thing to check would be to disconnect the throttle cable and look at the linkage travel.

BEFORE doing anything else make sure the governor spring is in the proper position that its supposed to be. on these engines (side pull governor) the spring is set from the factory in the 3rd hole from the pivot on the governor arm.

 

ive had problems with overspeeding, due to the flyball spacer coming loose on the camshaft nose.....

Edited June 8, 2014 by Martin

[Kurt-NEPA 755]

I fear you are right Martin.  Time for some governor surgery.  Hopefully it is obvious once I get in there.

 

The throttle plate opens fully with the linkage off, but once connected it will only open about 1/8 of the way.  I'm surprised I can get 3000 rpm with it there.

 

Thanks

[Martin 2,130]

just doing a bit of reading in the manual and the pin that is on the end of the camshaft (that holds the governor cup) allows a travel length of 7/32" for the governor cup. if this distance is less it allows the governor to race the engine, if it is more it won't hold the flyballs correctly. i couldn't find it written anywhere if it will limit rpm though? but i think that maybe this has something to do with your problem. 

 

like i said before, i have experience with the loose flyable spacer and over speeding, but not the other way around.

as you said the governor is certainly limiting the travel of the throttle plate when the linkage is connected though......

[Kurt-NEPA 755]

Thanks for the info Martin.

 

I think my Sunday afternoon will be spent reading the Onan manual.  Better than working in the garden in the hot sun.

[Martin 2,130]

pm sent

[Kurt-NEPA 755]

I decided to check out the governor.  With Martin's generous help, I got the shroud off.  The right puller got the flywheel off.  I just spent a hour cleaning off 25+ years of gunk from the entire area.  That's it for today.  I'll post back when I get the sator and cover off.

 

Thanks everyone.

[Martin 2,130]

Kurt, now that you have the shroud off check the governor arm without anything else connected to it on either end. the throttle bracket should have come off with the shroud, disconnect the linkage from the carb. just want to make sure it is still limiting movement before you tear off the timing gear case cover. 

 

if you still need to remove the cover pay attention as you pull it away from the engine. there is a small roll pin that sticks out from the back off the cover that locates in a plastic ferrule in the governor cup. it should be at a nine o'clock position as you look from the side of the engine. see if that is in position how it should be. maybe check out the manual first so you can see when you pull it apart if anything isn't how it should be. then i would check the pin length on the end of the camshaft. try to push the governor cup against the cam gear and move the balls toward the center location. let it go and they should move out toward the outer circumference of the cup.......

if there is problems there with things not being smooth, remove the clip on the pin and see whats up with the flyballs and spacer etc. in the manual it will tell you what to look out for, grooves in the balls or spacer, rough surfaces that would cause the balls or cup to hang up instead of smoothly doing its job......

have fun with it......

[Kurt-NEPA 755]

Thanks Martin, I checked the governor arm.  It has about 30 degrees of free motion.  Of course, that is with the engine off.  That seems about right based on what I understand at this point.   I read in the manual about the pin.  I'll play close attention.  This problem still does not make sense to me.  This fly-ball governor is very simple and nothing that I can see would have it limiting RPM.  I just doesn't work that way.  Maybe once I get the cover off something will jump out at me.

 

Any hints on getting the governor ball back in place.

[Martin 2,130]

i think the manual says to use a small bit of grease to hold the balls in the spacer. you should have 5 of them and the spacer should be a tight fit on the end of the camshaft. some spacers were keyed into a notch in the cam gear, either that or it should be tight enough to not be able to spin in its home. 

at this stage the only thing i can think of would be the governor is hanging up in its motion from in to out somewhere, either the back of the cup is limiting the flyball movement or the cup itself isn't traveling the whole 7/32 inch. grooves or rough surfaces may be causing that.

 

im puzzled why you have the full movement now and not before. was the throttle linkage on the left side of the engine limiting travel before? you should have been able to get the same movement then as you have now, although some of the motion would have been under the spring pressure that is there from the throttle spring. there is also a screw that adjusts the travel of the throttle, check that. I'm concerned that you maybe overlooking something in the linkage where the throttle cable hooks up, you did say that you could force higher rpm by holding it but then it would return to 2500 or there abouts. is the throttle control on the dash loose? the lever should have enough tension to hold whatever position you put it to. the throttle setup is designed to pull against spring pressure in the upper rpms. i am thinking that because you have about the right range of movement at the governor with everything removed that maybe you need to look closer at the linkage and cable, also the throttle on the dash. right now i would not be going any further on the engine tear down until all the throttle stuff is checked out and ruled out from being the cause here. i can video the movement for you but it wouldn't be until tonight.

[Kurt-NEPA 755]

Thanks Martin,  I am puzzled too.  From what I understand the governor movement is normal.  I do have that 30 degrees of free gov arm movement with the engine off, that is what I would expect.  With the engine running and everything hooked up,  There is movement, but its limited by the engine speed and the spring.   As I understand governors, the flying balls work against the spring to control speed.  The throttle just controls spring tension and therefore the engine speed.

 

I hadn't thought about the throttle control on the dash.  It seems to work normally, but a mounting screw is missing and the remaining 3 screws are miss matched.  So, some body has been working on it.  I'll take a hard look before I go further.

 

At this point I have to decide how to proceed.  Everything in my experience says I have a linkage problem, not a governor problem.  I have tried every adjustment on the cable, springs, and linkage - nothing seemed to help. I might just button up the engine and try again.  I'm missing something here and I don't want to throw big money at this yet.

 

Pulling the shroud was not a waste.  It was really dirty in there.  Cleaning that up was long over due.

[Martin 2,130]

Yep, that's what I think too. Right now you are at a point where going further into the engine is $$$ in just gaskets alone....

Take a step back and re assess the situation, time you have spent taking off the shroud was time well spent.....

Sent from my iPhone using Tapatalk

[Kurt-NEPA 755]

Sounds like a good plan Martin.

 

Thanks

Edited June 9, 2014 by Kurt-NEPA

[Kurt-NEPA 755]

Well, I put the flywheel and shroud back on and hooked up everything except the throttle cable.  The engine fired right up.  The same old problem returned as I expected.  I advanced the throttle bell crank with my thumb and the rpms went up to 3000 easily and then I got a lot of resistance.  The spring and/or governor were fighting me.  I pushed as hard as I could and got the rpm's up to 3500.  The engine was running well, but there is no way the dash mounted lever could hold the throttle open like that.  My thumb still hurts.

 

Fun!!!

[Martin 2,130]

Kurt, let me look at both of mine when I get home, I will see what sort of pressure is at the linkage. I know I tried to operate one without the cable attached before and the throttle bracket was hard on the fingers.

Sent from my iPhone using Tapatalk

[Kurt-NEPA 755]

Thanks Martin,  I'm the point now that I'm beginning to think the wrong spring is on there.  It take an awful lot of pull to stretch it only about 1/8".  I did go out and try all the positiona on the rod from the gov lever to the carb.  No help.  Moving the spring around seem to make a difference, hence I'm questioning the spring.

 

I'm going to run to the hardware store and see if I can get another spring.  Just to test things out and see if it makes any change.

 

A calibrated thumb on the throttle lever will be a big help.

[Kurt-NEPA 755]

Something Martin said earlier started to sink in.  He asked if my throttle handle on the dash was in good condition.  I got to thinking that the throttle uses the spring to balance the governor and set the carburetor.  If the throttle handle assembly was loose it can't keep tension on the spring.  Sure enough, the handle was very loose.  I clamped on the frame with some Vicegrips and put some tension on the handle and now the engine seems to be running perfectly - completely across the range of rpm.  I have ordered a new throttle handle assembly and its due to be here on Wednesday.  That will prove the point.  At this point I'm almost ready to declare victory, but its not time to celebrate yet.

 

In any case I was able to hold the throttle open at 3600 and run around the yard for the first time.

 

Thank you Martin!!!!!!!!!!

[Martin 2,130]

so do you think you have the right spring in there?

 

i will post some pics a little later of one of mine and you can compare......

 

congrats.....

[Kurt-NEPA 755]

I think the spring is right Martin.  I tried to order one at my dealer and they couldn't get it.  OnanParts lists them, so with my next order I'll get one.  For now, I'll wait for the throttle assembly and see what happens.

 

Thanks

[Kurt-NEPA 755]

Update and Success Story  - YEAH!!!!

 

I received the throttle cable assembly from my dealer this afternoon.  I got home and installed it, fired up the engine and all is well.  Full engine speed and no slippage.

 

My take on this is that the throttle assembly was not providing enough back tension on the governor.  So the governor was moving the throttle handle instead of the engine throttle plate.

 

All in all, it was a easy fix once I figured it out.  Not terribly expensive either.

 

Thanks to everyone for the help.  Especially Martin