520H firing on one cylinder. Update** in op

[Honda4828 2]

Update: added new plugs tonight, it fired right up. It is blowing gas out of the carb though. So correct me if I’m wrong, but the main jet must be stuck? 

 

 

Hello, 

I purchased a 91 520h yesterday that’s in excellent shape, but only fires on the front cylinder. 

 

The original owner I bought it from said it will only start and run with a spark plug grounded to the bracket on the rear block. This really confuses me, why would it not fire with the plug wire on the plug that’s in the rear cylinder. The plug that he has vice gripped to the  bracket is sparking. 

 

I plan on compression testing the rear cylinder. And also swapping the coil and wires from my 92 to the 91 to see if it will run. Anything else I could try? Pics attached 

Edited April 11, 2019 by Honda4828

[richmondred01 2,289]

Broken rod?

compression test will give you at least somewhere to start.

Edited April 11, 2019 by richmondred01

[ericj 1,578]

do the compression test, I think you'll find either low or no compression in the back cylinder.  Nice looking tractor, hopefully you got it for a good price with it having a bad cylinder. Does it back fire through the carb ? if ti does it could be a loose valve seat. Do the compression test, then depending on what you find pull the motor and do a tear down to see what the problem is. Good luck

 

 

 

 

 

 

 

eric j 

[Honda4828 2]

9 minutes ago, richmondred01 said:

Broken rod?

compression test will give you at least somewhere to start.

 

I agree. Ordered a tester the other day. Waiting on it to get here. 

[richmondred01 2,289]

Take the plug out, stick your finger in the hole. That will at least show you right now if the rod is broken. 

 

[Honda4828 2]

9 minutes ago, ericj said:

do the compression test, I think you'll find either low or no compression in the back cylinder.  Nice looking tractor, hopefully you got it for a good price with it having a bad cylinder. Does it back fire through the carb ? if ti does it could be a loose valve seat. Do the compression test, then depending on what you find pull the motor and do a tear down to see what the problem is. Good luck

 

 

 

 

 

 

 

eric j 

 

 

Yea I think I did ok ok it. I got it for $200. Figured a deck is worth that. I’ve got another 520h that’s a 92. It not in quite as nice of condition and has more hours, but it runs great. I think it may need a left rear hub though. 

 

If I can’t get this one running on both cylinders. I may sell it or part it out 🤷‍♂️ 

[Honda4828 2]

2 minutes ago, richmondred01 said:

Take the plug out, stick your finger in the hole. That will at least show you right now if the rod is broken. 

 

 

Ok this may sound dumb, what am I feeling for? Moving the piston easily? 

[ericj 1,578]

to feel if it's building any compression or at least trying to

 

 

 

 

 

 

eric j

Edited April 11, 2019 by ericj

[Honda4828 2]

4 minutes ago, ericj said:

to feel if it's building any compression or at least trying to

 

 

 

 

 

 

eric j

 

So put my finger of the hole and try to crank it up right? 

 

I think I got it. If there is any air flow at all then the rod isn’t broken. If there is zero air flow the rod is likely broken. 

Edited April 11, 2019 by Honda4828

[ericj 1,578]

4 minutes ago, Honda4828 said:

Yea I think I did ok ok it. I got it for $200. Figured a deck is worth that.

I would have been all over it for that price too

 

Just now, Honda4828 said:

 

So put my finger of the hole and try to crank it up right? 

yes just  becareful of the spark plug. if the motor has problems you could allways swap the motor over to this tractor since you are having issues with the other tractor's rear hub possible differential.

 

 

 

 

eric j 

[WHX?? 50,758]

If you have a messed up hub don't run it as you have a pretty good chance of messing up the axle.

[Honda4828 2]

3 minutes ago, WHX22 said:

If you have a messed up hub don't run it as you have a pretty good chance of messing up the axle.

 

 

Yea I’m going to pull the hub before I run it anymore to see what’s going on. Since it wiggles some hopefully it comes right off. 

[squonk 42,570]

Take a good look at the plug you take out of the rear cylinder. This engine fires both plugs at the same time. Once on compression and the other exhaust. The spark current travels out of 1 coil tower, thru a plug wire, across the spark gap to ground (block).  At the same time that current travels out of the block, across the other plug gap thru the wire and into the coil. The spark current basically travels in a circle. If there is an open in a plug It breaks the circle and eliminates the spark. That's why he needed to get that other wire grounded. I used to run into this on GM car's in the 90's with waste spark ignition. 1 plug would go bad and kill 2 cylinders.

[Honda4828 2]

3 minutes ago, squonk said:

Take a good look at the plug you take out of the rear cylinder. This engine fires both plugs at the same time. Once on compression and the other exhaust. The spark current travels out of 1 coil tower, thru a plug wire, across the spark gap to ground (block).  At the same time that current travels out of the block, across the other plug gap thru the wire and into the coil. The spark current basically travels in a circle. If there is an open in a plug It breaks the circle and eliminates the spark. That's why he needed to get that other wire grounded. I used to run into this on GM car's in the 90's with waste spark ignition. 1 plug would go bad and kill 2 cylinders.

 

 

Boy wouldn’t that be nice if it’s just a bad plug. I’m going to put new plugs in today I hope, and feel for the compression. 

[Honda4828 2]

Pulled the carb and cleaned it the best I could. Put it back on and it idles great. When you bump the throttle up it spits gas. Took the plastic cap off the adjustment screw and screwed it pretty much all the way in which is crazy. It ran the best screwed all the way in but would still spit some gas although it was less.  

 

I bought a new carb, hopefully this will fix it.  

[lynnmor 7,568]

6 minutes ago, Honda4828 said:

I bought a new carb, hopefully this will fix it.  

 

Rarely is a new carb needed, just service the original one.  Since you didn't have the plastic cap off when you cleaned it, tells me you didn't clean all the passages.  Until you come back with the compression readings, anything is just a guess.

[Honda4828 2]

14 minutes ago, lynnmor said:

 

Rarely is a new carb needed, just service the original one.  Since you didn't have the plastic cap off when you cleaned it, tells me you didn't clean all the passages.  Until you come back with the compression readings, anything is just a guess.

 

Yea I’ll be the first to admit I don’t know a whole lot about turning wrenches on stuff. I did get the carb off and taken apart, although  not all the way apart apparently. The compression testing kit will be here tomorrow   

[richmondred01 2,289]

I wish I was closer then 4 hours. I hope you didn’t put the cart before the horse. A new onan p220 carb is an expensive bet to place before checking a host of other issues that my be causing your problems.

Check back in with us. 

[Honda4828 2]

On 4/14/2019 at 2:22 PM, richmondred01 said:

I wish I was closer then 4 hours. I hope you didn’t put the cart before the horse. A new onan p220 carb is an expensive bet to place before checking a host of other issues that my be causing your problems.

Check back in with us. 

 

Got the compression tester. It’s at 5-10psi in the rear cylinder.  Looks like I’m going to more than likely be doing a predator 22 or 10hp diesel swap. Anyone have any experience doing these swaps and what is all needed. I’d really like the 10hp diesel as long as it would have the power for the mower. Then again the 22 predator is cheaper and better warranty.  Idk, thanks for all the help fellas. 

[richmondred01 2,289]

Just my two cents here:

pull the engine first and see what you are dealing with. 

Onans are expensive to work on but they are far better then a predator. 

I took 3 predators to the scrap yard last month. I didnt even try to start them up. 

[Honda4828 2]

32 minutes ago, richmondred01 said:

Just my two cents here:

pull the engine first and see what you are dealing with. 

Onans are expensive to work on but they are far better then a predator. 

I took 3 predators to the scrap yard last month. I didnt even try to start them up. 

 

Yea your right. I have to take it off anyways. I’ll take it apart and see what’s going on. If it’s the seat I’ll see what a local machine shop would fix it for, if not I’ll sell the motor for parts and swap in a new motor of some type.