Husqvarna riding mower with Kohler Courage SV730 MAJOR backfiring issues

[cmw]

I have a Husqvarna riding mower with the Kohler Courage SV730 engine and it has recently had a few issues. It started backfiring and revving up and then the valve lash adjustment nut on the intake valve of one cylinder fell off. I reinstalled this and adjusted to spec. I assumed that this backing off was the cause of my problems but it is still acting up. The engine RPMs sound much higher than normal and it will start backfiring and popping if the engine isn't under any load such as when it is sitting still. Doing anything such as speeding up, slowing down, or engaging/disengaging the blade will pretty much guarantee a big backfire. Letting it sit and idle will cause lots of backfiring like a machine gun. It is very loud and we are talking loud to the point of needing to wear ear plugs. You get that concussion feeling through your chest such as when a you fire off a high powered rifle.

The muffler appears to be bulging and has ruptured at one of the seams from this. The muffler was also glowing red and shooting enough flames that it caught some dry grass on fire. There is also usually some run-on or dieseling when the engine is shut off.

Besides all this mess, the mower has more power than ever and seems to not bog down as easily as before but does seem to be consuming more gas than normal.

I have also been running synthetic oil since I have had this mower and there wasn't a spec of sludge under the valve covers. Everything was shiny and clean like in a new engine.

Any ideas on what has happened here and how to best correct the problem?

 

[Rokon]

Since no one has replied I'll take a stab at it.

It sounds like your timing has advanced. How, is the big mystery.

The first thing to check is if the flywheel key has sheared. This will require removing the top engine shroud(s). Also unbolting the big flywheel bolt. Then pulling off the flywheel and inspecting the flywheel key. It's a little work...

Others much smarter than me may have other thoughts and will be along to help further.

 

[cmw]

I removed the flywheel today and they key and keyway appear to be just fine. There is no sign of the key being even a tiny bit sheared.

Something odd that may shed light on this came up when I left the key in the on position after it backfired itself to a stop and then ran the battery down over several hours. It blew the main fuse several times until I gave up and charged the battery with a charger for a couple hours. It then started right up and didn't blow the fuse.

I really need to take some video of this thing. I was sitting on it and showed it to a neighbor and she said the flames it was shooting were really something else.

 

[cmw]

I just went out and took some video. I could hardly stand in front of the mower because of the high heat. The front muffler shroud part of the mower was glowing for like 5 minutes after I turned the thing off.

 

[Rokon]

I just went out and took some video. I could hardly stand in front of the mower because of the high heat. The front muffler shroud part of the mower was glowing for like 5 minutes after I turned the thing off.

This is perplexing to be sure.

You have eliminated the flywheel key as a problem, which is good. My only other thought is that somehow there is a problem electrically. I wish I could offer more help.

 

[cmw]

I looked into this a little more. It doesn't blow the fuse when the battery is fully charged. I don't know what this means.

I was thinking maybe it was running lean or too rich but it is like all of the above. Sometimes the flames are a bright blue color and the front of the unit will glow bright red. This was really striking at night. Blue flames are very hot so I figured it might be running too lean. Then it sometimes has big yellow flames coming out. The engine is usually just racing as fast as it can when the blue flames are coming out while it runs at a more normal speed when the yellow flames are blowing out.

I have tried to attach some thumbnail pictures from the videos I took. It is obvious this is a fire hazard.

 

[hsherm]

"Backfiring" is generally caused from either a timing issue, bad (or wrong) fuel, or sticky valves, but it can also be caused from other issues. Make sure the carburetor is clean and that the float and needle are working properly. This shouldn't be the problem, but it never hurts to play it safe.
Since it apparently starts o.k., the timing is more than likely fine; However, it would be a good idea to make sure that there is no "play" in the flywheel. It shouldn't move at all without moving the crankshaft, and it should be a little difficult to remove if on properly. If this checks out fine, it may have a problem with the valves. Remove the head and check to make sure that the exhaust and intake valves are not partially open during the compression stroke. If your engine is equipped with a "compression release", the intake valve will open slightly to allow some of the compressed mixture to go back into the intake valve area, making it easier to start the engine. This can be checked by removing the cylinder head and turning the crankshaft by hand in a clockwise motion. The intake valve will open slightly then close right before ignition. The "red hot" muffler, and flames shooting out of the exhaust, makes it sound like the exhaust valve isn't closing completely before it fires, causing the fuel to ignite while the exhaust is open. This can also be caused from using fuel with too much alcohol (ethanol) added. As for the main fuse blowing, this would be caused from a short in the wiring or a surge in the current. I would check the diodes on the stator (alternator) to make sure they aren't damaged. The heat from the engine could have caused some internal damage to the alternator, causing a short, which would result in a surge in the current. (Technically, this is the same as a "short", but since there is probably still some resistance in the wire, some wouldn't call it a "short".) If the battery was low, there probably wasn't enough voltage to close the starting circuit on the starter. If the voltage goes down, the current goes up, causing the fuse to blow. I'm saving the worst for last. Look to see if the governor has a "rod" going into the crankcase. There should be a lever that the governor is connected to, which in turn controls the rod entering into the crank case. If the engine is designed like this, you may just need to adjust the lever. There should be some information on line (including youtube) as to how to do this. Make sure there is no debris preventing any linkage from moving freely. If the engine is designed like this, and you are not able to idle down the RPM's by adjusting the lever, the problem is an internal one. I've seen more than enough engines where the rod has gone through the block on a certain model engine, due to this problem. I hope this was (is) of some help!

 

[Fish]

Just to test things a bit. Start the engine with one plug wire unplugged and see what happens, then try it the other way around. I am guessing that the problem will point back to the original head.

Also, there Is a concern about your checking the flywheel key, if you didn't not put it back together with enough torque, then this could be a secondary problem.

 

[Fish]

Also, find the tag and post the model and spec numbers, as I see some variations on the ignitions on this series.

 

[cmw]

Just to test things a bit. Start the engine with one plug wire unplugged and see what happens, then try it the other way around. I am guessing that the problem will point back to the original head.

Also, there Is a concern about your checking the flywheel key, if you didn't not put it back together with enough torque, then this could be a secondary problem.

Ok, here are some updates and more information on this issue.

1. The extended spec number requested is "PS-SV730-0034".

2. The backfiring and fire breathing behavior have stopped. I think something was obstructing flow in the muffler and that might have been causing some of my problems. There was lots of backfiring, fire blowing, and the exhaust was glowing red until a large backfire blew the lower half of the muffler and all the guts off and then I ran over them with the mower deck as I didn't know they had fallen off. There was a large explosive backfire just prior to this so I think this blew part of the muffler off. It hasn't backfired, blown fire, or had glowing exhaust parts since this time. I plan to replace the muffler if I get the other issues solved as I now have to wear earplugs to mow.

3. I have had other problems though. The intake valve rocker arms and push rods on both cylinders have given me similar issues. The first issue was with the right cylinder as you look at it from the front. The first problem was when the lock nut came loose allowing the pushrod to fall out of place. I tightened it up and used Loctite and set the lash to .006. The manual calls for .004-.006 and I figured setting it loose might be better on an air-cooled engine. This then pierced the pushrod right through the rocker arm. I replaced the pushrod, rocker arm, stud, lock nut, and pivot and applied Loctite. The same thing happened again after about 2 more mowings. I then replaced just the rocker arm and pushrod and set the lash to .006 once again. It lasted just about one mowing before putting the pushrod through the rocker arm once again. I then replaced the rocker arm and pushrod again and set the lash to .004. I have had no more problems with this cylinder and made it several mowings before I lost the other cylinder while mowing. Of course I was pushing through grass and the engine just bogged down and died. It flooded and was hard to restart and blew black smoke for a while once I had it running. I then putted up to where I could repair it and removed the valve cover for the right cylinder because that is where all the problems had been in the past. It looked fine so I put it back on and removed the left side. The lock nut on the intake valve had backed off and the pushrod fell out of place. I put it back together and set the lash to .004. I have mowed with it quite a bit without issues since then. I guess the lash likes to be set to .004 and not .006, at least on my mower. The engine just seems to run better overall like this but there are other problems.

4. The governor seems to be acting up. Sometimes it just revs wildly and sounds like it is going to take off. This is great when you are going through heavy grass but not when the unit is under no load. It sound like it wants to explode when it does this and it isn't under load.

5. I have been running Rotella T6 synthetic 5W40 based on suggestions from several people including lawn services who have great luck running this oil in all their air-cooled equipment. This is diesel rated and supposed to be better in high heat and pressure situations so I can't think of it being bad in an air-cooled engine like this, especially since there are no emissions sensors to foul. The insides of the valve covers are clean metal with no sludge or deposits.

6. I put the flywheel on to the specified torque in the manual with a torque wrench. I don't remember what this was but don't think the flywheel key is the issue in any of my problems.

7. I talked to a small engine repair guy and he doesn't much care for the Kohler Courage line of engines in general. He says he sees lots of problems with them and just considers them junk. He figures plastic gears in the governor are now going bad.

Conor