really loud like hole in muffler and running horrible

[MountainBuck]

I am not smart enough to do internal assessment but I think that is my problem. I have super clean air filters and no loose connections at coils or water near plugs.
Does engine rebuild work out very often or is a multi thousand dollar repair? The dealer cannot look at if for two weeks. I’m on a bad way wondering. Thanks for any and all comments

I understand your hesitance.

Back 40 years ago, as a beginner mechanic, I would have changed the plugs and the wires for just a couple of bucks.

The reason I keep thinking about the plugs is that the engine service manual actually calls out the plugs as a reason for the muffler to overheat. You mentioned that you haven't changed the plugs, so it seems like a reasonable place to start.

However, Tomplum is right that there might be something more serious going on.

I would think it should be repairable, but that will take a little more than a high school kid mechanic to do it.

Was it more like a light switch turning off? Like were you mowing fine and then all of the sudden - boom - all of the power dropped out and it was running bad? That would point to more of a serious problem like valves and head gaskets and the like. If so, I would just call the dealer and pay the price. Yes those problems are expensive and with inflation like it is, who knows.

If you take it to the dealer, you should have them quote you on a full service while it is in there, like a full radiator flush and refill, hydraulic fluid service, etc. Yes that will be even more money but cheaper in the long run.

 

[prs]

Start simple. With engine totally cool, remove the spark plug boots by slightly twisting as you pull. They should be numbered 1-2-3, if not lable them. Use compressed air, even canned air is OK, to blow out the spark plug wells. Remove the spark plugs and inspect for cracked ceramics, damaged gaskets, excess rusting of hex, and gap. If plugs are in poor condition, replace. If rusted, use long swab saturated with KROIL or PB BLaster to clean the spark plug mating seats of the head. If rusted, consider running WITHOUT the rubber bushing that is or should be pressed onto the bottom of each boot. In humid areas, those boots trap condensation as the tractor cools. Do carefully check the two per coil electric connections, they should be very snug without wiggle. Bad plugs let unburned fuel into the catylitic muffler and super heated condtion.

The muffler cover with mineral filled blanket has been replaced by a new all metal shield that comes with fasteners. Much better.

Beyond that, with your mechanical experience, you will need a small engine repair shop and one experienced with Kubota gassers. Or an experienced mechanical friend to help with trouble shooting.

prs

 

[prs]

phunter; ya dun wint an' jinxed me. lol

I put a long day in HOT weather this past Wednesday mowing tall field fescue. Later in the afternoon I had finished about 11 acres with about 2+ acres to go and my fine running machine suddenly, under only modest load at 3,200RPM, started missing badly and sounded like it had blown part of the head gasket or exhaust manifold gasket. I was at a lower elevation and, like you, was barely able to "limp" back up to the shop building about a quarter mile away. At the shop, she was HOT at the muffler shield (mine is metal) and I had to let it cool to room temp over night before trouble shooting. Yesterday morning the exhaust system was good, the head gasket good, compression good, spark plugs good, fuel and air goo; ignition not so good. Intermittent spark on TWO ignighters (coils), #1 and #3. The 3 cylinder engine was running mostly on just one, the center, cylinder. (#1 being closest to radiator fan, #3 closest to fly wheel, firing order 1-2-3). The outer two cylinders dumping fuel rich exhaust into the catyltic coverter making the heat. I called my dealer and trailered the machine the hour and one half to them. The mechanic said he probably knew the issue, as it was rather common with the Z at about my hour clock (750 hours, I think). He got it to run briefly on all three cylinders by working/jiggeling the wiring harness to the coils. I noticed it had run correctly for brief periods while I was loading it to go there. He replaced the upper press on trigger circuit connectors to those two, but they would still only spark intermittently. I took it off the trailer and into their shop where wiring harness was removed and found to be damaged in its mid section and also at the larger connection at its lower end where it connects to flywheel pick-up sensor. He thought there was a new harness in stock, but there was not. Estimated two weekds to get the new harness from Ventrac, unless they have one in stock. Rats! There are three different lower end mulit-oin connecters, otherwsie I could make a new harness myself.

prs

 

[5030]

Usually, a hole in a muffler on any 4 stroke engine will cause diminished power output as all 4 stroke gas motors rely on a certain amount of back pressure in the exhaust to run properly.

 

[phunter]

Thanks for the replies. The tractor did act up really quickly. I’m hoping nothing serious since starts easily.

Unfortunately my dad’s health became an issue shortly after my last post. He had to have emergent transfer to Cleveland clinic. Once things are better for him I’ll get things sorted out. Ventrac worries are so small in comparison to the health of your best friend and father. God will see me and my family through.

Once I have a fix determined I’ll share with the group. Thanks again for all your responses.

 

[5030]

Prayers sent for your dad.

 

[prs]

Well, my problem, which matched the OP's description, turned out to be ignition. The wire harness taking signal to the coils was damaged. New harness installation revealed the Kubuta engine control module (ECM) was also damaged. The new ECM and harness did the trick. Odd how suddenly this happened and with no obvious causative event.

 

[phunter]

My dad remains in the hospital but he is improving. Thanks to all of you that prayed for his healing.

My 4500 z remains broken. I thought I was into something when I used my test light and did not get cylinder one to light up when cranking the engine with test light connected from plug wire to the plug. I do have power at connections going into the coil. Cylinder 2 and 3 do light the test light up. I replaced the cylinder one coil along with new plugs with no help. Still light won’t light up with new coil.
Anyone know why light won’t come on for cylinder one ? Is this my problem ? Thanks in advance

 

[prs]

We will keep prayers coming for your Dad.

You put a new coil at 1, the cylinder closest to the rear of tractor. You say the wires feeding the coil are showing voltage, yet the coil does not get its charge to the spark plug. Very odd. Make sure the high tension wire is firmly twisted into the spark plug boot, probably is; but check. I still suspect a problem with the wiring harness and/or the Kubota "brain" (ignitor). The ignitor is behind the front of the air cleaner, remove the air cleaner box to access. It is an expensive part, but less so from Amazon. The harness from the ignitor to the coils, I can not find on Amazon. Mine would fire coil 2 "most of the time", coil 3 "most of the time" and coil 1 very seldom. You will get it.

prs

 

[phunter]

I have replaced coil number one and pushed wire onto plug boot real hard. I’ll check that again in the morning.
If I have power feeding the coil at the connections does that mean the ignitor is okay or is it not that simple. Light comes on easy peasy when cranking for cylinder 2 and 3 but never for one.
Wonder what’s what

Thanks for your reply and helpfulness