On yours all you need to do is remove the entire airbox assy and you can run it easy enough to see a bit more to aid in troubleshooting. Yours won't have an accelerator pump. What you see is the fuel pump. Kohler does have sevice manuals online at no cost. When you change your fuel filter, "run" the line and catch some fuel in container so you can look for water and debris. Once that is done, run the line from the fuel pump into a container and crank the engine over to see if it is pumping a fair amount of fuel. Here is a link that might be useful: Kohler

***"I doubt a "defective air filter" is the cause of a wasted cam lobe on your machine. #2) I doubt the air filter has caused *only one* of your cylinders to give up the ghost either."*** I agree with that. When the air filtration is not keeping dust and grit out of the engine, the first components to suffer are the intake valves and piston & rings/cylinder walls. Secondary components to fail would be camshaft lobes, crankshaft rod journals and piston wrist pins. If you don't "see" any visible signs of filter leakage (obvious "dust tracks" or "dust streaks" showing in the areas "past the filter", dirt in the carb throat and intake manifold (some traces of "carbon black" in the intake is OK. Dirt, grit or "sludge" is not OK), about the only way to confirm the presence of inadequate filtration, is by doing "autopsy" to the disassembled engine and components. In an "autopsy", all engine components are measured with precision instruments (micrometers, dial indicators, "plastigage" to name some)and compared to the OEM specifications and/or wear limits. The two "most telling" things to measure when you suspect that air filtration has been "compromised" or "corrupted", are the diameter of the piston "skirt", and the diameter and taper of the cylinder walls. In measuring a piston, you DO NOT measure diameter anywhere in the piston ring area. The measurements are taken across the "skirt". The "skirt" of the piston is the "long, round surface of the piston sides". The skirt is the portion of a piston that actually "supports", or "carries" the side loading of the piston that occurs when the rod journals of the crankshaft are "half way between TDC & BDC" of piston travel. For this reason, the cylinder walls will wear where the skirt "rides" more than other areas. In most engines, you will be able to actually see the "track" where the piston skirt "touches" the cylinder walls. This track is where you want to measure the cylinder to determine how much it has worn. Measure the cylinder walls that are "perpendicular" to the skirt track AT THE BOTTOM OF THE CYLINDER. This point of the cylinder will give the original diameter of the cylinder when the piston was "put into service". Knowing the "new" measurement allows you to subtract that value from the measurement taken in the skirt track of the cylinder. The "remainder" from that computaion represents the amount of wear that has occurred to the cylinder. In measuring a piston, you take the diameter spec for a new piston and subtract the measurement from the worn piston. The remainder from that computation represents the amount of wear that has occurred to the piston. You can then compare all your measurement results to see if the engine would require "over boring" the cylinder to the next appropriate "oversize" of piston. Over boring a cylinder requires an oversize piston. And, you can't use an oversize piston unless you also over bore the cylinder (they only go as a "pair") If the engine features "cast iron" liners, and dirt and grit are getting into the engine, the wear to the cylinder walls will be worse than the wear to the piston. This is because the "softer" aluminum of the piston allows some of the grit to "embed" in it. The embedded grit acts like "emery" and will cut into the cast iron while the piston itself gets "less wear". Aluminum cylinders & pistons will wear about equally. Anyhow, if the cylinder walls and piston skirt exhibit "excessive wear", the wear is most likely due to bad air filtration. So, if you think you might want to "save" this engine by replacing the camshaft (which is obviously worn), you need to perform (or have it done by a "machine shop") an autopsy to determine if the engine is a candidate in the first place, and if unfiltered air was the cause. With today's costs of machine shop operations plus the high relative costs of individual replacement parts, you have to decide whether to save that engine, or replace the engine. If all other parts measure within acceptable specs, a replacement camshaft kit is likely a good way to go (even better if you can DIY). If the pistons and cylinders (even one piston and cylinder) are worn beyond the service limits, a complete new engine makes more sense. BTW, the 120 PSI versus 135 PSI on the "good" cylinder probably reflects the worn cam lobe more than the leaking head gasket.

rob, The camshaft did not wear because of the valves being out of adjustment. Valves being out of adjustment will not create high compression. The camshaft is not sensitive to compression in the cylinder at all. The ONLY pressure, or loading, on the camshaft, is due solely to the pressure of the valve springs. There are no other forces or phenomenons working against the camshaft. As to not exhausting enough gas, cycle of quick wear, higher pressures that even warped my head. None of that has happened to your engine. Those things simply do not take place. Sorry. The camshaft is worn out, most likely because of poor quality control during the finishing and hardening phases of manufacturing the cam. The camshaft ended up too soft as a result. Other factors might contribute to warping the head. If you have never removed the sheet metal to check your cooling fins for blockage, that might be a reason the head gaskets blow and the head warp. The other aspects of your thread are something only you can decide (fix, replace with same, replace with different).

Fixed it - yippeeeeeeeeeeeee Not sure which bit was not playing ball but this afternoon I've: -Adjusted the valve clearances (they weren't out by much but are now spot on) -Cleaned completely the petrol pump and blown through with an airgun. -Added a new in-line petrol filter -Re-cleaned the carb - took everything apart - washed and cleaned in neat petrol, used an airgun and blow dried everything and pushed fishing line wire into every hole I could find. I've completed a test cut of 40cm high grass in one of my paddocks (way higher than I usually cut with this tractor) and power was definately back to as it should have been and managed to wade through the grass cutting as we went without the engine dying on me. Yesterday it would have struggled to cut 10cm high grass and would have probably died several times in the process. Many thanks to all for your help and advice and the links to the papers (all printed out and in the file) and hope this post is useful to someone else later on. Off to fix the 4x4 now....