Hi all,
In relation to fuel flow...
1. Remove the fuel hose from the carburettor and turn the tap on:
a. If no fuel comes out, you either have no fuel, the fuel filter is blocked, the tap is damaged, or the hose is blocked.
b. If fuel does come out, proceed to step 2.
2. If fuel leaks from:
a. The float chamber, inspect to determine if the cause is a crack in the carburettor body, a crack in the float chamber cap, or, just the float chamber cap o ring. Replace the applicable component.
b. The hole in the primer bulb, inspect to determine if the cut-off-needle is getting stuck, the float is leaking, or the needle/float have worn and when the float lifts, fuel is not being cut-off by the needle. If the float needle is getting stuck in the float chamber cap, clean the needle hole, seat, and needle, with carburettor cleaner. If the issue remains and for all other components, replace the applicable component.
3. If fuel leaks from underneath the carburettor or is found where the carburettor connects to the engine block:
a. Check for cracks in the carburettor.
b. Check for cracks in the inlet manifold.
c. If no leaks are found, replace the carburettor to manifold and manifold to block o rings.
4. If no fuel is leaking from these points, check (In no particular order):
a. The decompressor valve.
b. Head gasket.
c. Starter o ring.
d. (With the spark plug removed) Around the crankshaft where it comes out of the engine.
e. The exhaust port
If you are not seeing any fuel leaks and you have filled the mower with fuel, to test to see if it's making it to the spark plug you can check to see if the plug is wet, and you can also try removing the plug and pulling the starter. If fuel comes out of the spark plug hole then you know fuel is getting to it.
If you want to confirm if you have compression or not, with the spark plug disconnected but still installed, rotate the blade disc. You should find that approximately twice per full rotation of the disc there is at least a small amount of resistance. This is the piston compressing on the head side, and then the chamber compressing on the starter side. You can use this to determine at a basic level if one side or the other may not have compression.
If your neighbour returned the mower to you with the fuel tank entirely empty, it sounds like they ran it dry (Which isn't great for them but they should survive), or they left the fuel filler cap off and it evaporated (You should find oil remnants in the tank). It's also possible they straight fueled the mower when they ran out of your fuel, which could have done damage. Remove the exhaust port and inspect the side of the piston for scoring.
Ensure the engine is balanced correctly. The disc and blades should all be mounted securely. If a blade is missing the balance of the mower can be thrown off and the engine won't run.
Check the throttle position. The throttle may be positioned incorrectly, or you may need to move it to a different position for the mower to start and run correctly.
Ensure that you have the vacuum hoses connected correctly. The decompressor should connect to the carburettor body just next to where the carburettor connects to the manifold. The vacuum hose should connect from the carburettor cap to the engine body.
Ensure you're using the right springs inside the carburettor, and if required, try adding 1-2 brass spacer washers to the carburettor, under the cam assembly. Over time these components can wear, and as little as a third of 1mm can throw things off. While you're checking this, give the carburettor a full and thorough clean.
Check the cut-off wires. Remember, for PT's with the LM carburettor, you're supposed to use the short-type cut-out plug and the wire going into the carburettor which is lifted by the cam should not be covered with rubber. If it is, you're most likely using the long cut-out plug, which you should not be using.
I hope something above helps and I really hope your neighbour hasn't straight fueled the mower.
