If it's easy to start warm then you would think that timing and spark is good , the first thing I'd try is the correct length plug,then check the carby is completely clean internally and float is set right (you probably did remove the emulsion tube for cleaning), make sure the primer is dribbling fuel out when held down.
A bad mower ignition coil can exhibit different behavior depending on its temperature. An ignition coil that is failing may work when warm but fail to start or run properly when cold due to thermal expansion affecting its internal components. When the coil is cold, the materials inside might contract, leading to poor electrical performance. As it warms up, these materials expand and might temporarily improve the coil's function.
When suspecting the ignition coil is the issue, you might experience symptoms like hard starting, misfires, or inconsistent performance, particularly when the engine is cold. Testing the ignition coil and possibly replacing it if itβs faulty can help resolve these issues.
"Generally, I'm very skeptical of old coils. Ignition coils are designed to last several years, often ranging from 5 to 10 years or more."
I don't like the short plug idea ,I've only done that when I put a larger carby on than necessary and the motor wouldn't start because it was getting wet from excessive fuel ,the short plug worked well in that case.
too short in reach for your lawn mower, several issues can arise:
Incomplete Ignition: The spark plug may not reach the combustion chamber properly, which can lead to incomplete or inconsistent ignition of the fuel-air mixture. This can cause poor engine performance, misfires, or difficulty starting the engine.
Reduced Engine Efficiency: A spark plug that doesnβt extend far enough into the combustion chamber might not ignite the fuel efficiently, leading to reduced engine power and efficiency.
Engine Damage: In some cases, if the spark plug is too short, it could cause damage to the engine or other components due to improper combustion or overheating.
Increased Carbon Build-up: Incomplete combustion can lead to excess carbon build-up in the engine, which can affect performance and longevity.
To ensure proper engine performance and avoid potential damage, it's crucial to use the correct spark plug with the proper reach specified by the manufacturer for your lawn mower.
The plugs can be bought from Villiers spare parts UK (Villiers Services) or machine up / buy a adaptor 18mm to 14mm then use the more common 14mm spark plug.Pic of adaptor below is an example ,you'd have to search if you want a cheaper one.
With the mix ratio ,personally I never had a problem in the old days using BP Zoom and that was 25 to 1.
The carby usually needs to be completely disassembled, cleaned and assembled and if the float level is not checked and adjusted, if it's set too low it makes starting a lot harder, sounds like this has been done already.
One problem with the old Villiers is the Coils are ancient now and were 30 years ago ,unless you load test them on a coil tester it's difficult to tell if it's working as it should.When I get a mower that's hard to start and everything else seems right I like to replace the coil with a good know coil to see if that's the problem or you could have the coil tested if you can find someone with a coil tester.
l've had old Villiers motors that were hard to start then after converting them to electronic ignition they start easy even if the crank seals are leaking a little.
The old Villiers just have a crank bush with no seal ,one check of crank case leakage is to run the motor then spray starter fluid around the crankshaft where the bush is and if the motor changes rpm you know there is excessive crankcase leakage.Your motor sounds ok in this department as you say no problem when running.
Sometimes people change the bottom barrel gasket with a thicker than original gasket which changes compression and port timing.
