AJS & Matchless Owners Club

Hello there, My 1959 matchless g2 is causing me a big headache!
The bike starts and runs well until up to temperature, when it runs very badly, when the accelerator is opened. It lacks any power and mis-fires. So far I have replaced the pionts,ignition coil,condenser and re-built the carb with all new parts,there are no air leaks from carb. I have by-passed the switch to check this is not the cause, no difference.
Any help/idears would be greatly appreciated
Thank you in advance. Bernie 600.

A common cause is the valve adjustment which if to tight when the engine is warm thermal expansion holds the valves open a little.

Another is do you have a spacer block 042187 between the head and the carburettor ?

Otherwise could something electrical be warming up and breaking down?

Hope this helps

Ian

We have had a lot of issue with pattern coils breaking down when warm also. Off the shelf jobs. If this is new it may pay to try another if you have one.

Ian

Just another thought when its warm have you stopped and checked the float bowl for fuel. It could be fuel starvation. If so check cap for breather hole or tap for operation (Tap Seals could swell when warm!)

Ian

or running retarded ?

Thanks for that, what parts could be breaking down when hot?
& what is running retarded? Bernie 600

When timing is retarded, peak pressure and heat is delayed, and is not confined to the combustion chamber. Delayed ignition causes the peak heat and pressure to occur in the cylinder body itself. The flame actually burns the lubricating oil off the cylinder walls, causing more friction. As the combusting mixture is not under high compression, it is less dense, again causing further delays in the burn. When the exhaust valve opens, extremely hot, still burning gasses are blown out the exhaust port. past the valve. This flame heats the valve red hot, and superheats the head and manifold. Running an engine retarded for any length of time, under load, will cause valve burn out, and excess wear to the rings, piston, and cylinder. Ian

Failure of parts like the coil, condenser etc can occur when the engine has warmed up even when just changed for 'new'.
The usual cause for a failing or failed coil is overheating. This can be caused by spark plugs with too large a gap, which causes excessive KV to jump the gap. The bigger the gap, the bigger the jump, and the more power necessary to make it happen.
A coil that is failing will cause a low-spark intensity. When this happens, the combustion is not efficient, and a driver will experience a drop in power. A weak coil will also have a more difficult time jumping the gap in the plugs and will also have the possibility of no spark in lean fuel conditions within the cylinders, resulting in an engine misfire.

Ian.

First things first, is there still good compression when the engine is hot ?. This should confirm whether sticking ex valve or tight tappet adjustment is the problem. The above, regarding retarded ignition is a little alarmist I feel, as the bike APPARENTLY runs ok till it gets hot. A simple thing like too rich a mixture can cause hot running problems. Don't get too bogged down with worst case scenario before checking the simple things first.

Thank you Ian i will look at timimg now!