Misfire.....

[skodajag]

I know it's very difficult to diagnose a misfire over the internet but because the symptoms of mine are specific and chronic I thought I'd ask for your advice.

The engine start and drives OK from cold. When warm it shows a reluctance to rev which becomes a misfire at high revs when the engine is warmer still. The misfire becomes progressively worse, though isn't all that apparent at a steady throttle at low speeds. It's only on acceleration/revving that it becomes chronic. If the engine stalls or is switched off it's impossible to start again until it has cooled somewhat. The engine is mainly standard, apart from Petronix electronic ignition. Am I right in thinking these ignition units either work properly, or not at all? I've tried changing the coil, to no avail. The condenser is my next hope, but any suggestions would be most welcome.

[abowie]

FWIW I have finally solved my misfire after replacing most of the electrics several times and fiddling with the carbs a lot over 6 months..
In my case the jet on the centre carby was not centred, meaning that the piston would stick, making the car miss. This was on a set of brand new carbs that I had had professionally overhauled prior to installation, which was why it took me so long to find.
Easy to check.
1. lift the piston with a finger and ensure that it drops freely with a nice clunk.
2. take the piston out and carefully examine the needle. If it is rubbing on the seat there will be a shiny stripe down one side of the needle.