Runs like a Swiss watch until you ask it for more at 70+ - then it misfires and judders until you let the pedal back up. Not really a prob. as it's only a run-around and rarely sees roads straight/long enough to get to 70, but it would be good to cure it if possible.

Must be fairly well set up as I got 44 mpg on a longish (250 mile) trip on single/dual carriageway A roads a few weeks back.

Your ideas please....

check condition of high tension leads and spark plugs!! Could be them. Was the problem on mine!

Good suggestion, but they are all recently replaced.

pinkpunto said:

Good suggestion, but they are all recently replaced.

Click to expand...

In that case make sure they are all connected properly and not loose check for corrosion etc...

Does it still misfire if revved while standing still, if it does it could be the ignition module, if it doesn't i'd say dizzy cap/wires or plugs. Are the plugs fouled any?

When it happens again try putting your hand on the carb, if it is very cold. Then your suffering from 'carb icing' this isn't some sweet cake covering but the carb running too cold. To cure it you have to check that the hot air pipe / mech is working on the airbox.

SuperUno said:

When it happens again try putting your hand on the carb, if it is very cold. Then your suffering from 'carb icing' this isn't some sweet cake covering but the carb running too cold. To cure it you have to check that the hot air pipe / mech is working on the airbox.

Click to expand...

Now there's one I hadn't thought of! Carb heat/icing was a vital part of my checks when flying the Chipmunk many years ago, and my old man had an Austin A40 that used to get carb icing until he modded the intake.

Checked this just now. A slightly dodgy bit of tin-foil tube runs from the bottom of the air filter to a plate welded to the exhaust manifold, (to provide the warm air?). The filter box has two air feeds, the other coming from funnel by the radiator, and inside the filter box is a spring loaded actuator that opens a flap on the top of the (warm?) air intake - perhaps the actuator mechanism is faulty?

perhaps the actuator mechanism is faulty

Click to expand...

Quite possibly. Mine was. I went to scrappy and got a new air box from a Panda. Not sure if it made a difference, but the mechanism certainly works.

I remember ages ago on these forums there was talk about air intake and this mechanism. Alex had a lot of input on that thread - can't quite find it now.

I think you could completely remove that mechanism by screwing it out?

Thanks to SuperUno for prompting me to look at the hot air intake - although I did nothing apart from take it apart and put it back together again, it seems to have done the trick. I did straighten out the tinfoil slinky-style hot air pipe, and that may have helped.