Were is the best place to start with a miss for that develops when hot after a run of about30 mins starts miss fire a power loss???

could be fuel vaporisation in the lines/carb or a slight blockage.
an airleak as stuff warms up and expands
sticky valves.
check the coil is not over heating.

could be any number of things.
if it misfires at idle just try popping the leads off and on one at a time to see which cylinder is not working

start with the leads one by one then go from there electrical is usually the best place to start

After everything I went through last year, substituting a coil would now be my first thing to try.

Had a chance to start messing with tonight and changed all leads for new, removed all plugs (Bosch W8AC)
they are new condition and all gaps equal and correct, however the plugs to cylinders 1&2 were black and sooty whilst those on 3&4 are a good colour.

Its a 1200 engine (34bhp) with single carb (Solex 30).

Changing the leads didn't change the running ie once it is run for a good twenty to thirty minutes starts miss firing and loss of power.

Any obvious ideas, all plugs went back into the cylinder they came from, I was thinking to swap all plugs from1&2 to 3&4 and vice versa to see if it follows plugs, the dizzy cap and rotor arm look ok and fitted correctly, thinking it could be arcing between 1&2??? I have checked the manifold for tightness and is ok and I can hear no whistling noises (air leak).

It has a Bosch ZV/PAU 4R5 dizzy fitted,  I have read that this is better suited to the 28PICT carb could this be an issue it starts and runs lovely until engine well warmed up as described...although this wouldn't effect one bank only???, the coil fitted is a Beru ZS106...I guess that the fault is not electrical other than a fault with the dizzy cap to only effect one side.

So what the best way to identify air leaks on the manifold???

Any ideas welcome.

I will recheck the valves in the morning to check not to tight and hence leaking when hot???

I normally spray some wd40 on all the joints, pipes,etc if the engine speed picks up then it's getting in somewhere

Check your spark plugs too.  I got a misfire from a heavily sooted plug, I've also had plugs go dud before.

have a feel on the inlet manifold when running  if 1 & 2 were black and sooty the pre heater pipe may not be warming the manifold up so the fuel is no staying vapourised to burn, chances are the left hand side 3 & 4 will be warming up thus the good plugs.
another check would be compression on the cylinders  1 & 2 may be low.

if your going to squirt around the manifolds I use brake cleaner as if its drawing in it will idle faster where the leak is...

Did you get this sorted in the end then?

Hi Guys not looked in as been away all weekend (Whitenoise)...all sorted turned out to be the dizzy cap, there was absolutely no visible defects or dampness but a new cap and other bits arrived Thursday and started with the condenser and points , (HT leads had been change earlier in the week and all settings and adjustments were checked) and so went for a drive with just the dizzy cap and rotor arm to change, miss fire started on que so pulled over quick change of the cap and not looked back.....but the cap was £49 an 80mm dia stubby, whoever said VW were cheap.

Thank you all for the help, someone else suggested an electrical storm was occurring inside the cap which was a common problem apparently for cars that had been sitting on car lots for a while, not ever having a car lot not experienced that one.

But start with the simple basics one at a time and got there in the end....anyone want a dizzy cap looks perfect???

Glad you got it sorted mate, some times it's just something really simple that can cause a hell of a lot of problems.