Paul you stil have plugs, plug leads and a coil.
Uhā¦yes. But all the really irritating bits are GONE!
The Jag ran so remarkably better with the EDIS: Margaret has an Allison, but still has a dizzy.
I know you said your carbs are spot on , I spent a long time setting mine up , HS8ās .
Tick over was fine , revved up fine , but once on the road under load it did not want to know , missing and playing up , a few turns down on the mixture screws solved the problem .
Got myself a colourtune and the car runās fine now
Only take a few minuets to add 1 1/2 turns , see what happens !!
1 thing on the prosses of elimination ,
Just because something is new , donāt rule that out of being the problem , there is a load of crap parts floating about 
I donāt see anyone having mentioned the vacuum advance on the distributor. Has this already been replaced? In my youth my first car was an MGA with this same issue. Replaced plugs, wires, condensor, coil, etc. until someone either told me or I read that the diaphragm inside the vacuum advance eventually fails after many years. Replacing it fixed the problem. Something to consider.
Hello Christopher,
Yes I have installed new vacuum advance as old one was a little weak. It advances nicely. Have not been able to check any of the suggestions as am having new soffet , facia and eavestroughig and garage is blocked. Wknd looks good to try and solve issues. Of course weather is extremely conducive for two seater driving. Thanks to all, will keep posting any results.
Re Vaccum advance - As I understand things, the vacuum advances the ignition further when there is more vacuum which occurs when the throttle is closed rather than open. I would think that missing under load, when the throttle is open would therefore not relate to vacuum advance. Please let me know if I am wrong about this as I have a 3.4 missing badly, only when hot, and only under load.
Have you changed the plugs? It could be a high pressure misfire.
As for advance, the ported vacuum used advances the timing under open throttle, then lessens advance as the throttle os closed.
Also check the small wire that connects the points to the outside run, point gap, and also the condensor.
Thank you, Paul. I appreciate the time taken to reply. I had read elsewhere that the vacuum increases with manifold depression which is associated with the closing of the throttle. That does make sense to me! The article also said that the extra advance was needed to allow more time for the weakened mixture to burn properly. By inference, when the throttle is open there is less vacuum so less advance. I do hope I remember this correctly! I have all new plugs, leads, capacitor, dizzy cap, points, h.t. coil and suppressor caps. The dwell is set by a meter at 35 degrees (points gapped at 15 thou) and the advance with vacuum disconnected, to 30 degrees at 3,000 rpm (crank measurements). I suppose there is always the possibility that one on the brand-new components is faulty.
Donāt forget the mechanical (centrifugal) advance may be stuck. Turn the rotor by hand and it should spring back
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I am new to this forum and am so impressed with the speed you guys reply and how you like to help - thanks. Yes, I have checked the centrifugal advance does work - it sits at around 7-10 degrees at 800rpm and advances steadily up to 30 degrees at 3,000 rpm (which is where I locked the dizzy). I have not measured the advance it at higher revs.
Ian, you said only when HOT and under loadā¦: 4 quick thingsā¦are there black insulators spacers between your carbs and the intake There should be. Hot carbs, thus hot fuel can cause problems. Swap out the coilā¦if you have a good spareā¦if no spareā¦wrap the coil in insulatonā¦reflective foilā¦whatever to keep it coolerā¦see if it makes an improvement. A hot coil can deliver a weak spark., and as Paul saidā¦put new plugs inā¦always an easy first step to eliminate that component. Check any of your spark plug wiresā¦just disonnect oneā¦both ends and measure resistanceā¦there should be almost noneā¦certainly not a high resistance. Modern car plug wires have extremely high resistance, not suitable for older cars without all the electronics. High resistance can cause issues and youād chase other things forever.
Nick
Thanks Nick. Carbs have insulators fitted. Also a brand-new Dizzy cap, brand-new new ht coil, brand-new points. All to no avail.
BUT 1 yr old ht leads and 1 yr old suppressor caps. The leads may have been touching the head in places. So, I have fitted new leads, new caps and ht lead spaces to keep them apart from each other and away from the head. I have yet to do a long run to test. I shall report back.
sometimesā¦in new made up wire setā¦there can be a gapā¦between wire and the connector. You said āsupressor capsāā¦do you mean just the connectors or are they really āsuppressionāā¦which you donāt need unless you listen to the radio. Nick
Both old and new ht cables are of the solid copper wire type and require (in the UK) suppressors. The āoldā caps (only 1yr old) were Champion 10k and the new ones are NGK 5k. The dizzy end are old-style acorn fit and I did notice evidence of a gaps on two wires that must have been slightly pulled out as there were black carbon deposits on the copper cable ends. I hope to get out on a long run (50 miles + is needed) within the next week.
There should be small brass āwashersā on the end of the HT leads. I had the same problem and soldered them onto the wire. That was 18 years ago so I guess it worked.
Iāve done the same thing, Pat. I also fitted Lucas 78113A suppressors at the plug ends, which also take the acorn fixings. I soldered those ends, too. Much more positive and secure than screwing self-tapping plug terminals into the copper wires, IMO. These suppressors were apparently used when a radio was fitted, and on some overseas market cars. I had to scour Ebay for a while before I got a full set together!
The brass washers are fitted and itās a good idea to solder them - thanks for the tip.