carbs

[Hobbo]

Hi Austin, just got carb back from professional reconditioners costing £120, so thought it would be o.k. but you never know Thanks Mike

[Ian Williams]

Then send it straight back to them!!! I assume all was well beforehand?

[Hobbo]

No it would not rev up before that's why I had it reconditioned, am looking elsewhere especially on the ignition side.Thanks Mike

[Ian Williams]

Mike if you have never had this carb working I suggest it is simply that the jets are the wrong size, certainly everything you have described is pointing to a week mixture. If you can tell me the carb type the venturi diameter and current jets I may be able to offer some suggestions, I will also need an outline on the state of tune the engine is in, cam, valve sizes etc.

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Ahh I have just read your OP again, am I right in thinking this is a big seven and that this is the original carb? Have you ever had the car running properly with it? I still maintain that you have a blocked jet or incorrect sized jets and or an air leak as we have discussed in earlier posts.

[Hobbo]

Hi yes it is the Big 7 I have never had it running properly. I bought it thinking that it sounded as though the timing was out popping and backfiring. Checked all the jets which were correct, even had a carb loaned which seemed to run a little better but not much, still would not rev up it just dies, on tick over it sounds quite nice and smooth, that's why I had carb reconned. Mike

[AustinWood]

In your first post you say you haven't taken the main and compensating jets out. They need to come out! I believe that the compensating jet may well be the cause of the problem.

[A G Wood]

Hi Mike, I don't claim to be an A7 expert [my expertise, such as it is, is with much much more modern vehicles] but I think you might be on the right track looking at the ignition side of things as the symptoms you describe also fit the parameters for an low HT secondary voltage. 
The  vehicle has never run right for you, so I suspect the problem is still on the car [if you know what I mean].
At the very least the carb reconditioner will have sent back a very clean carb and you have tried an independent fuel supply and a substitute carb, and checked for vacuum leaks as others have suggested to no avail.
You mention you have electronic ignition fitted?
FWIW try connecting a xenon timing light/neon timing light to the main coil to distributor lead and see what happens to the flashing rate when you try to rev up the engine, this is a rough and ready way to see whether you have a total ignition cut. Also check the HT lead integrity esp. if the are the non-metallic "carbon"  ones. Might also be worthwhile temporarily connecting the appropriate coil terminal directly to the correct battery terminal to bypass all the potential voltage drops. Don't forget primary system voltage and the earth return side of the ignition system as well.
Could be an esoteric A7 issue in which case one of the real experts will have other ideas.
Good Luck, and as one of my old Service Managers used to say, if one bloke has [insert adjective] it, another bloke can fix it 
AGW

[Hobbo]

Hi many thanks for that. Have just been into garage to have a look before I run this test, found out the ignition switched live is going to the CB terminal on the coil the SW terminal goes to the distributor, surely is that the wrong way round. The car has been switched from positive to negative earth before I got it. It had burned out the fuel gauge has the terminals had not been changed over. Thanks Mike.

[Hobbo]

Have since been on the internet, and found out that the wiring seems to be correct for change from positive to negative earth, which seems strange. It has now developed a missfire, will test tomorrow has AGW has described, failing that it looks like reverting to points and condenser which eliminates faults if there one with the electronic ignition as I know they can fail. Thanks Mike

[A G Wood]

(Usual disclaimer) my recollection from Auto Electrical classes is that an ignition coil with terminals  marked SW and CB is theoretically optimised for positive earth return vehicles. Also in theory they should work OK on negative earth return vehicles, however in my experience they don’t always follow theory... I suggest you beg/borrow/steal an more modern one with the terminals marked (+) and (-) , temporarily fit that and see what happens. (+) terminal  to battery live of course. Fitting a known good points type distributor is also a good Plan B to eliminate another possible cause. There is plenty of good material on this forum about retiming (or just ask)