1980 vauxhall royale coupe backfires when cold

what kind of fuel system does it have?

Sorry, not able to help, but would love to see photos. Get a build thread started - gotta love a Royale, especially a coupe!

Did you buy it as a runner? Check the easy and free bits first like timing, firing order etc.. Then the internal bits like compression etc. Once they're clear you'll know it's a bolt on bit and your engine is safe!

Here's an example of the kind of tomfoolery that goes on...

My old man bought a tr6 years ago that ran ok...ish, seemed ok once warm but kept cutting out in traffic or after an hour of driving.
Further investigation found:

Seller had swapped firing order around on two cylinders to mask a head problem. You wouldn't believe it...
Put the order right and it ran like curse word... Head off!

it should be a Solex 4A1 carb, these are a big old carb and I think the carb body used to warp causing all sorts of problems, there are also a few vac pipes that might be worth checking, as for the oil pressure it might be worth checking the pump cover on the very base of the timing cover, the gears sit down on this and wear a figure of 8 shape into the cover which affects the oil pressure, pretty easy to remove the cover and rub flat with wet&dry laid on a nice flat surface like a sheet of glass, the correct oil filter is also important and the correct grade of oil

It's hard to tell without seeing it but by backfire I assume you mean it spits back through the carb? That's almost certainly a sign of it being weak so either lack of fuel, faulty choke or airleak in the system. All fits with having the problem when it's cold too.

If it's backfiring through the exhaust it could just be a sticking valve, but check the timings first.

Appreciate you may want to work on it yourself but this guy is fantastic with old cars. I wouldn't use anyone else.
www.classiccarwebsite.com/west-coast-classic-workshop-ltd

Where in Scotland are you?

Thread needs pics......

That is gorgeous.