Hi,
850 LM1. Bikes running well no issues. Left plug is perfect brown colour. Right plug is black and sooty which I assume is running rich.
Idle screws both out 1.5 turns. Slides click closed at the same time.
Not checked anything else. Would someone mind listing possible causes that I can work though. It is still points ignition.
I do have a set of vacuum gauges and a decent timing light if I need them. Also have a colour tune plug so could also check colour at idle and off idle.
Many Thanks
Eddie
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Choke plunger!
Ian
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I would say its the choke plunger too - 99% certainty
Russell
The choke is very likely as Ian and Russell have said, take the plunger out and clean it, replace the seals if they are cracked or hard. If the seals are poor on the right carb, replace them on the left carb too, as they will not be far behind in the give-up-the-ghost stakes!
Have fun, it looks like a garage weekend having seen the weather forecast!
Much appreciated Chris Russell and Ian. Time to break out the manual.
Cheers
Eddie
Also make sure the choke cable isn’t holding the brass plunger up slightly due to a sticky cable or being adjusted a bit tight. You should be able to lift the cable outer out by a few mm without moving the plunger.
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+1 all the above. If the ‘choke’ plunger seal button is indented, or known not to seal, you could prise it out and turn it over to get a smooth surface again, assuming of course this hasn’t already been done. 
Left side where plug colour was ok. Moved adjuster to allow as much slack as possible (still not enough to not move the plunger though). Tried to flip the seal button at the bottom but couldn’t. Top seal looks ok. Bit of rubber grease on top and bottom and dab of copperslip on plunger after cleaning and then replaced. Managed to get right side off. Slackened the cable as much as possible and now there is a few mm of free play in the cable. Cleaned and added rubber grease. Seals again look ok.
Both now back in the carbs. Hopefully eliminated the choke. I’ll drop in the Colourtune at idle and check if rich on RH side and report back…
Many Thx
Eddie
They’re alright when they work. 
Quite possible all the choke cables and plungers etc. need replacing, given the bike’s age. I know what it’s like, you get to a stage when you think ‘you know what all this could do with being replaced’ 
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After a run on Wednesday, Right Hand plug still sooty. Left hand one fine.
I’ll try swapping plugs but clutching at straws here. Will probably need to strip and check carbs. One of the blogs suggested valve guide oil seal (assuming they have one). Maybe time for a top end strip too.
Cheers
Eddie
The choke plungers are cheap enough so I’d still say to replace them. Even if the seals look alright they go hard and don’t conform to the seat.
Ian
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If you strip the carbs, make sure both needles are on the same notch.
Needles and needle jets can wear, but I would expect both to be the same.
You should be able to swap the carbs temporarily from left to right to see if the problem moves with the carbs.
Great idea Don. I’ll swap carbs when I get time. May get choke plungers replaced for piece of mind too.
Cheers
Eddie
No valve guide oil seals on the old MG’s (don’t know about the new ones?)
If it’s burning oil you would see blue smoke from exhaust. Is it?
I think it’s getting to the stage of carbs apart for a coating of looking at, rather than keep guessing. One thing that occurs is the accelerator pumps have diaphrams, but i can’t remember what typically happens if one is split and leaking…
No blue smoke. I did a compression test on purchase so all looked pretty good at 160 for both sides. Few oil stains on the head so maybe do a top end and carb strip over the winter. In the mean time I’ll probably swap carbs to try and id the rich running issue.
Thanks for all your help.
Eddie