A little carb advice needed please

I need some advice on a little issue I have. The MGB GT with 1800 start and runs, but has just started to run like poop. I dont know if it is related but the tach jumps all over the place unless the head lights are on!!!
The car idles fine but if parked and slight revs the engine stumbels!!! I removed the air cans to see if its better and nothing has changed. I did find if I pushed the carb slides up they were rear slow and stiff. So my brain said the oil was too thick causing a slow rise of the jets making a lean situation, so I changed it for some thin oil and the same thing result.
It seems lean ,but if I restrict the front carb with my hand it runs great. And if I do the same to the rear it stalls the engine!!! So I think I narrowed it to the front carb but what are your thoughts? I tried just richening that carb but it just ran rougher and fouled the plugs to the point it now has a missfire!!

Before you go jumping into the carburetors with both feet I suggest that you start with the MOST BASIC of tuning processes, to wit, checking the battery, high amp supply, engine grounds and substitution of a known good ignition coil.

If that doesn't make a dramatic improvement you haven't lost anything, because from there you should plod through a proper tune procedure before spending time and energy chasing a fuel delivery issue anyway.

Jack

On the other hand, since you have already dinked around with the carbs, it is time to do a complete tune and FINISH be setting the carbs; mixture, sync.

I had a similar problem with my B. Sputtering, backfiring, stalling with any press of the accelerator. I was sure it was the carbs so tried retuning them without much success.

I then went and checked other things to do with firing. Checked the plugs, distributor cap, and then noted that my points weren't actually opening at all. I regapped the points and things have run beautifully since then.

While you may not have a problem with your points I believe the correct solution is to go for a full retune and check everything to do with the ignition of the car.

I have heard that a bad condensor can cause all sorts of mischievous symptoms.

Charles

--
Cry 'Havoc" and let slip the dogs of war.

"the tach jumps all over the place "
You seem to have an electronic tach? Don't know if that's correct for your car but it does indicate an ignition problem, so I'd check the usual, such as condenser, points etc.

I'm with Gert -
Sort out the electrics before you mess with the carbs. SU's I assume?

Just an update for all you non tecky guys.
After check the ignition and timing and basic maintance as per all your advice the car still runs the same. I was convinced it was the front carb that was the problem. so with further head scratching I jumped it with 2 feet and did a vacum test and it was ok. I pulled the jet and needle and fuel slide jet from the bottom of the front carb.
I figured that if I had threaded it all the way in and the car still runs that it was still gettin fuel. So the final verdict was the needle was worn and causing fuel to flow into the carb all the time and that was riching the mixture to the point it was so rich that when I restricted the air flow it ran fine. So my cheap fix for all that may have the same issue with worn needle is to pull the slide jet and file the top down to the point the needle no slides and closes. Now the jet is a little shorther but you can pull a little out of the plastic body its pressed into.