Mgb will only run on choke

[Lavo01]

A few weeks ago whilst driving on the motorway, my roadster began running rough, misfiring with no power. I managed to get off the motorway but the car just died and would not restart and Ihad to be recovered. Once home, I checked valve lash, removed and cleaned both carbs checking float levels and checking needles and seats by blowing down fuel tubes. All seemed ok. I found the vacuum advance on the distributor was broken so I replaced the dizzy. I checked for vacuum leaks using carb cleaner but could find none. Compression check showed 154, 154, 159, 154. I got the car started but only on full choke. As soon as I begin. To press the choke in, the car stumbles and dies. There is a sooty residue coming from the exhaust and all spark plugs are sooty. Today I replaced the coil with a new unit but this made no difference. Timing is set 10 degrees bedcovers and jets are two full turns down from the bridge as recommended. Does anyone have any idea where I go from here please.
Thanks.

[Statler]

Have you a fuel filter and has it been replaced recently?

I read a post on retro rides recently were a kit came with a shiny new filter which turned out to be the root cause of a similar issue. It didn’t flow and strangled the carbs.

[Paul Hollingworth]

It does sound like an air leak. I had something similar on an A series engine in an Allegro. I hadn't tightened the manifold studs properly after doing a de-coke. You haven't told us the vintage of you motor, does it have a PCV valve or brake servo, are they working properly ?. They other thing I would advise is to check your timing with a strobe.

[Lavo01]

Hi, sorry for the delay in replying, its a 1977 Roadster,. I have checked for air leaks using carb. I have checked the flow of fuel past the fuel filter and it seems fine. Its an after market pump so I fitted a fuel regulator to make sure it wasn't being over fuelled but still no difference. New plug leads and fresh plugs... still no difference. Looks like it's going to be a garage visit if I can get it there.

[Vic Butler]

Fuel regulator? Try running the engine without the regulator. It's almost certainly a fuel supply problem.