Reincarnated! Weird (and dangerous!) engine cutting out - what is it?

[dasadrew]

As a precautionary measure I've ordered up some stuff from Burlen. I hope the quality of their parts exceeds the quality of their spelling ....
Screenshot 2025-10-06 120330.jpg

[dasadrew]

Tick in the box No.1 - Temperature Compensators are good, all works smoothly and both move identically as far as the eye can see. Refitted with new seals from Burlen.
Tick in the box No.2 - Float chambers off - absolutely zero crud or foreign objects in them, so apparently no rusty fuel lines or whatever or filter is working 100%

[stagerooney]

Might be worth checking fuel pressure, the symptoms of your road side stalling and difficult restarting suggest over fuelling to me. A Filter King is a worthwhile addition to any classic car, not only can you regulate and experiment with fuel pressure, but is a visual filter as well. I have found over the years, the pressure from an SU type fuel pump (around 4 psi) is higher than actually needed with SU, Stromberg, Weber carburettors and can, in some cases, force fuel past seals.

[Philip Wardle]

IMG_5196.jpg

Absolutely, I set mine to 2.7 psi and I'm sure this has helped to deal with the flooding problem I had previously.

[dasadrew]

@ RTS: by "poppet Valves" do you mean the By-Pass Valve held on by 3 screws which don't seem to really fit?

[richardthestag]

@ RTS: by "poppet Valves" do you mean the By-Pass Valve held on by 3 screws which don't seem to really fit?

robbed from an MG forum, first pic show the poppet on the throttle disc https://www.mgexp.com/forum/mgb-and-...valve.2841813/

Temp compensators, wind the ******* things closed tight so they never open

check float level on same side as needle valve and without gasket in place

Main jet height to outer ring 80thou from bridge

[dasadrew]

no pic. I have the same problem since the crash that pics which I post don't show up for other users

[dasadrew]

Just found the pic which you probably refer to. If it's this, then no, my throttle "butterflies" are simply round discs.

https://www.mgexp.com/phile/1/460752/throttle_popit_1.jpg

https://www.mgexp.com/forum/mgb-and-gt-forum.1/how-to-soldering-throttle-plate-overrun.3665602/

[dasadrew]

IMG_5196.jpg

Absolutely, I set mine to 2.7 psi and I'm sure this has helped to deal with the flooding problem I had previously.

I have a Hardi electronic fuel pump which povides a nominal 2.8 psi (3.5 psi max). I would consider a Malpassi but, at the moment, I don't want to change too many things at once during the diagnosis of the problem, and a pressure regulator is an easy update after I've done all the carburettor checks and been on test runs.

[richardthestag]

I am not convinced that you are flooding, but then I haven't witnessed this issue first hand, I get the impression that the engine restarts easily but needs throttle to stay running. You can tell fairly easily and without taking the carbs off, remove the air filter and elbows once the engine is up to temp and off. Ignition on and lift each piston in turn, flooding will be evident by fuel dribbling out of the jet and pooling up around the base of the throttle discs. If it is doing that then you have too high pressure, faulty needle valve or wrong float height.

Alternatively I use an old baking tray on top of the engine, rest the carb set on the baking tray, connect fuel lines and switch ignition on. you should be able to gently tilt the set, i.e. simulate normal up / down hill driving, with no obvious gushing of fuel through to the pedestal.

[dasadrew]

Does the Stromberg have any dedicated parts, systems, valves or whatever which only play a role to keep the car idling?

What does the by-pass valve do?

[dasadrew]

Having some more thoughts on the scenario where my problem occurred, it was after a spirited run when I chose to take the next exit from the dual carriageway. So, I lift my foot off the throttle , but the engine is still running at a good speed. Does this mean that there is a depression in the carb, and would that cause the air valve to be drawn down? If yes, and if the air valve then sticks, could it cause starvation when trying to restart until everything cools off a bit and the air valve frees up?

[trunt]

Does the Stromberg have any dedicated parts, systems, valves or whatever which only play a role to keep the car idling?

What does the by-pass valve do?

The bypass valve gives some airflow through when the butterfly is closed. If it fails it causes a high idle speed.

No extra parts for idle really.. the temp compensators lean things off but it should still idle as they would be open anyway with a hot engine. The vent valves switch where the float chamber is vented to, unlikely intermittent issue there.

[dasadrew]

Thanks Terry!

[dasadrew]

Tonights conundrum is why in the gasket sets are there two square carb-to-pedestal insulators, but one has a cut-out which - if positioned correctl - exposes a hole in the carburettor body which seems to lead nowhere? Is this an "appendix" which has become useless over the CD175 evolution?