Postby Hasbeen » 28 Jul 2017 01:56
Your carbs are flooding, probably only the front one. It could be that some modification to the fuel pump, or it's instillation has caused it to pump at too high a pressure. Both the Stromberg & SU carbs fitted to 7s are designed to have no more than 2 PSI supplied.
However they can flood when the pressure is correct. When you shut off the motor the fuel pump still holds a residual pressure in the fuel line, & maintains this pressure to some extent depending on where the engine stops.
Our fuel pumps actually pump by the internal spring. The spring is compressed by the leaver running on the jack shaft cam. If the engine stops with this spring fully compressed the pump has the capacity to pump a fair bit of fuel.
If the needle & seat [valve] in the carb float bowl is a bit worn they will not seal completely, & will weep a little. With the engine running this does not matter, as the engine will be using fuel at a greater rate than this weep. However when you stop, the weeping of the residual pressure can raise the float level to rise enough to overflow the main jet in the carb throat.
Depending on how the car is sitting, this fuel may pool in the carb throat, or the manifold, run into the cylinder head , or soak the air filter. It usually means that on trying to start, before it has evaporated, raw fuel will be drawn into the thing, wetting out the plugs, causing hard starting.
To check this is the problem, after stopping the engine, immediately remove a hose from one carb. A squirt of fuel will occur. Now do the same about 10 minutes after stopping the engine. If no squirt of fuel, it has wept into your carbs.
Correcting the fuel pressure if it is above 2 PSI, or replacing the needle & seats in the carb, or both should fix your problem.
Hasbeen
