Fuel for thought

[staghunt]

After I had my running problem when engine hot, which proved to be faulty coil as per my previous thread. I had been convinced at the time that it was fuel pressure/evaporation for two reasons 1/ not much fuel even looked like no fuel in fuel filter but this seems to be normal or at least a red herring. 2/even after fitting Viton tipped float valves I would still get a slight dampness at overflow pipe but could see no petrol at overflow exit from carbs and no fuel in carb pedestal. So I had purchased a Petrol filter king which incorporates a pressure regulator from EBay, by the time it arrived I had fixed the misfire problem with new coil but decided to fit filter king as I have a non points fuel pump which I have heard may put out more pressure than standard. So before fitting filter king I checked pressure which was 4 psi, after fitting it showed 2.7ish psi but the interesting thing is that after a run and stopping I observed that the pressure had risen to 6psi. This high pressure can not builds up before the filter king pressure regulator but between it and float valves due to heat under bonnet. I wonder if there was not the pressure regulator fitted if this may have risen even more and may be the cause of the many hot starting problems for Stag owners.
FUEL FOR THOUGHT.
Cheers Greg

[staghunt]

Hi Greg , My car cuts out when hot and restarts after a few minutes repeatedly , i notice the fuel filter is more or less empty only a trickle of fuel when this happens , upon cranking the filter fills completely , then empties to same effect did you have this sympton with yours as i have replaced all the usual ign parts & needle valves etc , havent replaced pump yet ? Thanks Lloyd.

Hi Lloyd my fuel filter would more often than not look completely empty but it always seems to deliver fuel and this was a red herring and not the cause of my misfiring/low power. If yours is actually running out of fuel try listening to the fuel pump if it is not clicking at all the pump may be at fault (mine will always clicks slowly with ignition on and engine off and also slowly when ticking over). On cranking as you say the fuel filter fills, if yours pump clicks fast then maybe it was empty perhaps a float valve was stuck and engine vibration giggled it free. Don't know if this helps you solve your problem but I was 100% convinced it was fuel but it was coil, perhaps others would comment on how full their fuel filter appears and fuel pump clicks. Cheers Greg

[wilf]

When I put away my car hot, the fuel in the carbs usually vapourises, and pushes fuel back out of the filter, so it looks pretty empty the next morning.

When I turn the ignition on from cold, the fuel pump always runs like crazy for a few seconds.

This is just "normal" behaviour for Buttercup. She occasionally fluffs a hot restart due to fuel being dumped into the inlet manifold as it boils merrily away in the car float chambers, but ahs never needed more than two tries to restart. From cold she is an instant starter.

I will carry out the "fuel pressure release" mod some time to cure that hot start issue. In the meantime she is allowed to behave like the old lady she is.

[Stagsongas]

Greg,

The fuel pressure regulator, fitted in isolation may not be enough. It can only regulate pressure up to that point (up to itself!)

If fuel vaporises anywhere after the regulator, the in-line fuel pressure will still rise. If that fuel pressure rises enough, similar hot start problems will result. To prove that, modern cars have the fuel pressure regulator fitted on the return side (from the fuel rail) so the pressure within the rail and then fed to the injectors is always constant whatever the fuel temperature is.

For a more complete cure, a return to tank pipe (perhaps solenoid valve controlled) connected as close to the carb.s as possible could also be fitted, as mounting a pressure regulator there is neither reailistic nor adviseable.

For perfection, or as close to we can get, we'd be fitting a fuel return as a matter of course, and fitting the pressure regulator on that return side to ensure that pressure to the carbs and a little way after them is always constant.

Or we'd do what that manufacturers did 20 years ago - dump carb.s altogether and go for injection

Regards

Steve

[jbuckl]

The pump fuel available today boils at very low temperatures.

The original stag exhaust had a heatshield above the exhaust, which many stainless systems omit.

The fuel pipe is very close to the l.h. exhaust, hence potentials for a stag to be poor at hot fuel handling.

As already stated in previous posts, the fuel in a stag doesn't circulate, compared to moderns which manage to keep the fuel cool enough (just)

As a solution the heatshield can be checked for / reinstated.

The routing needs to be as per factory from the filter to the carbs. (bracket on n/s rear turret stud, pipe not too u-shaped - not closer to manifold than necessary)

Additional shielding can be considered for the filter to carb pipe.

The addition of a restricted bleed back to the tank can assist too.

A quality rubber fuel hose from the rear steel pipe to the filter may also help. (replacing the rear to front section)

In hotter countries than the uk the issues are quite severe, even with modern cars.

I understand that elements of un-pressurised pump fuel can boil at as low as 36 degrees C!

Just my 2p

[73stagman]

The filter king reg that I have regulates the pressure between the regulator and the carb.. mine is set to 4.5psi and never moves hot or cold. and its the first point of looking if the engine wont run....Is the fuel pressure up? If not fix the fuel pump.....

The question has to be, "how are you setting the regulator?"

You should do it with the pump running but the engine not running. Then when the engine is running the pressure will fall just a small amount as the pressure versus flow levels out.
The float valves open as the fuel level drops and as the float valves open the pump will fill the float chambers until the floats close back off and the regulator opens again to limit the pressure. All this should happen instantly but if the pump does not fill the regulator and filter bowl fast enough you will get a drop in pressure.
It is most likley that your regulator is being set whilst the float chambers are filling and emptying if you are setting the pressure with the engine running
You need to do the setting with the engine not running but the ignition on and the pump operating. You will then be setting the pressure against a full float chamber with closed float valves.

Thats how Ive set mine up anyway and have no pressure issues....