Hello everyone, I have read through quite a few posts here, however I still felt compelled to seek guidance. I have a 1970 XJ, US spec fitted with dual Strombergs. I have also recently fitted Pertronix distributor, coil and wires. My timing is set up now and after much tinkering I have managed to get the idle to around 1050-1100. When I lift the piston of the carb, the revs are dropping slightly which I believe means it is running lean. I have found the strombergs a pain, as there are so many variations of very similar models. This makes studying various videos and articles a challenge. The car does sound very good now though It hasn't left the driveway. Should I leave it alone or should I keep tinkering to get the RPMs lower at idle? I will also mention that I have a mechanical fuel pump putting out a regulated 3 PSI.

Sorry for the long winded post!

 

I don't have any experience with Stromberg's as I think Australian cars had SUs however the basic principles of carburettors still apply.
With those sorts of symptoms, I suspect you have a vacuum leak. Lifting the piston is introducing more air and sending it lean.
First culprit may be in the vacuum line to the brake servo. Try clamping off the line. It may also be a leaky servo.
Get a piece of PVC tubing and hold one end to your ear while you go around the inlet manifold and connections. You will hear a hissing noise if there is a leak.
Make sure you check under the manifold.
Your idle should be around 600 RPM.
Cheers

 

Good Morning Bill,

Excellent suggestion, My brake servo was just rebuilt along with my front calipers (the rear end is next). I have not replaced that servo hose yet, so it is likely quite ancient.

Thank you for taking the time to assist me, it is very much appreciated!

Jon

 

Jon
You are welcome.
I am now very suspicious of a leak in the line or servo after finding about the servo rebuild.
I would just blank off the whole brake servo system and see what happens.
cheers

 

Bill Mac, My car is now idling and running very nicely, around 800RPM. The vaccum lines were changed out (They may have been original) and a new brake resevoir added. Thank you very much for taking the time to help!