My other series 2 jaguar I have which is fully factory and original after taking it for a long drive today noticed when trying to overtake it seems to rev 90% fine in 2nd but mainly when its in 3rd with your foot down it doesn't seem to rev anymore or go fast, it acts like its trying to pull you back and rev but doesn't. Im thinking lack of fuel but not sure where to start looking? any common problems or anyone know where to check?

the factory points fuel pumps I have replaced with brand new electronic ones so its not them, the engine was rebuilt awhile ago and it runs mint just seems to hold back when your foot is down like its starving from fuel. was thinking fuel filter blocked but would that effect it? doesn't carbys hold a fair amount of fuel so it shouldn't be lacking any fuel or anything?

its the twin carb 4.2 straight 6 engine. is there just one fuel filter the one next to the pumps in the boot? or should I check on the carbys and maybe drain them or look elsewhere?
just trying to eliminate problems as wouldn't mind to be able to overtake sometimes ^.^

 

it gets to about 3500 rpm in 3rd then wont rev anymore sometimes if I take my foot off and try put it back down it will try and pull abit more then just lags out sometimes does it in 2nd as well

 

I'm not familiar with the carbureted series II. I have a fuel injected series III. When my jaguar was acting up in a similar manor it was not fuel related, it was ignition system symptoms (whew, say that five times fast haha)
Anyways, If your problem is fuel delivery related I may not be much help, but I suggest looking over your ignition system and making sure all your connections are clean and tight, especially around the coil, I had to replace mine. I would check the sparkplugs, sparkplug wires, distributor cap, and the rotor. All of those parts are cheap and easy to replace, and can make a big difference in your cars performance.
My real suspicion though is the vacuum advance on the distributor, if the diaphragm is leaking you will suffer hesitation at full throttle.

 

will have a check over that today as well and see if I can figure it out. not long ago car wouldn't start because the wire on the dizzy was loose so it may be ignition but jst assumed it was fuel because seems to rev fine in 1st jst when it trys in higher gears it gets sluggish

 

also what is that black screw thing which screws into the tops of each carby, one of mine has popped out a few times has weird clear oil stuff on it then I gota push it back down and screwed it back in, could that coming out cause something to get out of place of something, not sure what it was for. checked my ignition from looking at it everything seems algud there

 

Every SU and most Zenith-Stromberg carburettors have a piston damper which uses oil to do the damping, just like a shock absorber. Trouble is the oil eventually gets sucked into the engine and needs replenishing.

For SU carbs, normal light engine oil will work OK and level should be about 1/2" below the top of the damper tube. The black top should have the damper rod attached to it, if not there is something wrong. Once the oil has been replenished you screw back the damper finger-tight.

I have an MG MIdget with twin SUs and have to top up the dashpots regularly or it doesn't run too well.

http://en.wikipedia.org/wiki/Dashpot

 

ahh I see thanks for that, they both have oil still on the end of the stick and looks good and clear, How do I go about draining the carbs to check theres no **** in the fuel system and is there just 1 fuel filter which is in the boot or do the carbs have some sort of filter on them? I noticed the fuel lines goes to a random cylinder thing then into the carbs