New to XKE. Engine Missing Badly Under Load

[Shurst]

Hello, I just inherited a 1968 XKE 1.5 Roadster that hasn’t run in 10 years or so. Drained the tank, flushed the lines, rebuilt the carbs and the car started right up and runs great in the garage. However, when I try to drive it it misses badly and backfires and occasionally smokes under load. Further, the number 1,2,3 spark plugs have a white, sooty deposit on them. I have checked fuel pressure, compression, and changed the coil, distributor cap, rotor and wires. It has a Pertronix igniter. Am I burning brake fluid??

Any help would be greatly appreciated.
Thanks,
Scott

[Series1 Stu]

I would start by ensuring that ignition timing and fuel mixture are correct before disappearing down the various rabbit holes that may prove fruitless if the basics aren't right.

The white deposits could just be a very lean mixture.

Regards

[Joes66]

Sounds like carbs
Put some new plugs in replace all the ignition service parts
Leads
Points
Condenser
Cap
Rotor arm
Coil as well to be sure
Then set timing
By doing this you have pretty much ruled out an ignition problem and if it's been sitting for a long time something you should do anyways
If it still a problem then go back to the carbs
You could do a compression check as well
Joe

[malcolm]

I see you have pertronix. I had a similar set-up, and under load, on the road, it missed badly at higher revs. Eventually I was told that my plug leads can interfere with the ignition with the electronic set-up, and i should change to silicone plug leads. Did that, and the misfiring stopped immediately.
I'd suggest all the things said above, but go the silicone lead route as well (for leads and the king lead)

[mgcjag]

Hi Scott...have you replaced the fuel filter..it could be very blocked up...what carbs do you have...is it a US model on twin strombergs...i note you have already changed a lot of ignition components....re burning brake fluid..are you getting lots of white smoke....and are you loseing brake fluid.....Steve

[Shurst]

I have replaced both the fuel filter and the screen in the tank. It is a US car with twin Stromberg, professionally rebuilt. I am getting lots of white smoke on and off ... but the farthest I’ve taken the Jag is around the block. I haven’t checked brake fluid. I will tonight.