1970 OTS that has been converted to triple SU’s, normally very reliable. Recently it will run fine for the first 15 minutes or so on the road, then behave as if it is running on only 4 or 5 cylinders. Sounds like a lawnmower and I’d describe it as “missing”. I suspect that it’s probably more fuel related than electrical. I have added oil to each of the carbs, but it’s possible that I’m not using the correct weight, or something other than what was previously used. Any thoughts?
(This is my first posting, but I come here weekly to see the common problems and advice - great group!)

 

I would check the ignition system first. Try replacing your condenser and or coil. The fuel system gets blamed for a lot of ignition problems.
cheers,
Bob S
Jag of Michigan

 

Yeah, doesn't sound like fuel to me. Some component is starting to fail when warm. Rotor arm (even new "red" ones) are a common source of this type of problem. Or crack in dizzie cap. What ignition system are you on? Try the common electrical parts first. One at a time, to eliminate causes. Plug leads, HT lead can all cause this.

 

Thank you for the responses gentlemen. I’ll start looking at the ignition components.

 

Turned out to be the magnetic pickup in the Pertronix distributor…

 

What was the failure in the magnetic pickup?

 

David, the diagnosis was beyond my capabilities. I had it towed to my Jaguar guy who diagnosed it, did a complete tune-up and said “the problem turned out to be the magnetic pickup”. I’ll be seeing him this week with an XJS V12 I just bought, I’ll ask for more details because I’m curious too.