XK150 Starting Problem

Been with this group for almost 20 years but I’m stuck on an issue and would appreciate any help. My jet diaphragms were cracked and leaking and I replaced them. After fixing the various gas leaks, the car starts right up on the starting carburetor. As soon as the carburetor cuts out, it barely runs and then stops. I do have a hidden bypass switch and when I flick on the starting carburetor it runs again and will accelerate normally I did warm up the engine while on the starting carburetor. Both seem to be sucking air normally and the pistons are free and moving. Symptoms indicate it is running too lean. The mixture is set at the factory setting (2 1/2 turns down from highest jet point). Idle speed screws are also set at factory setting. Plugged the brake servo so no leak there. Don’t think it’s timing as it was running fine before. Any ideas out there in Jag-Lovers land?

Pat H.

Pat. it sounds like both jets are too high in the carbs and need to be lowered so as to get fuel out of the orifice.
Take the dashpots off and see where the tops of the jets are in relation with the plenum. I have mine set at about 1/8th down, this will allow enough fuel to keep the engine running at idle when warm

Thanks. I did solve the problem. The float valve on the rear carburetor was stuck closed and the bowl dry as a bone. I set the jets to the factory setting. Raise to highest point. Turn in the mixture screw until the jet begins to move then 2 1/2 turns further. This all started when both carbs started leaking fuel. The old jet diaphragms had disintegrated. Runs like a new car now.

Pat H

Excellent news, at no cost.

What 150 do you have ?could you pass on your Vin and eng #.


I need to apologize to my North Georgia Jaguar Club friends Ivan Ruiz and Dick Maury for their help in solving my carburetor problem. By saying “I solved the problem” would infer that I did it myself. It was their advise that pointed me to the solution and I thank them for it. The great thing about Jag-Lovers and car clubs is the ability to share information when there is nowhere else to go.

Pat Harmon