I had a similar symptom in my '83 last month. The tank was full of fuel from March of '10, and a small percentage was biodiesel left over from the tank of B99 I ran in it a couple tanks before the last fillup prior to going in storage. I changed the fuel filters and the problem disappeared.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.