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Triumph TR6 - '74 ZS Carb DIfferences

I was rebuilding a spare set of '74 Strombergs yesterday and noticed a couple of differences over my '72 Strombergs.

1. The jet on the '74 appears to be recessed lower beneath the bridge. On my '72, the jets are nearly flush with the bridge.

2. The 'finger' effort needed to raise the piston on the '74 (with 30W oil fill) is greater than on the '72's. The springs are the same. The damper rods on the '74 are of a different design.

Are these differences due to emissions changes?

Rick O.
Rick Orthen

Hey RickO

There were a few changes over the years not sure if emissions or just redesign. They are identical outside though right? Mounts etc.

Never thought of that although it shows in the parts books if I look with that idea in mind.

Great observation!!!

Thinking of posts with strange carb problems. Lean front rich back vise versa? Over the years carbs have been replaced in pairs and singly? Mixed and maybe not matched too well?

Trying to get my head around balancing with same airflow in total intake being upset? I don't think mixture could ever be right? May explain some problems?


Bill Brayford

Hi Bill. The '74 carbs are different in 4 respects: (1) pin-operated fuel bowl vent valve that is actuated by the throttle stop lever (at idle, bowl vapors are vacuum dragged to the charcoal canister), (2) additional vac connection to the charcoal canister, (3) starter valve doesn't have a return spring (meant to be used with solid choke cable), and (4) the bypass valve has an external vacuum sensing port. Items 1, 2, & 4 are no problem for me (plug them) and I can retrofit a spring on the starter valve or simply transfer my '72's over.

It's the jetting and piston effort that puzzles me. Guess I'll just bolt them up and see how it goes (or doesn't go).

Rick O.
Rick Orthen

Rick-The difference in jet heighth shouldn't make any difference as long as the needle has enough adjustment to get the correct mixture. My jets are about .110" below the bridge. Could the increased effort needed to lift the pistons be caused by petrified diaphragms?
BTP Price

This thread was discussed between 05/04/2004 and 09/04/2004

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