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Triumph Repair/Vacuum question


Hi Howard,

I have a 1974 1/2 TR6 that starts easily with the choke out every time. When I push the choke in, either hallways or all the way in, the engine revs up to 3000-3500 RPMs. This started happening when I plugged four open spots: (1) the connection from the valve on the manifold where the servi connects, that runs to the anti run-on valve, (2) the bottom port of the flame trap mounted by the EGR valve, and (3) two of the four openings near the radiator (not the two that connect to the two front mounted flame traps.)

Is one of these plugged opening causing this or should I be looking at something else?


Hi Steve,

No engine can run at 3000 to 3500 RPM without a lot of air entering the intake manifold.

If you are blocking off vacuum ports, then air is entering someplace else. First look at the carburetor throttle plates to see if you have the throttle plates that have the spring loaded valves in them. If so either solder them shut or replace them with the plain thtottle plates with no valves.

If your carburetors don't have those throttle plates you need to check the EGR valve to see it it is stuck open or you have a very large intake gasket leak.


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Howard M. Fitzcharles III


Triumph TR-4 up & Spitfire, and Engine theory


Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

Associate member SAE EAA member

Import Car magazine

ASE Master Auto with L-1 certification up to 2000

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