Converting to Cable Accelerator Linkage on Round Tail Spits


by Joe Curry

There are two reasons for converting to cable linkage on an early Spitfire (Mk1 through Mk3). The first is if you want to modernize the linkage (some people claim that the cable linkage is more accurate in controlling the carburetors). The other reason is to fix the situation where the bushings that secure the accelerator rod have worn out and were not replaced, causing the metal around the bushings to also wear out. In order to avoid doing body work to replace the bushing retainers, the cable linkage from a later (MkIV or 1500) Spitfire can be installed.

The first task is to remove the old rod type linkage including the pedal.

Next, the new pedal assembly must be carefully located so that it doesn't interfere with any of the wiring and structural components on the firewall and under the dash. It is important to do careful measurements before drilling any holes (Measure twice, drill once).

After drilling the mounting holes and attaching the pedal assembly, you must then drill a hole on the firewall ledge through which the cable is routed. Again measure carefully before drilling.

At this point the cable assembly can be installed and you can proceed to adapting the carburetors for installation of the linkage.

On Mk1 and Mk2 engines, the two tabs on the intake manifold that secure the return springs can be drilled and tapped to mount a piece of angled metal through which the adjustable end of the cable is mounted. The linkage that attaches to the rod type linkage can then be modified to accept the cable linkage. It will have to be moved on the interconnecting shaft between the carburetors so that it will have 100 percent travel as the pedal is depressed.

On the Mk3 engine, one can obtain linkage from parts suppliers designed for the British version of the MkIV (twin SU's). Alternatively, one can construct the linkage using the diagrams in the Haynes Manual as a guide.

I have found that this modification achieves a much greater and smoother accelerator function than the earlier rod type. (But you will never be able to achieve those 400 concours points again).

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