TR4 misfiring under load, fouling plugs

[GTP1960]

We've discussed this before; I believe the comment on Macy's site is wrong. Unfortunately, the "one more notch" comment is misleading.

The book is correct though. Sorry I don't seem to have a photo handy, but if you look at the vacuum advance module where it attaches to the main distributor body, you should be able to see some small grooves, kind of like the marks on a ruler. There is a larger groove in the middle (you may have to advance the thumbwheel/vernier to see it) and smaller grooves to each side. There is also a kind of corner on the dizzy body that serves as a pointer.

Each small groove represents 4 degrees of ignition advance. So if you set the timing "straight up" (TDC), you then need to turn the thumbscrew far enough to move the advance by one small mark to achieve the "book" 4 degrees BTDC timing. It takes more than one full turn of the thumbwheel to move it that far.

Note however, that it is common for people to modify the centrifugal advance curve to require more initial advance. I understand that when Jeff at Advanced Distributors does a rebuild for a TR2-4, he always installs a curve that needs more like 12 BTDC for proper operation.

Personally, I prefer to do the "road test" mentioned in the book. Get the engine thoroughly warmed up (even overheated a bit is better), and then floor the throttle at about 30 mph in 4th gear. The book says it is OK if it just barely knocks under these conditions, but I prefer to back off just a bit (about 2 degrees or so).