Triumph Repair: TR6 with weber carbs, weber carbs, negative electrode

Question
Howard-
I've now had the intake manifold resurfaced and both the manifold and header refitted with a new gasket. It starts fine and came down to idle after warming up the first time I drove it after everything was refitted. It accelerates well and seems to have power, but on deceleration it backfires and gurgles through the exhaust, especially bad down a hill or hard deceleration.  Now it's hit and miss wheither it will idle when it's warm and it occasionally misfires.  Any ideas?  Thanks.


Answer
Diagnosis by symptoms is a random hit and miss way to try to locate and problem. The only way to diagnosis a problem is by testing and dividing systems and the car into smaller and smaller areas.
First confirm the exact timing and check for advance when reved up. Once you have done that move on to mixture. Without CO equipment you are going to have to use other methods. First pull all of the plugs and look at the color. Even though reading plug color with unleaded fuel is more difficult, it can still be done. An over rich mixture will still be flat black on the plugs. Look at all of them to be sure. A lean condition will show the center insulator to be very white. Incorrect timing will blue and discolor the negative electrode. Normal will be a light colored center insulator and a lightly black edge of the threaded portion of the plug. This is general but pretty close. You must do a compression test and adjust the valves.
Next do the air leak test again by letting it idle and slowly restrict the available air allowed into the carbs and note the engine reaction. If it at any time during the slow restriction, it speeds up or smoothes out, it is too lean at idle or it still has a vacuum leak somewhere else. It should slowly slow down and get rough and quit as you restrict the air.
Many times a backfire out the tail pipe on decell it is just an exhaust leak before the muffler or close to the front.
An over rich mixture can also cause backfires on decel also.
Let me know,
Howard