Severe Backfire

[eastendjohn]

Having been told the donor car was a Mk2 I have been setting the timing at the prescribed 8* BTDC. A recently acquired manual for the 420G triple carb engine, that is actually fitted, I discover that the 4.2 420G with a compression ratio of 8.1 and triple SU HD8 carbs should have timing set to 9* BTDC. Could this be the remedy to my inability to set a steady idle speed and horrendous backfire upon increasing revs? I was begging to think it could be the fuel pump not delivering. This would have prompted the question how to test a fuel pump efficiency. I hope though the latter question will now not arise though the knowledge would be useful if there is anyone can oblige please.

[mike020150]

If you haven't already done it, a quick phone call to Ken Jenkins (number in magazine) who has an encyclopaedic knowledge of XK engine variants and their settings would be a good place to start. Mike.

[3.8etypephil]

A difference of one degree in timing would be unnoticeable. The problem of setting the idle and the backfiring are most likely to be caused by an intake air leak. If nothing is obviously disconnected / missing / perished, take a look at the brake vacuum reservoir for leaks caused by corrosion.