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.

[piman]

John,

the one degree difference won't cause what you describe.
A backfire is usually unburnt fuel being igited by hot exhaust gases.
If this engine is new to you I would suggests doing a full check starting with compression testing, another good guide is to see what colour the plugs are. They should be dry with a light brown colour at the centre electrode. Any variation gives a clue as to which cylinders to check.
Ensure the distributor internal is free, i.e. so the timing advances with speed increase.
If the fuel pump is not working well there will be a low level of fuel in the float chambers.

Alec

[eastendjohn]

Check that Alec many thanks. I have tried all of those and now with your help decided on a new petrol pump from SNG Barratt. I have also ordered the correct washers each side of the float chamber banjo.