Back firing and a little smoke.....

[Mountain King]

Thanks for the warm welcome and as promised have had a look through the posts and nothing is quite like mine so here's the first question:

I recently replaced the old fuel pump with the modern SU electronic version.

The pressure is now, I think, a little more and I now get considerable back firing when slowing down using either the engine braking or actual brakes.

A small amount of smoke is now noticeable when the car starts up, but this disappears when idling after a few minutes, though reappears if you accelerate, after 15mins or so, ie when the car is up to full running temperature, no smoke is present at all, no matter what you do with the accelerator...

So, my questions apart from the obvious are:

Am I now burning to rich a mixture?
should the return pressure vale to the tank be changed for the new pump?
Is it oil seeping in via the rings, engine is original, heads never been off to my knowledge, completed 40,000 miles
I have also replaced the radiator and fans with a V12s setup, is coolant seeping in via the valve guides, cylinder head etc, the "smoke" does not have a strong oily or fuel smell.
I am running the original stromberg carbs and they probably do need a tune up, I am delaying as the SU's are a logical upgrade.
Or is the problem likely something much more severe, the radiator did boil mid year when the thermoswitch to the radiator blew, hence the V12s radiator upgrade, oil is clean and not like a soup.

Apreciate any assistance, this is my winter project to fix :)


Andy

[MarkE]

Andy
I don't think that a higher pressure pump will make any difference to the running of your car...it will just determine how quickly your float chamber fills up, and how much more fuel is returned to the tank. No more petrol will be introduced into the engine as that's determined by the settings of the carburettors.

I have also fitted an electronic SU pump and the car is running fine.

As for the smoking problem, I suggest a good old Italian tune up! That is, get the car nice and warm, find a quiet 'A' road, and redline the engine through the gears for half an hour or so. Cruising along the motorway in 2nd and 3rd will also help.

With the mileage you have on your car, the engine isn't even run in yet, let alone run out. My car was also smoking a bit when I got it, with about 50k miles in the clock. When I stripped it down (for other reasons) the original hone marks were very obvious on the bores, and the cylinder walls had glazed with lack of spirited use. The car had lived in Los Angeles all its life, and even the interstate highways had a 55mph speed limit.

The bores were re-honed and the car stopped smoking. Obviously you can't do that without taking the engine apart, but a good thrashing will help to de-glaze the bores, un-stick the rings, clean out the valve seats and exhaust ports, manifold and system, and is more fun!

This was a very common practise in the 60s and 70s for Jags that were used in cities only. The old Cooper 'S', Lotus Elan and Lotus Cortina also started to misbehave if they were subjected to gentle / city driving, and also responded well to being thrashed mercilessly!

[Mountain King]

thanks Mark,
An Italian tune up may be an option! but it was the presence of the back firing which was a concern, as you say, maybe the old Strombergs do need a thorough clean and diaphrams checked as they may be letting too much fuel in which is not all combusting.

cheers

Andy

[MarkE]

I've had my carbs re-built 3 times in 15 years, partially down to lack of use, but also they have gummed up with modern fuels and the diaphragms have failed a couple of times. I really don't like Strombergs much any more!