The 'E' Type Forum

OK, to be honest, I have never been at my best when tuning cars and multiple banks of cylinders and carbs only makes it harder!

Now I don't pretend that the car is set up perfectly, but I have a distributor that has been stripped and lubricated, so the weights are free to move. I have a new vacuum unit, rebuilt carbs with good diaphragms and I believe they are well rebuilt. There is oil in the dashpots and I did my best to balance them with a flowmeter. I really expect to have to take the car for tuning, but in the meantime I want to adjust them for comfortable driving, even knowing they won't be as economical as they might be (OK, it's a V12 - I know not to expect real economy!).

But, I can't even get the idle speed down below 1000 rpm. It is a warm day, if that makes a difference and the car hasn't run for a while due to the work I have been doing elsewhere. I have the idle screws backed off all the way but the idle speed is still too high. Is this the mixture too rich, which seems logical, or something else? I'm sure it was OK before, I was quite happy with my first attempts at tuning, but the engine may have loosened up now, nevertheless I am at a loss to explain why I can't get the idle speed down any lower.

Any thoughts?

Regards,

Simon.

Dear Simon,
Logic says too much air is getting in, either straight through via the throttle plate or bypassing it somewhere or other.

Typically the latter would be called a vacuum leak and you can look up the plethora of advice to chase down the source, be it vacuum pipes, solenoids, bypass valves, temperature compensators etc.

As a start, you could disconnect and plug everything except a direct line from the LH rear carburettor to the distributor and that should narrow it down to the one pipe and its ruber elbow beneath the LH rear carburettor, or the carbs and throttles themselves. Then if all is good, add back all the pointless additional vacuum plumbing, one by one.

Prior to going to fuel injection, I had all of that stuff plugged because, frankly, it doesn't do anything useful.

kind regards
Marek