Countach Technical Thread & Questions

I've got hold of the video my mechanic made. From about 1:40 to 3:00 shows the issue best.

What do you guys think? Does this confirm your ideas or give you any news ones?

Thanks again for your help.

 

By any chance do you have a catalytic convertor? If so it might be clogged.

So googling around I did find this.

There is a condition called "standoff" that blows fuel vapor (and it is very visible) out of the carb throat. Technically, at whatever RPM you experience this, there is a reverse pressure wave inside the intake manifold that is blowing back harder than the engine can suck it in! Depending on your cam, venturi size, and other details, you can get standoff at high or low RPM's.

I don't know what size venturis you have, but the first thing I'd do is drop a size and see what happens.

 

No, the car doesn't have a catalytic converter. I very much doubt the cam is not OEM and my mechanic tells me the venturi size is OEM. Although you are not the first person to suggest reducing the venturi size, so maybe that is worth looking at.

I spoke to another Countach specialist today who has not seen this before but suggested that we check the ignition advance curve all the way through the rev range as a starting point.

 

It does look like fuel stand-off but it looks excessive. Having the deck lid off creates a low pressure area over the carbs exaggerating it a bit but I still think it is excessive. I would look at the cam timing, specifically I would be looking to see if the exhaust timing is retarded. Late exhaust timing could cause high cylinder pressures when the intake starts to open resulting in a reversion out the intake.

Thinking more about it. As mentioned above, a plugged exhaust would also cause high cylinder pressures as the inlet opens. Maybe the easiest thing to do first is to remove the muffler and do another run before looking at the timing.

Cheers Jim

 

Thanks Jim,

Both good ideas. Plus it would be fun to hear the car with no muffler - apparently the very first owner used to run a straight through exhaust on my car!