Brown liquid

[Tezza7]

This may have been asked in the past but here we go again.

Can anybody give an explanation as to why I get a brown liquid (not a lot) coming back out through the air filters from my VX1600 Weber carburetters. It streaks down the side of the car when I have been running at a constant speed down the motorway or similar. It is really only a small amount but still very annoying.

[Jonathan Kay]

Is it oily?

Do these engines have a crankcase breather into the inlet side somewhere?

Jonathan

[Tezza7]

No, the crankcasebreather is quite separate.

Tezza

[revilla]

It's not just filter oil is it?

[Roger King]

This is usually "stand off". This is basically fuel/air mix bouncing out of the inlet tract due to the tuned length and will only occur at certain revs. The brown mess is fuel mixed with oil and muck from the filters. If you run an engine without air filters on the dyno you will often see this as a cloud of fuel vapour hovering around the inlet trumpets, but only at very specific revs. In your case it seems to be occuring at the same revs that you use on the motorway. If you are able, you might be able to reduce the effect by altering the total length of the inlet tract, but this is likely to have other side effects such as changing the shape of your torque curve or the need for different jetting which may or may not be an improvement.

[Andrew Walker]

There is a great YouTube clip of Chris Goodwin driving his McLaren M1B at Goodwood Revival - it has a camera pointing at the 8 inlets and you can see the 'stand off' at 3:30 and 4:20 into the film:

 

[Jonathan Kay]

Fascinating. Thanks x2.

Jonathan

[Tezza7]

Roger & Andrew

Your posts are very interesting as the problem only arose after I had the carbs re-jetted to make the car more smooth for road use, as opposed to full out running which I believe the engine was originally intended for when supplied by Caterham. Before re-jetting it did not like running at low revs in traffic despite adjustment. After re-jetting by a very well respected engineer and checked on a rolling road, it became much more user friendly without any loss of power for everyday use. 110bhp at the rear wheels.

The utube clip certainly seems to show the problem.

Perhaps if I gave the K & N filters a good clean it may at least reduce the residue.

I have been told that the VX1600 was originally developed for the Graduate race series but I don't know if that is true or not.

Tezza

[Baz Hemsley]

My 160bhp xflo throws it all over clam shell, stone guard, and mist of it on o/s Brooklands. Always has done, ie the last 47000 miles. You name it I've tried it. Now just put up with it. It's not too bad if you slow down.