Set the mixture screws all to 2 (720 degree from fully closed) turns out (air screws as you call them)

The balance screws are underneath the carbs, there are only 3 of them. They have a 7mm hex head with a screw in the middle.



You can see them circled here.

They adjust how much of the butterfly is open at any given time.

Providing you have fuel in all the carbs (which you say is correct) and they are clean then I would look at the balance screws first.

After fuel was sprayed directly into the rear carb throats the rear cylinder exhaust pipes remained cold. This is the method I have used to determine if the rear cylinders fired. Admitedly I only sprayed a small amount of fuel in using a garden sprayer to test. I think I will give the carbs a good flush through again and re-set the balance screws as suggested. Failing that I am out of ideas. Carbs brilliant when they are working a pain in the arse when they aren't. It is so frustrating as the front two cylinder start on the button with very little effort.

Where in the world are you,Maybe there is a member near you that could help.

Based just outside of Weston Super Mare, Somerset.

If you're really stuck you can send the carbs to me. I'll clean them and balance them no problems.

I will give the carbs another clean out this weekend and try to re-set the balance screws to 2 turns out as suggested if that fails, I may take you up on your kind offer Thunderace. Do you have an ultrasonic cleaner or do you just use carb cleaner?

fasttom wrote:I will give the carbs another clean out this weekend and try to re-set the balance screws to 2 turns out as suggested if that fails, I may take you up on your kind offer Thunderace. Do you have an ultrasonic cleaner or do you just use carb cleaner?

balance screws do NOT go to two turns out.

The air / fuel screws goto 2 turn outs, they are in a completely different place.

Balance screws need to be set by eye first with a drill bit and then ideally with vaccum gauges on a running engine.