Hitchcocks Forum

I have a 64 crusader continental and after having problems tuning,noticed that there is a small drilled hole in the bottom of the carb manifold where it bolts onto the head. This sucks in air and makes tuning difficult. It only seem to be a feature on later 1960s carbs as the carb on my 1960 crusader doesn't have this hole. Does anyone know what this hole is for? Will it cause problems if I block it off? Cheers
Chris

Hi Chris, block the hole and give it a go - it can't do any harm. Regards, Paul.

You don't say what sort of carb it is. Monobloc? Concentric Mk1 or 2? Mikuni? It would help to know...

REgards, Mark

If the carb is set up correctly for the bike this drain hole is taken into account and is there to stop the engine filling with petrol if it is left turned on. My Super Meteor has the hole and just blocking it with a finger causes bad running. This is not the cause of your problem. But easy to block temporarily to see what happens.

Oops, sorry Mark, it's an Amal monoblock. The hole sucks in air so you can almost run the engine with the mixture screw screwed right in. I'm sure the screw should be adopt 1.5 turns out ??

Thanks Dennis, at least I know what it is now. The older carbs don't seem to have them.

Cover the hole with gaffer tape.. give it whirl. If it doesn't help, then no harm done.

I'm with Dennis, Amal settings usually work fine on the bikes they were designed for. I suspect your carb body or slide or most likely both are worn leading to air bypassing the slide leading to the symptoms you describe.

REgards, Mark

It works perfectly if I block the hole (approx 1.5 turns out) I have no problem with blocking the hole but wondered what the hole was for 'cos it will obviously suck air in!!

Then perhaps you carb is on the settings for the earlier bike without the drain hole?.But whatever works for you is good.