I'm currently using a charcoal cannister to collect the vent fumes from the gas tank. I have the cannister's purge port hooked up to a constant vacuum source, but the vacuum hose has an inline orifice block in it that has a very small hole in it. The orifice limits the amount of vacuum draw but it is still a constant draw. Is there an inherent problem with this setup? if so, how else would you handle the cannister purge with a '7747 that doesn't support cannister purge?

 

I use a ported vacuum source on the TBI. This supplies vacuum only when the throttle blades are above idle.

RBob.

 

Thanks Rbob.... do you use an orifice block in the vacuum line or a wide open vacuum line?

 

Actually the vehicle I used this method on has an orifice at the fuel tank. Then the line from the cannister to the TBI is open. IIRC the TBI may also have a small orifice at that port, I'd have to check to be sure. I wasn't worried about it as the tank end is restricted.

The cannister that I used only has two ports and no solenoid. It is from/in a '78 vehicle that originally had a carb and is converted to TBI.

RBob.

 

That is the way the TBI trucks are hooked up. You might just get a canister for one of them to hook up.

Greg