single downdraft carb

[sblake01]

I've seen maybe 4 or 5 Zs w/4bbls on them that actually preformed well and many that didn't. The main problem is getting the jetting right. Take a lot of trial and error. Out of the box, a 390 CFM Holley 4BBL, which is generally the one used on Zs, is too much carb. It was designed for engines like a larger displacement V6, 3.8 litre, 4 litre, etc. or small displacement V8s. I think people just give up on them before they get it right.

Edited March 3, 2011 by sblake01

[ozconnection]

I've seen maybe 4 or 5 Zs w/4bbls on them that actually preformed well and many that didn't. The main problem is getting the jetting right. Take a lot of trial and error. Out of the box, a 390 CFM Holley 4BBL, which is generally the one used on Zs, is too much carb. It was designed for engines like a larger displacement V6, 3.8 litre, 4 litre, etc. or small displacement V8s. I think people just give up on them before they get it right.

That's true, people give up too early.

The biggest stumbling block is the accelerator pump. The squirters and coloured cam are there for delivery adjustment, but people still don't realize that the total VOLUME of fuel delivered for our little engines is too much. You can easily drown the engine by just blipping the throttle, to the point where it actually stalls. I've done it. As you've stated, its a carb that's used on a wide variety of engines. That's why the pump is so big and without tuning this properly, people just say...."Them too big those Holeezzz" Easy trap and most of the write ups often fail to address this situation properly, if at all. I know how to do it, simple really but someone needs to start a new thread for this kind of discussion! :bulb:

The size of the primaries, both the venturi and the throttle plate are not too large at all for our engines (List 7002 390 cfm 4 barrel) and the secondaries are progressive (Vacuum operated) so that's appropriate in terms of airflow.

The 390 is an excellent carb IMO if done right!

[dhoneycutt]

... It'd be alot of fun to talk about the good old days, but I guess Ol Dave's so *****whipped these days that he's not allowed to talk to me... I'm absolutely shocked... NOT!!! Cheers, Scott

You're the one who moved and didn't pass on contact information Scott! I don't check this forum everyday! We will get in touch with you and "catch up" Busy, Busy, Busy.