Q-Jet What's the correct way to adjust the secondary butterflies??

After getting some of the minor bugs worked out of my car,it all of the sudden took off like a screaming idiot then fell flat on its face when I shifted into 2nd gear.As soon as I left off it revved up again. At first I thought it was the stock fuel pump,but it's brand new and worked from the start of the motor.When I took off from a standstill,it opened up then some blue/whitish colored smoke came from the exhaust according to Dylan.I had the hood off and air cleaner off to see if it was spewing gas or something else. It is an extreme bog situation. I rebuilt the carb (72 455 auto carb) and it idles great and holds great vacuum. I was stumped,until I watched the carb when I flogged it. The secondaries fluttered like there was no resistance. After I pulled back in the garage,I could flop the butterflies with no difficulty and they even stayed open. I took a small screwdriver and a hex head and tightened it up. I want to race this car so street manners aren't at the top of my list. How much tension is needed on the secondaries, and whats a good method to use other than trial and error,if something exists??

 

Pat, there are two mechanisms that dictate air valve opening. The spring is one, but when running the front vacuum break also limits the rate of travel. See if this helps at all:

http://www.v8buick.com/showpost.php?p=799923&postcount=13

Devon

 

Sorry to hijack the tread but how to adjust the airflaps if there is no vacum break?I have the early Q-jet 66' and there is only the little spring on the shaft of butterflyes... is it possible that this spring went soft overtime and is no sufficient to hold flaps closed?They tend to open when i rev angine at parking.And if i try to stiffen that spring a bit more it just falls of .:rant:

 

I have tried running Qjets without the vacuum can on the front and ran into bogging troubles. With light air valve spring tension (just enough to close the air valve) the car would REALLY take off at WOT from a stop.

However I ran into some big bogging troubles when going WOT from part throttle. To avoid this bog (without the vacuum can) I had to tighten the air valve spring so much that it detracted from the hard launches.

My solution was to install the air valve vacuum can and adjust its release time to about 1 second. The adjustment is done by changing the size of the orifice.

With the air valve spring set just tight enough to close the flaps PLUS 1/4 turn, and the vacuum can set for 1 sec release, I get a very hard takeoff and no bog.

 

Pat, stupid question but are you running the Stage-1 fuel pump? That sounds like every fuel pump problem I ever had. Don't think because it is new it cannot be bad. Also if you changed to bigger lines or rubber etc. you could have a flow issue and the pump cannot overcome the larger size line or rubber line collapsing while under pressure. Also clogged strainer in fuel tank can cause this problem. Ever had the tank open?

 

Also with the butterflies just tighten them enough so they will close on there own when you push them open by hand. A little more spring action is probably better than a little less. They need to be able to close on there own.

 

The early Qjets has a "dashpot" controlling the secondary valves. It was essentially a piston, connected to the valves at one end, and the other resembled an accelerator pump, immersed in fuel. The air valve was controlled by the air valve's having to raise the piston through the fuel. A new pump does not mean that it is working correctly. It is possible that the bowl is emptying out, removing the controlling medium for the piston. First, make sure that the bowl still has fuel in it after the hard launch. When the vehicle begins to surge, quicly shift into neutral and shut the engine down. Then check the bowl for fuel. If it has fuel in it, it is possible that the piston has issues, but from what I read, the first gear launch is goood, but it bogs after a few seconds. That sounds like fuel starvation to me, regardless of the reason. Let's start there. Ray