help tuning quadrajet
Thread Starter
Heel & Toe
Joined: Jan 2004
Posts: 21
Likes: 0
From: petersburg Mi
help tuning quadrajet
I replaced cam and added headers set valves and timing as per lars paper everything went perfect engine fired first pop. Im going to change the advance on the dist. tomorrow and reset timing as per lars. I took it for a ride today engine runs real smooth but it doesnt feel like the four barrel is kicking in. When i take air cleaner lid off and hit throttle back flaps dont open. Are they suppose to? Ill will need help with jetting and choke setup if anyone has sugestions in that area any help will be apperciated. Also removed egr . On my choke housing there is a vacum line hooked to it does this have to be hooked up and if so what port does it go to . thanks for any help DRM78 :banghead:
Racer
Joined: Dec 2003
Posts: 275
Likes: 6
From: NY
Re: help tuning quadrajet (drm78)
Q-jets have a mechnical secondary lockout that is locked until the chock is fully open. Its a metal tab that is visable on the passenger side of the carb just behind the throttle shaft.
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
Re: help tuning quadrajet (drm78)
Lars has a QJet tuning paper over at http://www.corvettefaq.com -- as with all his stuff, it's highly recommended. Also get a copy of the book Rochester Carburetors by Doug Roe.
The secondary top flaps will not open when you open the throttle. But if you blip the throttle to high rpms with the engine running, you'll see them pop open momentarily.
The secondary top flaps will not open when you open the throttle. But if you blip the throttle to high rpms with the engine running, you'll see them pop open momentarily.
Melting Slicks
Joined: Jul 2002
Posts: 3,128
Likes: 3
From: Deltona (son of Deland and DAYTONA) FL
Re: help tuning quadrajet (page62)
.
The secondary top flaps will not open when you open the throttle. But if you blip the throttle to high rpms with the engine running, you'll see them pop open momentarily.
The secondary top flaps will not open when you open the throttle. But if you blip the throttle to high rpms with the engine running, you'll see them pop open momentarily.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: help tuning quadrajet (drm78)
My normal response is that you can't flick the throttle in neutral and see the secondary airvalve open on a Q-Jet - the manifold vacuum usually does not drop far enough, and airflow is usually not high enough, to cause the airvalve to open under a no-load situation. However, you can slam the throttle to WOT and hold it there shortly (very shortly) and see the airvalve just crack open with an associated shot of fuel that will spill across the airvalve. I just usually don't recommend doing this, since rpm can get a bit high and it simply doesn't prove much: As long as the lockout lever is not engaged (and you can see this easily), the airvalve WILL open when you go to WOT under load - there is nothing that will keep it from opening.
Le Mans Master
Joined: Mar 1999
Posts: 6,744
Likes: 1
From: delmont pa
Cruise-In I Veteran
Cruise-In II Veteran
Re: help tuning quadrajet (drm78)
i have seen Qjets that the top was distorted from over tightening the screws that the secondary air was stuck. see if it will open with finger pressure with the engine off :chevy
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