The primary choke pull off has a dual purpose. 1 to open choke after start up so engine doesn’t run too rich while choke is warming up. 2 the pull off has a metered orifice that controls the secondary opening rate. As the top plate secondary air valve opens its uncovers and pulls fuel out of secondary accelerator orifices,(tiny holes just above the air valves) and aides in smooth transition into 4 barrels. The air valve spring controls opening rate. Bogs are caused by these controls not being used or properly adjusted. When everything is properly set transition is smooth and strong. There also is metering rod height (hanger holes). Properly tuned quads shouldn’t bog unless during low RPM, high gear deep throttle jabs. Secondary jets should measure .136 and if they measure .140 or higher they are worn and will run rich and bog. Get a Quadrajet book by Doug Roe and learn how to tune. Most modifications aren’t needed for smooth street driving, just jetting and stock adjustments as outlined in rebuild sheet.

Hey Bud thanks for the info I've worked on quadrajets for about 45 years but I really like how you explain it on KZfaq. I had some ask me the other day why his secondarys wasn't opening and I told him it had to be with the choak it has to be all the way open for you secondarys to open. Thanks for your video.

Great video. This was exactly what was going on with mine and now I completely understand why. Thanks!

We just fixed mine yesterday by replacing the transmission vaccum modulator on a 1989 hydromatic 400 Chevy. $16.00 , it took 15 minutes. Now the tranny kicks down perfect and the secondaries open for the famous roar. Try it first...you'll like it. 💣

Great video just what i was looking for

Perfect explanation. Thank you.

the air door adjustment is critical, was hoping to see the best way to adjust the air door tension.

Back about 72’ I had 68 SS Camaro L78 396 my uncle and I overhauled but the secondaries didn’t open and did the quadrajet also but as I recall there was a piece broken on top that was called an eccentric cam that allowed front and back to and it took care of it.does that sound right to you it’s been a long time ago

This is about the 2nd or 3rd comment I've ever left, but maybe it will help somebody in the future. i recently went through the no secondary engagement thing on an M4ME Quadrajet and found something I haven't noticed anyone else bring up yet. Turned out that the fibre base gasket had swollen up so badly the holes became smaller than the secondary butterflies. This caused them to hang up and not fully open beyond a crack, and sometimes get stuck in that position. Fun. Not sure if this particular carb had something sprayed on/in it that shouldn't have been, but at least now I know it can happen. Might not be common, but have a look there if the usual problems don't seem to present themselves, and your carb/engine is still a complete turd.

,,,,,,,,,,,,,,,,There's a great book out ; by Cliff Ruggles about Q-jets , published 2006.......If you don't have it , you are gonna need it.................................

My issue with my 750 is idle, just cant get it down under 1100 rpm... everything moves smoothly, not sure if its my accelerator pump rod, seems like it might be stopping it from moving further down to touch the idle screw

Great video! If the secondary is not working that will make for gas saving? I know that You said this would just let the carburator work at 30 percent capacity, but benyond that will help to gas saving. I wanna save gas using this carb.

I love your content but your audio quality is not very good. Might be worth buying a better mic or examining the placement, etc.

Your audio is bad! Ugh