Hello Fellow Buick Heads, I am thinking seriously about switching back to a Q Jet. I have never run one on the car after going to the stick trans. Some people say that Holley double pumpers are great for stick cars with cams and low gears because you floor it repeatedly when "going through the gears" and Q jets don't keep up with the air/fuel delivery like a Holley would. Please chime in, anyone with any experience with this. I did own a 78 Firebird with a 350 and then a 406" SBC. IT had a 4 speed Muncie, but with 3.08 gears, tall tires, and smaller cam, it isn't the same situation as with my Lark. Gracias!
I used a Q-jet for many years on my 67 GS with a 455 / 4spd. It worked great. As with all q-jets, you have to get them adjusted right. The critical area I found was to make sure the secondary air valve spring is tight (but not too tight obviously).
Wow, that is interesting. I had thought that it would be better to loosen it up, so that the secondaries open quicker. I guess that it is all dependent on the car. I am concerned about the carb keeping up with the quick gear changes. As far as I remember, there are 2 small passages just above the top secondary butterflies which provide a little extra fuel when the butterflies initially open. I don't know much else about it, but I believe that it takes a few seconds to refill those resiviors (sp). If I floor it again only a couple of seconds, like a 1 to 2 shift, I don't think that I'd be getting the enrichment fuel the second time. With a Holley DP, you always get a lot of fuel. Maybe too much in some cases.
Hi Andrew, I've got a QJ on my GS also , it took a little bit of fiddling to get it right, still not perfect but I have only had the car for 22 years.... :laugh: It works really well at WFO power shifts nice, no drop off or bog. I still don't think it pulls as well as the thermoquad I had on it but it is a better all around carb for me. Adam. :3gears:
That's what most people think, which is actually backwards - and it's why the Q-jet gets a bad rap. Opening the secondary air valve too soon (spring loose) is what causes the "Quadra-bog" - too much, too soon. Those secondary transition wells *should* be able to keep up no problem. If not, you can get a bigger fuel inlet valve and/or open up the passages leading to the wells. Get a copy of Doug Roe's excellent book "Rochester Carburetors", it covers pretty much everything on the Q-jet. Used to drive a '68 442 close-ratio 4-speed with 4:11 gears, never had a problem with the Q-jet keeping up. Traction, however... :3gears:
I've totally removed the vacuum operated dampener. I control the air valve opening solely with the spring tension. Yes on the concept of mechanical secondary carbs on stick cars. Stick cars allow you to do all kinds of things an automatic car won't allow (i.e., gear ratios and cam combinations that just flat can't work when you throw a torque converter in the mix).
I am running a 800 CFM Q jet in my 350 4 speed Regal. I don't run a vacuum break to the secondary air valve. I instead use the spring adjustment only. The vacuum break will open the secondary air valves slower, or smoother as some would say. The spring tension still works with the vacuum break, but not using the break makes it more sensitive. But fiddle with it as you go cruisin' or racin'. When you get it just right with the stick you'll know it. Its like BAM.
Hey we posted at the same time with the same theory. You know what they say about great minds :3gears:
Very Helpful! Thanks Guys. There is a lot of good info here! I think that I'll be keeping an eye out for a cheap Q Jet at the Rod Run this weekend. It would be VERY cool to get performance similar to my Holley, with a stock looking Lowly ol' Q Jet!
Yeah - I can go with that. And yes - when the secondaries pop open without the vacuum break it is like getting hit from behind by a cement truck.
