I am in the process of rebuilding/modifying a 1979 Quadrajet for my 455. (17059213) First question; Should I remove the 'dummy' black plastic cup from the main body that sits beside the fuel bowl inside? And would it be beneficial to open this up to allow extra fuel for the bowl area? Second question; What tool to use to adjust the APT screw after I remove the top plug and tap it for a socket screw? This carb has the adjustable APT srew located ahead of the power valve.
Well, ignore the second question as I have made my own T-handle tool for adjusting the APT through the top of carb. Still looking for ideas on the first question though.
If you're referring to the float bowl baffle, it shouldn't be left out. It may be modified to increase bowl capacity a bit though...I've never tried it, maybe the q-jet experts will chime in. See http://bosshosshelp.com/Menu Items/quadrajet/MikeQuadrajet/quadrajet.htm , about 2/3 down the page. Devon
Good article but not what I'm after. It's not the float baffle I'm referring to. Here is a pic of the body of my carb. The hole on the front left corner, under the pencil, holds a plastic cup that was put in to take up the space in the casting left over from the 1976-77 carbs and is no longer used on the later models. I was wondering if it can be removed and if so; can a transition slot or hole be ground from the bowl area to provide more fuel. It may not even be necessary to do anything with it. o No:
I was told by Cliff R that the baffles should be left alone, as the stock shape helps direct incoming fuel.... but Buford's talking about the cup that sits in the cavity used by the '75 style APT.. When I did mine, I left it in and havent had any bowl capacity issues on long pulls, but technically it would increase capacity if you left it out. I've found over the years that GM/rochester/etc.. didnt put anything that cost money in their products without a pretty good reason. Unless you're doing flat out Bonneville type speed runs, I'd leave it in.
The slightly increase in bowl capacity from leaving out the cup in the front of the carb isn't going to make any difference. You either have a good enough fuel system to keep the carb full on hard runs, or you don't. I've read a few complaints from folks that have removed them that they will get a stumble or slight flooding condition when braking real hard. I've tried to duplicate this on my 1977 Pontiac carb with the cup removed and it never gives the first hint of trouble anyplace. Anyhow, as a general rule we leave them in place. For full race carbs and serious street/strip set-ups they are left out. I figure every little bit helps even if the real key to running hard with a q-jet is to keep it full all the time.....Cliff
Thanks Cliff! I was thinking the extra fuel wouldn't hurt but didn't know if it would help any. Does the fuel just flow over without the cup in there?
I've been running a 1977 Pontiac carb for about 25 years now. The cup is NOT in place. To date, it has never once stumbled, hesitated, bogged, or given the first hint of trouble, once I upgraded to my current fuel delivery system. I've never once had to remove the top for any reason, but I have had it off several times to test some parts. Specifically different fuel inlet seat diameters, accl pumps, and floats. I would mention that it gave me all sorts of troubles when I tried to run a Carter HP mechanical pump about 15 years ago. Flooding on hard stops was one of the problems. I installed a fuel pressure gauge and it was reading around 9.5psi. Currently I'm using a sumped stock tank, Comp 140gph pump behind the tank, and 8AN lines/fittings everwhere. I also use a return line, to take some load off the pump for "normal" driving. It has proven to be dead solid reliable to low 11's over 120mph in full street trim. Here are the last two runs I made at our local track, DA was about 3300', I made them 23 minutes apart: R/T: .505 .514 60': 1.6230 1.6289 ET: 7.3169 7.3188 MPH: 94.35 94.36 .......Cliff
