I'm getting ready to reinstall my BBB after a rebuild and try to fire it up. I've got a new TA284 88H cam and higher compression than stock (about 9.5:1) with cast iron heads converted to Stage 1 valves with unshrouding and mild polishing. I've got a Qjet calibration kit from TA on order and I'm wondering what changes I should make to the carb... at least for break-in purposes. Should I mess with it? It ran ok before it was parked 9 years ago but the engine was bone stock. The Qjet is a bit dirty so I'm at least gonna take it apart and clean it. Any guesses on jet/rod changes? I talked to Greg Gessler briefly about it and he opined that using a Stage 1 carb setup would be a good place to start. I've also heard that you want to use a carb that you know works when starting a motor for the first time. Any comments or opinions? I would appreciate any input that I can get.
Great progress there! So, as for the carb action, my fist question is have you ever taken apart and successfully re-assembled a Q-jet?
Define "successfully" :laugh: No, not a Qjet... yet I'm working on reading through Cliff Ruggles' "How to Rebuild and Modify Rochester Quadrajet Carburetors". Looks like I need a few small tools like small diameter punches etc before I start. Doesn't look like rocket science, but I'm a bit scared of trying to install primary shaft bushings without trashing the base plate. Also, Idle tube removal looks a bit dicey. Mostly, it looks do-able.
Successful defined loosely in this instance has a graduating meaning: 1) all parts actually made it back into the carb; no pieces or little check balls left out:Smarty: 2) when finished unit is installed and attempting to start engine, it starts and does not catch on fire:eek2: 3) ...engine actually runs smoothly, idles, and is tuneable <----:beers2: :birthday: :beers2: It is not rocket science, just not a Holley either:TU:
I cracked open my 72 Buick Chassis Manual... amazing how much stuff is in there. 1972 455 Auto (standard) used .073" main jets with .044" metering rod... 455 Auto (Stage 1) used .075" main jets with .045" metering rods. I guess I should start with the Stage 1 setup for my carb.
Doug, most likely you'll need to have mods done to the idle circuit itself. Contact Norm Dihle at 313-418-6773. He rebuilds/re-plates/modifys etc... He has the best performing and idling Qjets I've seen/tested. HTH
Thanks Rob. There's not a ton of overlap on this cam... I was hoping that the stock idle circuit would be ok...
I see you are in Newtown. There is a place in Collingswood NJ called Carb Exchange( not too far from you) 856-858-5445 I had two different Q-jets rebuilt there including the one that on my new 462. Had it set up perfect for my combo. Very pleased with tem a good price. Friend of mine that runs 7 & 9 sec cars used him as well. Just and FYI. Mike
Thanks for the info Mike. I'm one of those idiots who like to try to do everything themselves... hence me unshrouding my valves by hand with a die grinder and attempting to do bowl/chamber work ... then sending the heads to Gessler for a Stage 1 conversion... If I was going to send the heads to one of the best head shops in town, why would I spend hours and hours grinding on them myself and end up with a half-assed end result where, for a few extra bucks, I could have had Gessler do everything? The world will never knowou: I guess it's the same with the carb. Half the fun for me is messing it up myself... just for the sake of messing it up myself.
Update: Now that I'm finally fiddling around with a running motor, I'm thinking that the lump in the cam means more overlap and more effect on the idle circuit than I thought... Idle isn't very smooth and drops a ton (almost stalls) with 10 deg initial timing and 800 rpm in neutral. Maybe more initial timing needed? I started measuiring all the idle circuit orifices per Ruggles' book. My idle tubes are around 0.050 (56 drill bit fits but 55 doesn't) This seems awful large compared to the 0.039 sizes I've seen referenced elsewhere. Can anybody comment on this? The carb is a 7042240 Thanks in advance...
Hmmm.. I think my issue is that the idle tube restriction is at the bottom of the tube and I'm measuring at the top...
Here's a good article on Q-jet mods http://www.highperformancepontiac.c...hester_quadrajet_carburetor_tuning/index.html
... and an interesting article on a related subject... http://www.highperformancepontiac.com/tech/vacuum_advance_tech/carburetor_modification.html
I just finished doing the mods from Cliff's book using a kit I bought from him. Going to fire it up tonight after work. My engine has behaved like it is running lean at idle since I rebuilt the engine last year. I'm hoping opening up that idle circuit will have cured it. ray:
Often the power piston can be the culprit if idle vacuum is insufficient to keep it down. After a cam upgrade I often have to cut one or two coils off the spring to allow the piston to come down with less vacuum. If the piston rises at idle, the primary jets can allow fuel to flow causing an unnecessary rich condition. Running vacuum advance off manifold vacuum will help idle quality, too. Devon
I want to check this on my carb before I start opening up idle circuit orifices per Ruggles' book. I think I can see if it'll push down through the vent while the engine is idling. I've got about 11" vacuum with no carb mods and the new cam. Not sure if this would pull the piston down or not...
That might not be enough, but sometimes the vac advance gets you a few more inches by cleaning up the idle. You're right on the money checking the piston with a screwdriver...too easy. Q-jet's an awesome design when you think about it. Devon
