It appears the Quadrajet on my 1971 350 decodes to the California application. The carb number is 7041544. If this is correct, it may mean that my carb has some emissions stuff on it that most other 71 carbs didn't have. I'm in the process of tuning up my car, and so far I've replaced the broken divorced choke diaphram with a new one (you can see it in the pictures, it's white). The choke works great now. I still have off-throttle "thump, thump-thump" light popping thru the exhaust, so I know I'm not there yet. Today I reset the dwell back to around 30, it was down to 25. This didn't solve the issue. I am also going to replace all of the vacuum lines with new rubber lines, before I do anything else. Just curious, what is that vacuum diaphram on the rear passenger side of the carb? It's opposite the choke diaphram that I just replaced, and has a vacuum line that runs down vertically into the carb baseplate. Also, in front of the throttle cable and linkage, is an electrically-operated piston, is this a cruise control item? Also, is that big 3/8" rubber hose that runs from the front of the carb baseplate to the rear of the intake manifold, the EGR line? The engine was originally out of a 1971 Skylark.
The large hose is the PCV Positive Crankcase Ventilation The secondary pulloff - the rearward one - pulls open the choke to a degree on a cold start once the car starts running.
7041544, I believe, is the standard issue # for a '71 350-4V Buick. The piston you have on the intake is called an idle control solenoid. When set-up it prevents the throttle lever from falling below a given "set-point" while the key is in the ON position. 12V supplied via the engine harness with a separate pigtail feeding both this solenoid & the trans. controlled solenoid on the other side of the carb.. Idle solenoid energized when key is on, trans. controlled solenoid energized when trans.in 3rd gear & applied more vacuum to the vacuum advance on the distributor. This was a midyear '71 change from the dash-pot. The '72 cars had a different style set-up. The rad. cover on the original car would have had an extra decal explaining how set up takes place. If you won't be using it take it off & offer for sale. There may be a few guys looking for the brackets which are next to impossible to find in any condition.
Sorry old thread I know, but thanks for the info Steve. Hmm, I wonder if I should wire up 12 volts to that trans switch to make it think it's in 3rd gear all the time, for more vacuum advance? My car now has a 4 speed manual and that 350 engine has a 1964 harness on it, so no provision for wiring the trans solenoid. so, that bracket that holds the trans solenoid is valuable to original 1971 guys?
Just run a single vacuum line from the carburetor to the vacuum advance. Then you can remove the other vacuum hoses and the thermovacuum switch in the intake.
I like the idea. Maybe I've been leaving hp behind. I'm gonna make that change and floor it and see what happens.
It won't make a bit of difference at WOT. At WOT, vacuum drops close to if not 0. With no vacuum, there is no advance from the vacuum canister. The canister has a spring that OPPOSES vacuum pull. At high vacuum, the vacuum overcomes the spring and advances the timing. When the vacuum goes away, the spring pulls whatever timing was there, out. Running a vacuum hose straight from the carburetor will give you vacuum advance all the time at part throttle, in all 3 gears. You may notice a difference from that in driveability, and possibly fuel economy.
Just a note. When you took the dwell & re-set it to 30* from 25* you also retarded the timing 5*. Re-check your timing. Tom T.
Ah yes thanks Larry for the explanation. And BTW don't you mean all 4 gears, hehe, I have that trusty rusty Saginaw that keeps my right arm busy
Yes, dwell changes timing, but timing does not change dwell. If the dwell and timing was set together correctly at your last tune up, then the timing will be correct now that the dwell is correct. Yes, I mean full time vacuum advance, in all gears:grin:
Hi Kevin, As you've read, most just remove the entire set-up. Intended for economy & emissions it was usually the first thing to go when trying to get more out of an engine. Anyone restoring back to purely stock set-up may be looking for the brackets. Pretty hard to find as they were introduced mid-run for the '71 model year. Somewhere about May was the introduction date, stopping in July/August when factory changed to the '72 set-up. '72 operated on a similar basis but the solenoid had a bracket built/stamped on & were not a separate piece. I had a NOS kit a few years back that had all the brackets for 350 or 455 & a solenoid with the intermediate harness.
