Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Fine tuning Q-jet
bob69:
Thanks for the suggestions. I'll order the rebuild kit, adj apt kit and return jetting close to original. The carb was very clean when I bought it. I used long shaft numbered drills to measure the idle tube size, .039 fit - .040 did not. I also ran a slightly larger drill in the tubes to make sure they were clean. They were. The carb has the original short pp spring. Is the orange pp spring different? Can I get by with changing the upper mab and leave the lower mab alone.
I live in Calif and 91 octane is highest available in my area. Also, a gallon of 91 octane is over $5. Gets real expensive when you go for a drive. And the state keeps changing it's formulation over the years to make it "cleaner". My cars run hotter and get less gas mileage. One one the reasons I try to build an engine to run on 87.
Which brings me to another observation. When I pulled the 186 heads, all of the exhaust valves were bright white and you could see where the heat discolored the head about 2" around the exhaust valves. I had 67 jets and 36 rods in the carb at the time. I changed to 69 jets in the hope the engine would not run so lean. Any suggestions on how to tune the carb for Calif reformualted gas.
I agree completely with your comments about using the 350hp 327 cam. My machine shop also recommended the same. They rebuilt my 1968 camaro vert 327 / 4 speed using the 350 cam. They decked the block to get zero deck height with the 30 over pistons and shaved the heads to get a clean flat surface. The engine started as a 275 hp 327 with 291 heads. After a little tuning the car is a blast to drive. Runs smooth at 750 idle, does not "run on" with 89 octane, revs easily to 5500, and never went hotter than 190 degrees on the drive up the sierras to Hot August Nights. Which is why I could not figure out why the 1969 ran so badly.
I use the 69 camaro for cruising. So max power is not a priority. Just clean running. When I have a need for speed I jump into my 1969 Nova SS 396, which has a stong 454 in it. 😁 And all have q-jets.
quadrajam:
bob69, I tried to send a PM but your message box is full...??..
bob69:
Quadrajam, sent you a pm. Did you get get?
quadrajam:
Yes, thanks. but was unable to reply. Check your e-mail and see if that worked.
bob69:
Finally rebuilt the carb using one of Cliffs rebuild kits. The MAB and idle tubes were changed back to their original sizes. The jets were changed to 68 (stock 66), rods changed to 39 (stock 36). Float set to 1/4. The engine started right up and ran good. Had to turn down the throttle screw as the idle was high. About 1/2 turn. Idles good at 820 in park - 600 in drive.
Idle vacume is relatively stable at 15 inch. The steadiest reading has the idle screws at 3 turns give or take 1/16 turn.
Light acceleration is about the same. Really jumps off the line. Most likely due to timing. Initial set at 11°. Timing goes to 17° at 1000 rpm. Distributor vacuum advance pluged for the test.
Moderate acceleration is not as good as before. Seems down on power. Just don't know if the jet/rod combination is lean or rich. Heavy acceleration is also down some from before. But need to work out the moderate acceleration first.
Cliff, the engine still has a tendency to run on. Just not as bad. I think the timing is ok. Could the carb be lean?
Can you explain a little more on the APT. What impact it has on idle, cruise and acceleration. I measured the original apt height before replacing it with your adjustable APT set to the same height.
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