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1982 3.8 liter 4 barrel Rochester quadrajet vacuum reading at idle.up

6

60grit

Member
Just rebuilt 4 barrel Rochester carb. replaced points and condenser on prestolite distributor. Motor fired up right away. Dialed everything in with timing light and dwell/tach meter. I rigged up a T off of the vacuum for the choke and installed a vacuum gage. At idle 550 rpm and 12 degrees btdc of timing, points at a loose .018 and dwell meter at 35 I was only drawing about 10 on the vacuum gage. I turned the air/fuel screws on the carb and did not see any real change( very hard to get to when motor is running) I could get the vacuum to drop out a little but I could not seem to be able to make an air/fuel adjustment that would bring that vacuum pressure up to 15 or so. Is this normal? What should I have for a vacuum reading when I am dialed in with timing , points, idle and air/fuel mixture?
 
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Is the vacuum reading steady? Turning air/fuel mixture screw is not going to change vacuum reading.Have compression tested on each cylinder. Possible bad gauge?
 
The vacuum reading was rock solid and would appear to be normal. I use to tune my 318 Chrysler with a vacuum gage with a hase off of the intake manifold. I would adjust the air fuel mix at idle to point that I was see highest consistent vacuum read. Usually around 15 to 18 I just assume the same would apply to a Chevy v-6 with 4 barrel. The motor purrs like a kitten. At idle and up on plane at 3300 rpm so. I should also note that I am in Colorado and at altitude 7200 feet. I feel I am tuned and jetted properly just because of performance is good.
 
Maybe purring like a kitten at idle, put that's it. I did the tune up and carb rebuild because my port motor is loosing vacuum around 2000 rpm. When the carb looses vacuum the carb starts dumping fuel into the secondary ( Rochester 4bbl ). The fuel is coming out of 2rectangle holes in the air horn and coming out of the two tubes that are pressed into the air horn. The port motor will come up to speed only very slowly and will not go past 3300 rpm. I took the carb apart on the lake and made drastic adjustments to float. First bent it up for more fuel and did not see any change. The second time I took it apart I made the float adjustment I bent the float down. This time the motor was very sluggish but eventually made up to 3300 rpm so. Asking for some troubleshooting help. Could it be a fuel pump issue? To much fuel pressure? I think I have ruled out a vacuum leak by running and spraying carb cleaner around the carb and intake. The tune up I did by the numbers is perfect. Distributor is advancing dead on the factory numbers. Both fuel filters have been changed and were spotless clean. Not sure we're to go from here ?????????
 
Not really sure what you mean about loosing vacuum , do you mean bogging down ? if you back off the throttle does it smooth out again?
 
The vacuum operated choke plunger releases and the motor is really sluggish. I put a rubber band around the choke plunger and it sounds better but the secondary has fuel just spraying into it.
 
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