Rebuilt carb only runs good when very rich......

[Aprules2]

Hi everyone I am new to the forum and could use advice from some seasoned carb builders. I have a 75 Cadillac Coupe Deville, the car has a true 67k miles on it. It sat in a garage from 1979 until October 2013 when I put it on the road. When I got it the previous owner had gotten the carb rebuilt and some how got a chevy 350 carb back instead. I replaced the fuel lines got the fuel tank boiled out, replaced the fuel pump, and tuned it up. It never ran right because of the incorrect carb.

I bought a good used carb from a Cadillac only junkyard. Its a true 75 Coupe Deville Carb. I sent the base plate to a local rebuilder where it was cleaned, checked, and rebushed. I soaked it in chemdip for a few days and then blew it out with compressed air followed by spraying every orifice out with carb cleaner just to be sure everything is clear. Then I rebuilt the main body of the carb. I did a full tune up, replaced all the vacuum lines, turned the mixture screws in until they seated lightly then back them out 2 turns and started the car. It ran rough and idled low. I checked my timing its set to factory specs. I set the idle to 700 and turned the drivers side screw out an 1/8 of a turn and saw the vacuum go up, then I did the passenger side and kept going an 1/8 at a time revving the engine occasionally to clear it out. As the vacuum rose the idle picked up so I set it back down to 700. Finally I got 24 inches of vacuum at 700 rpm but the mixture screws are 4 turns out. I know that's too much for a q jet, not to mention it stinks incredibly rich. Ive checked with a can of carb cleaner and cant find any vacuum leaks, Im not sure what else to do. Can you guys help me out?

[Aprules2]

I worked on the car a little more today trying to diagnose it. I checked everything a second time, and then started messing with things. I plugged the hose going from the carb to the PCV valve and I noticed i was able to set the carb much easier. I had it set with each screw between 2 1/4 and 2 1/2 turns and it idled pretty smooth with 22 inches of vac. Then I put everything back together and it idled like crap the vacuum was bouncing up and down, between 21 and 22. So I tried tuning it again and it just wants me to set it very rich. it starts to idle better when I hit 2 3/4 turns and idles best at 4. I know you need to run PCV I just dont know what to do about it..... I think Ill pick a new one up tomorrow to see what happens.

[ejowrench]

Be aware that a PCV valve is nothing but a precise 'vacuum leak'.  Most aftermarket companies do not know this and supply you with a 'universal' PCV valve-no such thing. Engine size, engine family, carb specs, etc. are taking into consideration when the engineers decide on what flow a valve should have. Try an AC-DELCO valve.

[Marx3]

24 inches of vacuum is alot! and since you can set the idle down to 700 rpm or even lower? you can not have a real vacuumleak...
In your case I would not worry too much about exactly how many turns the screws go out to get the highest reading, I would just trim the screws for best vacuum and back them down a little...
I have the exact same car btw :-) I took the original carb off and put a freshly rebuild 800 cfm unit on I had on the shelf. It was calibrated for a 450 hp 383 SBC build, and it turned out to be a tad lean on the stock 500 :-) No wonder the car ran bad with a just stock 350 carb on it!