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After reading all about the DVCS, and running through the test to see if it is working,( not sure it is because I can blow air thru the center and it comes out top with or w/o jumper) I though I would experiment with direct manifold pressure to the Distributor. In looking for a source , I don’t really see any in the throttle body area. There is a piece that appears to be broken ,looking at carb from front , on left bottom. Looked thru the carb section but did not see this area in pics. ?? Also suggestions on a direct source. Ok to T off from directly off the Intake manifold.
I looked up a couple of your threads/posts. This is a 1972 cutlass. Do a search for DVCS on my member name - you'll find several discussions & pictures of my DVCS delete.
Thanks Norm. I actually have read your posts and was going to attempt that however when looking for a non ported vacuum , I’m came across what appears to be a broken piece on throttle body. Yes 72 cutlass 350 4MC carb. I was looking for a suitable port to use.
It would be to your benefit to validate the model number. I believe the 7042251 was used on the (1972) 455 and the 7042250 was used on every 350 in 1972. Using the 2251 on the 350 is fine, but it's best you validate the model number. There were subtle differences between model years on these carburetors.
Unfortunately, I have a dinner engagement & I must leave. Others will certainly chime in. In particular w/ reference to your "possible" broken orifice which I can't validate with the limited time remaining. Good luck!
If you look at the DVCS on your engine or a vacuum diagram you will see there is a manifold vacuum connection, a ported vacuum connection, and a connection to the distributor vacuum advance canister. If you want full manifold vacuum, unplug the vacuum lines from the DVCS and use a tubing connector to attach the full manifold line to the vacuum advance canister line. You can also experiment with attaching the ported vacuum line to the vacuum advance canister to compare that to the full manifold vacuum source to see which works better for your engine.
Speaking solely to your question/suggestion regarding possibility of a broken piece (vacuum orifice tube) on bottom LH corner of throttle body (reference your image Post #1) - I cannot say unequivocally if it's broken. I'm not a Rochester Q-Jet expert by any stretch of the imagination. The limited viewing available in your two images 'appears' to suggest this to me. The air horn (top) & float bowl fuel assembly (center/middle) are correct for a 7042250; however, it 'appears' the throttle body 'may' be from a 7043250 carburetor? Hate to say it, but again, double-check the model number for certainty. If the throttle body is in fact from a 7043250 it would suggest that manifold vacuum source port orifice tube is broken off. I don't see/find that additional manifold vacuum source port on the throttle body (base plate) of the 7042250. Hey, anything is possible, it's not uncommon to find Chevy Q-Jet parts on Oldsmobile Q-Jets. I have a golf tournament and need to head out. Others with far more specific knowledge will surely be able to assist. "If" that piece is broken, you'd surely have a vacuum leak at that throttle body vacuum port. Good luck!
Thanks so much Norm. I have been scratching head as well in my research. Of All the 2250 pictures I did not see that port on any of them. If in fact that’s what I have , a broken port. I’m going to get it running and complete some of the tests for vacuum leaks and see where that takes me.
Mike
March 10th, 2023, 12:03 PM
