Okay – here is volume #3 in the saga for the search of the mystery vacuum leak…
Quick recap - car runs like crap (350/TH350 combo), have diagnosed it as a vacuum leak somewhere on the passenger side of the carb base….
I found a thicker carb gasket at the local parts house and gave that a spin – no luck. The car still appears to have a vacuum leak around the base of the carb on the passenger side where it meets the intake manifold. A quick spray of carb cleaner makes the RPM’s spike about 200-300 RPM – so it has been diagnosed.
I pulled the carb again tonight and took a good hard look at it again. The trick kit I installed did not have a new gasket where the base of the carb attaches to the center section, so I took a look at that area as well. The gasket looked as if it was old, but otherwise in decent shape. I took a turn on the 4 phillips head machine screws on the bottom of the carb that attach the base to the main section, and they turned about ¼ of a turn with very little effort. I turned the 4 screws, and got 3 of them to tighten a bit – so that may be where the leak was coming from.
I decided to put a microscopic layer of RTV (1/16”) on the carb gasket – one layer between the intake and the gasket, another between the carb and the gasket. I did not see any squeeze out, so I should be okay. That will dry until tomorrow evening and I will start the car again and see what happens. I also found that the 2” piece of rubber hose that connects the intake manifold to the lead for the TH350 is less then totally air-tight, so a trip to the parts house again is in order for tomorrow. Perhaps I will block that off tomorrow and see if the engine works better (someone gave me that advice – may just give it a whirl).
I will let you know how it turns out.
TJ Ringlein
Clovis California
72 Chevelle, in shambles
Oh – the car seems to run about 150 RPM higher with the air cleaner on. So I guess I get it where it will run okay, and turn down the idle about ¼ turn before buttoning up the air cleaner. If there is no gasket between the air cleaner and the carb – would that cause some of my engine stumble problems?
