The engine is a GM 1984 5.7L V-8 with a Rochester quadra-jet carburetor. The vehicle is actually a 21' cabin cruiser but I believe the information I'm looking for would be the same regardless of the vehicle type. I replaced the original salt water damaged carburetor with a rebuild. They were both Rochester 4-barrels, same bolt pattern, same linkage... so that so far was a quick task. The only difference was the rebuild had a small nipple front where a hose attached. I believe for a PVC valve hook up. The old carburetor didn't have this. So I put a tube on it and plugged it. I backed both air/fuel mixture screws out 2 1/2 turns and it started right up, sounded great let it idle for 5 minutes or so and shut it down. To fine tune air/fuel mixture, I was told to get a vacuum gauge and watch the you tube videos. So I used the nipple in the front of the carburetor to get manifold vacuum instead of ported since it is constant.
I started the motor and the gauge instantly went to 30, buried it. I started closing the air/fuel mixture screws one at a time until both were all the way in. There was no change in the way the engine ran or the vacuum reading. (In the videos the vacuum was between 9 and 10in Hg and it increased or decreased while adjusting the air/fuel mixture). When I unplugged the gauge from the valve, the engine accelerated and that's where I shut it down. I'm obviously new to this. The first vacuum gauge I've ever had and still watching You tube videos but what I really don't get is how adjusting the air/fuel mixture screws had no effect at all. Not even when they were both turned all the way in. I had the idle adjustment set a little high but it didn't move either until the gauge was disconnected. I'm at a loss as to what to look at next and I would sure appreciate any suggestions or ideas you could throw this way.Thanks again
I started the motor and the gauge instantly went to 30, buried it. I started closing the air/fuel mixture screws one at a time until both were all the way in. There was no change in the way the engine ran or the vacuum reading. (In the videos the vacuum was between 9 and 10in Hg and it increased or decreased while adjusting the air/fuel mixture). When I unplugged the gauge from the valve, the engine accelerated and that's where I shut it down. I'm obviously new to this. The first vacuum gauge I've ever had and still watching You tube videos but what I really don't get is how adjusting the air/fuel mixture screws had no effect at all. Not even when they were both turned all the way in. I had the idle adjustment set a little high but it didn't move either until the gauge was disconnected. I'm at a loss as to what to look at next and I would sure appreciate any suggestions or ideas you could throw this way.Thanks again