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Good afternoon fellow Olds enthusiast's. Working on a Quadrajet from a 1970 350, carb number 7040250 and I'm hoping someone out there has this pull off bracket that the previous owner found unnecessary and discarded. I've searched sites and found the pull off for sale but not this bracket. Don't understand why they would get rid of it, secondary's won't operate without it. Any help anyone an give would be greatly appreciated.
Good afternoon fellow Olds enthusiast's. Working on a Quadrajet from a 1970 350, carb number 7040250 and I'm hoping someone out there has this pull off bracket that the previous owner found unnecessary and discarded. I've searched sites and found the pull off for sale but not this bracket. Don't understand why they would get rid of it, secondary's won't operate without it. Any help anyone an give would be greatly appreciated.
The secondaries operate just fine without that diaphragm. The name is inaccurate. It is not a "pull off". Quite the contrary, the purpose of that diaphragm is to delay the opening of the secondary air valves - at part throttle the higher manifold vacuum retards the opening; at W.O.T. vacuum drops to zero and the air valves open more quickly. For a drag race only application, removing the diaphragm lets you set the secondary air valve opening solely with the warp spring. Of course, many people do stuff they see without fully understanding that a mod for the drag strip is usually NOT what you want on a street car.
Thanks for the info. Though I would still like to find this bracket. For it to work as it was designed. Just not having much luck. Don't intend to see any strip action.
Thanks for the info. Though I would still like to find this bracket. For it to work as it was designed. Just not having much luck. Don't intend to see any strip action.
My response was to the "why" part of your question. Any bracket you find will likely come with a carb attached.
The secondaries operate just fine without that diaphragm. The name is inaccurate. It is not a "pull off". Quite the contrary, the purpose of that diaphragm is to delay the opening of the secondary air valves - at part throttle the higher manifold vacuum retards the opening; at W.O.T. vacuum drops to zero and the air valves open more quickly. For a drag race only application, removing the diaphragm lets you set the secondary air valve opening solely with the warp spring. Of course, many people do stuff they see without fully understanding that a mod for the drag strip is usually NOT what you want on a street car.
Joe, I disagree with your statements regarding the operation of the secondary air valves. I you don't have the vacuum break (pull off) in use, the vehicle will tend to have a bog when you floor it. The vacuum break has a metering orfice in the tube where the hose is attached. By varying the size of the orfice, you can tailor how quickly the vacuum bleeds off at WOT to control the rate that the air valves open. The spring changes the relative point at which the air valves start to open. The tighter the spring is wound, the more air flow is needed to pull the air valves open. On our "drag only" Stock Eliminator car, we did a lot of tuning between the air valve spring and the vacuum break. On a cooler day, we would back off the spring tension by 1/8 of a turn to get the valves to open sooner, thus lifting the secondary metering rods to get more fuel to the engine. Obviously, there is much, much more to all of the fine tuning that goes into a Stock Eliminator national record setting car, but I just wanted to expand on your statement "The secondaries operate just fine without that diaphragm".
Joe, I disagree with your statements regarding the operation of the secondary air valves. I you don't have the vacuum break (pull off) in use, the vehicle will tend to have a bog when you floor it. The vacuum break has a metering orfice in the tube where the hose is attached. By varying the size of the orfice, you can tailor how quickly the vacuum bleeds off at WOT to control the rate that the air valves open. The spring changes the relative point at which the air valves start to open. The tighter the spring is wound, the more air flow is needed to pull the air valves open. On our "drag only" Stock Eliminator car, we did a lot of tuning between the air valve spring and the vacuum break. On a cooler day, we would back off the spring tension by 1/8 of a turn to get the valves to open sooner, thus lifting the secondary metering rods to get more fuel to the engine. Obviously, there is much, much more to all of the fine tuning that goes into a Stock Eliminator national record setting car, but I just wanted to expand on your statement "The secondaries operate just fine without that diaphragm".
Agreed, but that doesn't "prevent" the opening of the secondary air valves, it lets them open too soon. If all you care about is WOT performance at the drag strip, and you're launching the car at a high enough RPM, the engine vacuum is already close to zero and the dashpot is irrelevant. By eliminating the dashpot you can tune air valve opening with just the wrap spring. And once again, I'm in no way advocating this, I'm merely offering a rationale as to why someone would remove that part. This certainly isn't a mod one would use on the street.
June 27th, 2022, 11:06 AM
