Hello guys, im really hoping you can point me in the right direction here.
I recently swapped out my old Holley double pumper for a new Edlebrock 1806 with electric choke on my 65 impala with SBC 350 and t300 trans. I installed the carb with no problem and also added a fuel pressure regulator to drop the pressure from the pump from 7 to 5.5 psi. The car starts right up and idles beautifully at around 900-1000 rpm.
When i put the car in gear the rpm drop to a little above 500 and if i don't feather the gas and break it stalls. I did not have this issue before the swap. I double checked my vacuum line were connected correctly and that my power brake vacuum is plugged since i don't have power brakes. Do i have to re-time the motor because of the swap? I am at a loss so any help is appreciated!
I might add that i don't have a lot of experience but i am pretty mechanically sound so i try to do as much as i can myself. Thanks in advance.
Two things: 1,000 RPM is far too high an idle for a stock car (top fuel motor maybe, but not a stocker). Second 500 is too low an RPM for the motor in gear at idle. You want around 750 at idle and about 550 to 600 RPM in gear.
There is no reason for the car to idle higher from just a carb swap. If you swapped the cam I could understand it. Assuming your cam is stoner stock the stock torque converter should work with it. If you swapped a cam that requires a higher RPM stall converter then everything you pointed out would be expected as "normal with a long duration cam
I dont know the cam specs but it is very mild. the car idled t 900 before the carb swap so i tried to keep it in the same general vicinity. If i lower the idle rpm wont that in turn lower the rpm in gear. I have tried looking for a vacuum leak anywhere and i cant find any. I will play around with it again this evening. Thanks for the info.
If it won't idle down below 900 to 950 that is probably more cam than a stock converter can handle.
They are called stall converters because the motor stalls when you put it in gear with a converter that is too tight. A slightly smaller converter (as you reduce diameter you increase the stall RPM) is the one used in the Corvette that has an additional 600 RPM over the stone stock one. Because it isn't sold as an aftermarket converter but as a stock service part for an expensive sports car it is generally only $20 to $30 more than a stone stock service part (Which is usually $45 to $60 compared to the $450 to $1000 for an aftermarket converter). That little bit of added stall RPM is apparently all you will need to get your car back on the road with your cam and it's new carb.
Though for the life of me I can not understand why a carb change would cause this problem.
I would keep a torque converter swap in the back of my mind. Your car is on the edge of a whatever you have in the car. Read up on stall speeds to test to see what you have inside your car now (you may already have a Corvette torque converter installed).
They are expensive, but you will enjoy driving your car a whole lot more with a looser converter. It will allow your motor to generate a little more power before the car starts to move and load down the motor. As you have found out the motor will stall if loaded to quickly.
A lean idle mixture can cause the engine to stall when put in gear. At idle in neutral or park, the engine needs the least amount of gas. In gear, it's under load and needs a bit more fuel even at idle. Opening the idle mixture screws 1/2 to 1 turn will solve that.
But as others have said, check for vacuum leaks first.