DanLewis
Jedi Trainee
Offline
I think I may need to reconfigure my vacuum advance, but first I wanted to see if anyone here could offer some sage advice.
I have a Weber 40DCOE on my BE. The Weber didn't have a vacuum port but the manifold did, so I connected the vacuum advance unit on the distributor to the vacuum port on the manifold. However, I have a suspicion that the vacuum advance unit was designed to work with a carburetor vacuum port and not a manifold port. I say this because of the way the car behaves. When I step on the gas, the power drops unless I back off and slowly let the rpms come up. I.e., before opening the throttle, there's a lot of manifold vacuum, and I get lots of vacuum advance. But when I open the throttle, the manifold vacuum drops significantly and the timing is no longer advanced until the rpms come up.
IIRC, the vacuum port on a carb is usually above the throttle plate. If so, then I think the vacuum would behave almost opposite to what I just described: Before stepping on the gas, there would be very little vacuum above the throttle plate. As the throttle is opened, however, more air is drawn through the carburetor causing the vacuum presented to the distributor (and thus the amount of advance) to increase.
I know someone will tell me to just disconnect the vacuum advance, but my understanding is that the additional advance from the vacuum advance unit actually is supposed to improve low-end throttle response.
Does anyone here know enough about these things to tell me if my reasoning is on track? If I need to connect the vacuum advance unit to a vacuum port on the carb, I think I saw in an exploded parts diagram that the 40DCOE actually does have a provision for adding a vacuum line. I think it's normally blocked off by a screw, but maybe it could be replaced by a fitting that could be connected to the vacuum advance unit. (See part #48 here.)
So - what do you guys think?
Dan
I have a Weber 40DCOE on my BE. The Weber didn't have a vacuum port but the manifold did, so I connected the vacuum advance unit on the distributor to the vacuum port on the manifold. However, I have a suspicion that the vacuum advance unit was designed to work with a carburetor vacuum port and not a manifold port. I say this because of the way the car behaves. When I step on the gas, the power drops unless I back off and slowly let the rpms come up. I.e., before opening the throttle, there's a lot of manifold vacuum, and I get lots of vacuum advance. But when I open the throttle, the manifold vacuum drops significantly and the timing is no longer advanced until the rpms come up.
IIRC, the vacuum port on a carb is usually above the throttle plate. If so, then I think the vacuum would behave almost opposite to what I just described: Before stepping on the gas, there would be very little vacuum above the throttle plate. As the throttle is opened, however, more air is drawn through the carburetor causing the vacuum presented to the distributor (and thus the amount of advance) to increase.
I know someone will tell me to just disconnect the vacuum advance, but my understanding is that the additional advance from the vacuum advance unit actually is supposed to improve low-end throttle response.
Does anyone here know enough about these things to tell me if my reasoning is on track? If I need to connect the vacuum advance unit to a vacuum port on the carb, I think I saw in an exploded parts diagram that the 40DCOE actually does have a provision for adding a vacuum line. I think it's normally blocked off by a screw, but maybe it could be replaced by a fitting that could be connected to the vacuum advance unit. (See part #48 here.)
So - what do you guys think?
Dan