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Vacuum advance


beedlejpott
02-25-2008, 06:54 PM
Does any one have the correct routing for the vacuum advance on a 1974 B?

paul J
03-01-2008, 07:09 AM
Does any one have the correct routing for the vacuum advance on a 1974 B?
Do you mean, where do you pull the vacuum from? Intake manafold or ported?

beedlejpott
03-02-2008, 01:09 PM
Yes, that's what I mean. This car is connected to manifold vacuum, but I suspect that is wrong as all other "B's" that I have seen have ported vacuum. I cannot find a vacuum diagram to confirm this however.

paul J
03-02-2008, 03:55 PM
Yes, that's what I mean. This car is connected to manifold vacuum, but I suspect that is wrong as all other "B's" that I have seen have ported vacuum. I cannot find a vacuum diagram to confirm this however.
Not all "B"s are ported vacuum! What carburetters are on your car? 74 MGBs came with a 25D4 distributor. 75s and later came with a 45D4 or 43 D4. If you have HIF carbs on your car, look at the rear carb on the firewall side next to the manifold flange and see if there is a blanked off tube the size of the vacuum line. Some carbs had one and some didn't. If your car has it, and the distributor hasn't been changed, more than likely it is ported vacuum. If not it is probably manifold vacuum. But, the vacuum advance diaphragm has to match one or the other. Give me a little more info. Is the dizzy a 25D4 or a 45D4? What carbs do you have? Also, is your car a chrome bumper 74 or a rubber bumper 74 1/2? I run manafold vacuum on my 72. Jeff at Advanced Distributors set it up for me that way. PJ

Contact Jeff at www.advanceddistributors.com (http://www.advanceddistributors.com) or email him at jeff@advanceddistributors.com . (jeff@advanceddistributors.com)

He has a top knotch distributor repair and replacement service.

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