Testing vacuum advance

[John P.]

Just starting to go thru my 65 roadster, 365 HP L76.(recent purchase). I had a question about the vacuume advance. The vacuume source is located on the passenger side of the primary metering block. The vacuume line connects to the threaded port using a brass fitting. With the fitting removed I can see a small (~ 1/16 inch) hole @ the 9 o'clock position in the opening. Should I be able to measure vacuume, from this scource, with the engine running? Is this hole (vacuume scource) plugged with the engine shut down? I have not been able to measure vacuume when connected to this port at any RPM, and am unable to blow or suck any air through this opening with the engine shut down.

Thanks, John

[William C.]

Re: Testing vacuume advance

Assuming a 2818 Holley carb, you you should have vacuum from that port. I feeds the line to the distributor vacuum advance mechanism.

[Wayne M.]

Re: Testing vacuume advance

Something doesn't sound right. I have a List 2818 3A3 apart on my bench, and the threaded vac port on the side of the 4094 metering block goes directly to the manifold (vacuum) and exits under the throttle plates. As a check, a shot of carb cleaner shows the path. So you should get a vac reading with the engine running. Is it possible that you have the wrong gasket between the block and the main carb body ? (or between the body and the carb base plate ?) that is blocking this routing ?

[Timothy B.]

Re: Testing vacuume advance

John, First make sure you have the correct # metering block, can you post the # stamped into the top.

[John P.]

Re: Testing vacuume advance

John, First make sure you have the correct # metering block, can you post the # stamped into the top.

Thanks all. I suspect that it has one or more of the issues mentioned. The number on the primary metering block is 4904. It is a 2818. The numbers on the secondary metering block are 4099.
The numbers on the air horn flange are as follows
3849804
LIST-2818-1
533

Thanks for helping!

John