No Ported Vacuum on AFB

[Shadetree]

I have a ‘70 model Hemi with Dual AFB Carbs and the rear carb isn’t producing any ported/timed vacuum leading to the distributor at any RPM.

Info- The engine is making 14 lbs of Vacuum, the idle mixture screws work perfectly and a 1.75 Turns out each, fuel pump is producing 6 PSI. The car runs ok but not great.

Any ideas?
Also, my timing is at 12 Degrees Initial and all in at 2500 RPM/36 Degrees. Do I need any additional advancement from the vacuum canister with those number?

 

[turbine68rt]

Pull your cap and connect a hand vacuum pump to the vac advance and see if its working properly. I already had a cracked diaphragm producing no advance.

 

[HALIFAXHOPS]

If not coming off of the cab probably a clogged port that needs to be cleaned. Should be a straight shot into the throttle body luckily.
Easy check put the vac pump on it if it builds it is clogged.

 

[Shadetree]

Pull your cap and connect a hand vacuum pump to the vac advance and see if its working properly. I already had a cracked diaphragm producing no advance.

I have and it’s advancing properly with a vacuum pump. Problem-The distributor isn’t getting any vacuum from the carb at any RPM

 

[pnora]

I have and it’s advancing properly with a vacuum pump. Problem-The distributor isn’t getting any vacuum from the carb at any RPM

Is the vacuum hose direct from the carb to the dist.? If so pull the carb and make sure the gasket is correct and the port is clear.

 

[HALIFAXHOPS]

It is just above the throttle plate.

 

[Dragon Slayer]

Put your vacuum gauge on the hose end that goes to distributor vacuum can. Does it register vacuum? If no, attach directly to the carb? Either hose is clogged or the vacuum slot in the carb to the tube is plugged/clogged. Picture show slot on the right side primary. Hard to believe it is clogged, but tube migh have something in it and hose could be plugged. Folks use to use ball bearing to plug vacuum hose for performance while retaining stock look.

 

[Shadetree]

Put your vacuum gauge on the hose end that goes to distributor vacuum can. Does it register vacuum? If no, attach directly to the carb? Either hose is clogged or the vacuum slot in the carb to the tube is plugged/clogged. Picture show slot on the right side primary. Hard to believe it is clogged, but tube migh have something in it and hose could be plugged. Folks use to use ball bearing to plug vacuum hose for performance while retaining stock look.

View attachment 1468986

Thanks for your input. I have tried both with and without the hose and no vacuum at any RPM. I agree that it’s odd for that port to be clogged. I like some of the previous ideas also, I’ll try all of them until I figure it out. Keep the ideas coming. Thanks, everyone

 

[Shadetree]

Is the vacuum hose direct from the carb to the dist.? If so pull the carb and make sure the gasket is correct and the port is clear.

It is. Ok, that’s a possibility. Thank you

 

[Fran Blacker]

Maybe hose is collapsing, hose not made for vacuum.

 

[Dragon Slayer]

If you have no vacuum at the nipple on carb. Shut motor off. Open primary wide open, place catch rag/towel under bore slot for vacuum. Shoot carb cleaner through the vacuum tube. Should come out the slot. If you get a lot of dirt/grit. I would remove carb and thoroughly clean. Have rag around nipple too. If clogged the cleaner is going to kick back.

 

[493 Mike]

Yes, you should use vacuum advance on stock/mild type engines. They will live longer and get better MPG.
Mike