Maintaining the idle speed on a Carter AFB carb

[Garry E.]

I'm having trouble maintaining the slow idle on my '64 327/300 with PG..... I rebuilt the Carter AFB about a year ago and it was running (and idling) fine. Now, on a regular basis, when the car is stopped, the idle speed will drop to the point where the engine will stall and die. At speed, the carb seems to be working fine - only the idle is the problem. The engine timing and the vacuum line have been checked and both are fine. I know that AFB's have a reputation for being "bad boys". But I just can't figure this one out.

I'm ready to remove the carb and do another re-build..... Is there anything I should be looking for when going through this process (again....)

thanks

Garry Eastwood
#38705

[Frank D.]

Re: Maintaining the idle speed on a Carter AFB carb

Could be a 1/2 dozen things, I'd check fuel pump pressure AND volume first, and fuel filter, if OK then maybe time for a rebuild make sure passages are clean, could be just some crud in, or, a worn needle valve - perhaps a float sinking (leaky). AFBs are not "bad boys" - there is a reason Edelbrock copied the design..

[James W.]

Re: Maintaining the idle speed on a Carter AFB carb

Garry,

I have a 1964 327/330 with a 4-speed and the original AFB carb. I have had great luck with the carb. Before I started taking it on road trips, I had it restored back in 1993 by NCRS member Gary Hodges who is listed on the NCRS Contacts page for carburetors. Contact him at fuelishgary@live.com.

James

[Duke W.]

Re: Maintaining the idle speed on a Carter AFB carb

The engine timing and the vacuum line have been checked and both are fine.


#38705

That really doesn't help me help you. How about giving us the actual numbers you measured and what you think the specs are. And keep in mind that the original published specs in the service manuals may be wrong, maybe modified via TSB or determined by experienced users to be a problem. IIRC there was an issue with the OE VAC and a TSB was written on it.

The primary issue with the AFB is a dirty choke vacuum break piston that causes problems with both fast and cold idle. It's easy to remove, disassemble and clean, but it MUST be installed with a small O-ring to seal the choke vacuum break vacuum passage to the main body.

Another issue is throttle shaft bore wear. Try wiggling the throttle lever. If you get a variation in idle speed, the throttle shaft bores are worn.

Regarding the VAC What is the VAC ID. IIRC the '64 300 HP VAC did not pass the Two-Inch Rule. It should be replaced with a modern 12" B26.

Also check all other vacuum systems for leaks like PB and AC.

Duke

[James W.]

Re: Maintaining the idle speed on a Carter AFB carb

So a 327/300 should have a B26 vacuum advance can and not a B22?

James

That really doesn't help me help you. How about giving us the actual numbers you measured and what you think the specs are. And keep in mind that the original published specs in the service manuals may be wrong, maybe modified via TSB or determined by experienced users to be a problem. IIRC there was an issue with the OE VAC and a TSB was written on it.

The primary issue with the AFB is a dirty choke vacuum break piston that causes problems with both fast and cold idle. It's easy to remove, disassemble and clean, but it MUST be installed with a small O-ring to seal the choke vacuum break vacuum passage to the main body.

Another issue is throttle shaft bore wear. Try wiggling the throttle lever. If you get a variation in idle speed, the throttle shaft bores are worn.

Regarding the VAC What is the VAC ID. IIRC the '64 300 HP VAC did not pass the Two-Inch Rule. It should be replaced with a modern 12" B26.

Also check all other vacuum systems for leaks like PB and AC.

Duke

[Duke W.]

Re: Maintaining the idle speed on a Carter AFB carb

I recommend the 15" B22 for base cam engines with manual transmissions. PGs should also idle at 500, in Drive, if not a little lower, but pull less vacuum due to converter load, so I recommend the 12" B26 for PG. All '66-'67 327/300s both manual and PG had a 12" VAC equivalent to the B26 and IIRC the ID is 355 16.

Duke