63two

Help I'm trying to get a 1963 327 to correctly idle. The motor has a .490 lift 280 degree cam and is happy with a 800 r.p.m. idle But it runs rich (power valve is good) I had to open up to primary throttle plates quite a bit and expose alot of the transfer slots what do I do next Thanks Steve

Coves4me

63two, I had this same issue on a Holley 4180C that I had on an 85 Mustang 302 engine that had a cam similar to yours. I'm assuming that we're talking about a Holley, right? First, check your initial timing and centrifugal and vacuum advance timing. If that's OK, what I had to do at Holley's recommendation was to drill a 3/32-inch hole in each of the primary throttle plates on the front side of the throttle shaft. This fix took care of my idle and the car ran great. Good luck.

DansYellow66

Drilling the primary plates is how I fixed mine too - but before you do that take a look at your Holley and see if you can adjust the secondary throttle plates to rest slightly more open and lean out the idle mixture. I'm not sure just how many Holley models have this feature but a number do. I think you may have to pull the carb off and turn it over to clearly see the adjustment screw which is on the underside of the casting. My Holley book says initial adjustment is to screw the set screw in until it makes contact with the primary plates and then give it a 1/4 additional turn. So you can experiment with that as a starting point. If I was doing mine all over again I would try this before drilling the primary plates.

Dan

rgs

I've corrected several vehicles with low intake vacuum by drilling the throttle plates. Personally, I would not crack open the secondary to fix an idle issue.

lars

Holley and BG carbs discharge idle fuel on both the primary and secondary side (even if it's a 2-corner idle screw system), so you need to have the secondary throttle cracked open at idle just like the primary side. Here's how:

Set the primary throttle blade angle (idle speed) to expose .020" of the transfer slot below the throttle blade when the throttle is closed (.020" will make the transfer slot appear to be a square hole at the edge of the blade). Once done, hold the carb over your head up against a light and look up the bottom: Adjust your secondary idle speed screw so that you obtain the same "light gap" around the secondary throttle blades as you have around the primary side blades. This will make all 4 blades balanced for equal airflow at idle through all 4 bores. This is the optimum idle setup. Now, bolt the carb back on the engine and check idle speed. If it's a tad high, lower the primary and secondary idle speed screws evenly to obtain the correct idle speed (you will have to pull the carb back off the drop the secondary side idle, but the work is worth it). By setting the idle speed evenly between the primary and secondary side, you can obtain good quality idle without the need to crack the primary side open too far into the transition slot (which will produce a rich idle condition and off-idle hesitations). I've never had to drill a blade...
For complete instructions on setting up a Holley or BG in this way, drop me an e-mail reuqest for the Holley and BG carb setup papers:
V8FastCars@msn.com

Lars

rgs

Lars,

I thought that there is a separate circuit for idle that is below the transfer slots on each of the primary venturis only. They are not part of the secondary system. On a stock application at idle, none of the transfer slot should be exposed, only the idle circuit. Exposing the transfer slot brings in fuel that is metered through the main jet and air bleed orifices. These can only be adjusted by changing mains or drilling air bleeds, the latter I do not recommend.

The reason I've had to drill primary plates is to compensate for aftermarket cams that have created low intake vacuum at idle. This results in too much of the transfer slots being exposed at idle and washing out the idle mixture screws from noticeably affecting idle mixture.

I understand and agree that cracking the secondary would do the same thing, as long as you do not expose the transfer slots, but how would you do it on a 2300 series 2 bbl?

lars

On Holley and BG carbs, even ones without secondary idle mixture screws, there is an idle fuel crossover passage through the throttle plate that feeds primary idle fuel to the secondary side: The secondary throttle bores actually have idle fuel discharge holes below the throttle plate. The secondary bowl also feeds into the idle circuit on the secondary side to keep fuel circulating through the secondary bowl, even without using the seceondaries. That's the reason you want to have a little air on the secondary side as well - you don't want to discharge idle fuel on the secondary side with no air to mix with it. By cracking all 4 throttle blades open the same amount, you get a very even air/fuel distribution through the engine while allowing the primary side to be closed up nicely, even with a big cam. (Flip a regular Holley 4-barrel over sometime and check out the secondary bores: You'll see the idle fuel discharge holes below the throttle blades)

About .020" of the transfer slot should be exposed below the throttle blade at idle on the primary side, but it's okay with a litle less exposure, too. Fuel discharged at idle, therefore, comes from both the idle discharge hole (controlled by the idle mixture screws) and from the slight amount of the transfer slot that is exposed below the throttle. The fuel feeding the idle circuit and the transfer slot comes through the main metering jets, through the IFR (idle fuel restrictor), and then splits into 2 circuits: The idle fuel goes through a circuit controlled by the idle mixture screw, and the transition fuel goes directly to the transition slot. Thus, the fuel discharged at the slot is controlled only by the size of the IFR (since the main jets are too big to control or restrict the flow). Fuel coming from the idle discharge is restricted both by the IFR and by the idle mixture screw. Thus, if too much of the transition slot is exposed, the engine can idle rich, even with the idle mixture screws closed, as you've stated.

On a 2-corner idle mixture screw carb, the secondary transition slots are set much higher up in the throttle plate than on the primary side. Thus, you can set the primary side to show .020" exposure of the slot and crack the secondary blades open to produce the same "light gap" as described above, yet the secondary blades will not expose any of the secondary side transition slot: the secondary side will only discharge fuel from the idle fuel hole below the blade and mix it with air from cracking the throttle open identically to the primary side. This produces outstanding idle quality with instant throttle response from the correctly-exposed transition slot on the primary side.

You're right: on a Tripower with 2-barrel secondaries, you're kind of screwed on this setup - you can only do this on the 4-barrel carbs.

Lars

rgs

Lars,

I never noticed the idle fuel hole on the secondaries. Learn something new every day.

A few pics for those following this discussion.
Primary showing idle fuel port and transition slot exposed.


Secondary closed to stop showing idle fuel port.


Secondary cracked showing transition slot.

rickm63

We (63two) replaced the teflon bushings on the secondary shaft and still have play in the shaft.Is it worth finding another base plate or will there be other wear issues else were.Do you think we should start with a new carb or chase our tails and try to figure it out.We are afraid of gas washing the new motor.

Thanks Rick

lars

Good shots! Thanks for posting the pics - they're very good and show the concept clearly.

lars

There are 2 concerns with sloppy shafts: 1. Vacuum leaks and 2. throttle plate seating.

1. The vacuum leak caused by a sloppy shaft is so slight that it's negligible in almost all cases. There are so many intentional leaks into the engine that the small amount of air that is able to get sucked by the length of the shaft has virtually no effect on most engine operations. Brand new Q-Jet carbs came from Rochester with throttle shafts so sloppy that you could wiggle the throttle lever back and forth. Holleys were tighter, but can still take a lot of looseness before it has any effect on engine operation.

2. If the shafts are sloppy enough in the bore, the more serious problem is that the throttle plates can get "cocked" and jammed slightly in the bores, causing a very high return-to-idle speed and inconsistent idle speeds. Only by "tapping" the gas pedal will the throttles seat in the bore to produce the base idle speed. If this is the case, I would either bush the plate or replace it - a carb that will not return to a consistent idle speed is a real pain and makes the car no fun to drive.

Sloppy shafts will not contribute to flooding the engine or a rich condition. There is no possibility of throttle shaft wear causing the engine to flood and "wash out." At worst, it could be a touch lean, but you will easily compensate with idle mixture screw adjustment.

Matt Gruber

i had a 4165 with #2
ordered a NEW baseplate complete, $111
cheaper than a new carb, and works like new