80atez

OK folks, I'm sure this has been discussed, can't find it on my brief CF search...

I have a 1965 327 / 300hp synchromesh Carter AFB vette I'm tuning up for my daddy... I have the 1963 shop manual and the 1965 supplement I'm working from

I have a new choke spring just installed, I adjusted that after aligning the hash-marks for the syncromesh, and then adjusting so it fully opens when hot. Will check tomorrow when it's cold that it closes fully...

But the questions are mounting... Here's a few:

1. I assume you don't just put the choke spring cover at the hash marks and assume it's perfect, you need to adjust it as I did above, as the new spring is way way different than the old one... Ultimately the goal is perfect running and airflow when hot, so I got it hot and made sure it just fully opens on its own, and I'll work backwards from there... Any other better way?

Next I'll do the other items in the shop manual you can do on car...

2. Adjust the idle screw - it says see the specifications. Only spec for idle listed is "hot in car" whatever that means, at 1750. What does that mean? I assume hot idle would be around 800, but I need guidance... I don't see where 1750 can be set and be correct.

3. Adjust vacuum. So how do you measure the vacuum? I connected a vacuum meter to the tube coming off the passenger side rear of the carb going to the small diaphragm thing, then I turned the two screws on the front of the carb to get to the highest stable vacuum . This is sort of self explanatory in the manual, but did I connect the meter correctly? Or do I connect to that little nipple covered with the red plastic cover off the backside passenger side top of the carb instead?

I realize these are novice questions for carburetors... My first car had FI in 1986! Any basic info on what order to do this stuff, and basics of how to attach stuff and measure stuff is appreciated.

Any and all info or links would be greatly appreciated! Thanks.

tbarb

When checking vacuum to adjust the front emulsion screws you want a hot engine at curb idle, these screws simply trim the air/fuel mixture for a stable idle. Connect the vacuum gauge as you did but "T" into the line so the vacuum diaphragm is connected when doing adjustments.

Choke spring is properly adjusted at approx. 70* to just completely close the choke blade.

Set the fast idle on a hot engine (choke open) then raise the fast idle lever to the highest step and adjust the screw. This is what is described in the shop manual, when the engine is cold the speed may be just a little slower but that's the correct method to set the fast idle.

The AFB is a nice carburetor and the 63 shop manual is a good guide.

SWCDuke

Use a tee to connect the vacuum gage hose into the VAC signal line. It should idle smoothly at 500 if the camshaft is OE equivalent and vacuum should be 18-19" Hg.

Set the fast idle speed with the engine fully warmed up. That's what "hot on car" means, but it does sound a bit esoteric. The 1750 hot fast idle should yield about 1500 initially after a cold start.

How do you know the new choke coil is correct if it's way different? What''s wrong wiith the original?

Duke

80atez

The old one was rusted not round and would not really respond to heat or cold. I tried to futz with it waiting for the new one from Zip. Didn’t have any range to it it seemed. The new one has about 5 coils the old one had about 3 1/3. Not positive either is oem but Zip


i initially installed the new one in same orientation as old. but that didn’t go well. turned it 180 and it now has force to close and will open choke. old one might be non oem and put in wrong or visa versa. i’ll confirm soon with use.


part is listed as for this carb. but the car popped alive this morning. that was cool. Awesome advice guys. thanks. I’m close to returning it to the man!


ok couple follow up qs.

so do you need to somehow set it for fast idle on the driver side of the carb to adjust it when hot? (like when the choke is engaged by flooring it prestart) otherwise the car idles hot at about 600 now. I assume the 500 you mentioned above is when setting vacuum? or hot slow idle should be about 500 period. assuming oem cam. thanks

SWCDuke

It's pretty clear in the 1963 Corvette Shop Manual. Thoroughly familiarize yourself with the AFB section. It's very detailed. Once you get the choke and fast idle cams properly adjusted by bending links as necessary start the car, warm it up fully and set hot fast idle speed at 1750. Then drop off the fast idle cam and set the hot idle at 500 and vacuum should be 18-19". Then go through the idle speed/mixture adjustment procedure.

Before you do the carb work you should check that the VAC is functional. Report the number stamped on the bracket. You may have to unlock the cap and move it aside to see the number. Check and report the start and stop points with a vacuum pump. There were some issues with the '65 300 HP VAC so let's see what you have and whether it works. You should also check initial timing and the spark advance map. Specs are in your '65 Supplement.

As the original owner of a SWC I have been working on these cars for over 55 years and have seen more screwed up distributor sand carburetors than I can remember. If fact, tomorrow I'm helping a friend of a friend correct a screwed up distributor installation on his '65 396 that is the likely source of severe "trailer hitching" at 1500-2000 light load. I already know that the plug wires are improperly indexed on the cap and suspect the dimple on the drive gear is improperly indexed. We're going to remove, disassemble, and inspect the Mag Pulse distributor, clean and replace any worn parts, shiim up the end play... a complete overhaul that will probably outlast the owner.

If you don't understand how to integrate a vacuum gage into the VAC signal line to check idle vacuum do and advanced search, threads started by me, and download the tuning seminar. Pay particular attention of the "tools of the trade" photo of the vacuum gage hoses and tee. The golf tee is to plug the VAC signal line when you check initial timing.

Duke

80atez

Thanks so much.. I actually used lawn sprinkler connections for the tubing, and my US General cheap vacuum gauge read 19 peak and steady!

I'll keep asking questions until you stop answering so be aware!

It's hard to get to the vacuum adjustment screws with the air cleaner on as the manual states! But I got there. I have small hands.

One question that remains is what is a fully open choke? Is it perfectly vertical?It actually goes past vertical I think.

Also, when I'm playing around with the actuators with the car off, I can't get the secondary ventures (or valves??) to open. It seems impossible to confirm these are working with the car running because it seems you'd have to floor it.. How do I confirm they work other than the car does haul butt pretty good.

I'd say I have a decent tune right now. Maybe an occasional mild hesitation from low rpm in 2nd, just momentary, then it gets on it.

I appreciate the help and will review your posted videos when I get a chance. To be clear, this carb was not terribly out of wack, the choke spring was really all I needed, I thought, but I think I got it closer to spec with your help! cheers.

SWCDuke

A fully open choke valve should be near vertical. It has an offset shaft, so high air flow will take it to vertical if it isn't quite there. The secondary side has an offset shaft, counterweighted auxiliary air valve that is opened by manifold vacuum in the 2000-2500 range. When you floor the throttle at low revs the throttle valves open, but the aux. air valve prevents the bog that would occur at very low revs.

Open the throttle fully and use a popsicle stick to open the air valve. You'll also see them open if you blip the throttle real hard. Also, look at the exploded parts diagram in the shop manual.

The OE air cleaner has no silencing feature, so if you floor the throttle at low revs you begin to hear a lot of induction noise when the aux. air valve opens.

Duke

80atez

I just cleaned the gas tank of the pebbles in there, new gas and tweaked a few things and took it for a long drive. The choke is perfect now, it starts first try cold, and after the long hard drive, the plate was perfectly vertical. I'm pretty sure that spring was all it needed, and it was fun to work on the easy parts of the carb otherwise. I appreciate the help.

It has been returned to my dad, and he's quite pleased... I got a bottle of rye out of the deal!