leif.anderson93

Mike,

I believe the spring hooked around the arm not through a hole in the arm.

tbarb

I have tried the spring through the cotter pin hole and around the plastic bushing like the picture above. In the cotter pin hole, it seems to pull the rod crooked where it goes through the rubber but around the bushing all seems to stay lined straight. The diameter of the spring loop seems to match well with the plastic bushing.

Many think it goes through the cotter pin hole though.

MikeM

My WCFB has the spring looped around the rod, OUTBOARD of the throttle arm. Don't know if it's right/wrong but the car is basically unmolested.

The illustration in the P&A book shows ALL carb linkages to be the same. Again, right or wrong, I don't know.

Frankie the Fink

Wow - I don't feel so bad not figuring it out right off the bat now....

rtruman

Mike took off the short spring seems to be fine still idles good a lot lighter on my food and kina smooth so I left it off. Good deal !

abe g

On my original (since Nov 62) 63swc 340 hp AFB There is a small hole on the carb arm that connects to the return spring (s). A cotter pin is on the end of the rod. (there are 2 return springs) Looking at the various pictures, I do not see a hole on the arm. Any thoughts? Regards, Abe G

MikeM

Some engines of that general era used a double spring. One inside of the other. Both of them kinda' lightweight. Can't remember which engines.

fastfreddie63

Thanks Rich! I read this thread and went home to check my 63' 340. Sure enough 'Bubba' (me) put the end of the spring through the cotter pin hole of the throttle rod and it had sufficed as the cotter pin. I moved mine to go over the plastic bushing sleeve and installed a cotter pin.

Thanks Guys!

Freddie

Frankie the Fink

I did the cotter pin to secure the rod and the spring around the plastic bushing. That seems to be the natural best fit for the arrangement.

Had to replace the primary throttle shaft out of a junker carb this morning (the old one was scored and sticking like mad) now I'm fighting trying to get the car to idle below 1,000 RPM (and no I'm not 'up' on the transfer slots). Backed off the timing some (I have it cranked up quite a bit) and it barely came it to specs on the curb idle. Don't know why a throttle shaft swap should have caused this.. I was super careful putting the plates back in and they are right on. Carb runs great other than that.

W Guy

Are you sure the AIM shows a cotter pin in the rod hole?

Verne

tbarb

On these AFB's when the idle speed screw is backed all the way out the transfer slot is still just barely exposed. Are you certain the blades are in correctly and adjusted right..

Did you monkey with the hot air choke, that's a calibrated vacuum leak as well as the PCV. No chance the throttle shaft you installed is a smaller diameter than the one removed, did you mic it, that could be a leak point.

Frankie the Fink

The shaft is identical in diameter; the swap was between two 3721SBs and all the parts went back on nicely. The throttle plates are on correctly....

I finally got the car to idle down to 700RPM which is as low as I want it. I need the 'fudge factor' for when I cut the aftermarket A/C on as it drags it down 100 RPM. But that is with the idle speed screw just barely touching its stop.

rtruman

My carb likes 800 plus at idle your close.

tbarb

Are you using the factory hot air choke and factory PCV valve. What's the total idle timing (initial plus vacuum advance) and what's the engine vacuum at 700 +- RPM's

I take it the idle speed screw is backed all the way out.

Frankie the Fink

Factory hot air choke with original housing, internals, fresh air tube and hot air tube...initial timing has been set back to 4* (factory spec) from 12* to get the idle down.

Engine vacuum is a rock steady 21* at 750 RPM and you can balance a nickel on the air cleaner at idle speed. Yes the idle speed screw is all the way out.

I'm gonna check all hoses, PCV valve and carb gasket this evening....have to believe its a vacuum leak. I'll get out the propane if I have to ...

Frankie the Fink

Beyond mystified now. No vacuum leaks that I can find and I've swapped out PCV valves, hoses -- you name it. Thought I had things fixed for a short drive when the car idled down and I had to screw the speed screw in a few turns to get back up to 700 RPM. Next thing you know the RPM's were pretty steady at 900-1000. Linkage not binding...still resting against the idle stop. The primary throttle shaft that I replaced is tight too.

Went into the dizzy again and checked the weights - NO issues.

About ready to toss the AFB carb in the lake and put the original, restored stuff back on....

tbarb

Is there a chance you removed the hot air choke from the main body and forgot the little gasket when reinstalling. Make sure the PCV is a AC 590C.

To slow the idle you can remove the hot air choke housing and install a jet in the bore where the vacuum feed is located. Get a 6-32 brass set screw and drill the set screw to .055 +- and experiement. It's got to be large enough to pull hot air and expand the spring but the hole there now is probable over .100" Very easy to do and easy to tap that bushing for 6-32 threads.

Remove the assembly and hold you finger over the hole and see how much the engine slows. Usually there are a lot of leak points in this system. The way you have it now there should be full manifold vacuum through the exhaust manifold to the clean air tube this smaller restriction should slow the volume.

Got to run but let me know your thoughts on this, as long as there is enough hot air for the spring you can slow the volume down and slow the idle by this mod.

I am convinced many of these tuning issues are from the gasoline today, you may not be doing anything wrong providing the throttle shaft does not need bushings, that usually reveals itself by different idle speeds depending on how the throttle gets returned down.

Frankie the Fink

We think alike...pulled the choke housing off late yesterday on a whim and ensured the rubber gasket was secure, not bunged up and sealed well and that choke housing cover plate and gasket were in place and OK. Tried two PCV valves including a new Zip correct repro (no dice). Even zip tied the vacuum hose to prevent leaks temporarily.

I actually had the idle down to 500rpm for a brief time and it migrated back up to 800 and the vacuum was still strong. I think the carb is just worn out. I'm pretty experienced in this area but I'm gonna talk to my rebuilder at Daytona Parts now.

I think maybe the throttle shaft I moved over is not allowing the plates to seat consistently or leaking air. That's the only thing I've changed of note.

Appreciate the help.....you clearly know your way around these old carbs!

W Guy

I don't mean to be a pest, but can anyone answer this question?

Verne

Frankie the Fink

You tell me ??!? There are three working AFB theories. (The WCFB is eliminated as the AIM CLEARLY shows a hole for the spring in the throttle plate).

1. The spring hook goes through the throttle lever hole, inboard of the throttle plate, and secures the rod.
2. The spring hook goes around the nylon washer on the the throttle lever and the lever is secured with a cotter pin.
3. The spring hook goes on the outboard side of the throttle plate around the throttle lever and the lever is secured by a cotter pin.

The AIM looks like #3 to me which is strange as hell and conflicts with the pics in Noland Adams book. I'm beginning to think these were connected a variety of ways depending on who was on the ***'y line that day. The AIM does not show the cotter pin but with this arrangement how else could the rod be secured?

Each of these theories has an issue in my mind. E.g. #2 seems to work but the spring hook abuts the rubber washer that goes through the throttle plate hole and that seems to be a source of excessive friction. However, this is how mine is mounted right now...