Steve59

I have a stock 283 engine in my 59 Vette. The distributor has been converted to a Petronix III with a Blaster Coil and NGK XR4 5858 plugs. The fuel pump is stock and at 6.5lbs and the engine is running with about 15 inches of vacuum. Other than the below change in intake, nothing else was done to the engine.

I had purchased a matching set of WCFB dual carbs and had Bob Kunz rebuild them. I took off the 1X4 manifold and have installed an aluminum, correctly dated 2X4 manifold. I installed the carbs and reinstalled the distributor. The issue began when I tried to set the timing. I have it set at 11* BTDC because I can't get the idle to go below 1000/1100 rpms (I still am using a Vac can, timing was done with vac plugged).

When I cold start the engine, in the fully choked position, I'm running about 2200 rpms, when the engine heats up (I have the butterfly open and have used the block-off intake gaskets), the lowest rpms I can get is 1000/1100 rpms. I have both front and back carb idle screws fully backed off. I talked to Bob and he suggested that possibly the adjustment screw tang on the rear carb was hitting the carb base as they sometimes get bent in. I adjusted that but still no luck. I took off all of the linkage and played with the primary throttle shaft. It appears to be as fully forward (and the plates closed) as it will go, I felt no binding, nothing grabbing. I moved the primary throttle shaft arm forward and back as far as it would go and everything moved freely. I have not driven the car with the 2x4 set up but have run it stationary for a total of about 40 minutes. The plugs (which I installed new) appear to be clean with the appropriate grayish appearance.

I'm not a Carb guy and am quickly approaching my limit on the knowledge of the subject, esp 2X4's. I'd like to go back to Bob but right now, I don't know what to ask. And I'm not sure whether it's a carb issue or an intake issue or something else.

My plan right now is to take the carbs off and visually inspect for any binding, bent items, worn stuff, but I'm pretty sure Bob would have caught any problems during the rebuild. I certainly don't feel comfortable taking the carbs apart at this stage.

I have done some research here and on the NCRS web site but am at a loss as to how to proceed. I need a plan of attack and possibly a lead on written material explaining how WCFB carbs work and help with some nomenclature and rebuilding.

This is really starting to frustrate me and any advice is appreciated.
Steve

GTOguy

A long shot but it's happened to me before: make sure the mechanical weights in the distributor are not sticking in the advanced position. The shaft can get gummed up and you'll get a high idle all the time and sometimes, kick-back at start-up. Super easy to check, and if not the problem, you've ruled it out at least.

Frankie the Fink

Generally, fast idle problems fall into 3 areas:

1) Too much advance (too much initial timing or dizzy weights kicking in as noted),
2) A vacuum leak somewhere, or,
3) You've chased the idle speed to the point you've cranked the mixture screws too far and you're up on the carbs' "transfer slots".

Soooo... you can rubber band or even remove the dizzy weights temporarily to see what effect that is; might even crank back the initial timing to 8* just to see if that helps.

You can snug up all of the 18 screws in the top of both carbs CAREFULLY; don't strip'em and then check the carb mounting nuts (usually 1/2"). You can also try an unlit propane torch around the base and other areas of the carb to see if the idle speeds up; if it does there's your vacuum leak.

Another very likely problem is you're up on the transfer slots; try gently seating all four mixture screws and back each out 1 turn and see if the car idles down with the speed screw backed out. If so then adjust the mixture USING A VACUUM GAUGE...

IF YOU ARE GOING TO TAKE THE CARBS OFF ANYWAY. Then don't touch any adjustments and flip them over and look down the bores. You'll see the transfer slots and there should only be enough exposed with the plates closed so that it looks like a square hole -- see picture.

Another thing to try is to check the linkage adjustment -- both carbs have threaded rods and if the swivel barrels are adjusted too short the carbs will never return to fully closed even with the idle speed screws backed out. And all this assumes your throttle return springs are correct and operating like they should.

Then you can report back results on all of these.

FYI - I like my idle slightly high on my dual quads at 850 RPM -- the car "likes" it there and that is where the mixture adjustments sort of fall into their sweet spot as well.

I have a ton of documentation on WCFB carbs - but here is one I use a lot:
http://www.google.com/url?sa=t&rct=j...92885102,d.eXY

Ironcross

I would check the rear throttle plates and see if they are closing, if open you will never slow it down....

DansYellow66

This would be my suspicion also based on the linkage on my 2x4 ERA Cobra (if the linkage is anything similar).

I don't remember the rear barrels of Carter carbs being adjustable for idle setting but maybe that is something inherent in their linkage between primary and secondary plates and certainly worth checking. As long as Bob Kunz has been around though, I would believe he had carefully adjusted this.

Steve59

Thanks gentlemen. FTF, thanks for the documentation. I now have at least a plan.
1. Read documentation
2. Do what I can (tests, propane, adj advance, check for leaks) with carbs ON engine (I won't mess with the idle screws until the last step.
3. Take carbs off, check what I can visually and as per FTF's recommendations.
4. Reinstall carbs and see what happens.
5. Start playing with the idle adjustment screws.

Frankie the Fink

One other test, that I'm loathe to tell the inexperienced, is to disconnect the linkage entirely and see how the car idles -- this will absolve the linkage. HOWEVER, do NOT blip the throttle as the return springs will be OFF unless you find a way to jury rig them... You don't want the engine to 'run away' on you !!!!!!!!!!!!!!

Also, ignore any narrative about the "idle air bleed screws" in that document; unless you have one-year-only '56 carbs it doesn't apply !!

tbarb

Does the engine have a PCV valve installed. If so, this is another source of air at idle speed and the calibration of the carburetor may not allow for this if it originally did not use the PCV.

Steve59

1. FTF- I actually did that last week as part of my testing. I was VERY AWARE of the possibility of a run-away engine because years ago, I had the return spring pop off while I was in the car with foot on gas. That was a VERY INTERESTING 5 seconds, getting out of the car, opening the hood and closing down the throttle.
2. No pcv...just a road draft tube.

Steve59

Update:
What does a guy do on Mother's Day? Killing a little time, went out and played with the carbs.

I adjusted the choke to slightly open when cold, that moved the tang down on the cam slightly and dropped the cold RPMs down to about 1800.

I separated the carbs by removing all linkage and using the springs to pull back on the throttle shafts. The rear carbs throttle shaft didn't move any further forward than last time, but the front carb's throttle did move ever so slightly forward, so I played with that for awhile making sure it was fully closed.

I manually took off the choke and fired the car up and it was struggling to hold 500rpm's until it warmed up. Then it kind of sat at about 1000rpm. I operated each carb individually and it appeared that the front carbs throttle plate was now closing slightly more than before, but the engine's rpms were still around 1000 so I did the propane vac leak test and:

First rookie mistake- When the propane got near the vac take off on the carb, it sped up slightly. Apparently I cracked what was a brittle tube and there was a vac leak. Now using new rubber lines.

Hooked up my timing light and tac/dwell meter. Timing was perfect at 8* BTDC with vac plugged, and my RPMS were at 750 also perfect, but (second rookie mistake) the tack in the car was reading 950, it is high by about 200 rpms and that was the tach I had been using before.

So now I'm feeling a lot better. I adjusted the front carb's idle screw to just barely touching the tang and now have adjustment room on the rear carb, so I adjusted the rpms to 800-850. Did this with the tach/dwell meter (in-car tack reads 1050), then the rpms started to wildly gyrate and the engine quit...WTF???.....quick look at the glass fuel filter....ran out of gas...

To end this Mother's Day saga, I believe I'm good to go. Thanks for all of your help, especially that propane test, don't think I would have found that leak without it.

Steve

Frankie the Fink

Well it really did turn out to be a Happy Mother's Day....
Good for you !