fastrad

my 63 250 hp with original carter idles too low 450 to 500 rpm. car has a little more aggressive cam. had carb rebuilt and if I increase idle it will open the idle circuit and drip gas inside carb. have increased timing with no luck, and tried idle mixture. Is there anything else I can try short of replacing original carb?

tbarb

You may get some joy experimenting with a different PCV valve, on a Holley there is a secondary throttle blade stop screw and the secondary blades can be opened a little to help this exact problem. The carter AFB may be a better choice.

If turning the idle speed screw starts the boosters check the float level it may be to high, I find it hard to believe the primary blades are open far enough at idle to initiate the main fuel circuit.

fastrad

Had the carb rebuilt by a well know carb rebuilder, I turned the idle up very little and carb started dripping, called and they stated that you cant turn up idle without the idle circuit opening when it sits. they readjusted it again-no drip. The car wont stay running at 450-500 rpm. Tried to bump up a little and started dripping again, at a loss but they did state I cant adjust the idle this way on the original carb

AzMotorhead

How much did you try increasing timing by?

fastrad

went to the timing was off the scale, advanced to the point it was hard starting and backed off a few degrees to where it would start. cant advance any further.

fastrad

may go with an aftermarket Edelbrock 600 cfm and make it drivable. Wife's car and don't want it to keep stalling

Frankie the Fink

Sounds like you are being fed a line by your rebuilder....if you couldn't bump the idle up from 450 RPM without getting a drip then how does a PROPERLY running carb's "fast idle" work when its cold ??

I'm sure a cold carb, idling at 1,400 RPM or thereabouts isn't dribbling fuel down the bores... I think you got a bad rebuild...

I have a 63 WCFB on my 250h car -- no issues...

fastrad

may not have stated it correct, when the car is off it will drip down the bores, and into the crankcase. I know when I turn the main adjustment that works the pedal it will start dripping, by turning it back it will stop. always adjusted all my cars this way, but not this carb. could be missing something. It all started when I rebuilt the motor and went with a little larger cam and had to increase idle. Crankcase filled with gas. Changed oil and found carb dripping, I rebuilt it and same results. Decided to have it professionally rebuilt. Got it back and increased idle and drip returned. Talked to rebuilder and they stated I cant adjust idle this way because it opens the idle circuit.

histoy

I'm a little confused about the carb dripping fuel when the idle speed adjusting screw is opened to the off idle position, but your idle adjustment problem sounds similar to issues I've had when running a big block Mopar with an aggressive cam. Sometimes in order to get these to idle properly you end up opening the throttle plates to the point you're coming off the idle circuit into the transition to the low speed circuit. Other guys had this problem and made this suggestion to me.... drill a small hole in each primary throttle plate. This passes more air and allows you to close down the throttle plate opening adjustment to stay off the transition point. You can still adjust the fuel mixture using the emulsion screws. I drilled a 1/16" hole in each plate, which worked for my big block. You might be able to find a smaller sized drill bit to use with your small block.

DansYellow66

As histoy said - you can drill a small hole on the primary plates - on the back side above the idle transfer slots. Kind of tough to do on an original, restored carb but that's the classic fix. Most Holleys have an adjustment that allows opening the secondary throttle blades a bit more than stock to pass more air which sometimes restores proper idle function. But I don't believe any Carter or Edelbrock carbs have a similar feature.

Frankie the Fink

Well - I had thought the cam upgrade wouldn't be all that aggressive in an otherwise stock, base motor. 250hp car (sort of an oxymoron)..

I, also, would be reluctant to drill original throttle plates, but maybe that's the fix...

tbarb

Need more information about the camshaft. I think what the carburetor rebuilder is telling you is by increasing the idle speed screw you are over exposing the transfer slot at idle. That itself can cause problems with hesitation at a higher RPM when the idle circuit and main circuit overlap.

FWIW, the idle circuit consists of the curb idle ports (low idle fuel supply) and the transfer slot, both are fed from the "idle circuit " fuel.

I am not sure the AFB will work on a stock 250hp cast iron intake manifold, maybe Frank can help there. If you decide to drill small holes in the primary throttle blades I am sure you can purchase blades if you go back, what PCV valve are you using.

Frankie the Fink

Yes, more camshaft info - I'd like to know what the idle vacuum is too.

The WCFB bore size is unique - a carb swap will mean an intake swap and, depending on the carb selected a rash of dealing with hood clearance issues.

I am unclear as to how moving to an AFB (that was used on the still low-HP, hydraulic cammed 300HP motor) would help this particular issue....and the Edelbrock's are just modernized AFBs.

And, yes, its easy to chase that 'perfect' idle between the mixture and idle speed screws until you are "up" on the transfer slot and all the air/fuel flow dynamics change...

Changing throttle plates (as tbarb knows) is not for the faint of heart - it involves removing staked in screws and peening over the new p!ss ant-sized screws so that there is ZERO chance of them falling into the intake.

Before I went medieval with drills and hammers I suggest the OP give Ron or Tim a call at Daytona Parts: 386-427-7108. Those are my 'go to' guys when I get stuck on a carb issue... They've 'tweaked' untold thousands of carbs for unique applications.

If they confirm drilling the throttle plates as a solution as others have mentioned then I would say go for it...

tbarb

Frank,

The AFB has a larger bore so more air will flow around the throttle blades the with the smaller bore carburetor.

Frankie the Fink

Yeah - that thought hit me as I was typing and I edited the post.

Weird problem IMO. I know of several C1s with upgraded cams and WCFBs that operate flawlessly. Devildog has dual WCFBs on a motor making 500hp!

If the cam is an asphalt-eating configuration and affects engine vacuum dramatically then the venturi effect through the carb bores changes - the OP needs to tell us what he's done there...

However, we're all under the assumption the cam swap is the culprit; I'm not so sure. For the OP's crankcase to get soaked with raw gas that's a lot of leakage. I'd be curious about fuel pump pressure....

fastrad

will try to get cam specs but it is not all that aggressive, just wanted a little more sound out of exhaust, not sure that is the problem either. Carb Junkies rebuilt carb and were responsive and went back and reset carb after I adjusted the idle. Tired of chasing this problem. After I got the carb back it would idle and stay running but seemed really low. Car sat for 2 years and is at the edge of idling and will stall about 1/2 the time. I am running and edelbrock on my 65 and can get idle up around 700. Will the square bore edelbrock fit my manifold? The Edelbrock website list the 1400 as a replacement.

Frankie the Fink

You'll have to show me that - I don't think its correct, but I could be wrong

If you were nearby I have two WCFBs rebuilt to factory specs I could try out for you...

I see only three alternatives:

1) The new cam is making you increase the idle until you are off the idle circuit and transitioning into the cruise circuit, or,
2) The carb's needle valves are being overdriven causing the bowls to overfill and the nozzles to drip (fuel pump pressure?), or,
3) You still, after all the rebuild work, have carb issues.

Edelbrocks come off-the-shelf with one-size-fits all characteristics to make them plug-and-play for the average hobbyist. Unless you also get into tweaking them you won't have an optimized setup IMO, largely defeating the purpose of the enhanced cam.

Again, I'd talk to Ron or Tim and hear from somebody that knows more than most...

Just my $.02 worth.

I should have asked earlier; you DO have the vac advance attached and hooked to FULL manifold vacuum....right?

My 250hp WCFB is set to idle at 750RPM to compensate for the idle drop when the aftermarket A/C compressor kicks in - no issues.

Pilot Dan

If you want a reliable trouble free car that you can set any idle speed you wish and still have plenty of power, install an AFB and matching GM manifold and configure all the plumbing the way GM designed it. That's what I did with my 327 350HP motor and have not had to touch it in 8 years. I get in, blip the throttle to set the choke and it always fires and runs very smooth. At this point your current problem might not even be originating in the carb itself, depending on what else is mixed and matched. Your car would run OK with a WCFB as well, but won't make the power without the extra CFM's of the AFB. Pilot Dan

tbarb

How old is the gas in this car? Are these carburetor rebuilders close by to hear the engine. Does this carburetor have it's hot air choke connected, this is another calibrated air leak along with the PCV valve.

fastrad

worked on 63 today, tried a new vacuum advanced, original one seemed to be sticking. Getting about 18 inches of vacuum. My 63 corvette manual stated idle at 450. That is where it starts to die out. It comes off fast idle and motor wont stay running at 450, lopes then dies