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Dual WCFB help needed

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Old 08-09-2013, 02:57 AM   #1
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Default Dual WCFB help needed

61 245hp dual WCFBs, California Car with PVC set up on rear Carb.

Had both carbs and intake rebuilt by Chuck Smith years ago and never had any problem with them until now. Car starts and runs fine from cold (Choke works properly) and also after reaching opt temp on the freeway at speed but when I venture into town the engine dies at every stop light and when I restart I have to hold the revs way up to keep it from complete Bog down. I have ruled out heat as even on hot days here in the desert car never gets over 190. Wrapped all the fuel lines and made a shield for the exposed glass fuel bowl so I do not think its the heat but it keeps me from longer trips and events with my local Vette club. I would appreciate any information that may help in fixing this problem. I am at the point now that I am ready to pull the 2 fours off and replace them with a standard alum intake and single four carb set up, It would make it more dependable but I really hate to take away from the originality of an original car and option.
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Old 08-09-2013, 07:07 AM   #2
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Don't jump ship on the dual quads yet....I run them in 100*+ heat in Orlando with no issues. First rule: COOLANT TEMPERATURE HAS LITTLE TO DO WITH PERCOLATION. Your car can run at 160* and you can still get percolation. But first things first. Simplest to hardest:

1) Check tank venting...you should have a long rubber tube going from the gas tank to the gas tank filler cap cavity that is your tank vent...it MUST be clear.

2) CAREFULLY check the ENTIRE PCV system - from the special crankcase draft tube hole adapter gaskets (and tightness), the rubber line, the PCV valve, etc..

3) Check the snugness of carb mounting nuts - take a 1/2" wrench and just give them a twist to make sure they are seated well. Take a screwdriver and snug the 18 screws in the top of the air horn on each carb. You have to take the air cleaner-to-carb gaskets off and the little vent cap cover off the front of the carb to get to all the screws...do NOT over tighten. Test drive afterwards.
Check throttle linkage for smoothness and COMPLETELY returning to idle via the return spring - make sure nothing is binding at the ignition shielding.

4) Check engine for vacuum with vacuum gauge and if its fallen off from the baseline or the gauge indicates problems check for leaks. With the vacuum gauge on the car go ahead and reset the idle speed and mixture adjustments.

5) Get a Harbor Freight I/R temp gun for $26 and shoot the carb bowls when this problem occurs...if the temps are heading north of 150* you might well be percolating - if so get back here; there are things you can do to help (which I have done). Its unlikely though if the carbs were running well for a long time before the problems. Make sure the steel carb fuel line coming up from the pump is well away from the engine head - bend outwards if needed (carefully).

6) Check your fuel pump pressure (if you have a vacuum gauge that will do the job); the pressure should be between 4.5 and no more than say 7.5. Check your fuel filter in the glass bowl carefully and also the sintered bronze filters in the carb inlet passages. Any debris or crud in these devices will indicate a problem. Run the carb line into a mason jar with the coil wire disconnected and crank the engine...you should have good flow (this is DIFFERENT than pressure) and also no debris or crud. These issues are also somewhat unlikely if the car is running well at highway speeds though.

7) At this point you will have to open up the carbs and check the float level and drop and inspect/replace the needle valves (possibly) and check for general cleanliness, issues, etc..

I have a large manual on these carbs I can email you (too big to post) if you provide an email address...

Last edited by Frankie the Fink; 08-09-2013 at 07:20 AM.
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Old 08-09-2013, 12:58 PM   #3
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Frank's spot-on with his advice. Don't give up yet. I've been running my 2x4 setup on my '59 for 27 years. I'll never change them out. I have however had problems in the past and have rebuilt them several times over the years.

One other thing to consider is a defective float. If/when you take the tops off, remove the floats and check for a bad one. Shake them to check if fuel's inside. Running at highway speeds uses lots of fuel and may not show a bad float, but if a float is stuck or dropped it'll be too much fuel at low speed stop 'n go driving.
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Old 08-09-2013, 01:12 PM   #4
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Thanks all, I have a whole weekend to trouble shoot this problem.
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Old 08-11-2013, 07:57 PM   #5
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Thanks for the info guys. I have the same problem with my 59 but it seems worse with the hot weather. I will go through each and see what I can find.

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