WCFB Problems
Thread Starter
3rd Gear
Joined: Aug 2007
Posts: 3
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WCFB Problems
Hello from England,
I'm the very proud owner of a numbers matching 225hp 1956 Corvette with dual fours, the engine suffered from a cracked cylinder bore so had to be rebuilt. At the same time I sent the carbs off to Dick Katter to have them restored, due to one thing and another the carbs and engine have sat around for a couple of years. The engine is standard apart from a hotter cam and Pertronix II.
The engine is back in, timing at 12-14 degrees BTDC, idle by-pass screws are screwed in tight and the mixture screws set at 1 turn out. With a vacuum gauge and tachometer connected the engine ran very rough with black smoke so gradually screwed the mixture screws in and the RPM and vacuum increased. Thing is the vacuum and RPM continued to climb until the screws are all the way in with no drop in idle speed or vacumm at all and it runs lovely and the vacuum reading is around 15.
Has anyone experienced this before? I guess fuel is being drawn in by other means, there are no signs of flooding. Off idle it runs great too apart from a puff of black smoke when opening the throttle.
I'm puzzled!
Thanks in advance,
Paul.
I'm the very proud owner of a numbers matching 225hp 1956 Corvette with dual fours, the engine suffered from a cracked cylinder bore so had to be rebuilt. At the same time I sent the carbs off to Dick Katter to have them restored, due to one thing and another the carbs and engine have sat around for a couple of years. The engine is standard apart from a hotter cam and Pertronix II.
The engine is back in, timing at 12-14 degrees BTDC, idle by-pass screws are screwed in tight and the mixture screws set at 1 turn out. With a vacuum gauge and tachometer connected the engine ran very rough with black smoke so gradually screwed the mixture screws in and the RPM and vacuum increased. Thing is the vacuum and RPM continued to climb until the screws are all the way in with no drop in idle speed or vacumm at all and it runs lovely and the vacuum reading is around 15.
Has anyone experienced this before? I guess fuel is being drawn in by other means, there are no signs of flooding. Off idle it runs great too apart from a puff of black smoke when opening the throttle.
I'm puzzled!
Thanks in advance,
Paul.
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If you have all four idle mixture screws all the way in that means the engine is receiving fuel from another source.
With the engine running did you look down the throats of the carbs with a bright light?
Look for any fuel dripping from the boost venturies.
If this is the case then either the float levels are too high or you might have something on the needle and seat preventing it from shutting off the fuel.
Joe
With the engine running did you look down the throats of the carbs with a bright light?
Look for any fuel dripping from the boost venturies.
If this is the case then either the float levels are too high or you might have something on the needle and seat preventing it from shutting off the fuel.
Joe
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I'll bet those carbs were run on an engine to tune them, then shipped. After sitting years gas turned to varnish, and things are gummed up. You may need to redo them or run them for a while if you can with Stabil or some cleaner in the gas. Tapping the housing front and back may unstick the floats if stuck...lightly!
Especially if run in on an ethanol mix.
Especially if run in on an ethanol mix.
Thread Starter
3rd Gear
Joined: Aug 2007
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Thank you both, I've had the top off the front carb and changed the float needles. The floats were also out slightly, will do the rear carb tonight.
On the 56 carbs should both idle adjustment screws be used in tandem? I've read conflicting views on using the rear only with the front one adjusted just enough to open the valves, yet others say to use both.
Thanks again,
Paul.
On the 56 carbs should both idle adjustment screws be used in tandem? I've read conflicting views on using the rear only with the front one adjusted just enough to open the valves, yet others say to use both.
Thanks again,
Paul.
Le Mans Master
Joined: Apr 2000
Posts: 5,093
Likes: 1,350
From: New York New York
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Thank you both, I've had the top off the front carb and changed the float needles. The floats were also out slightly, will do the rear carb tonight.
On the 56 carbs should both idle adjustment screws be used in tandem? I've read conflicting views on using the rear only with the front one adjusted just enough to open the valves, yet others say to use both.
Thanks again,
Paul.
On the 56 carbs should both idle adjustment screws be used in tandem? I've read conflicting views on using the rear only with the front one adjusted just enough to open the valves, yet others say to use both.
Thanks again,
Paul.
Paul,
On my set up I close both throttles and the on the front carb I turn the idle speed screw in about a 1/2 turn. I then do the same to the rear carb. Then I turn the four idle mixture screws in lightly till they bottom and then back out one turn each.
After engine has warmed up I then use the back carb. to set the idle speed.
I start with the front carb and slowly turn the idle mixture screws in until the RPM slows and back out 1/8 turn. I do all four screws this way until the are even. I readjust the idle speed as necessary.
At no time should any of the screws be closed completely to get the best idle.
It has been about nine years since I installed and adjusted my carbs and I haven't touched them yet.
Joe
Thread Starter
3rd Gear
Joined: Aug 2007
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Thanks Joe, will try your suggested adjustments.
After a lot of head scratching the problem was traced initially to a faulty Flamethrower coil, a replacement improved things a fair amount but the engine was still not 100% correct. Further checks showed that the fuel pump was delivering well over the recommended pressure. Just waiting for a rebuilt one to be shipped over.
Cheers,
Paul.
After a lot of head scratching the problem was traced initially to a faulty Flamethrower coil, a replacement improved things a fair amount but the engine was still not 100% correct. Further checks showed that the fuel pump was delivering well over the recommended pressure. Just waiting for a rebuilt one to be shipped over.
Cheers,
Paul.
Team Owner
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Army
When you get to the point that your mixture screws are having no effect you are generally running off the carbs' "transfer slots" inside the bore....that is how the car stays running. This is an abnormal condition and well-maintained WCFBs should have the idle mixture screws from 1-1/2 turns out to 3/4 turns out at the most. I set mine for the most vacuum at the specified idle speed and then lean each mixture screw out (clockwise) about 1/16 of a turn...this adds a slight roughness that will settle out eventually but keeps the carbs from running super rich at idle (and these is what the factory dual quad tune up procedures recommend). Here is the service manual for these carbs: http://www.carbkitsource.com/carbs/t...fb-service.pdf
These carbs can handle up around 6.5lb of fuel pressure - past that things get dicey.
These carbs can handle up around 6.5lb of fuel pressure - past that things get dicey.
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