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Question about something strange on my front 2x4 carb.
I have a complete 2x4 setup that I have had for over 40yrs, and it has sat on the shelf for over 30yrs. It was originally on a 327 in my 51 Chevy. Then when I got the 56 Vette, I put it on the 350 in the 56. When I added FI to the 56 in 1986, I bagged and put the 2x4 on the shelf, where it has been ever since. The 383 I built and installed in the 51 had a broken piston from detonation. So I'm replacing all the pistons and new rings.
Now, I'm going to put the 2x4 setup back on the 383 in the 51 (after all these years).
Finally, here is where I'm going with this---------------------and I need everyone with a correct, matched 2x4 setup to remove their air cleaner and take a CLOSE look down the secondaries of the front carb. Something I've never noticed before and never heard it mentioned.
The secondary AUXILIARY air valves do not fully close on the FRONT carb (ONLY at the front side of the blades), but they are fully closed on the rear carb. The stamped part numbers on the auxiliary blades is the same for both front and rear carbs. The shafts and weights are the same on both carbs. There APPEARS to be NOTHING interfering with or preventing the air valves from fully closing. When the auxiliary air valves are closed on BOTH carbs, the weights on both carbs are in exactly the same position. I pulled the top off of the front carb so that I could more closely examine the auxiliary blades, shafts, weights. NOTHING seems to be wrong. SOOOOOOOOOOOOO, does anyone of you with a 2x4 setup want to take a look down the secondary side of the front carb and see if the auxiliary air valvbe blades are fully closed?
Not the best picture, but this is looking down the secondary of the front carb. As can barely be seen, the the front of the blade is not fully closed (the rear of the blade is closed).
This is down the secondary of the rear carb. The blades are fully closed.
I ran these carbs for several years like this and NEVER had any issues.
I see what you're talking about Tom - I've sold off my dual quads (and clones) but don't recall that condition and none of my pictures are zoomed in that tight. Maybe somebody else can help out or I can give you Bob Kunz's email address in a PM if you like..
My '56 does not show that to the degree yours does- but secondaries on both carbs appear to be tilted slightly. I don't know the history of my carbs but they are either new or very nicely rebuilt.
Something almost has to be interfering with the throttle shaft. That thing would idle about 80 mph I would think.
Not really - the counterweights will keep the flappers closed until engine demands cause them to open at off-idle throttle...
The flappers are on their own shaft in the main body- not the throttle shaft...which is in the base. They work independently.
If it were me and the both carbs' counterweights were in the same position when the flappers are fully open I'd flip the front carb over and examine how the flapper plates are peened ... if it looks original I'd just leave well enough alone..
HOWEVER - pulled out 6 of my WCFBs (single carb applications) and all the flappers close completely - so, a bit of a mystery..
Last edited by Frankie the Fink; 04-24-2019 at 10:41 AM.
The valve is supposed to be completely closed just like the one in the rear carb. I've rebuilt dozens of 2 X 4 carbs. and have never seen that before. My guess is that the blades were not centered in the bore when the screws were tightened as there is a slight amount of play because of the size of the holes in the blade. This could have happened when it was originally built or during a prior rebuild. As long as they open and close without binding, I don't think I would worry too much about it as the slight mis-match isn't enough to cause a bog or lean pop.
The valve is supposed to be completely closed just like the one in the rear carb. I've rebuilt dozens of 2 X 4 carbs. and have never seen that before. My guess is that the blades were not centered in the bore when the screws were tightened as there is a slight amount of play because of the size of the holes in the blade. This could have happened when it was originally built or during a prior rebuild. As long as they open and close without binding, I don't think I would worry too much about it as the slight mis-match isn't enough to cause a bog or lean pop.
As i mentioned earlier, when I had the 2x4 setup on a 327 in the 51 Chevy years ago, there was never any functional issues---------------NONE. I just accidentally noticed this several days ago after pulling them off the shelf 30yrs later. I supposed if they worked OK many yrs ago, they should still work fine today. I just thought maybe someone else may have a carb to look at and see if the auxiliary air valves on their front carb were completely closed.
Additionally, this morning, I removed the throttle plate to see if I could see something going on from the bottom side of the fuel bowl body. Everything looks fine.
As i mentioned earlier, when I had the 2x4 setup on a 327 in the 51 Chevy years ago, there was never any functional issues---------------NONE. I just accidentally noticed this several days ago after pulling them off the shelf 30yrs later. I supposed if they worked OK many yrs ago, they should still work fine today. I just thought maybe someone else may have a carb to look at and see if the auxiliary air valves on their front carb were completely closed.
Additionally, this morning, I removed the throttle plate to see if I could see something going on from the bottom side of the fuel bowl body. Everything looks fine.
I looked at my 60 270 HP carbs before I posted above. If I was you, I'd bolt them on and find something else to worry about.
With the throttle plate removed from the front carb, this is what the auxiliary air valve looks like. As can be seen, the rear of the blades are completely against the bores.
HI Tom. I looked at mine (1961 270 HP) and it is like yours. The rear carb air flaps have the slight gap, the front carb does not. My gap is about 1/3 what yours is, though. I have run this set-up for the past 4 years without issue. Great idle quality, great throttle response and performance. My throttle shafts are original as are the screws.....not messed with. So, I would bolt them on and run them, personally. If you have an issue, easy enough to pull the rear carb and tinker with it. Odd how the front carbs don't have a gap. I certainly am not going to mess with mine. Good luck.
Jeff
HI Tom. I looked at mine (1961 270 HP) and it is like yours. The rear carb air flaps have the slight gap, the front carb does not. My gap is about 1/3 what yours is, though. I have run this set-up for the past 4 years without issue. Great idle quality, great throttle response and performance. My throttle shafts are original as are the screws.....not messed with. So, I would bolt them on and run them, personally. If you have an issue, easy enough to pull the rear carb and tinker with it. Odd how the front carbs don't have a gap. I certainly am not going to mess with mine. Good luck.
Jeff
I'm not sure what you would do to correct it that might not be more trouble than its worth, possibly with no discernible effect...
Nope. Because of the way they are made, the blades on the auxiliary shaft can only be installed one way.
Also, with the throttle plate removed, I have examined the thread ends of the screws which attach the blades to the shaft. The ends of all 4 screws have what appears to be virgin factory undisturbed peening.
HI Tom. I looked at mine (1961 270 HP) and it is like yours. The rear carb air flaps have the slight gap, the front carb does not. My gap is about 1/3 what yours is, though. I have run this set-up for the past 4 years without issue. Great idle quality, great throttle response and performance. My throttle shafts are original as are the screws.....not messed with. So, I would bolt them on and run them, personally. If you have an issue, easy enough to pull the rear carb and tinker with it. Odd how the front carbs don't have a gap. I certainly am not going to mess with mine. Good luck.
Jeff
OK, thanks. Good to know that. I've concluded that since they worked fine on a 327 30+yrs ago, I'm going to just go with them. I'm anxious to see how the 389 works with them.
The block is cleaned up, everything looks good, the new pistons are pressed onto the rods and the rings are installed.
I just got to get motivated to put it all back together. It only took 6yrs to get the 51 off the lift and tear into the engine.
04-23-2019, 10:53 PM
Question about something strange on my front 2x4 carb.
I'm not sure what you would do to correct it that might not be more trouble than its worth, possibly with no discernible effect...
