Some idle issues with a 7041263

[Ncal71formula]

     I have a 1971 Firebird with a rebuilt 455HO engine. The engine is essentially a stock rebuild except for a high volume oil pump and a points eliminator kit in the distributor. I didn't have the original carburetor, so I bought a 7041263 which according to the seller was set up to function like the original 7041267. The carb then sat on a shelf for a few years before I used it due to a delay in getting the engine reassembled.

     I had trouble with it since the very first startup. Gas would shoot out of the float bowl vent when I tried to start it, and when it did run, the idle was rough and I had trouble getting the mixture adjustment to work right. The problem with the mixture adjustment was that to get the strongest vacuum at idle, the passenger side screw was turned almost all the way out, and the driver side screw had to be turned almost all the way in. Even at that setting the idle was still rough and I only got 16 inches of vacuum. The seller asked me to send the carb back so he could repair it, he later told me that the float was too high and it had idle tubes that were two small; he fixed both of these things and sent the carb back to me. The problem with the fuel shooting out of the float bowl was fixed, but the idle was still not right and the mixture screws behaved the same way as before. I contacted the seller again and he instructed me to block the "fixed idle air bypass" holes in the base of the carb. This did not fix the problem (though I did have to readjust the idle after this). I have also noticed that the airhorn gasket is wet when the engine is running as if it's being saturated with fuel. I tested the fuel pressure at cranking speed and I got between 5 and 7.5 psi.

     I'm not sure what to do next. I was unable to find any vacuum leaks, or any other problems with the engine mechanicals or ignition, so I'm thinking there is something wrong with the carburetor. It was freshly rebuilt at the time I bought it, but it did sit for a few years. Could that be the problem? can a 1263 really be made functionally identical to a 1267 like I was lead to believe? The engine seems to run fine at above idle speeds, but not at idle. I'm willing to disassemble the carb if it would help to find out the issue.  Any advice will be greatly appreciated.

[omaha]

I think that the fuel pressure is too high. you only need 4.5 (or less if you can get away with it).
Q-jets like lots of volume but not much pressure. I think I would go through it and check everything out.
Something is really funky with those mixture screws!  16 inches of vacuum is not bad really for a 71 pontiac though. Sure. this carb could be set up like the orignal but you need to know whats inside it. I'd at least get one of Cliff's needle and seats and accel. pumps and the top gasket. (you might as well buy a kit) (get the book too if you dont already have it).  It sounds like some blockage is in the idle circuit. I'm sure it can be fixed . Just my .02.             good luck, keep us posted.

[Cliff Ruggles]

Bad news is that the 263 and 267 units use different calibrations.  Good news is that the 263 can easily be set up to work flawlessly on the 455 HO engine, we've done quite a few of those as the 267's are rare and expensive in comparison.

It's going to need a lot more than just larger idle tubes to get it up to par, and we would install modern Viton parts at the same time for todays fuel and improved performance/efficiency, etc.....Cliff

[Ncal71formula]

Thanks for the replies so far. It's good to know that I might have a carb that I can use.

I decided to take apart the carb today, and here's what I found:

Main jets are marked "73"
Main metering rods marked "39"
Secondary rods are marked "cc"
The float is marked "1080 k84"

are these the correct parts that should be in there?

I also noticed a few things that seemed wrong.

First of all, the plastic retainer on the power piston is cracked and a chunk is missing. I also noticed that one of the idle tubes looks like it might be damaged. The passenger side idle tube looks like it was pushed down in the middle, as if someone tried to drill it out or remove it before, it definitely doesn't look right to me. Another thing that looks wrong is the opening in the throttle body for the ported vacuum. It looks like somebody drilled a small hole next to the original opening, it's rough as if the drill bit slipped. I'm not sure if this is factory or not, but it is above the throttle blade and doesn't appear to affect the sealing of the throttle blade.

I'm thinking that the damaged idle tube might be the source of my problems, not sure about the other two issues.

[omaha]

hopefully the actual main casting has not been damaged in the area of the idle tube. The idle tube is pressed into a collar at the  top. then both are pressed into the casting. if you can get the collar out, as long as the casting is not too screwed up. usually a new idle tube and collar can be pressed back into the main casting.  be aware of the small ridges, they should be intact around the idle tube area. the other small hole drilled  next to the ported vacuum can be filled.

[Toronado]

Sounds like you got a BAD unit and the seller
is full of it, why not avoid future problems &
by a rebuild kit and book from Cliff it
is only correct way to fix the problems since
there are several problems. Or send
it to Cliff if you have time to wait for rebuild by a pro. Allso sounds
like the power piston is the main cause of the problems.

[Cliff Ruggles]

Our HP rebuild kits come with new idle tubes, and the plastic collar for the power piston, as well as everything else required for a complete/correct rebuild.....Cliff

[Ncal71formula]

Just an update here,

I bought a rebuild kit and some idle tubes from Cliff, and rebuilt the carb. I'm getting higher vacuum now and the idle screws are both about 3.5 to 3.75 turns out and much more responsive. The idle is also a bit smoother and it's not running as rich as before.

However, the airhorn gasket is still wet with gas like before but worse, it's actually dripping down the side of the carb! (to be exact, it's around the front of the carb under the bowl vent and extends to about halfway around the drivers side). I noticed that my airhorn is warped a bit and strangely enough, the gasket that was on the carb before is thicker than Cliff's gasket from the kit. I guess the seller knew about the warped airhorn already and thought a thicker gasket would help. 

So, is there anything other than a warped airhorn that would cause gas to leak out this way?

[Cliff Ruggles]

We have gaskets that are .015" and .030" thicker than the stock gaskets for that carburetor number.

I would recomend to flatten the front of the airhorn slightly with a belt sander and go to a thicker gasket. 

This will make sure it seals up effectively between the two parts......Cliff

[Ncal71formula]

Ok, I'll try to sand it down a bit. Would it be ok to just use two gaskets? The gasket that was on there before seems to be in good shape.

[Cliff Ruggles]

Two gaskets is just too thick, and I don't like doing this.  We have .015" thicker gaskets that are made of a very good material, and .030" thicker as well.  I very seldom use the .030" thicker ones, the .015" are usually fine for what you are trying to do.....Cliff