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I have a 1970 Corvette 350ci/300hp, A/T. I purchased a rebuilt Rochester carburetor from a Corvette parts supplier back in 2012.
It was only recently installed on my 1970. There was a gasoline leak at the airhorn gasket... long story short, the airhorn had a prominent warp on it, and while trying to "fix" it, my mechanic cracked the airhorn.
I was able to source another used airhorn, but it is not exactly identical, but very very close.
I'm attaching a few pictures of my new airhorn (which is now cracked), and the old air horn that I want to use, and a picture of the new airhorn gasket, and the old airhorn gasket.
The only difference is where the pen is pointed in each picture of the airhorn. On the new airhorn, there appears to be a simple hole that is vertical... on the old airhorn, there appears to be a hole but on a 45 degree angle... and if you compare the 2 gaskets you can see where this difference exists where it's a "hole" on the new gasket, and more like a "tab" on the old gasket.
Basically my question is whether I can use the old airhorn on my new lower portion (bowl of the carb) with no issues? And would I need to use the old gasket if I use the old airhorn or can I use the new gasket on the old airhorn despite the fact that they are different where the circles are on the attached pictures.
Looks like I have my answer actually... I had sent this same information to Lars Grimsrud, and he said they are not interchangeable... one is for a passenger car, and the other from a truck and that they cannot be interchanged. Truck carb parts need to be used only on truck carbs - no parts interchange with passenger car carbs and vice versa.
From: At my Bar drinking and wrenching in Lafayette Colorado
The truck carbs use a different booster venturi design than the passenger car carbs, intended to provide a stronger fuel metering signal to the main discharge nozzles at low rpm high throttle opening conditions (such as when you're pulling a horse trailer up a mountain pass at 2000 rpm...). Mating up with this special booster venturi design in the float bowl is a special design of the airhorn. In addition to having a different venturi/booster design than the passenger car carbs, the truck airhorns and the float bowls have completely different air bleeds and fuel bleeds to tailor the fuel curve to these enhanced booster signals. Even the throttle plates have different sized idle air bypass bleeds in them than the passenger car carbs. Thus, none of the major components (bowl, airhorn or throttle plate) can be interchanged between the truck carb and the passenger car carb - it simply won't work. But even if the airhorns shown were both from a passenger car carb, it appears that the one airhorn is from a 1974 carb (the truck airhorn shown is a '74 light duty truck, or a late-70's heavy duty truck). Due to changes made every year in air and fuel bleed calibrations of the carbs, it's generally a bad idea to try to mix-n-match airhorn/bowl/throttle plate parts between years (even if they're both passenger car carbs) - it's a really good way to come up with a really screwed up carb. The commercial carb builders (like the "new" carb you have) do this all the time, and sell "mix-n'-match" carbs that are complete junk (as you have now experienced). The carb was junk before you broke the airhorn - you did the world a favor by getting a commercially rebuilt carb out of service...
How in the hell does one crack an airhorn? I just went through two of these carbs last weekend after 20 years of never seeing one and it was surprising how simple it was......you have to have three fingers to get the airhorn back on but it is how I remember it......if it plops down flat, how does one crack something?
Not that this helps your current problem but I do know Cliff Riggels (Cliffs High Performance) and maybe others use a jig that sometimes helps reshape the air horn.
I also know Cliff (at least for my 77 carb) offers a thicker than standard air horn gasket.
Standard & Thicker
I made the same rookie mistake too a couple years ago with a commercial rebuild off ebay. Since the '68 BB carb ending in 209 was around $1250, I opted for a restamp to at least have the car representative of what St. Louis installed.
This carb sucked.... it stumbled at idle even after warming up it ran rich to the point I had to change out all spark plugs and I crop dusted everyone behind me with white/black raw fuel smoke. I removed this carb and threw it in the **** can. I guess the garbage man has it on his dashboard lol....
I found from a local friend also on this forum a near new in the box Edelbrock 1901. it was a bolt on and go. I believe due to it's age now it needs the power piston replaced. I run WaWa or Speedway 93 octane fuels.
It was a $300.00 mistake, but a priceless lesson.
Marshal
Interchangeable Carb Airhorn?
