Hi, I just swapped my 350 for a 1971 455 in my 72 Skylark. I had a new carb on the 350 so I put that on the 455. I have the new engine running but I am getting popping though carb mid-throttle. Seems to clear up at WOT but it seems down on power. Timing is at 8 BTDC and steady. Idles nice. Tried running without vacuum advance and that didn't help. Could the smaller 350 carb cause this? thanks, -Dan
The carbs are designed and calibrated for each engine so no the 350 carb will not work properly unless it is taken apart and completely modified. It is much easier to just use a 455 carb.
thanks the engine came with a 7044240 ka carb (ran worse when I tried it) That should be a 74 carb for a 455 If I rebuild that one should it work on my 71 455?
7044240 is a 74 455 carb so sure rebuild that one and you should be good! I only use the rebuild kits from Cliff Ruggles as most of the rebuild kits do not stand up to modern fuels.
It's NOT just a matter of rebuilding. You'll need/want to alter the fuel curve as well. Unless you calibrate the carb to your engine and application, you're likely to be unsatisfied with the power or the driveability, or both. This will screw-up the emissions calibration, but the carb is spec'ed for an application with EGR which you won't be using, so emissions calibration won't do you any good anyway.
Yes, the 350 carb is calibrated completely different. It would work fine with some major changes in the circuit. The 750 cfm isn't your problem. The 455 carb you have is a great carb. 800 cfm and originally set up for the Buick 455. Should have 73 jets, CT secondary rods, and .033 or .032 idle channel. Setting it back to stock will be very close to what you need if your new 455 is stock. If you have cam, headers and other things, it will need a few more alterations to work best. If you are ding it yourself, get good parts, like from Cliff mentioned above. I now, always replace the jets and primary rods, front choke pull off and power piston spring in all my builds plus all the normal items and recommend that. Always best to rebuild the baseplate with primary throttle bushings. And the air horn to replace the plastic cam for secondaries. At least half that I build are broken. Bottom line, stick with that 7044240, it will be a great carb for any Buick 455.
Thanks! I am on a budget so I am going to rebuild it and take it from there. I don't know much about the engine other than it had port work. It was a craigslist deal so I am happy it runs at all although the I was told it was just rebuilt and has ported heads. I was wondering if the 350 carb could be causing my carb pop at mid range but I guess it's anyones guess.
Sounds like a lean condition to me. Quite likely the 350 carb is running leaner than the 455 likes. They have those CZ secondary rods too so even at WOT it would be pretty lean, possibly accounting for some of the down-on-power feel. Check for vacuum leaks too that could lean out the mix. Go thru the 455 carb and get it on there it will be much happier
If I'm not mistaken, the '74 carb you have will be set up for a car with EGR. I don't think it will work properly on a 71 non EGR intake. Especially part throttle. Also, the '71 heads should have smaller chambers than the '74 heads, that will also affect carb specs.
Could still have problems with a used engine.could be some cheap rebuild or flat cam.Got to be a reason they gave up on engine.
