General Category > Quadrajet Carb Talk and Tips
17058213 carb
old cars:
So let's try this again. 7029207 carb was used on 1969 chevy 350-325hp vette #66 main jet 36b rod and correct if I am wrong had small air bleed of aprox .050" main body and .050" air horn. This would reflect the use of small jets. ( smaller main air bleed / smaller jet). In 1970 the chevy carbs starting using Larger main air bleeds . This is why we suddenly see larger jets .Example: 1970 chevelle/corvette 350/300hp 7040202 carb with #76 main jet 44b rod. Main air bleed aprox .112" main body and air horn.
The truck carbs of 1977/1978 used early style main body castings with a SMAB of aprox .050"
The question is (and I will try to put this politely) In first recipe of Cliff's book we have
Main air bleed (main body) .070 inch
Main air bleed (air horn) .070 inch
or
Single main air bleed: .045 to .060 inch
Main jet*: .071 to .073 inch
*For late-style single main air-bleed carbs with .060 to .080 nich main bleeds, use .074 to.076 jets
Being the 17058213 carb with SMAB .050" originally had #63 main jet and 40b rod going to .071 to .073 jet would be a huge step
So is this a typo in the book?
I am not looking for parts. I hope the is a discussion for learning purposes.
Than you
Cliff Ruggles:
Your answer is in my first response.
Some of (not all) of the 77-78 divorced choke non-CA emissions Chevy carburetors used an early single main airbleed design. They are somewhat rare so I didn't spend time covering them in my book as Car Tech limits both word and page count and I didn't want to waste a lot of time there. Bottom line is that they are excellent units. Downside is divorced choke and APT screw in the baseplate. For anyone building one I would leave the main airbleeds at the stock sizes.
I've also found virgin units with 64 and 65 main jets in them, so the factory may have been experimenting some with them during their brief run.
Interesting but the 7029207 carbs also showed up with main jets as small as 64 and as large as 66, but posted literature on them doesn't show this. So NEVER believer everything you "google-up" on the Internet.
Anyhow the 77-78 SMAB divorced choke models calibrate similar to the later design but having a smaller bore and different booster it's best to leave the small main airbleeds as-is and calibrate them per application. This is IMPORTANT because they use pretty large upper idle bleeds so already killing the transfer circuit some requiring improved fuel from the main system as low throttle angles/light engine load. As mentioned I highly recommend removing the APT screw in the baseplate and installing one of my adjustable APT screws instead. This makes they much easier to tune like the later SMAB models with the APT system in front of the power piston.......Cliff
old cars:
Thanks Cliff. Great info. So if I was building the carb as per First recipe in your book (mild 350 / 210 duration cam at .050" lift) would #64 jet and 36b rod richen it up enough or would #68 jet and and suitable rod get it closer?
old cars:
By the way I'm up in Canada (ontario) . Until this winter we were limited to 5% ethanol in gas. This spring new rules limit Ethanol in gas to 10%. I believe regular gas being closer to that limit. Our premium fuel I'm told is still around 5% ethanol. Wandering how that compares to other areas
Cliff Ruggles:
Don't be the first bit afraid of ethanol in the fuel. So many misconceptions about it on the Internet, like many other topics, and most of the folks scaring the chit out of the general public need to keep their day jobs and quit regurgitating inaccurate information on the subject.....IMHO.
I use it in everything here and have for quite a few years with zero issues. Just make sure that you address any potential long storage of it in a vented system as it will soak up some water. Also be aware that it doesn't like rubber, nor does it like "soft" blue accl pump seals, and will KILL buna rubber or neoprene seals (still being sold in many kits) in less time than it took me to type this. Hopefully you bought or are going to buy one of my rebuild kits because nothing else out there is going to hold up in that area. My kits are also more complete and much higher quality components than anything else out there. Not to mention I substitute high performance parts, such as smaller floats, larger fuel inlet seats and shorter accl pumps per request at no additional charge.
Ya, I know, sound like I'm "selling", which is true. I have to make money to keep the website open and feed my family, but also important is for folks to end up with good results with these things. I sell more accl pumps than I can count, and nearly every customer has already bought into the BS that the blue seal they got in their over the counter kit or from another vendor is "ethanol resistant". Mine is WAY more than that, it is lifetime warranty and to date I've never had to replace one.
....continued
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