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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
I just recently purchased a 1985 Z28 with 42000 miles. I prefer to keep the car mostly stock, but I need a new carb for it.
The number on the carb is 17085204. My question is should I just go with a rebuild or swap in a Holley? I am more,
interested in low end performance and not high end. I cannot find anywhere what the CFM rating is for the Rochester.
Is it 600? If I go with a Holley any recommendations? According to the CFM calculator tool it recommends a 450 CFM,
based on 305 CI and 6000 max rpm. any advice is appreciated.
The factory Q jet is a 750CFM. You can either rebuild or buy a rebuilt one. Rock auto is one option but you can look around. There is no good reason to swap to another carb on a stock or near stock motor
Q-Jets don't have "CFM ratings". Wrong question to ask. About like asking how many gears a bicycle for a fish has.
Which of course is NOT the same as saying, the "idea" of "CFM ratings" doesn't apply; of course, they have a flow capacity; just, the factory doesn't "rate" them like that.
The basic Q-Jet flows around 750 CFM, as midias pointed out. There were certain ones on early 70s 45x motors that had larger primaries and flowed closer to 850 but that's not going to be an issue here. The ones they put on 305s had a little "stop" that prevented the air valve from opening all the way, such that they flowed maybe 625 - 650 or so. FAR more than a 305 would ever need. Butt, that's what the air valve is all about: properly adjusted, it allows the carb to continuously resize itself to the engine's exact requirements, in real time, when the secondaries are open (the only time "CFM ratings" have any meaning anyway). The primaries alone flow around 180-200 or so.
The carb list # you posted looks like the exact right stock carb for a 85 LG4. 1708 = electronically-controlled Q-Jet, 5 is the model year, 204 is the application wherein 2 is Chevy, even #s like 04 are auto trans, and 204 is well and widely known to be the one found on LG4 w auto trans.
What makes you think you "need a new carb for it"? Like Tuned said, what you have can be rebuilt; and it'll be just like new, if it isn't already too far gone and the rebuild is done right.
The car is difficult to start and rough idle until warmed up. I took it to my mechanic who I have known for
20 years and has never tried to scam me and he said the carb either needs to be rebuilt or replaced. He
even offered up another shop that has a guy that is very proficient in Rochester carbs.
I just recently purchased a 1985 Z28 with 42000 miles. I prefer to keep the car mostly stock, but I need a new carb for it.
The number on the carb is 17085204. My question is should I just go with a rebuild or swap in a Holley? I am more,
interested in low end performance and not high end. I cannot find anywhere what the CFM rating is for the Rochester.
Is it 600? If I go with a Holley any recommendations? According to the CFM calculator tool it recommends a 450 CFM,
based on 305 CI and 6000 max rpm. any advice is appreciated.
Unless there's a cracked casting or unrepairable stripped threads on your original Q-Jet, obtain a copy of the Factory Service Manual (NOT Haynes, Chilton, or any other non-Helms pub) from ebay and a good-quality rebuild kit. For your application, there isn't a 'better' option than the carb the car came with from the factory.
Trying to swap-in a Holley presents a number of issues that you don't need to have to deal with on an otherwise stock engine. Additionally, 'rebuilt' carbs sometimes don't have the correct linkage or the right vacuum ports even though being claimed by the seller to be the correct replacement part.
I prefer Holley carburetors and that is what all my cars have, but that’s just it, personal preference. If you have a properly working Holley vs a properly working Quadrajet both cars will run amazingly.
I have only had the car for a month now. When trying to start the car in the morning, I either pump the accelerator 1 time or not at all and spin motor and no start. Shut the key off and spin it a second time with hitting the gas and it starts. Any other time of the day I try to start it, no problem just turn the key and no gas and it starts. ITs only after it sits overnight that I have the issue. And when it does start its very rough idle for about a minute. After that the car runs fine. I was told the carb needs to be rebuilt or replaced.
