Alright, I can get the car to start, but it's def gettin way to much fuel at idle and while running, to the point that it bogs. Tried messin with timing, but that just made things worse. And it's now to the point the car doesn't start. It's deff too much fuel cuz I pulled the plugs and most had gas, but all had a ton of carbon buildup. And the plugs have less than 5k on them. So how do I get the q-jet to lean out. I know the front 2 screws controll idle mixture, but does that also affect the mixture while driving?
leaning out a q-jet?
- Thread starter 413Cutlass
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first i'd try lowering the float or checking for a non-seating needle. if that's correct and it is a calibration problem, you change the rods and jets. smaller jet or larger rods.
I'm really not keen on taking the air-horn off this thing, it's abit older and worked just fine 2 months ago on a small block pontiac. It's just abit rich at idle, and I'm sure the bog at WOT is just because the secondaries need to be adjusted to open slower.
carbs generally need to be retuned when you switch engine sizes. i'm assuming you went from a 307 or 350 to a 413? the greater air flow will pull more fuel, if the idle mixture screws don't do enough then you usually have to go into the carb. if it has an APT adjustment it might help at part throttle. as to the secondaries, remember that the flaps at the top are mostly controlled by air flow (and the flap movement is what controls fuel, not the lower flaps), so time adjustment is minimal. you can try to adjust the spring tension or the vac pull-off. changing the air valve shaft cam might also help as a smaller one would keep the rods farther into the jets, thus leaner. if you PM 85cutlassbrougham he can help more as he's played with them alot more than me and may know some tricks.
honestly, if you want the best performance out of it, pick up one of Cliff Ruggles books on rebuilding and modifying them. he now also sells kits and is a great guy to deal with. he'll help you to pick parts and calibrations/mods. it's not hard to do and the q-jet is a lot easier to work with than most people think.
honestly, if you want the best performance out of it, pick up one of Cliff Ruggles books on rebuilding and modifying them. he now also sells kits and is a great guy to deal with. he'll help you to pick parts and calibrations/mods. it's not hard to do and the q-jet is a lot easier to work with than most people think.
yeah the carb was originaly on a pontiac 400 I think, it's now on my 307 since well it was a free non CCC q-jet.
Sounds to me that your carb needs to be overhauled. Without getting into detail, there are a number of things that could be causing the problem. I think that once you have gone over everything, you could eliminate one by one.
Was this carb working OK before and is this a new problem?
Was this carb working OK before and is this a new problem?
Generally speaking, Q-jets from a late 60's-early 70's big block are set up way too rich for a stock 307. From idle up to 2000 rpm or so, fuel metering is regulated by the idle mixture circuit and the primary jets. Definitely adjust your mixture screws. You likely will be able to go considerably leaner while still maintaining the highest vacuum / rpm reading at idle. However, a primary metering rod and jet change will likely be needed to really dial it in to your 307. I have not read the Ruggles book, but the book "Rochester Carburetors" by Doug Roe has been my Q-jet bible for over 30 years. I highly recommend that you find and read a copy. With some practice, and a few inexpensive parts, you should be able to dial in your carb for any engine. If you have a '75 or later carb, all the better. The leaner calibrations used to meet emissions standards of that era makes them easier to tune for a lower-power small V8.
Bill
Bill
well it's not from a big block, it came out of a trans am with either a 350 or 400, pretty sure it's later 70s too. And yes it worked fine on that engine, so I'm thinkin I need to just lean it out at idle a bit, and fix up my throttle cable linkage and make sure the tv cable is properly situated. Pretty sure it is since it never came off the bracket, only the carb, but I'll check it anyhow.
Just a thought but are you sure your Secondary Airvalve is opening? I thought the samething as you till I took it in to a guy that still races using QuadraJets and he notice that they were not opening and that is why I had no power at wot and why it was running rich.
He is a site with a lot of infomation and Tuning how to.
http://www.florida4x4.com/tech/quadrajet/index.php
He is a site with a lot of infomation and Tuning how to.
http://www.florida4x4.com/tech/quadrajet/index.php
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