Guest Posted April 21, 2002 Share Posted April 21, 2002 I've got a 1970 Monte with a 350 44bl Q-Jet (300hp). I screwed the mixture screws all the way in and backed them out 4 turns each. Then I pulled the vacuum advance lines and set the car in drive and adjusted the idle speed to 630 RPM (per manual with car is at operating temp). Then the manual says to screws the mixture screws back in equally trying to obtain 600 RPM. I got no response at all and eventually screwed both mixture screws all the way in and it was still at 630 RPM. What gives? Thanks, Allen Link to comment Share on other sites More sharing options...
Ben N Posted April 21, 2002 Share Posted April 21, 2002 Allen, Sounds like the float might be stuck. Or the needle inside the carb might be stuck thanks to "white death", if the car has been sitting for a long period of time. My guess is a stuck float, because you were able to get it running. Good Luck! ------------------ Best Regards, Ben http://thenunz69.tripod.com/ Link to comment Share on other sites More sharing options...
Guest Posted April 21, 2002 Share Posted April 21, 2002 Sounds typical for a Q-jet. When this happens to me, I take it apart and blow it out. You can use carb cleaner to squirt into the passages. Ideally you should soak it in carb cleaner. I don't bother with a kit unless the gaskets or the acelerator pump is bad. After doing this you "must" blow it out with air. Wear saftey glasses as you dont want to have the air blowing stuff in your eyes. If you have never rebuilt one before, it can be very tricky to get it back together. The passages in the bottom of the carb get coroded/dirty and the fuel/air no longer flow properly. The mixture ideally are set at about 1 1/2 turns out. Or with a good working carb, where the engine runs smoothest at idle. ------------------ George Lines [This message has been edited by George Lines (edited 04-21-2002).] [This message has been edited by George Lines (edited 04-21-2002).] Link to comment Share on other sites More sharing options...
Guest Posted April 21, 2002 Share Posted April 21, 2002 Thanks guys. The carb, as far as I can tell, has never been out of the car. I'm afraid if I take it apart, which I've never done before, then I'll have trouble trying to get it back together. I'm betting the gaskets will come apart also. Is it possible to remove just the top part and get at the float. Maybe you could recommend a good Q-Jet rebuild book? Thanks again, Allen Link to comment Share on other sites More sharing options...
Guest Posted April 21, 2002 Share Posted April 21, 2002 Hey, Allen--> Ever build model cars when you were a kid? The Q-Jet's not much worse, as far as difficulty goes. A rebuild kit comes with instructions. If you're careful and pay attention, you can do it. I did it with no previous carb experience at all, and it went fine, except that when I put the carb back on the engine, I couldn't the idle to come down for anything (sound familiar...?). It turned out that for some reason the "fast idle screw" was screwed way in and throwing everything else off. So before you start looking into a rebuild, I would suggest that you check the fast idle screw. I THINK it's tucked away behind the choke linkage on the passenger side of the throttle plate (at the bottom of the carb). Make sure that it's backed out to a reasonable position. I'd check that first just because it's gotta be the easiest thing to do. Then, go ahead and try what everyone else posted. Good luck! Link to comment Share on other sites More sharing options...
Guest Posted April 21, 2002 Share Posted April 21, 2002 Gotcha. I checked both my manuals and they tell me exactly how to adjust it. Unfortunately, they don't tell me what the RPM speed is supposed to be for the "Fast idle setting"? HELP AGAIN! Thanks, Allen Link to comment Share on other sites More sharing options...
wallaby Posted April 22, 2002 Share Posted April 22, 2002 The Q-jet is notorious for developing leaks from the well plugs. They drill passages durring manufacture, and close them off to the outside with soft metal plugs that tend to lossen over time. The darn things are located under the fuel well portion of the carb, and the baseplate with the throttle butterflies will have to be removed to acces them. They recomend that they be repaired by using epoxy to cover them up. The darn things leak fuel, and even if you shut off the flow with the idle screws, the engine keeps going. Get a rebuild kit, and do the plugs while you're at it. Link to comment Share on other sites More sharing options...
Guest Posted April 22, 2002 Share Posted April 22, 2002 The Q-jet is notorious for developing leaks from the well plugs. Absolutely correct. I completely forgot about these, and I just rebuilt a Q-jet for another member and changed these out. The new plugs should have O ring groves on them for better sealing. Any parts store should have these, they come as a separate kit, you need to know what size your old ones were. When you remove the base of the Q-jet, you can tell if the old ones were leaking. ------------------ George Lines [This message has been edited by George Lines (edited 04-22-2002).] Link to comment Share on other sites More sharing options...
Guest Posted April 22, 2002 Share Posted April 22, 2002 HP books has a great book on Q-jets. I can't remember what it's called, but I picked one up at the local speed shop for about $15. It is an invaluable guide when doing any work on a Q-jet. Pick one up and you will know more than you ever wanted about Rochesters. Link to comment Share on other sites More sharing options...
Guest Posted April 22, 2002 Share Posted April 22, 2002 The Q-jet is a good carb but after about 40,000 miles the nitrile plastic float can start to absorb some gas. Most of the time you wont notice it untill it gets pretty bad and starts to flood. The idle channel is located just below the primary throttle plates. Its possible that some dirt has got into the idle system but I would check the throttle shaft first. Grab the bracket that the throttle cable hooks up to and rock it back and forth. If the shaft has play in it, it will bypass air and not idle down as much as it should. This would be the only effect of worn throttle shaft bushings. Take a tiny squirt bottle of gas and while the car is running spray around the throttle shaft. If it idles up,there is the culprit.Also check the fast idle screw on the left side of the carb, back it off and see if it makes a difference.Make sure you dont have any vacuum leaks anywhere. Check your vac advance make sure its not leaking,, as well as the choke pull off and all vacuum lines. Any unmetered air will make accurate idleing a pain.Only the early Q-jets were prone to leakage in the metering wells. If yours has the metal lip rolled down around the plugs its probly not leaking. If you want to be safe and you have the carb down that far you can take an 8th inch rod and put a slight bend in the last 1 1/2" of it. Then,from the top put the rod in the secondary fuel passage and just tap the plugs out,grind off the peened material,clean the wells, put the plugs back in and J-B Weld them in place. Normaly the only reason to drill out the mixture screw orafice is if your running big cube motor. On a stock small block I think a factory size idle port is fine. Which is why Im thinking the shaft is worn. Sorry to babble on,hope you get it figured out Link to comment Share on other sites More sharing options...
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