Sam (Bones) Posted April 7, 2015 Share Posted April 7, 2015 I am usually very good with carbs, I have been stumped by an idle issue I just can't figure out on my numbers correct (7040203) Q jet, my idle will change from adjusted good to going rich, adjust it again and close the idle jets and it will stay idling, then is goes back to being lean where I can adjust the idle jets correctly, runs fine above idle, have changed the float, checked and rechecked the float level, for vacuum leakes this change isn't happening right away, sometimes it's fine until I drive it, other times the switch happens as I'm backing out of the garage Quote Link to comment Share on other sites More sharing options...
cny first gen 71 Posted April 7, 2015 Share Posted April 7, 2015 Do the springs on the screws have enough tension on them ? Maybe there vibrating and moving some, Just a thought. Quote Link to comment Share on other sites More sharing options...
Murphy Posted April 7, 2015 Share Posted April 7, 2015 Just a thought Sam, I had some irratic issues with mine also, even after the rebuild. I was informed by an older gent that my airhorn mine be slightly warped. He said to remove the airhorn and lay a straight edge across the bottom of the horn. If there was any gap, usually in the center area, I would experience problems due to leaking. Warpage of the airhorn is due to over tightening of the bolts over time. I performed this test and he was correct. I carefully filed the perimeter edges of the bottom of the airhorn until the gap was gone, you need to use a large file. Once the gap is gone, thoroughly clean the airhorn of metal filings. Also when reinstalling the gasket between the airhorn & the base, lightly cover the gasket with a white lithium grease on both sides. This will also help to eliminate any leaks and do NOT over tighten the bolts. Good Luck! Quote Link to comment Share on other sites More sharing options...
rsorg Posted April 7, 2015 Share Posted April 7, 2015 I also had the same problem ,car ran great but very erratic, My auto mechanic took a propane bottle ( unlit of course) opened the bottle a very little and while the car was running at idle he would slowly point the propane bottle at the base of the carb and if the idle would raise I new I had a vacuum leak, so i checked the plate with a straight edge ,which was fine.so I found a guy on the web that rebuilds q- jets and he replaced the brass bushings on the bottom plate , that will wear out over time , car runs perfect now . Quote Link to comment Share on other sites More sharing options...
Bluemalibu Posted April 7, 2015 Share Posted April 7, 2015 I concur with the rest Sam... classic symptoms of air infiltration due to warpage / wear / dried gasket /or a crack. The worsening symptoms after running a few minutes tends to make me lean towards warped mating edges or a crack, as the warming metal would open a fissure wider. I had one that started acting up (Surging due to a vacuum leak) that I rebuilt twice.... without success. I then turned it over to the best mechanic that I have ever met. He too struck out. The carb was mailed off to The Carb Shop, and after a month they contacted me, stating that they had completely gone through it three times; piece by piece, and could not find the source of the leak. They then offered to rebuild a replacement core for free, if I would send them one. Problem solved. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 7, 2015 Author Share Posted April 7, 2015 well I've found http://www.cliffshighperformance.com/ who specializes in Q jets, I've joined his forum too and he has given me a few things to check I would agree with you guys on the warpage and bushings but this throttle plate, shafts have no slop and this condition flip flops back and forth once it's warmed up, it just doesn't change I am going to start with making sure it has the correct float, correct gaskets, a quality needle and seat and see where it goes from there Quote Link to comment Share on other sites More sharing options...
Murphy Posted April 7, 2015 Share Posted April 7, 2015 Since you need to remove the airhorn to replace the float, you should definitely measure how flat the bottom is. I too have dealt with the guys at Cliff's inreference to my past issues............. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 7, 2015 Author Share Posted April 7, 2015 WOW! Cliff is a wealth of information, can't wait to get my parts from him I will check that too Murph Quote Link to comment Share on other sites More sharing options...
Murphy Posted April 7, 2015 Share Posted April 7, 2015 I also bought his book! Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 7, 2015 Author Share Posted April 7, 2015 is it as good as I think it is? Quote Link to comment Share on other sites More sharing options...
Murphy Posted April 7, 2015 Share Posted April 7, 2015 It's very good with lots of detailed pictures. One section was just on high performance mods.......... Quote Link to comment Share on other sites More sharing options...
GatorDog72 Posted April 8, 2015 Share Posted April 8, 2015 Could be leaky bottom plugs, that would cause raw fuel to drip straight down the manifold. When I rebuilt my q-jet, I used some JB weld epoxy to seal these up Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted April 8, 2015 Author Share Posted April 8, 2015 Already been repaired Quote Link to comment Share on other sites More sharing options...
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