so i rebuilt my q-jet carb as some may or may not know. got it all adjusted to factory specs and it runs great.. but if im cruising at highway speeds after about five minutes check engine light comes on with a code 45. o2 reading rich. so i got home parked in the drive way and reved it up to 2500 rpms and sure enough after five minutes check engine light comes up again. 45. what should i be looking at to adjust or fix? other than the check engine light and poor mileage the thing runs amazing

 

check your timing. for some reason u are getting to much gas or are not burning the fuel properly. float valve set right?

 

timing is spot on. went through and checked the float valve adjustment and the mixture control solenoid adjustment several times. mixture screws set at factory specs of 4 turns out and idle air bleed is at 3.5 turns out. am i missing something? im thining maybe adjust mixture screws a quarter turn at a time and see if that makes a difference.

 

there u go, try adjusting the low end mixture and see if that helps. what about the choke got it set right. could be its not opening all the way at operating temp, also the air cleaner, is it in good shape and flows good. ill tell u this much i dont like qjets and have done my share of rebuilding them. i like the edlebrock series carbs and have used them in replacing qjet and holly dpumpers.

 

choke is dandy. air cleaner is brand new. i would love to put on a new carb but cant because 1. in california smog laws require me to keep the stock carb on unless i upgrade to fuel injection. and 2. i dont have the money to do so. so i gotta work with what ive got

 

Oh yeah, now I remember why I don't like Quadrajets!
How big is your Q-jet, cfm's? You might want to jet it down some. Your secondaries aren't opening too soon are they? You can tighten the secondary tension spring if they are.
And fiddling with the idle mixture screws isn't going to fix your "rich at cruise" problem. As soon as the throttle plates crack open, the idle circuit is bypassed.

 

hmm...ok. ill take a look at the secondaries. is there anything else i should look at? i never got codes before the rebuild

 

As long as you're looking, check the choke butterfly spring too. If it's too loose, vacuum could be sucking it closed some as you're cruising.

 

ok. ill check that. anything else?

 

Maybe there's a prob with the timing...