Hey guys, yeap, it's me again...lol Alright, quick easy question I'm sure for many of you... The Z is finally on the road and running great, I however live in Aurora, CO, so major emission laws out here... Naturally I've restored everything back to the way she should be, computer, cat, pump, etc., etc... Well took her to the emissions place, she ran perfect numbers at idle, but when they accelerate and hold at 2500 rpm's, she came in a little high on carbon output (hence burning rich), but not by much, I'm alotted 1.20 and she ran 1.70... Of course this being the computer carb, it's not adjustable, which I'm guessing means that my timing is just a smidgin off... Which way would I need to turn it to lean it out a smidgin?... Anyone know what timing mark I should be at for my altitude?... Also, I'm assuming that to set the timing correctly, I should unplug the computer connect, time it, then reconnect, correct?...

 

Make sure your timing is right. It needs to be advanced at 2500 where it is failing. If that is fine then you are looking at rods if a qjet. 2500 is in to the main or cruise circuit, so idle circuit adjustments won't help. The CPU controlled qjets have rods that are controlled by CPU, but I didn't think those were till 82 or 83 for maro. Is there a vacuum or CPU advance on dist? Advancing will help, but be careful as you don't want too much initial. Does it have centrifugal advance? If so you could recurve to advance more in by 2500 and leave initial alone. You could also get a rod with a bigger end in cruise circuit, I think they still had those rod hangers on CPU carbs on back flap. You could do the quick fix and add two gallons of race fuel to 1/8 tank right before going to burn a little cleaner, but they would smell that. Let me know how it goes.

 

Yes, the distributor has the CPU control, officially the 1981 were the first years to come with the carbs and distributors across the board, at least for GM that is... I know that I'm just ever so sightly out of time, I'm just really not sure where it should be for my altitude to be perfect, I had pulled the cpu plug, tossed a timing light on it, the mark showed at the top left portion of the indicator on the block, is this retarded or advanced?... I'm thinking advanced is getting the mark more towards the right, correct?...

 

So when you state adjusting it at 2500, are you saying that I should unplug the cpu from, rev it up to 2500 and set it with the light at that point?... Any idea what advanced/retarded number I should be going for?... As for recurving the distributor, I really I'm exactly sure how to do that, but the engine is a 100% stock L81 from an 81 Corvette with appx. 83,000 miles on it, runs great, no smoke, so really trying to keep it at it's stock settings... I can however go ahead and replace the needles just to eliminate that as a possibility, and that's just removing the screw on top, pulling them out and putting new ones in, correct?....

 

And that's the needles that go down into the jets, yes?...

 

Richer burns slower so advance. Yes the rods go into the jets. When they are pulled up it allows more fuel to flow through jet. Bigger rod or smaller jet accomplishes same. Take your dist cap off. Does it have weights and springs? I think the first few years did. If so put lighter springs from advance curve kit you will have to buy for $5. That will kick in more timing sooner and initial will be the same. I would just try some race gas and see, then you got a year to figure out. Oh also leave the CPU hooked up on CPU controlled. You want to know what actual total advance is at 2500. I think it may not have centrifugal now that I think about it. I replaced carb and dist in my 84z. If it does try that. If not bigger rod then change back after test.

 

Well, adjusted the timing ever so slightly, it actually ran worse, but passed with flying colors, go figure...lol Thanks again for all your help, you are the man...

 

No problem, glad you got it passing. I know people who have a "special" carb they put on when they have to test. Then they swap back for more performance.