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Hey all I have a 307 that has been bored 60 over with a mild cam. I have a 670 street avenger that I just swapped jets on today. I have been having issues when I'm deep in the throttle and shift to 2nd it wants to pop through the exhaust and sounds like ****. Also it is gas smoking at idle so I changed the primary jets from 65 to 62 and the secondary from 68 to 65. I haven't got to drive it yet due to trying to find parts for new shifter but it still seems to be gas smoking. Also was curious what base timing should be. Right now I'm at about 10. The mixture screws are set at 1 1/4 turns out. Thanks
 

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Start with getting idle right. If you turn the idle screws in, does it stall? If not, you're throttle is too far open at idle and your pulling fuel from the transfer slots which causes a rich condition. You can try advancing the timing a bit to bring up the idle speed, so you can close the throttle some. Did you disconnect the vacuum advance when you checked timing? If not, you're timing is way retarded. If you are running a stock distributor, 12 degrees at idle should be about right. If you can check advance at around 3000 rpm, You should be around 36-38 degrees. Jet changes shouldn't affect idle much, they are more for driveability. If you're deep in the throttle and it misfires, you likely need to go to a bigger secondary jet. Misfire is usually because you are lean. If I was taking a stab in the dark on jets for that car, I would probably go 68 on the primary and 72 on the secondary and adjust from there, or whatever it came with stock, then adjust from there. If you have a vacuum can on the distributor, it should have a number you can see like 15, or 20, or 25 on the can bracket. That tells how much advance the vacuum can will add. If it's a 25, you might want to limit vacuum advance some. Summit sells a kit for like $3. A good investment.
 

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Start with getting idle right. If you turn the idle screws in, does it stall? If not, you're throttle is too far open at idle and your pulling fuel from the transfer slots which causes a rich condition. You can try advancing the timing a bit to bring up the idle speed, so you can close the throttle some. Did you disconnect the vacuum advance when you checked timing? If not, you're timing is way retarded. If you are running a stock distributor, 12 degrees at idle should be about right. If you can check advance at around 3000 rpm, You should be around 36-38 degrees. Jet changes shouldn't affect idle much, they are more for driveability. If you're deep in the throttle and it misfires, you likely need to go to a bigger secondary jet. Misfire is usually because you are lean. If I was taking a stab in the dark on jets for that car, I would probably go 68 on the primary and 72 on the secondary and adjust from there, or whatever it came with stock, then adjust from there. If you have a vacuum can on the distributor, it should have a number you can see like 15, or 20, or 25 on the can bracket. That tells how much advance the vacuum can will add. If it's a 25, you might want to limit vacuum advance some. Summit sells a kit for like $3. A good investment.
Thanks for the reply! I do know when the screws are turned in it does not stall it actually raises the idle speed. I have tried this by adjusting one screw until the idle starts coming up and then match the other three but it still seems to gas smoke and smell super rich. My msd distributor doesn't have vac advance. I messed with it last night and advanced it by hand and raised the idle but wasn't sure how high was too high for base timing. I will try messing with the timing some more and look to adjust jets back. Thanks!
 

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Base timing can be 20 degrees, no problem, but if you advance it that far, you may have too much timing in it under load. You really need to know how quickly the timing is coming in as rpm goes up, and also how much you have when all the mechanical advance is added to the base timing. A timing light with adjustable timing is what you need to find out, unless you have a harmonic damper that has 0-40 degree timing marks. You can also buy a sticker for your damper that has the timing marks on it.
I would add just enough timing that so you can close the throttle down enough that the engine will stall when you turn the screws in. Then drive it a bit. Get it warmed up and listen for spark knock under load, and also do a few hot restarts. If it is difficult to crank during a hot restart, you know you have too much base timing. Let us know how that goes. My guess is if you go back to the jets you had(maybe a few sizes richer on the sec to cover the 1-2 shift issue), and get the idle right, it will run like a champ.
Also, if you put all your specs, like the cam, rear gear ratio, trans type, intake model, headers, dual exhaust, and all that sort of stuff, there are people on this site that can tell you how to jet that carb, and recommend other things that will help you.
 

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Discussion Starter #5
Base timing can be 20 degrees, no problem, but if you advance it that far, you may have too much timing in it under load. You really need to know how quickly the timing is coming in as rpm goes up, and also how much you have when all the mechanical advance is added to the base timing. A timing light with adjustable timing is what you need to find out, unless you have a harmonic damper that has 0-40 degree timing marks. You can also buy a sticker for your damper that has the timing marks on it.
I would add just enough timing that so you can close the throttle down enough that the engine will stall when you turn the screws in. Then drive it a bit. Get it warmed up and listen for spark knock under load, and also do a few hot restarts. If it is difficult to crank during a hot restart, you know you have too much base timing. Let us know how that goes. My guess is if you go back to the jets you had, and get the idle right, it will run like a champ.
Thanks for the info! I sure will.
 
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