FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Thumperbird on June 10, 2018, 08:12:36 AM
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Background:
445 stroker, lightly ported edelbrock heads and RPM dual quad intake, maybe 3 or 4 hours run time so far.
Moderate cam with 6 degrees advance built in, about .560 lift.
1. Idle is a little rough, Air/Fuel ratio seems to bounce around quite a bit at idle (1 to 1.5 counts), I can affect it between say 12 and 16 with idle mixture screws but never really settles down, smoothest idle comes from screws 1/2 turn out and roughly 15:1 A/F but it is not smooth at any setting really
2. It seemed to get up and go OK with 18 degrees advance at idle, 1 heavy and 1 light silver spring in distributor, black bushing, but idle advance bounced around a bit, should I worry about this? Thought that was partially responsible for rough idle?
3. Went to 20 degrees initial (idles a little better) and 2 heavy silver springs, initial timing bounce calmed down but does not respond nearly as well, almost hesitates when I get on it.
4. Idle vac is a little under 10 or so, was trying to get that up a bit to make it easier to set the trans modulator. Had to turn the screw in a long ways to try for more crisp shifts to compensate but ended up with no 3rd gear.
Thoughts on these items?
Thanks.
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I should also mention that I changed the accelerator pump nozzles from .025 to .032, can definitely tell it is a larger squirt, not sure if this is playing in to the worse response or not.
Should also mention it comes to life at 4K rpms's, used to be lower rpm's, makes me think timing is coming on too late now?
Thanks.
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First, to comment on your 15:1 idle, I'd ignore that first, with decent overlap on a performance cam, and O2 sensor has no idea what's going on in the chamber and tends to read lean.
Second, I think you need to take this in chunks. Set timing to a standard curve and leave it alone, then move on to the carb problem. I would say that to rule out any ignition curve issue, I'd put that setup at 18 initial, 36 total, all in by 2700, and nothing coming in at idle. For troubleshooting, run without any vacuum advance if equipped for now. That setup should do everything you need it to do and allow you to focus on the carbs
Third, I think you need to get your idle right. Setting the primaries then equally adding idle to the secondaries to get idle speed to where you want it will help you greatly. Adjusting a/f on both carbs as required and resetting idle as required, soetimes youll have to tweak both a couple times as you change secondary plate location This of course assumes you have good carbs and no internal problems
If at that point, the idle isn't good and the vacuum gauge is bouncing, you likely have a tight valve, a valve or two not seating, or a vacuum leak. If the idle is good, and you have issues at WOT, which I suspect you won't, you can start looking at the main and enrichment circuits
I think if you don't do this in order, I think you'll be chasing too many variables.