Going lean when shifting...

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7milesout said
  • On the primaries: Yes.
  • PCV hooked up: Yes.
  • PCV working: Dunno.
  • Automatic: Yes.
  • Headers: Yes.
  • Holding the gas pedal steady: Yes.
  • Only during the shift: No, but I was going to mention it later. It also does this same lean spike about 1.5 seconds after easing into the throttle from a dead stop. This could be a different issue. This could be a an accelerator pump duration issue. But if indeed the low throttle position is lean, then it may just be that the AFR is returning to it's pre-pump leaness.
  • Completely related is my theory. So fixing one, should fix both. Maybe
  • Intake manifold: I believe is the stock LA 360 manifold
  • At what rpm: It shifts at about 2,200 - 2,400 rpm. As I mention, I'm just easing it around when it does this.
  • Idle timing: Static 11°~12°
  • Timing Advance all in: ~2,600 rpm or so. I'm guessing it's the original distributor.
  • Cam Specs: Dunno. Slightly aggressive, not a big loper. Ok, got it, that's all I need
Your reading of my situation ... here's where I can identify possible differences.
  • Secondaries closed: Yes.
  • Metering rods down: I doubt it. I've got the biggest spring in there available from Edelbrock. At least I think it's the biggest spring (I'm starting to 2nd guess myself). The friggin colors are difficult to distinguish but I spent a lot of time staring all the barely different colors in an effort to try to choose the stiffest ones. And squeezed them too. That's not to say I didn't flub it up. But I was careful.

  • A1: When the engine is not fully warmed up, it tends to nose over. That's lean for sure Especially 1.5 seconds after gently accelerating from a full stop. Full throttle or just aggressive starts, this is not an issue. But the poe-lease around here don't like it when I do that. It noses over a bit at 1.5 seconds from leaving a dead stop, even when fully warmed up.this could be pump-shot

A) I sure hope my VA is not vacillating. Hey uhhh ... what's vacillating mean?
vacillate; To sway unsteadily from one side to the other; oscillate.

My vacuum gauge doesn't have a long enough hose to watch it while I'm driving. Guess I could just swing by Home Depot and correct that though. I'm just learning all this stuff, so, the screw inside (the distributor?) inside the hose nipple of the VA can. sounds difficult, because I've not done that or learned about that screw before. What does this screw do? it controls the amount of vacuum required to drive the VA to it's maximum value thus allowing full VA earlier to later.​

B) I'm assuming the PV system is the Power Valve? Does an Edebrock have this? The metering rods are your PV system. I've heard of this on Holleys, but not on Edelbrocks. Or maybe you're referring to the Power Mode portion of the metering rods. This is my leading theory, the rods are not pulled up out of the mains, or fall below the step when it shifts. And the AFR's go lean. I can feel the power loss, when just toodling along, slowly accelerating. I'm going to double check the springs I've got in there, make sure I have the stiffest. This may not be the best course of action. When you do this A) more fuel than necessary only costs you money at the pumps, and B)tends to wear out the engine faster. You want to run it as lean as possible yet be driveable,lol.

C) Not running a 3200 TC. Not full timing by 2,000 rpm.good/good

D) I would not worry about it either, if I weren't feeling it.

E) Not following the T-port. What is a T-port? Throttle port? Is this related to the screw you mentioned previously? Read about it here; AJ's guide to Transfer Port Synchronization; oops linkey no workey. Click on the link at the bottom of the post, with the blue M

Very helpful. Thanks for the info.


7milesout
Click to expand...

Ok well in your case
What is your idle vacuum, and at about what rpm does the vacuum peak? Stop if over 3600
I'm gonna guess it idles at 16 or more in Neutral, and peaks at about 2200ish
I usually start with the T-port sync first, but you're probably pretty close with 11/12 degrees of idle- timing. But Personally with the stock TC, I would slow the all in to somewhere just over 3000Rpm, But I don't think this is a contributing factor.
Outshifting this early, you'll probably be deeper into the throttle, so the PV system will probably be on line, AND the VA will probably be off-line.
What rear gear are you running?
The metering rods are your PV system. So at this point I would set the mixture screws to 1.5 to 2 turns out, and reduce the in-gear idle rpm by about 50 if required.Then get a longer vacuum hose and take her for a spin with the VA disabled, and the carb-port plugged.I usually use a wiper blade to hold the gauge in place at these low speeds. Notice the max vacuum just before the shift, and what it drops to.
Assuming no change,and with vacuum readings above 12 inches,I would remove the PV springs completely, and retest. This might make the car somewhat difficult to accelerate to the upshift speed so just take it easy until you get close, then level off at the previous vacuum reading as the shift approaches, and let her do her thing. Ok so no change means the mains are lean. You've proved it. Now it's just a simple matter swapping in rods with a smaller cruise step or a bigger MJ.
But before you do, I would verify that the fuel level is correct and that the fuel is fresh if it's oxygenated.
The fuel level is very important to low rpm/low throttle settings.If the level is even just 1/16 low, fuel pull-over from the low-speed circuit will be negatively affected, especially when the engine is cold. To thatend all tuning should be done with the engine fully warmed up and the engine should be running a minimum of 180*F, with 195* preferred. If your cooling system has problems at 195; fix it. The warmer she runs the leaner you can run it and the longer she'll last.Well that's a bit misleading, due to it being a run-on sentence,lol. Warmer engines can be run leaner, And then the engine will last longer than if it was running too rich;how's that?