And here's a WOT pass, right after the previous light acceleration pass.

Try the middle hole for pump shot, and double check the measurement from top of stem to air horn. Definitely going lean on the tip in. It would really be sweet to see throttle position, that definitely shows a bit of information. You might need to increase the size of the nozzle (and amount of pump shot accordingly) to keep it from leaning out. As the book says, go for the minimum pump shot to get you accelerating correctly.

For the accelerator pump, if the middle hole doesn't get rid of the lean spot, I may need to go to a smaller squirter to lengthen the duration of the shot, right?

The only thing I've seen in regards to measuring the accel pump (on an Edelbrock vs Carter) is someone mentioning to make sure at full throttle the pump is all the way down, and to bend the arm to make that adjustment. Which I guess does make sense to me; make sure you have maximum travel and that it doesn't pump air at the top of the stroke.

I had thought about how nice it would be to have throttle position, but have yet to find a good way to connect a potentiometer to the throttle shaft. Instead I came up with the vacuum idea, which has actually been quite useful as well.


As for the cruise AFR; am I ok as long as I don't feel any surging or bucking? I can richen that up a little, but figure if it's running fine and I won't burn a hole in the pistons... might as well stay where it is and enjoy the (mild) mileage gains.

If moving to the middle or even back to the top hole doesn't correct the lean spot, you might need to increase the nozzle size so it discharges fuel faster. It really depends where the lean spot is and how long it lasts. If it feels like a 2 second hesitation, then a smaller nozzle would cure it by lengthening the shot. Full throttle bog would probably require more fuel faster, so bigger nozzle and higher up on the hole. To start, I would put it in the middle hole, and check to see if the pump shaft top is 13/32 above the air horn so you know you are starting at factory spec and continue from there.

Cruise AFR looks ok. I run 15-15.5 and it doesn't surge in my W350 with TBI. I notice about 17 or so is when it feels like it's going to fall on it's face and starts bucking a bit.

If you are goig to be pulling that trailer,I would richen up the part throttle mixture. You will lose torque a lot faster on the lean side of stoich. Add in the fact that you are tuning without a load right now,you will have more throttle opening(less vacuum) while pulling your trailer. Just hate to see you go too lean and hurt something.
Keith

Earlier today I put 70-52 rods in (one step richer on cruise).

Much much better overall. I still have a lean spike off idle at low acceleration that I can barely feel. I'm thinking a smaller nozzle will extend the duration of the shot, and should probably cover that?


I've also noticed at part throttle in enrichment (under 5"hg), the AFRs are mid to high 12s. At WOT, the AFRs are in the mid 13s. I think this is saying it could use one step richer jets on the secondary side, right?

I think I'm nearly to the point where it will 'just drive'

Sure sounds like you are getting it dialed in! I should also mention that with oxygenated fuels that are at most places at least in this area,I have found that just about everything likes to be a little bit richer than what you would think.
The stoich numbers are different for different fuels so you have to adjust accordingly. I know some guys are trying to lean everything down for mileage these days but fuel qualities vary and it can be frustrating when you fill up out of town and get some fuel that makes you get lean surging and pinging all the way home pulling a trailer.
I would fatten it up a tad more.

Keith

So that stumble I've been chasing

Finally got time to hook up with Jeremiah yesterday and take him for a ride to see what he thought. The off idle stumble I thought was fuel related, he thought was ignition related. He had the electronic distributor and a spare box & harness, so a few hours later, the points distributor was out, and it was running.
Wow, it's never run this well before All of the off-idle hesitation/stumbles are gone.

So NOW I can finally get to tuning it

Currently running:
mid to high 13s at cruise (55mph, ~12"hg)
mid-high 11s at part throttle enrichment (I think this is still a little rich?)
mid 12s at WOT

If I floor it from a stop, I can see the AFRs go to mid 11s, then to 14ish (over the course of a second), then it evens out in the mid 12s. I think I still need a smaller squirter to lengthen the pump shot. Otherwise I don't feel any stumbles off the line. I can only see it in the log.

So, big thanks to Jeremiah for giving me the electronic disty & Orange box and fixing the issues I've been chasing for a few years now

Excellent info!

Your cruising a/f might be a tad rich but you won't know until you try. I would suggest low to mid 14's for cruise.
Your mid 12's sound good for WOT and this should be your richest a/f reading. Your 11 readings for enrichment are too rich. I would suggest making your part throttle enrichment a/f numbers be in between your mid 12's for WOT and 14's for cruise. The enrichment numbers may vary pending on the seat of the pants feel of the driver.
My cruise numbers from 30-70 are currently at 13.6 to 14.6. My enrichment for light throttle is 13.8 to 14.2 and my WOT is 12.8 to 13.0.
Each motor combo will be different, but over the last year of driving with an a/f sensor, the above numbers are what my current combo and my butt-ometer feel are good driving numbers for my car. Hope this helps.

Got some more testing done. Current set up is:
95 mains
101 secondaries
68/52 rods
orange springs

Cruise is mid 14s
Part throttle enrichment is low to mid 12s
WOT is 14ish
(Remember, I'm at 4000' here)

Other than the weird WOT numbers, I'm pretty happy with the driveability and overall tune. I guess part throttle enrichment could probably be a little leaner.

I think once I get everything dialed in, I'll keep a second set of rods that are a tad bit richer for the rare times I do have to tow something. 98% of my driving is highway just moving things around.

Your definitely making the correct changes. Your numbers are falling right into place.
I would suggest that you tune the part throttle until it "feels good". I played with mine from low 14's to low 13's and it felt better/crisper in the upper 13's to 14.0. Your low to mid 12's (part throttle) is where you might end up for a WOT reading, so once you lean the part throttle out your WOT will go even leaner, so be carefull.