So, I finally got my wideband O2 hooked up, and leaned it way down to where it is now. I also made an intake vacuum sensor that hooks up to the LMA-2 RPM thingy, so I have that logged as well.

'72 W200. Edelbrock 1406. Currently jetted with 0.095 mains, I think the secondaries are also 95s, 73/52 rods, stiffest step up springs. IMSs are ~1.75 turns out. Idles with 18"hg. New plugs. Initial timing is ~15ish, total ~35ish @2500. With vac advance it's hitting ~60* (). With vac advance unhooked it actually seemed to make my stumble worse.


At cruise it's running ~16:1.
Part throttle acceleration ~12-12.5ish
WOT 13.5ish (why it's higher than part throttle, I'm not sure?)

At very light acceleration it dips into the 11's, and has a pretty annoying stumble/hesitation, which is currently my main frustration that I've been chasing for a while now. It seems to clear up once the RPMs get a little higher, and with more throttle.

I think the stumble is a rich stumble, but I'm not sure how to lean that bit out any more. I had the Orange step up springs in and it made the light accel stumble horrendous. I saw it dipping into the 10s off idle

Any thoughts how I can get rid of that stumble before I have to pull a horse trailer next week?


FYI, attached is 'tunabrock.xls'. It's an excel file where someone entered every jet and rod combination showing the resulting areas for economy and power. Makes it easy to go richer/leaner in one mode or the other and know exactly what rod/jet to use. It has been VERY handy.

edit: ok, maybe I can't attach it. If anyone wants it, PM me and I can email it.

""At cruise it's running ~16:1.
Part throttle acceleration ~12-12.5ish
WOT 13.5ish (why it's higher than part throttle, I'm not sure?)""

I will say that your cruise number is lean, your part throttle accel is rich, and the WOT is a little lean. Try aiming for the 14's at cruise (maybe low 15's), the high 12's to the mid 13's for part throttle accel, and the mid 12's for your WOT and see how it acts.

Can any of the Edy/Carter guys help him out?

BUMP

Looks like you need to try a different metering rod size. The bigger the number,the leaner it gets. I would go for something around 68/52 if you have something close to that. Not sure what is in the kit,my sheets are out in the shop.
I like to get the metering rods sorted out as far as getting the A/F numbers I want, then work with the step up springs to get them working in the right rpm/throttle position range.
Keith

Do you have a 195 degree hi flow thermostat??
Today's gasoline requires it.

Typically too much gasoline collects inside the intake when using the lower operating temperature thermostat which makes it difficult to get consistent a-f numbers.

Yep, it has a 195 thermostat in it. I forgot to mention it also has a 1" 4 hole spacer

It does tend to run warm, but I think that's another issue entirely. I just need it to work until I can build the new engine and fuel inject it

Is the stumble off-idle or part throttle? Could be the accel pump nozzle having the wrong size. Sounds like it's dumping fuel if it goes rich, but it also could be too small of a pump shot if it goes rich then lean. You may need to move the linkage to the top hole for more shot and a smaller nozzle to allow that shot over a longer period of time. I'll brush up in the Carter tuning manual...

Float level becomes really important when using the top hole, because if the accel pump is above fuel level you will get air mixed in with the pump shot leaning it out. The nozzle only controls timing via length of shot, not pump volume which is controlled by which hole you are using.

If you are using the stiffest step up springs it will go into power mode faster which may be why it's going rich. I always use the orange springs but I'm also at 5000' so I get about 14" of vacuum here. You may want to try the pink springs first for your application.

There's a couple good pages in the Carter book. Let me see if I can scan them.

Page 1 of 3.

Sorry for the camera phone pics, scanner is more trouble than it's worth but these should be readable.

2 of 3

3 of 3

Wow, that was actually a good read and explained the stuff well.

Looks like I should probably back off 1 or 2 steps on the springs, and move the accel pump back to the middle hole (and maybe even the farthest hole).

I need to go get some stuff later today, so I'll test it then and report back.

1st, thanks for the file.

2nd, is there any chance you could explain the "area economy" and "area power" numbers and what they mean, or how to use those numbers to tune your carb ? I'm lost with that chart.

I understand using the o2 sensor and changing jets, metering rods, etc to get the mixture within a certain range so its not rich, not lean. But I dont get what this chart does or what I'm suppost to do with it.
Sorry, I dont have much experience with this.

The "area" is the amount of area left open after being filled with the metering rod. Let's just say .100 jet with a .070 rod would leave you a .030 area. It gives you a comparative chart of what rod and jet combination may best for your setup. Economy is the fatter part of the rod, and power is the skinny part which is when the step up springs push the rods up. The chart is in thousandsth of an inch.

Ok, I think I got it.

Thanks

Yep. Typically you would start with whatever jet/rod combo is 'stock', and looking at the chart, you can see the effective areas of each. More area = more fuel = richer.

Then to go leaner on say economy, you find another rod with the same area for Power, but smaller for economy. Or vice-versa to richer. Or, if you can't go leaner with a new jet, you can go to a smaller jet and know which rod to use to lean the economy side and keep the power side the same or similar.


Just got back from a drive. Before hand I moved the accel pump to the 3rd hole (farthest from body), and it got much much better. Then I moved to (what I think) is the pink spring. The springs are old and the paint isn't really there anymore

Still under very light throttle it's running in the high 11s:1 for AFR and popping lightly. Get into it more and it goes to mid 12s. So, I think I'm still hitting the enrichment circuit at light throttle, so I think I need to go to the orange springs and test again.

I've fought and messed with this carb for 5 years. Now a week and half after getting the O2 sensor installed it's almost perfect. Should've done this years ago

Going in the right direction!

Since you have a way to datalog manifold vacuum, check to see where the problem is. That will let you know where the enrichment is coming in, and where the springs needs to be.