Bluetooth O2 sensor and a carb

[Steeveedee]

Looks good! I'd never get into that area for an install, with AC and a BB. What carb are you running, again? A carb won't really give smooth transitions because of steps in the metering rods. Not necessarily a bad thing, just different.

[AcampoDave]

I have a 500 CFM Edelbrock pt#1404

[theastronaut]

Originally Posted by AcampoDave

Today I got it up and running. It works exactly as advertised. My steady cruise is solidly in the 14's. It's hard to be exact at any given moment because after the decimal, the AFR is bouncing around quite a bit. I saw it bounce occasionally into the low 15's as well as the high 13's but as an average the engine was cruising at about 14.5 or so. Foot to the floor got me to high 11's and my idle was rich, in the 10's. I adjusted the mixture screws and got that into the 14's with a few bounces to the 15's upon deceleration.

What do you guys think? It seems to me like I am well within the ballpark. I suppose seeing things more into the 15's at a steady cruise wouldn't hurt but going up one rod size on the primarys may just be too much. I dunno. I'll get some more behind the wheel time with it to get a better idea over a wider range of conditions. Could I also anticipate it leaning or enriching itself as air temps change. Today it was mid 70's outside

You can go 16-17 at light throttle/low load cruise if you have a way to add more vacuum advance at part throttle (and only part throttle). I believe you can get adjustable vac advance units for HEI distributors. Like the forum thread I linked before states, timing and afr are not independent of each other; when you adjust one you'll have to tweak the other a little.

I'm not familiar with your particular carb but if it uses rods that insert into jets like a monojet/quadrajet you can use a thicker rod and if its too restrictive/lean you can chuck it up in a lathe or drill and file/sand down the area that's too restrictive. I've done this with my Monojet.

WOT afr should be right around 12.5-12.75. Any richer wastes gas and the unburned fuel is diluting the oil on the cylinder walls. Running richer also makes the engine lazy, the added fuel cools the mix in the chamber and is harder to burn- hotter fuel vapor burns much more easily than colder liquid fuel. The forum thread I linked goes into a lot of detail about that.


Running at the "ideal" 14.7 isn't where you want to be at cruise, it adds unnecessary heat and uses more fuel than if you were leaned out to 16-17 with more timing. The unburned fuel at WOT (richer than 14.7) acts as coolant, as does the unburned oxygen at leaner than 14.7.


For idle, don't go by afr, use the "lean best idle" procedure described here, it will give you the most stable idle across varying temps/weather/altitude.

http://www.redlineweber.com/html/Tec...lean_best_.htm

[AcampoDave]

I've had more time to mess with things and I tried leaning the primarys out by another 4 percent. (I was already at 8 percent from its out of the box setting) but that was clearly too much. The truck ran poorly and AFR values were bouncing around up toward 17plus just cruising gently. I pulled my choke, it ran good again back in the 14s, so I dropped back to my previous setting and focused on the WOT where I was actually getting high 10's on the AFR guage with the out of the box secondary jetting. I leaned that by 4 percent today and was rewarded with a faster engine that was responding well to having an AFR bouncing around in the mid 11's with an occasional burst into low 12's. Sometime soon I hope to drive it into the mountains where I can climb steep grades and spend greater amounts of time with my foot to the floor. That should provide a better picture of where I really am. Blasting down country roads is really becoming a bit too much for my comfort (even with a 283). I'll let you know how it goes when I get to it again.

[AcampoDave]

Today I made that trip into the mountains. When I left home the ambient temps were in the upper 30's and I noticed that the AFR gave me readings higher than I expected like 17even 18 at cruise and it proceed to read too lean to become believable considering that the actual running of the motor did not reflect the lean values. After a while I stopped the motor and rebooted the connection and I was back to the readings I had previously become accustom to with cruising in the mid 14's. I'm not sure why it did that and I wondered if goofing around with the carb had caused a bit of crud to land in a primary jet and stopping the motor dislodged it.

Anyhow.... since readings had again normalized I performed a few full throttle blasts up some steep grades and saw mid to low 11's but as I kept climbing in altitude I noticed I eventually reached a point where my cruise had dropped into the mid 13's and WOT was getting down to higher tens and lower 11's. Time to turn back as I needed numbers which reflected where I live.

[AcampoDave]

As I came home I got back into the foothills and hit a bumpy road. I noticed how a good jolt to the suspension resulted in a rich blip on the AFR which I attribute to sloshing in the carb. I also noticed coasting down hill in gear provided a nice lean 17 up to 18 on steep declines but with all the trial and error I decided I had room to lean the secondaries by another 4 percent, which I did.

Now I'm getting the WOT numbers that I was looking for at low to mid 12's. The engine has really come alive from where it started. It even sounds different seeming more growley as it winds up faster than ever. It is actually rather exhilarating at wide open. A little ol' hot rod 283 giving its' all is a joy to behold.

Anyhow here's the final tally on the Edelbrock 1404: I leaned it 8 percent on both the primaries and the secondaries from its out of the box configuration, and I leaned the pump shot to the lowest hole. It would be the same with a 1403 as well since they are both 500 CFM and come jetted the same. The only difference is the choke.
I think it's fair to say that the 500 CFM Eddys are good carbs but they come jetted "pig rich". The application description says "For performance applications on 305 cu in and smaller or dual quad applications. "

If anyone has any questions that I may be able to answer don't hesitate to reach out to me via this thread or a PM, and thanks for reading my thread. I tried to keep it simple just using the calibration kit from Edelbrock and went for a close enough type of calibration. I never messed with the springs or tried to squeeze every drop by altering timing or filing rods as the Astronaut suggested although I'm sure there are gains to be made if I did. I'm just not patient enough for that but I appreciate his advice nonetheless.

The distributor is a "Proform" HEI and timing was set at 15 BTC, with my total at 29 all in by 2000rpm. My vac can adds another 19 on ported. I would like a few more degrees total but its mechanical limit is non-adjustable and getting the initial beyond 15 causes hard starting in the heat. I'll recheck those numbers pretty soon because the tach I had back then was really old (and the wife was watching it. )

Thanks for reading!

[Arne]

Hmmm. The 305 SB in my truck came to me with a 1405 (600 CFM manual choke) on it. I haven't had it on the road yet, but I have the feeling that it is too rich, and probably too much carb for a stock 305. I will probably need to lean it out similar to what you have done. Or maybe I should swap it out for a smaller carb.

[Steeveedee]

I had a '68 Skylark that I put a 305 SBC in, and had to slightly increase the out-of-the-box E-brock 1406 jetting, but then I had headers. It had a slight stumble that the jets and needles cleared up.

[Arne]

Originally Posted by Steeveedee

I had a '68 Skylark that I put a 305 SBC in, and had to slightly increase the out-of-the-box E-brock 1406 jetting, but then I had headers. It had a slight stumble that the jets and needles cleared up.

Interesting, and good to know. I also have headers, shorty block huggers. Maybe it is closer to correct than I think. Pretty hard to get any kind of feel for it when you have no exhaust beyond the aforementioned headers. That will be addressed by the end of the month.

[Steeveedee]

Originally Posted by Arne

Interesting, and good to know. I also have headers, shorty block huggers. Maybe it is closer to correct than I think. Pretty hard to get any kind of feel for it when you have no exhaust beyond the aforementioned headers. That will be addressed by the end of the month.

Yeah, headers change things a bit, maybe not much. You'd be best off to wait until the rest of the exhaust system is installed, I think. I bought the tuning kit that had jets, metering rods and springs, and ended up going richer on both rods and jets by 4 numbers each. Not a big change, but it worked OK, and I was getting 18.5 MPG on my commute, the afternoon of which was bumper-to-bumper from LAX up to about Sunset Blvd, on the 405. I'm sure the mileage would have been better if I could have jetted home like I went to work in the morning, which was pretty much 75 mph the whole way.

[Braunschweiger]

Thanks for sharing your experiences, I will do that when my truck is on the road, I have a 350 truck engine with 600 Edelbrock, let's see how it goes.

[AcampoDave]

Since I've made a few wide open blasts today, I pulled my plugs to get a color check. They have a fresh coat of a more grayish color. I could rub it off with my fingers back down to the chocolate colored deposits from before. Do you think I took the secondaries a bit too lean? Or is it normal?

[AcampoDave]

I've driven around quite a bit and the white deposit haven't come back. The plugs are staying very clean. I think the white stuff was from the lean condition I described in post #30. I'm gonna take another long trip when I get a chance and if I'm still looking at nice plug color I'll transfer the whole deal over to my stock truck with a 2-jet Rochester. It may take a little while but I'll get back to this thread and let you know what I find there. I think I bought the 2-jet decades ago as one of those Tomco rebuilt jobs from the auto parts store. It seems great but I'm curious to see the AFR on it. I'm sure some of you guys still run a 2-jet too so maybe there will be some useful info there. I don't know as much about those carbs as do the Eddy but I have rebuilt mine in the past so....like The Terminator "I'll be back."

[Braunschweiger]

I think the color of your plugs is okay, I should have kept an eye on the deposits.
You did a good job on that.

[AcampoDave]

Today the stock truck got it's turn with the o2 sensor. It has a stock 283 except for an HEI, dual exhaust and an ME Wagner PCV valve in the draft tube port. The old Rochester 2 jet dosen't have its choke connected, but after I got things warmed up, the first thing that struck me was how even the mix is at idle with the stock cam. It did vary slightly but hovered closely around 11.6. I brought that to 12.4 before it lugged a bit then I hit the road.

I was pleasantly surprised to see the numbers. It holds low 16's on the cruise and low to mid 12's when you gas it hard. It was easy to see the responsiveness of the little carb with changes in acceleration immediately having an effect on the AFR. The whole stock set-up gave such ideal readings that there really is no room for me to improve it. It's quite a testament to the accuracy of those early small block Chevy designers when you see it confirmed by technology that they could only imagine.