Interesting info:
Just talked with a guy from a carb shop who said that if I passed emissions, my jets are waaaay too lean for daily driving and could be even hurting the engine. He said most have a pair of jets sitting around for emissions, and a pair for daily driving, with the daily ones being much larger. He listed off several symptoms and they're exactly what I've been experiencing. Lean surge off idle, etc.

 

what size jets are you running now. I just changed out my stock 51's to 49's. the plugs and exhaust were all sooty black and was foulin them up. Put the new jets in and new plugs and it idles good. i havent driven it yet because im working on the body, but when i do what are the problems your having, and did they happen after you changed the jets. On my carb i have put #49 jets in, Stiffer 2nd spring, changed out the pump shooter to a .037 and the pump cam. Like i said i havent driven it since i did the jets and the pump cam.

 

I had the 49s in for a week or two after the emissions test so I could keep an eye on the O2 sensor readings and really get an idea of what was going on. Had a size .040 pump shooter with a pretty aggressive cam, and a dual stage powervalve that opens somewhat at 10.5vac and full at 5.5vac. The secondaries have the stiffest spring so I can get the primaries figured out.

No matter how I accelerated, whether a soft, gentle pedal or slamming the gas to the floor, it would stumble, hesitate, and then finally accelerate. If I stomped the gas with WOT, it would actually kill the engine. Whenever I would, the O2 sensor reading would bottom out at super lean. As I was saying, the guy at the carb shop was asking me if I was experiencing all of these exact symptoms before I even mentioned them.

To be on the safe side, last night I put in the largest jets I had on my shelf, which were 55s and it ran SO much better this morning. After driving it around with leaner jets for almost a month, it felt like I had my old engine back (fun!). They do appear a little rich on the O2 reading, so I think some 53s might be where it needs to be set.

As for yours with the 49s, it's hard to say. I'm at 2500 feet elevation and it's on average about 20 to 30 degrees out right now. If you're at sea level or 5000 feet, and it's 70 degrees, you might need something completely different. I know I will when the 100 degree summers hit.


The reason I was trying leaner jets was, as you said, the tailpipe was just caked in soot. I'm not sure what's up with that.
I'm almost wondering if the black soot might be cleared up with some hotter plugs. Thoughts on that?

 

It seems like these engines might like an AFR a little richer than one would think. I tried to lean my carb out by two sizes which would generally be appropriate on elevation alone but ended up going back to the stock jets and I get a lean to lean/stoich burn at cruise speeds. The blue cam on the #1 setting along with a shooter two sizes up covered the lean acceleration/tip-in problem for me once the jets were readjusted back up.

 

That's what I experienced with the 51's in it. It would idle okay but stumbled and had little power off idle (I had to feather it to get it to accelerate) Once I got the power valve to open (or it may be the secondaries) it would run great and had awesome power. Now that I went to the 59's I can't tell when the power valve opens.

I know it is somewhere between the 51's and 57's.

I finially have a day where I can take my exhaust off and get the bung welded on and the heated O2 sensor wired up.

I'm going to look and see if I can find some jets so i can play around with the carb.

 

At least you have your range, that's only 6 jets (about $40) to give them all a try and find which ones work best. If you have them all, you'll have the complete set for your engine and will be able to change them out for winter/summer/elevation, etc.

IF it were me (from my own experience), don't mess around and just get them all. That way you don't have to keep tromping to the store, waiting for them to come in the mail, etc.

I know what you mean about the PV. When I had mine lean, I'd watch the vacuum gauge, and have to hold the gas down until the vacuum dropped into the power valve and could feel an immediate burst of power and the engine would open up.

 

I'm heading to the exhaust shop now and will have the O2 sensor up and going this afternoon. Looking forward to see what the engine is doing.

I haven't called around too see if anyone around here carries holley jets or not. I have 2 box sets but they are all too big for what I need. Maybe I could find someone who would like to trade! LOL.

Update the post after I get the O2 sensor up and going.

 

Holley Carburetor Main Jets Demon Carb Main jets:eBay Motors (item 290375379327 end time Dec-05-09 14:17:03 PST)

That eBay store usually has listings for Holley jets starting at 47's. Not many if any parts houses carry the smaller jets if they carry any at all.

 

Thanks Harte3,

That's good to know where I can find what i need and get it all at once and save on shipping.

Got my exhaust and O2 sensor to install now. So got to go. Let you know how it turns out.

 

Well I'm good to go. The heated O2 sensor is working. I still have the 59's in it and it reads .98 volts. Way to rich. I'm going to get some gas and go to the store and see how it does once completely warmed up.

Going to change to the 57's and see how it does. Probably will still be on the rich side. May try the 51's and see just how lean it runs.

 

The real test you're looking for is while you're holding speed. Even with the 49s in, I would get a .95 volt reading while cruising, but realized I wasn't keeping at speed. Once I did, it would drop to about .1 volts and would stay there. The 55s are at around 0.85 volts at cruise.

Maintain several different speeds from 45 to 75 and note what the voltage is when cruising and pressure on the gas. You're looking for that perfect 0.5 volts.

Awesome on getting it set up!

 

Once I got the truck warmed up it changed a little. It stays between .85 and .88. Only time it drops below that is when I shift gears and then it comes right back up. It is very responsive, not much lag at all.

AbandonedBronco, is yours a heated O2 sensor?

I'm going to put the 57's in tomorrow and see what kind of change that makes, That's what I had in when I was getting 18.5 MPG.

 

Mine is a heated O2, but the heater wire isn't hooked up. I didn't know how to apply it. What kind of difference does it make that you know of? For all I read, it only made a difference for applications that were further away from the engine, such as behind a cat, but I could be wrong.
Was the 18.5mpg with the Holley 390?

 

Yea the 18.5 was with the 390 on it. The heated part gets the sensor up to temp so it will read accurately. I haven't tried it without the heated part.

I got on the electrical forum and the told me how to hook it up. Mine has 3 wires, There is the signal wire, which you already have hooked up. The other 2 wires are for the heated part. Doesn't matter which wire is for what. Just hook one up to a switched voltage source (turns off with ignition switch) and gound the other.

Took me about an hour to get the exhaust back on it and get the wires hooked up. I'm really satisfied with the results for what little money I've put in it. $6 for a sensor, $10 to weld bung on, $10 for the new digital multimeter.

 

wow with a 390 at 18.5 mpg thats awesome