Finally got a single-wire O2 sensor installed yesterday, and did some driving and watching. What a neat item! Things really start to make some sense. Besides wanting to do some "super-tuning", I have developed a "bit-o-bog" (that's BOG) in my truck, and am trying to approach this scientifically.
The questions I have: what readings should I get under cruise and acceleration with my 600 Holley/Edel Performer-equipped 390FE? And, should I tune for loaded conditions (camper, wife, and dog); or tune empty, and let the carb adjust as it's designed to under load?
Presently, my VOM reads .85-.86 volts at cruise (2300 rpm). When I accelerate, it drops to .02-.03 or so while the engine bucks and snorts and pops momentarily, and then jumps back up to around .81 volts +- and runs like a scared Easter Bunny on up to 5000+ rpm (and sounds REAL GOOD thru the open-element air cleaner I just installed ). From the www.bob2000.com Holley Tuning Guide, I'm a bit rich at cruise, and can't wait to see what leaning out can do for my mpg's! But it's way too lean at initial acceleration(I think??). Before I start tearing into jetting and acceleration pump circuit too radically, I'm hoping that you more learned types have some target values to share, and maybe some suggestions for incremental jet and pump changes?!?
KarlJay, that's your cue! :-) And I'm hoping maybe there are a few more of you out there with seat-of-the-pants experience too!
Thanks in advance, Steve

 

First put a vacuum guage on it and see where your vacuum is when you are cruising and under lite acceleration, the vacuum should not drop lower then the power valve rating, then the lean spot is from the accelerater pump shot is too lean, with holley carbs you usually can run a little more initial ignition lead, use the horse shoes to ajust the pump shot , on stock engines I've found the like bigger pump nozzels then holley puts in their carbs after that get the vacuum sec spring kit and get the sec to open as fast as you can without bog, then after that play with the jet sizes . record the voltages on cruise and lite accel then on heavy accel and WOT and only go up 2 sizes with holley jets , going up one size on holleys usually amounts to no changes.It may seem like alot of work but it it worth it. The autometer air/fuel ratio guage works great too

 

Sounds like you've found the problem, glad to see the O2 helped! This is sounding like a power valve - I'm not an expert on Holleys, but I think the power valve kicks in (adds more gas) then vac drops. And it sounds like this is not working properly. Holley is known for blowing powervalves when the engine backfires and I think most rebuild kits have a new one in them.

It sounds like it's really lean during this time and that wouldn't be a jet size thing, I'd think if the jet size were wrong, it would just be a little lean not a lot lean. Jegs just started selling a power valve protector that might be helpful for stopping the backfire - broken power valve problems but you do need to replace it to fix it.

I'd get a rebuild kit and check every single passage for clogs and check the vac secondaries for leaks, they have a rubber seal that can go bad and have cracks. I assume this is a 4v vac sec holley.

Let us know how thing go.

 

Thanks, men, for those good words.
I've had a vacuum gage in the truck nearly since it was new, so am well aware of what happens when the power valve kicks in (gas gage lopes rather than trots towards empty).
I pulled everything apart today for a look-see. The accel pump worked great, managed to squirt some gas onto the ceiling with the shooter and needle out! I bumped the shooter size to a 31 from the original 25, just for openers to see if that helps. The boss man on the Bob2000 site says my cruise 02 readings are not far off for a carbed engine, so decided to stay with the #63 jets for now. But I did install an MSD "Blaster II" coil to go with the old BorgWarner breakerless ignition, and I'm going to open the plug gaps to take advantage of the extra zap and see if that cleans up the combustion any.
Any suggestions on how wide to gap?.
The power valve is in fine shape; I installed one of those backfire blowout preventer check-valve gadgets a few years ago, so guess it has been doing its job. Watching the vac gage in coordination with the O2 sensor readout reveals that the power valve is coming in right on schedule, so don't think that's a problem. So, I'm still looking for something radically wrong but not finding it. I'm half expecting to see an improvement with the bigger shooter (please let it be so!). It's pretty strange to me that everything seemed to operate just dandy when I first swapped manifolds, and it's more than a bit frustrating that it isn't still. But that's how you learn, not when everything goes according to the book! I guess. :-)
And also on the bright side, the engine compartment is really looking spiffy with all these new brightly colored items!
Steve

 

With out knowing just how bad the bog is it is hard to say if going up a couple shooter sizes will really help. Mine was pretty bad. In no way could I push hard on the gas with out a problem. I went from a .25 to a .40 shooter (in steps), bought the accel pump cam kit and after all that I still had a bog. Started to get expensive and to be a pisser. After MANY emails with holley they told me about the 50 cc accel pump kit. Put it on and the bog was gone - fantastic difference.
This is on a 300 6 with a clifford manifold, holley 350 2 barrel, blaster II coil and MSD 6A ignition.

Hope this helps. Good luck!!

 

rlbertrand -
Very interesting! Did you wind up staying with the 40 shooter after hanging on the 50cc pump? Are there any disadvantages to the 50cc? I took today off, and get to go see a periodontist tomorrow, so probably won't be doing much road tuning for a day or so. But at least I know there may be light at the tunnel's end from what you say, and that may save me a whole lot of frustration! Thanks!
Any input on how wide to gap plugs with the hotter coil? I have pretty fresh "Platinum Pro" (double platinum) installed, but haven't pulled them yet to change the gaps.
Really do appreciate your input. Steve