Tuning a Holley 390

[AbandonedBronco]

Yeah, I think I'm going to give Holley a call, and see if they have any ideas. I tried turning the cam several different ways and pulled it all apart and put it all back together, and nothing made much of a difference.

[F-250 restorer]

Originally Posted by AbandonedBronco

Is this normal? Yesterday when I was out tuning the idle on the carb (got it to go from 17 vacuum to 19), I noticed that when ever I revved the throttle, it would stumble and then quickly race in RPM. If I just kept blipping the throttle (a quick tap to race it from only 700 to 1200 RPMs), it would continually stumble, stumble, stumble, and then die. I think it was just getting flooded with fuel and wasn't using it.
I notice this when I rev the engine at idle and while I'm driving around. I don't think the squirter is too big, it's only a .031 (and it really struggled off idle with the 0.025 that came in it), but maybe the pump cam isn't the right one? I was wrong on the color earlier, it's a light orange cam. Too much fuel too soon?

What do you think?

I thought it might help to know that at www.ponycarburetors.com, they list how to interpret the readings when tuning with a vac guage. Good luck.

[AbandonedBronco]

Well, I got it figured out. Turns out, I actually misunderstood how the cams work, and was trying to put them on sideways. At least nobody was looking...

After I put it on correctly, I fired it up and away I went. Nice to drive it after it sitting for a few weeks. With the rebuild and all the new jets, it ran great!

Pump squirter went from an 25 to a 35
Power valve from a 6.5 to an 8.5
Primary jets from a 51 to a 53

Currently, I'm running the blue cam, but it's puffing some black smoke when I snap the throttle, so I'll try taming that one back a bit.


And, for the record, a secondary spring quick change kit is an absolute must.

[F-250 restorer]

Good for you, AB--

I think I'll copy and paste your posting into a file. I'm sure I'll see people asking about tuning that carb for a 300.

We should set it up with a 'payment' link to paypal, so all the people asking can just pay you $10 a pop for your research.

[AbandonedBronco]

Always glad when my trial and errors can help someone else, because I know there's been plenty done by others that have helped me.

However, a little extra car parts money showing up from time to time sure would be nice.

[300/6 Freak]

yedah thanks for this R&R Abandonded.....as you know i'm trying to figure this conversion or one very similar right now LOL

[AbandonedBronco]

It's fun stuff, but definitely do your research. Nothing sucks more than getting it all on and then wondering how it all works. I think I spent several months reading over posts and researching exactly what I wanted before implementing. I'm glad I did. Of course, having to fix other stuff first gave me the time to do it, whether I wanted to wait or not.

[300/6 Freak]

tell me abouit it i need afew things like money and time to actually do what i need to. Its fun planning it out and waiting cause then when it finally gomes to that day it usually goes super smooth because you know what to expect and will be driving alot sooner then if you jsut start slapping random parts on

[AbandonedBronco]

Exactly. By the time I finally got all my stuff and put it on, I knew every obstacle ahead of me. I had the conversion done in an hour or two, and was out driving around having fun.

[AbandonedBronco]

Speaking of which, I think I have it finally tuned to just about how I want it. Puffs a little black smoke when I hit the throttle, which I need to address, but it doesn't bog anymore and drives like a dream. I didn't get to drive it today because my wife wanted to drive it so badly.

Went and put it through some tests this weekend on a couple local trails and it was flawless.

http://www.youtube.com/watch?v=-NeR2Kq_q5s

[Harte3]

Looked like a little bit of black smoke showed up on the video but that is from a hard blip under no load conditions. I would say it is good to go. Mine will do the same thing under the same conditions...just barely discernible...but my cheap gauge shows the AFR to be correct under the varied conditions of running.

So what's next? The wife going to enter the local mud drag races with it?

[AbandonedBronco]

Yeah, that's the only time I've noticed the black puff of smoke is when I floor it under no load. Other than that, there's nothing. I figure if it's not bogging when I accelerate and not puffing black smoke, it's doing pretty well. Now I just need to pass emissions in a few months. As said before, if I can get the carter 1bbl to pass without the EGR or the smog pump hooked up, I'm hopeful.

I'm still working on it, but getting my wife to drive the Bronco off the road is something she still won't do. At least that leaves all of that fun part to me.

[300/6 Freak]

yeah that dang bronco of yours runs crazy good. I hope my 300 runs half that smooth when i finally get it going LOL

[AbandonedBronco]

Thanks for the compliments. It's been a fun project, and it's nice to finally start seeing the results.

[AbandonedBronco]

Hey everyone, still seem to have some tuning ahead of me. Took the Bronco for a long trip this weekend. It was through winding mountain passes, a bit of up and down, from about 2500 to 6000 feet elevation. Speed limits of about 35 - 55 max. It was about a 300 mile round trip.

The engine ran great, pulled hard, accelerated smooth, and overall, I couldn't be more pleased with the performance. However, I only got about 12 - 13.5mpg . I'm just not sure what to more to do. I know it was a bit of up and down and speed changes, but that still seems really low to me, and I wasn't exactly powering out all the hills or anything. I have 30" tires and a 3.00 rear end and I would imagine I probably would have gotten around 17 - 21 on this trip with my old 1bbl setup.

Any ideas on what kinds of things I should check? 12 - 13 on the highway just seems really low to me.