Tuning a Holley 390 - Page 3

Harte3 · #31 (**permalink**) 04-12-2009, 02:44 PM

If you are going to do some serious tuning, obtain a wide band O2 system. This is about the least expensive one I have seen AEM 30-4100 - AEM Wideband UEGO Controller Air/Fuel Ratio Gauges. A narrow band like I have is not definitive...it's more of a light show than anything else.

AbandonedBronco · #32 (**permalink**) 04-13-2009, 09:52 AM

I'd love one of those, but probably a bit out of my price range for the time being. So you'd say that, even for some form of reference, a narrow band air/fuel meter isn't worth the time?

Either way, I'm curious what step I should take next. Something was definitely not running right in the system. I put the advance back a few ticks (to about 6, which is factory), and the pinging lessened. It didn't seem to make much difference on the freeway though.

I still don't think it was an OverDrive issue though since I did the whole trip in 3rd at 65, which is my 1:1 and got around 11 - 12mpg. With the 1bbl, I'd do the same trip at 75 in OD and get 17, so I know something just isn't right.

Not sure where to start though. Some theories I have are that either my main jets are too small, which is causing me to not have any cruising power and I am forced to continually dip into the powervalve and the secondaries on a constant basis just to stay at a cruising speed. Or they're too large, causing me to run rich, lose power, and use way too much gas.
I removed the secondaries for part of the trip to see if maybe they were coming on too early and drowning the engine, but I just noticed a lack of power going up some hills, so I don't think they were an issue.

Ideas? I got worse mileage on the highway cruising at 65 than I did ripping around town having fun with my new setup.

Harte3 · #33 (**permalink**) 04-13-2009, 12:19 PM

A too lean condition can cause loss of power, ping, and lower mpg. Sounds like you have a lean hole in the fuel deliver at the speeds you are driving. A change in PV to one that opens sooner or to a two stage power valve...possibly a change to bigger Jets...all this is going to be 'Trial by Ordeal" until it's dialed in the way you want. I have somewhat of the same dynamic in mine at 70+ speeds but I generally run 62-67 with no problem. I may go from an 8.5 PV to a 9.5 or 10.5. If I go to a 10.5 it will probably be a two stage PV that opens some at 10.5 and full open at 5.5 or 5.0. Or, I might go back to the richer Jets since I did drop two sizes before running this carb. All part of the fun of tuning a Holley.

If you go the narrow band 02 sensor route it will take some time to get used to what it is indicating and it helps to compare what is happening with the vacuum gauge at the same time. The narrow band will show a rich, lean, or stoich condition but no specific numbers. Some have used a voltmeter with the 02 sensor and a chart that converts the voltage to a specific AFR.

AbandonedBronco · #34 (**permalink**) 04-13-2009, 12:31 PM

I think I should try bigger jets first. I was getting the 11 - 12mpg with the vacuum around 10 - 15 on average. On that basis, a change from a 6.5 to an 8.5 wouldn't factor into that, except for the hills and acceleration. The two stage seems like a good way to go as well. But as said, one thing at a time.
Fortunately, main jets are the cheap ones.

Harte3 · #35 (**permalink**) 04-13-2009, 12:49 PM

The Jets are the easiest to change...only have to pull the fuel bowl and not the metering plate and becomes much easier with the non-stick gaskets. When you get to tuning the secondaries the quick-change secondary spring kit is well worth the investment too.

AbandonedBronco · #36 (**permalink**) 04-13-2009, 12:59 PM

No kidding. I've changed the secondary spring twice, and it's a PITA trying to hold everything in place, relax the diaphragm, keep the spring straight, not tear the holes the screws go through, etc, etc. Quick change kit is a must!

Harte3 · #37 (**permalink**) 04-13-2009, 01:37 PM

Once you get the quick-change you won't leave home without it. Two screws, swap the spring and away you go...piece of cake. I have an 1850C/600 cfm I'll be tinkering with and before it sees the manifold it will have the quick-change installed.

AbandonedBronco · #38 (**permalink**) 04-21-2009, 06:05 PM

Alright, did a little work over the weekend. Went and got the cam tuning kit and fiddled with that for a while. Wow, carb cam tuning is a whole division in it's own.

I started out trying the more aggressive blue cam, but whenever I tossed the throttle, it was just belching black smoke out of the tailpipe and was obviously dumping way too much gas. Went through several variations of it with the #1 and #2 setting, then moved on to the green cam, red cam, etc. Each seemed to make it either blow black smoke, or stumble when I first revved it. From there, I decided to start from ground 0 and go with the mildest cam and put in the pink one.
The engine seemed to really like this one the best, and it was the first time since I put the 4bbl in that it didn't stumble when I throttled it. I guess it was just getting too much gas. ((Not that I like saying my Bronco needed the pink colored one.

)) Until I up the primary nozzle (which I think it still may need), I'll stick with this one for a while. Seems to like it.

On another note, I think I know why I was getting such poor gas mileage. After letting my engine cool for about 10 minutes, I opened the hood and it just reeked of gasoline. I could also hear a faint hissing coming from the fuel bowls on the carb. I'm guessing that it has a bit of a fuel leak and I never saw it because it burned off as fast as it came out. Ordered a rebuild kit for it and will be installing all new gaskets. Hopefully my mpg goes up by a few numbers.

Just thought I'd give an update. Never know when someone may come across it in a search and find what they need.

Harte3 · #39 (**permalink**) 04-21-2009, 07:37 PM

The pink one?...Really? That is interesting. There is something like six different positions for that cam?

AbandonedBronco · #40 (**permalink**) 04-21-2009, 08:04 PM

Yeah, it has three holes, and I think I put the middle hole on the #2 spot. *shrugs* I guess whatever makes it happy. The blue one just belched black smoke when I throttled it.

Harte3 · #41 (**permalink**) 04-21-2009, 08:42 PM

There you go. The big end of experimentation is eliminating that which doesn't work.

AbandonedBronco · #42 (**permalink**) 06-09-2009, 08:45 PM

Okay, I think I found the problem. I finally got around to rebuilding my 4bbl and have it completely taken apart right now. Most everything looks alright, some gaskets a little worn, whatnot, but nothing to overly cause concern.

However, my parts diagram says that there is supposed to be a check ball, weight, and needle right underneath the pump squirter. When I removed it, there was only the needle, and no check ball or weight and they appear to be missing. Are all of them supposed to have this check ball/weight? And if so, would one from my carter YF 1bbl work? (Have a couple lying around.)

Secondly, it says that some came equipped with a ball in the secondary spring housing and some didn't. Mine doesn't have one, but I'm curious how to tell which ones were supposed to and which ones didn't. There looks like there's a hole that one went in, but nothing's in there.

Lastly, if all this stuff is supposed to be there and all of it's missing, where can one locate such parts? Also, would the missing check ball/ weight explain the poor off the line performance and the bad gas mileage?

Thanks!

AbandonedBronco · #43 (**permalink**) 06-09-2009, 08:54 PM

Double post...

AbandonedBronco · #44 (**permalink**) 06-25-2009, 01:04 PM

Hey everyone, curious if there's anyone who might be able to give me some insight.

I finally got my carb (Holley 390) put back on last night after a complete tear down and rebuild. It started up fine, adjusted the idle, mixture, RPMs, etc. Got it to idle really nicely.

However, I'm having a real pain of an issue with the accelerator pump. For some reason, I cannot get the pump cam to engage the accelerator pump arm. The pump works fine, because if I operated the arm by hand, I got a nice, clean shot of gas into the primaries from the pump squirter.

I tried adjusting the screw on the pump arm from all the way in to all the way out, and no adjustment made it do anything. I had it to where I could just tap the arm with my finger, and it would squirt a steady shot into the primaries, and still nothing. The cam just wouldn't engage the arm.

I finally got it to where I would get a tiny little drizzle out of the pump squirter when I moved the accelerator to WOT.

I am completely clueless of what to try next. Turning the throttle (and therefore turning the pump cam) is just not making any gas squirt into the primaries.

Any ideas?

Harte3 · #45 (**permalink**) 06-25-2009, 01:32 PM

You didn't get the cam turned around backward when mounting it? The long sloping curved part goes to the left toward the pump. A call to the Holley Techs might be in order.

I didn't remember the part about you trying the blue cam so disregard what I said about it in the Email.

Finally got mine "fined" in. I removed the #55 jets and re-installed the factory #57's. That took the extra lean out as indicated on the AFR gauge. I also moved the pump cam to the #1 position and adjusted the arm to it and that took out the rest of the tip-in hesitation. Much nicer response through the whole range now.