Holley 390cfm Questions

[Explorer]

Engine starts, runs, idles fine. Acts like it reaches a point when no more fuel is being supplied, like not getting full throttle range. last 1/2" of travel has no effect. In high gear doesn't want to rev over 3200rpm. First and second pulls 4500rpm easy.
1) How can I tell if secondaries are opening?
2) Gauge on fuel reg is irratic, could it be not enough fuel pressure?
Doesn't bog and start back up, just acts like a governor.

 

[bubba22349]

1) How can I tell if secondaries are opening?

You can hear and feel them. They can be tuned to come in sooner or later with the spring rate.

2) Gauge on fuel reg is irratic, could it be not enough fuel pressure?

How much on gauge? You only need around 3 to 5 psi too much is as bad as not enough.

 

[cjperformance]

What intake manifold or adaptor is the carb on?

What mods are done to the engine?

What intake vacuum do you have when this problem occurs?

When does the gauge get erratic?- at any rpm or just when the problem occurs?

 

[Explorer]

What intake manifold or adaptor is the carb on?

What mods are done to the engine?

What intake vacuum do you have when this problem occurs?

When does the gauge get erratic?- at any rpm or just when the problem occurs?

Build info is in my sig line. Fuel pressure gauge is mounted at the regulator, sometimes reads 5psi, other times zero, think it's defective. I'm going to pull the reg off and see what happens. Can't remember vacuum reading when I have it floored, I'll have to check. It's up to 17hg vacuum now at idle.
I'm used to hearing a 4 bbl moan when she's opened up. But I'm used to a V8. My first six.

 

[JackFish]

Stock fuel pump I assume?
Isn't 5-6 lbs about max for a mechanical?
Perhaps it's failing?

 

[80broncoman]

....1) How can I tell if secondaries are opening?

Unhook them and see if it changes the way it acts.

 

[Explorer]

JackFish: Stock pump, new but that doesn't mean anything. I'm going to pull the reg and I'll check pressure then. Only reason I put the reg on anyway was it was suggested on here 5 psi was what this carb liked
80broncoman: I'll give that a try.
As far as normal driving, none of this is an issue. Just tweaking the setup and making sure everything is up to its full potential. It will still cruise interstate speeds no problem.

 

[CobraSix]

Checked the fuel filter lately?

You'll normally feel the secondaries come in. I know on my 390, I feel a slight dead spot when it floods the engine. I plan to eventually re spring the secondaries to come in later.

 

[Explorer]

Everything is new. Just got 500 miles on it and changed the oil this weekend. Still need to look at the advance curve but I've got her burning clean and it seems to get stronger the more it gets broke in.

 

[66200i6]

Confirm that the lower part of the throttle linkage is able to swing past the top surface of the intake. I had to remove the lower part to get the throttle plate to open fully.

Good luck, Ric.

 

[Explorer]

Confirm that the lower part of the throttle linkage is able to swing past the top surface of the intake. I had to remove the lower part to get the throttle plate to open fully.

Good luck, Ric.

Yep, noticed that. Mounted mine with fuel bowls inline with engine and primary to the back with a Lokar cable pulling from the front. I was worried about even flow to the cylinders, but all plugs look the same. Can't see anything on the valve cover side interfering. I'm piddling with it as I get time. Enjoying driving it after a years work while weather is good. Trying to get the 66 Mustang going for my son too, so it's taking up most of my time. I'll get to all the suggestions one at a time and report back.

 

[69.5Mav]

You can hear and feel them.

According to Holly if you can feel them then they are opening too early and you are leaning out.

 

[cjperformance]

Double check the fuel pressure, so it's not fooling you.
These carbs have a metering plate in the secondarys not removable jets. It may pay you to check if the fuel passages in the plate are clear, if they are blocked you will just feel less power as the secondarys open as the engine go's lean. Then if you lift off the throttle slowly the engine will feel better but not want to rev out.
As said, try it with sec's dissconnected so you know the feeling of just primaries, this gives you something to compare to when testing the secondarys.
When the secondarys are set right for the best balance between power and economy you will not feel a dead spot as they open but you will feel a good linear increase in power, you will hear a difference in induction noise too if you run an open element air filter.
Have you checked the secondary float level? This will affect the secondary performance too.
Looking at your cam I see you are after economy. Why use the 390 4bl for this task? You would do better in the economy stakes by using one of the many staged 2bl carbs and there are plenty that will still supply enough air/fuel for great performance too.
Your sig states an iron head, USA head or Aussie head? If USA head, what are you doing for an intake setup?-ie to adapt to the 4blcarb.

 

[bubba22349]

You might want to re-check your carb mounting. It is usually recommended that carb is mounted cross ways and so that the primaries are next to the head.

 

[Explorer]

cjperformance: You must be reading wrong sig line. Classic Inlines aluminum head and intake. Chose the cam for the torque curve, it's a 4x4, need power low rpm not highend.
bubba22349: Yea, I read all the posts on mounting the carb. Not real solid evidence that I found. Figured I'd try it this way before hacking up a brand new carb linkage. Spark plugs are telling me I have good fuel distribution, all burning equally. I also have the 2 bbl. plate for the intake if I decide to try that.

 

[cjperformance]

cjperformance: You must be reading wrong sig line. Classic Inlines aluminum head and intake.
Ah yes i mistook the 'CI' for casr iron! not Classic inlines!, too early in the morning.


Chose the cam for the torque curve, it's a 4x4, need power low rpm not highend.
quote]
Yes this is why I suggest a staged 2BL carb, With a cam like that and a weighty 4x4 you would be hard psessed to get the engine to ever fully open all 4 barrels. A staged 2Bl will still give enough total air/fuel for your use but return better economy and light cruise economy/tunability. I've been thru this many times on these type of engines from 144's thru alloy head X flow and our current 4Lohc I6.