Anyone know a direct extension at Holley who knows their stuff?

The guy WAS right in telling you to jet it back to the factory settings, Holley's Double Pumpers are jetted rich out of the box. These are race oriented carbs, they were never intended to give good fuel economy. What exactly, other than the plug color, is telling you it's running lean?

 

It is not getting enough fuel at cruise, and is starving for gas. I feels like the fuel pump is going out when I hold it at a steady rpm.

Works GREAT on acceleration, idle, and full throttle (for the short times I have put it there), but when I try to cruise 2500-3500 rpm (highway speeds), it will run fine for maybe 5-10 seconds, then start to sputter and hesitate. It gets worse over the course of the next 20-30 seconds and then it starts to feel like I am hitting strong gusts of headwinds.

It almost feels like the spark plugs are arcing and not getting spark to 2-3 cylinders. But only in this range of cruising rpm.

I am going to check for 1) plugged/dirty air bleeds, 2) I may have rebuilt the carb with the wrong rebuild kit, and the gaskets are not correct. Maybe one or more of the little holes in the metering block may be plugged, or blocked by an incorrect gasket.

So I might take it apart, and make sure all holes are free, and gasket is not covering anything it isn't supposed to.

After this, I will be saving for a new carb or sending it in for professional work. It is starting to not be worth my time, and I really need to be done with the engine so I can finish interior work and start bodywork.

 

If there's nothing wrong with the carb itself, then I'd suspect the fuel pump or filters. Yea, filters. Did you unscrew the fuel bowl inlet fittings and remove the bronze "rock" filters when you rebuilt the carb? Your problem sounds exactly like what happens to my Ranger's (89 V8) 5.0 when the first filter in the fuel system gets clogged. It runs fine at first then gradually under hard accelleration, it starts to cut out and misfire. I have one filter between the tank (in bed 35 gallon) and electric pump, another filter/water seperator downstream, then the two fuel bowl inlet filters. I bought a used (slightly) 3310 750 from a local speed shop a few years ago. When I tore it down to kit it, the primary bowl rock filter was plugged solid with what looked like red mud. The secondary side was clean as a whistle. This told me several things about the previous owner............... He never ran an inline filter before the carb and he never bothered to tune the carb to where the secondaries would open up. The plugged filter was his reason for selling it. It quit working and he gave it up, without ever looking to see what the cause was.

 

Put a vacuum guage on it. If you have a big carb, you may not have enough vacuum to maintain a constant pull on the carb's venturi which means your over supplying the engine with too much air, and not enough vacuum to handle that air wont mix fuel well and activate the circuitry in the carb to its full potential. when the vacuum is high, it will be richer, when its low it will lean out. 750 is kinda big fo the everyday runner, Id say a 600 wouild be bout right for what you wanna do. Smaller carb will have more vacuum than the same engine with a big carb. It sounds as if the carb is way to big, and its losing the ability to pull fuel thru the circuits properly.

 

If he was running a 750 I'd agree with you in this assessment, but a 600 is right at perfect for what he's got, although I'd have chosen a vacuum sec carb.

 

At this point, I am not even using the secondaries...all my problems are in the primary block...

I think it will be a "damn!, that was stupid" error when I find it.

 

Scoop, are you running a roller cam? is it the stock roller or a high performance? Mine has the stock roller cam with a 2 barrel motorcraft carb,,,, they say the vacuum pressure is higher on these engines than the traditional 5.0. Maybe, just maybe, if you have done some mods,, the 600 might not be big enough. I was thinkin you had a 750,,,,,, my bad,,, but if its that old style holley,,,, I have never had good luck with em, other than a door stop. I bought a new 750 holley once,,,, mechanical secondary, was an awesome carb till one day it popped thru the carb,,,, I still today dont know what happened,, but after multiple rebuilds and countless hours in it, I ended up with a rochester quadrajet.. yes, on a ford 302,,,, I used one of those adapter plates and a spacer plate to hold it all together,,,,, ran like a raped ape!!

 

At the RPM where the surging exists what is the overall timing? A very advanced ingnition will cause a surge like that.
Remove your vacuum advance hose and plug it - then check the timing at 3000 RPM. If it is more than 34-36 BTDC retard it to 34 degrees and test drive your car.
I doubt your problem is a carburetion problem unless it is running so rich that it is flooding out.

 

It blew the powervalve. As for the stock roller cam, these actually make the carb work better. Running a 570 SA on top of the roller 5.0 in my 89 Ranger. This one's got the 94-up F4TE roller used in all the pickup/van 5.0's and later used in the Explorer 5.0. Great cam.

 

I agree, the advance mechanism could be the culprit, but could be not enough advance as well.

 

I posted a reply earlier, but it must not have gone all the way thru...

The gist was I hope it is a simple fix like Paul says. I am running off the charts on my advance when it is all in. At around 2000-2500, it is running more advanced than the lines on the balancer can show, so I would estimate 40-45 degrees.

I hope that disconnecting the vacuum fixes this. It would be a nice finish after I previously stated

And is 14 initial too much?

And my cam is bigger than most 5.0 cams, but not phenomenally large. .531/.567 total lift, a little lopey, but street friendly.

I have family coming over today, so I probably won't get a chance to test this out. Unless granny wants to go for another ride...

 

If the vacuum advance is the culprit, should I just run it at 14 initial and live with only the mechanical advance, or should I increase the initial mechanical, or what?

I don't plan on "re-curving" a stock distributor. I will just ride without the vacuum and eventually put in a better dizzy.

 

scoop, your in way over your head on all this.
There have been to many changes made for this to be a simple fix.
The surging you feel is to much ignition timing at light load.
I also suggest you jet back to stock, get the timing re-curve near correct, then play with jetting.
This can take weeks of trial settings by recording every change one at a time so you can go backward to the last setting when needed.
I have been thru this years ago and ended up with a motor that had nearly the throttle response of a fuel injected motor.
So it can be done by the seat o the pants if you realize what's involved and the relationships they have.
You know*******relationships!!!!!!! it's all relationships just like humans.

 

I got you Bluegrass. I just went out and plugged the vacuum ports and will run it and if it runs RICH, which I hope it does, then I know where the original jetting was and I can set it back. I have kept track of it all along. So, in 10 minutes, I could be back to "stock" configuration and ready to fine tune.

I also remembered, as I was plugging the carb vacuum port, that the previous owner did not even have it installed. He had a plug in that hole and I had to install a vacuum port in there for my vacuum advance.

At this point, I hope it runs pig rich, so I at least know that the problem is solved, then I can proceed to tune it and not have this little demon bothering me.

My fingers are crossed...

 

You are using the vacuum port on the side of the main metering block aren't you? If not, then you should be.