Out of the box this 650 dp is pretty good. I need a little help with tuning. I have a wide band O2 sensor hooked up. I tried setting idle at mid 14's but it didn't idle well and stumbled a lot. So we brought it down to low 13's and it idles nice. I idle around 750-800. The motor is a low compression 331 with a T5, by the way. When I idle and I press the gas pedal I get the dreaded holley stumble with A/F going to 16-18 and then goes to high 12's-13's. If I try to cruise in gears 1-4 past 2K RPM I am right around 12-13 but I get these bumps or stumbles that just basically make the car jerk a little. It's hard to see on the A/F meter but I guess I go lean during the stumbles, sometimes to 14. In 5th gear I'm ok cruising and don't notice the stumbles. If I floor it on straight surface I will do low to mid 12's. If I floor it uphill I am more in the 14's.
That's where mine ended up, 13.2 - 13.3 at idle. Sounds like you need a bigger pump/shot to cure the off-idle. These 2 may be float height or dirt/trash in the needle & seat?
First thing you're doing wrong is using an A/F meter and trying to make the A/F ratio the same everywhere in the rpm range and at all driving conditions. This isn't fuel injection, it's a carb. It's going to have transitional differences, no matter what you do. The off idle stumble can be fixed usually by removing the slack between the pump arm and cam lever. The other stumbles are likely as RA said, trash in the metering passages or inadequate fuellevels in the bowls. It could also be ignition related. What ignition system are you running ?
I'm running an MSD 6AL2. I was worried going uphill at 14.5, thought that was a little too lean. But I will definitely try cleaning the needle/seat and I will adjust the float level too. I will the pump arm adjustment too.
Just a thought, but when tuning with a wideband O2 sensor you need to make sure that your fuel pump is suppling a "constant" 5-1/2 to 6-1/2 at all RPM's and all load conditions..................repeat.........All Load conditions. I assume you have and electric pump and fuel pressure regulator...........if not that would be the first thing on my list. When you say going up hill gives you a leaner condition.................I think of two things, first is fuel pressure............if you are going up hill it takes more fuel because you are fighting gravity.............second is the air vent in your gas tank. The old rule of thumb is that for every gallon of fuel you use it has to be replaced by a gallon of air in your tank. Just a couple of thoughts and observations. IMHO
My fuel pressure gauge is manual and it's in the engine compartment, any tricks to checking my fuel pressure? maybe I can mount a video camera or something in there? I have a good electric fuel pump and a regulator. The vent in the tank is my stock vent but I'll check to make sure it's not bent up anywhere. I believe on the maverick that's the hard line that travels all the way up to the blue canister.
Checking fuel pressure is difficult but I've bought tubing and taped the gauge to the windshield for testing. As others have said, the lean AFR pulling a hill may be float level but raising the rear float level too high can cause stalling on a hard stop. You can disconnect the secondaries to determine if it's on that side of the carb.
Oh boy this problem isnt a tough one in person but over the net I dont even know where to start. I guess my biggest piece of advice is dont try to set a up a carb based solely on what the O2 reads. Alot of it is seat of the pants and experience. You can really get on a wild goose chase staring at that mixture gauge. Holleys are trial and error to a point. Try a bigger Accel. shot. thats an easy one.
