Holley Sniper Stealth EFI - Part 1

After multiple attempts to adjust the carburetor, I ultimately lost motivation.  I adjusted the high idle screw on at least four different occasions with mixed results on the idle RPM.  Strangely, once it would start, it would often just slowly have the idle increase rather than decrease.  If you were to press the pedal to take it off high idle, it would just stay at the RPM you reached when briefly pressing the pedal.

Besides the high idle, I had another instance in which the accelerator pump didn't want to work with the new carburetor.  I can't explain it as the pump cam is unadjusted and seems fine.  The fuel bowls had fuel in them.  I took the pump nozzle off and then it didn't happen again but I can't imagine it was blocked.  It was another oddity that causes you to lose confidence in the plan.  

I've decided this winter that I'm going to work on upgrading the Mustang with a EFI system rather than continue to work through these carburetor troubles.  The money spent on the carburetor is somewhat wasted with this plan but I don't honestly care.  I'd like to work on the car again and want something that will reliably operate.

There are a few additional benefits beyond reliability.  The car has a hard start problem when hot despite fuel line insulation, carb spacers, and more.  The idle doesn't reliability adjust when the AC turns on.  The high idle has never worked causing the Mustang to often want to die for the first five minutes of driving.  Lastly, I'd rather not worry about adjusting the AFR to be right for the car and instead have a system that adjusts it automatically.

It is hard to continue to invest in the Mustang with the condition of the body and the paint.  However, I've about decided I'm going to get someone to restore the body and paint it.  I do want the car running reliability before I do that.  I'll then decide if I take it all apart to have it painted or how I handle the step in the process.

For today, I started by cleaning up the garage a bit to have a nice work area, removed the carburetor, and checked the wiring a little to pre-plan how the new Holley Sniper Stealth (550-870) will wire into the vehicle.  With those few things done, I placed the order for just the sniper unit as I don't expect to reliably place an order for everything I need and will just work through it bit by bit ordering parts as I need them to go get the job done.

I don't plan to rush and actually expect this to increase in scope and might include some rewiring.  I'll be happy if I the job is done around mid-February or early March when it is a good time to start driving around again.  

Returning to Work

Taking the list from when I returned from Power Tour and adding a few new items, I have the following on the list to address:

• Install driver headlight wiring
• Replace transmission fluid
• Front disc brakes squeak
• Rattle behind rear seat back
• Buzz noise from behind dash
• A/C vent tube 
• Hot start issue
• Clutch reservoir
• Throttle return spring
• Fix Broken positive battery clamp

New Holley Street Avenger 670 - Part 3

Tonight, I swapped the primary jets from the original size 65 to 67's.  I also sapped the accelerator pump nozzle from the original 31 to a 35.  I didn't drive the car as it is a little late so I'll need to drive it another time and update with my findings.  

New Holley Street Avenger 670 - Part 2

I decided to do a bit more work on the new carburetor today after work.  I put a vacuum gauge on the engine and planned to set the curb idle and the idle mixture screws.  Unfortunately, the car would not start and in checking under the hood, I found the accelerator pump nozzle wasn't squirting.  It's strange that I have that same problem with a new carb but the front float is full.

I didn't have any gas sitting around to put down the carburetor so I just keep working the gas and it ultimately started.  After it idled a while, I adjusted the curb idle down to 800 RPM.  At that RPM, the AFR was 15:1 and the vacuum was at about 11.5 inches.  I made sure the choke was off and the engine temp was 180 and backed out the idle screws an 1/8 turn.  This raised the vacuum to 12, the RPM increased to 900, and the AFR to 14:1.

I turned the idle screws out another 1/8 turn.  The vacuum went up to 13 and the AFR was 13.5 to 1.  I didn't adjust the RPM before and it was now at 1,000 RPM.  I adjusted the idle screw down to get the idle back to about 850 to continue working on the setup.  With this changed, the vacuum was still 13 inches and the AFR was around 13.7:1.

I backed the idle mixture screws out another 1/8 turn (3/8ths in all).  This dropped the AFR down to about 13:1, raised the vacuum to near 14, and the idle stayed in the 900 RPM range.

I decided to go further and went another 1/8 (1/2 turn in all).  This dropped the AFR down to the 12:1 range.  The vacuum went up to 13 and the RPM was about 950.  I decided to go back to 3/8 turns out from the original setting and go for a drive.

Strangely, when I went for a drive, the engine was really lean.  When cruising, I was at 15-16:1 AFR.  I don't really know what changed since the last time.  The idle mixture is much more rich so if anything that would have helped.  The temperature was about 60 so perhaps that was much different than last time but I can't imagine it having that level of impact.  I was however a little low on gas but I can't imagine that doing it either as the float bowl shows as full.

I decided to stop for the moment and came home.  Since the engine was now off, I checked the idle mixture screws and found that they were not the same at the start.  I adjusted them out 3/8 of a turn.  When I checked them, the passenger side (with the 02 sensor) was a total of a 1/2 turn out (1/8 out as a starting point) and the driver side was 5/8 turn out (1/4 turn out as a starting point).  

I might need to turn them in an 1/8 turn but I'm going to leave them at this point for now.    

Baseline with New Holley Street Avenger 670

I installed a new Holley Street Avenger 670 carburetor and was surprisingly able to start up the car immediately.  The idle was decent and the air fuel mixture wasn't bad.  Without any tuning, I decided to drive it around the block just to see what it was like out of the box.  I didn't have any trouble but watching the AFR gauge, I could tell a little tuning was needed to get it to run good.  

I decided to go ahead and start tuning straight away and went with the float level first.  As a starting point, the front bowl level was about the middle of the view window.  I drained a little out of the bowl using one of the four bolts which hold the bowl in place.  I loosened the set screw and turned the nut for the needle and seat a half turn clockwise.  When I turned on the key, the electric fuel pump filled it right to the bottom of the sight window.  Done.

The rear fuel bowl was about 3/4 of the way up the sight window before any adjustment.  This one took two adjustments to get set to match the front bowl level.  The first adjustment was a 3/4 turn clockwise followed by another 1/2 turn clockwise.  It was then in good shape.

At idle, the car was at 13.5:1 so I thought I'd check the idle mixture screws.  I turned them in to see how far they were unscrewed and found they were only screwed out 1/8 to 1/4 turn each.  I just set them back as they were originally and left them alone.  

When driving, the AFR was about 14:1 which isn't bad.  When I really get on it, it seems to need a little more accelerator pump but I'll wait to change that.  However, I'll wait on that as there are other things more important and I'd like to work through this in a good order.

Stock Configuration of 670:

 Front Jet: 65 

 Rear Jet: 68
 Pump Nozzle: .031