Author Topic: Setting the fuel pressure...  (Read 19325 times)

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Yellow Truck

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Setting the fuel pressure...
« on: June 11, 2016, 04:13:19 PM »
I know this is rather important, so I put some fuel in my baby today and pressurized my new system for the first time. Good news was there were no leaks, but the fuel pressure was acting oddly.

When I first turned on the pump it filled the carb (it is a QFT so it has the nice little windows - front one fuel was half way up the window, back one you can just see air at the top of the window). Initially the pressure ran up to between 6 and 7 PSI and I was pretty happy, but after checking for leaks I turned on the pump again, the gauge had shown pressure dropping to zero pretty quickly, but when the pump came on it shot up past 9 PSI, and it sat there. I turned it off and looked for the tools to adjust it, when I came back I tried it again, and it jumped to 9-10, then fell back to 6.

A few more tests and it is now consistently sitting above 9 PSI. I backed off the nut and backed out the screw as far as I dare, but the pressure is remaining up above 9 PSI.

What are the odds of a bad regulator vs a bad gauge? Is my process wrong (i.e. do I need to have the engine running to set the regulator?
1969 F100 4WD (It ain't yellow anymore)
445 with BBM heads, Prison Break stroker kit, hydrualic roller cam, T&D rockers, Street Dominator Intake with QFT SS 830.

Paul.

My427stang

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Re: Setting the fuel pressure...
« Reply #1 on: June 11, 2016, 05:13:50 PM »
I'd adjust it running, that's what matters

However, 7 is a bit high, I'd rather see 5 or so.  Pressure doesn't help a carb, it only needs volume, the pressure can make it fussy, especially in a truck where you may be bounding around
---------------------------------
Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

tomsfe64

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Re: Setting the fuel pressure...
« Reply #2 on: June 11, 2016, 05:24:40 PM »
I just went through the same situation. Took the regulator apart looking for problems. It looked fine. Should have since it was brand new. Couldn't get pressure to come down. Cure was another regulator which worked great out of the box.

Yellow Truck

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Re: Setting the fuel pressure...
« Reply #3 on: June 11, 2016, 06:16:18 PM »
Mine is brand new as well. I'll try starting it tomorrow, if that doesn't work I'll get a new one Monday.

The carb documentation calls for 6.5 PSI, so 9 is NOT good. The gauge seems to be responding - I turned the adjuster screw in most of the way and ran the pump for a fraction of a second and it jumped to 14 PSI, so I'm thinking it is a bad regulator, but we will see when I get a few extra hands to start it for the first time (mostly need the extra hands for the fire extinguishers!)
1969 F100 4WD (It ain't yellow anymore)
445 with BBM heads, Prison Break stroker kit, hydrualic roller cam, T&D rockers, Street Dominator Intake with QFT SS 830.

Paul.

fastback 427

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Re: Setting the fuel pressure...
« Reply #4 on: June 11, 2016, 07:44:36 PM »
What regulator do you have? I've had a couple new Holley regulators that were doing the same thing, pure junk imo. I use aeromotive and have good luck since.
Jaime
67 fastback 427 center oiler 428 crank Dove aluminum
top end toploader
67 fairlane gta cross bolted 12:1 390 Dove aluminum top end c6 3600 stall
65 falcon straight axle project
67 mustang coupe project
76 f350 dually 390 mirror 105 4bbl 4spd
74 f100 xlt 390 c6 factory ac

Yellow Truck

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Re: Setting the fuel pressure...
« Reply #5 on: June 11, 2016, 08:18:37 PM »
Holley 12-803. Came with the fuel pump. Sadly it is kind of set into the fuel line routing now so changing the form is a bit of work:



1969 F100 4WD (It ain't yellow anymore)
445 with BBM heads, Prison Break stroker kit, hydrualic roller cam, T&D rockers, Street Dominator Intake with QFT SS 830.

Paul.

Yellow Truck

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Re: Setting the fuel pressure...
« Reply #6 on: June 11, 2016, 08:23:30 PM »
Holy crap - Jaime at that price they'd better be perfect!
1969 F100 4WD (It ain't yellow anymore)
445 with BBM heads, Prison Break stroker kit, hydrualic roller cam, T&D rockers, Street Dominator Intake with QFT SS 830.

Paul.

fastback 427

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Re: Setting the fuel pressure...
« Reply #7 on: June 11, 2016, 10:17:00 PM »
They are a little pricey. Try the aeromotive 13205. 102$ from summit. That's the one I have and works great so far.
Also on edit, it's been a while since I changed mine but it was easy to do, looks like with the way your fuel system is set up, would be almost a bolt in.
« Last Edit: June 11, 2016, 10:24:19 PM by fastback 427 »
Jaime
67 fastback 427 center oiler 428 crank Dove aluminum
top end toploader
67 fairlane gta cross bolted 12:1 390 Dove aluminum top end c6 3600 stall
65 falcon straight axle project
67 mustang coupe project
76 f350 dually 390 mirror 105 4bbl 4spd
74 f100 xlt 390 c6 factory ac

Yellow Truck

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Re: Setting the fuel pressure...
« Reply #8 on: June 11, 2016, 10:39:12 PM »
Thanks for that - when I looked on the Aeromotive site they only listed that in a kit with hoses and connectors that sells for over $150.
1969 F100 4WD (It ain't yellow anymore)
445 with BBM heads, Prison Break stroker kit, hydrualic roller cam, T&D rockers, Street Dominator Intake with QFT SS 830.

Paul.

My427stang

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Re: Setting the fuel pressure...
« Reply #9 on: June 12, 2016, 07:02:29 AM »
Does it say it wants 6.5 or 6.5 max?  I don't generally use QFT, but pressure doesn't do much for a carb, all of it's metering is in the unpressurized bowls

I'd still stay on the low side of it if I had a good regulator controlling things, but interesting if they really do want a
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Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

Yellow Truck

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Re: Setting the fuel pressure...
« Reply #10 on: June 12, 2016, 09:19:50 AM »
Ross - the instructions with the carb say (note the poor grammar is theirs): "This QFT carburetor has been ran on an engine to insure all components are functional. The calibration should be very close for all adjustments. Different engine combinations could require adjustment of idle mixture, idle speed, and main jets. The fuel pressure was set with 6 1/2 lbs. of fuel pressure. The recommended fuel pressure for this carburetor is 6 1/2 PSI"

Seems they want 6 1/2 lbs.
1969 F100 4WD (It ain't yellow anymore)
445 with BBM heads, Prison Break stroker kit, hydrualic roller cam, T&D rockers, Street Dominator Intake with QFT SS 830.

Paul.

My427stang

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Re: Setting the fuel pressure...
« Reply #11 on: June 12, 2016, 03:02:43 PM »
Wow, surprising, all that does is work the float and needle and seat a bit harder, but I agree, sounds like they want 6.5,  If the man wants a ham sandwich, give him a ham sandwich :) 6.5 isn't horrible, but it's also why every time I talked to a QFT guy I was left scratching my head.

It's a like the back of the toilet though, the pressure only affects how much the float needs to push up.  Once the fuel is in the bowl, it is completely unpressurized
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Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

HolmanMoodyStroppeGang

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Re: Setting the fuel pressure...
« Reply #12 on: June 12, 2016, 03:28:42 PM »
Drag car vs street car...

I'd agree with whats said on a hot street car but if you drag race this bad boy, pressure can compensate for 4 large jets and maybe 2 carbs living at Wide open throttle through the gears and out the back door,,,for you MPH number. If you make a lot of power, run slicks and low gears and want to see how it affects the time slip, watch the fuel pressure upstairs, under load, grunting to post your best MPH number and ET too....   More pressure can keep the fuel bowls higher than lower and often provide a more consistent fuel curve and better tunabilty and consistency.  For me, there is a line where the car launches hard enough to need jet extensions because the fuel is rising and uncovering the jets.  That can happen down track too.

Looks cool,fast and FUN !!  Nice job. For hot street, no need to over pressure the needle and seat for cruising and an occasional mash of the loud pedal for us too....but we all ran a lot of the Carter and Holley, manual pumps set at 7.5 PSI for many reliable passes or miles.

Looks like a fast and fun Summer for you...!  nice...


My427stang

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Re: Setting the fuel pressure...
« Reply #13 on: June 12, 2016, 03:36:51 PM »
Need volume for a carb, not pressure, running the bowls dry is a volume problem regardless how the engine is used

Problem is, you cannot easily measure volume during the race, so you watch pressure and if it drops you know you are running it out of fuel.

If you can hold 5 psi through the traps you won't run out of fuel any more than if you can hold 6.5 and inversely, if you can't hold 5 psi, you can't maintain 6.5

---------------------------------
Ross
Bullock's Power Service, LLC
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, Erson SFT cam, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 461 cid FE, headers, Victor Pro-flo EFI, Comp Custom HFT cam, 3.50 9 inch

HolmanMoodyStroppeGang

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Stroppe race Trucks
« Reply #14 on: June 12, 2016, 05:49:06 PM »
Hi Ross

I hope I said on the old forum, but will do so again, I always really liked your work there.  I recall you being an excellent resource to many FE cars and my pals and I always enjoy your work. And that Fast Back, well, I have one too and yours is S 'peach' !. How fast is she in the 1/4 I always wondered, I bet she scoots. Love that Mustang.

On this truck, I just share how we raced and won our trucks for FORD. We handed FORD a long row of trophies off road, and di the winners for parnelli, Walker Evans, Ben Ford himself, Larry Minor, who later sponsored the McDonalds funny car and rail, Rod Hall, and many others, James Garner even

We did a lot of R and D for Holley too, since we had the trick Heinan Freud Dynos with Fords EEE instrumentation, plus, we had the Autolite Dyno

On Holley testing, with their engineers in the cells, we always stayed at 7.

On the Ford Drag Team Winternations cars, and the 12 Ford Drag team cars we did in 68-9, we also shot for 7

Now here is a trick few recall but what the heck.   and off road race truck does NOT like the cathedral bowls.  We used many race Holleys, 750,850 Double pumpers, modified 780s, 750s, and changed the bowls on every one to race better, at 7 PSI. We re fitted the side hung 1850 style bowls because they take a lot more pounding and abuse, off road, and also, flat spot less in the rough stuff.   I bet you and some of the old guys recall that era. Ford would budget us a bunch of money to enter 7 truck classes, and we usually won all 7.  I see a truck here and wanted to add, if he plans to get her in the air, fly a bit over some jumps, and hammer her off road too, we had another key trick

We would take soft copper tubing, remove both steel bowl vents, then fabricate a u shaped tube, to plumb the front and rear bowls together.  You bend the tube to go around the air cleaner stud boss, then drill 094 or so holes on the vertical axis, pointing up.   These holes allow the atmosphere to balance both bowls, but during sever fuel slosh, and chassis attitude pitch and roll, aand let the fuel that tries to exit, move forward or back, and maintain supply

Same deal launching a car hard if the bowls are mounted inline, traditional. We had better luck with heavy cars pushing in to the 10s and 9s, using cathedral center swung bowls, sideways


Early examples would be Per AFX, or AFX, then Pro Stock FE's running 2 carbs, then 2 Dominators.   Dyno Dons Maverick had 2 110 GPH pusher pumps out back, and 2 lines, to 2 regulators.   Back then, we could run rubber, often 1/2 inch too, from the tank to the carbs.

I never know who is going how fast, and how much power we have, the goal, etc, so I want him to check a few more things

The Holley Mechanical pump says right on the box, 7.5 psi.  It fits all FE's and here is my concern, that extra .5 in a way, helps compensate for the many Fords that only have a 5/16 fuel line

My 67 was always power limited by the 5/16 line that makes a lot of bends. By 68, our Drag Team cars, helped FORD re fit a 3/8 fuel line, and we went further in some cases.

Ford us, once we had a Big Block in to the 10s, and 2 carbs, we often had the good mechanical pump up front, and a carter or holley, electric pump close to the fuel tank helping

On the low 9 and 8 second stuff, a dual bung set up is good, since the launch sloshes fuel back then up the gas tank, so we silver soldered big female bungs to the back, no need for a center mounted pick up, and sediment trap

I think he has to fix this deal, reading closer, maybe his regulator has a latent issue, or defect?

Maybe debris, contamination? 

I wonder if he needs a return

I do try to cover a lot of bases when I can, since it is real hard to tune by typing,,,,at some point....

I bet that if he gave you, or many other fast guys here an email, or phone call, you would dial him in just right.

You, for example, would be the kind of man that we would feel very thankful to have help fix a Hot Rod if we sent it to ya.

Keep up the exemplary work and thanks for your service...