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sd4me · 11-09-2006, 04:14 PM

Guys:

Just put a newly restored carb #17054910 on my 73 SD which replaced a standard 750 s/r carb. Car pulls hard but noses over at about 5K at wot. I believe with the larger bore (800 cfm) I am running it out of fuel. I am running a holley 110 gph mechanical pump with stock stainless lines and new pick up in the tank. The holley pump does not have provisions for a return line (but it is plumbed all the way from front cross member to tank). The car is newly restored stock w/engine mods. and I want to keep the stock appearance. Am I creating a high vaccum condition at the pump by not having the return connected? When I put gas in it, I get substantial pressure release when I take the cap off, as it did before the new carb. Maybe a simple float adjustment? Any ideas are appreciated...

Larry Navarro · 11-09-2006, 05:06 PM

I had the same problem with my old '73 SD clone. Installed an electric pusher pump at the rear by the tank and problem was solved.
I used a Mallory COMP 110 which is internally regulated to 6-7psi.
The COMP series pumps are of a "draw-through" design meaning that a suction from a downstream source(mech. pump) can pull fuel through the pump, even though its not running.
I hooked up a switch to operate the pump on demand, in tandem with the mechanical pump to prevent fuel starvation.

sd4me · 11-09-2006, 07:42 PM

Larry:

Appreciate the response. Where did you install the mallory pump, and where did you pull power from? Does it need to be switched or can it run continuously in tandom with mechanical pump? Did you run a return line? I live in the northeast and want to get this thing resolved before the flakes fly...

Check your PM's on another subject.

Thanks.

sd4me · 11-09-2006, 07:42 PM

Larry:

Appreciate the response. Where did you install the mallory pump, and where did you pull power from? Does it need to be switched or can it run continuously in tandom with mechanical pump? Did you run a return line? I live in the northeast and want to get this thing resolved before the flakes fly...

Check your PM's on another subject.

Thanks.

sd4me · 11-09-2006, 07:43 PM

Larry:

Appreciate the response. Where did you install the mallory pump, and where did you pull power from? Does it need to be switched or can it run continuously in tandom with mechanical pump? Did you run a return line? I live in the northeast and want to get this thing resolved before the flakes fly...

Check your PM's on another subject.

Thanks.

Larry Navarro · 11:15 PM

I installed it just above the rear of the tank, on the sloped section of truck floor panel, using brackets from the hardware store. You can operate it with a toggle switch and a relay with 12volt power fom the fusebox. I ran the wiring under the carpet to the rear.
Can't recall if I used the return line.

Oh yes, for safety purposes, utilize a pressure switch. Using a branch tee, mount the swirch off the sending unit port on the filter housing and wire the switch "in-series" with the pump power circuit. This way, the pump will only operate when the switch senses oil pressure. If you were to have a accident and the key in the "on" position...........the power would be constant to the pump without the pressure switch. You don't want that thing pumping gas if no oil pressure.

2manyT/A'S · 11-10-2006, 02:26 AM

Quote:

Originally Posted by sd4me

Guys:

Just put a newly restored carb #17054910 on my 73 SD which replaced a standard 750 s/r carb. Car pulls hard but noses over at about 5K at wot. I believe with the larger bore (800 cfm) I am running it out of fuel. I am running a holley 110 gph mechanical pump with stock stainless lines and new pick up in the tank. The holley pump does not have provisions for a return line (but it is plumbed all the way from front cross member to tank). The car is newly restored stock w/engine mods. and I want to keep the stock appearance. Am I creating a high vaccum condition at the pump by not having the return connected? When I put gas in it, I get substantial pressure release when I take the cap off, as it did before the new carb. Maybe a simple float adjustment? Any ideas are appreciated...

Larry's got the fix for your fuel delivery problem,but if you want to stay "stock looking",you might want to try this FIRST.

Take the Holly fuel pump off & give it to somebody that's running a two barrel.
That's about all they are good for.
Go to your local parts store & order the CORRECT stock mechanical fuel pump for your application.

4bbl & a/c cars used a pump with a reservoir (small can) on the bottom.

This is the one you need.

Your "so called" high performance Holly pump can't keep up to the large round port motors fuel demands,but the factory style pump with the reservoir should do the trick.

I've experience the same problem with BOTH 455HO & SD engines & found the stock pump with quadrajet will take you into the mid 12's if you're set up properly.

It will also resolve your return line issue.

If you can still buy the correct stock pump,it shouldn't be any more than 35.00 & 1/2 hour to find out.
GOOD LUCK!

sd4me · 11-10-2006, 10:52 AM

Great info Larry & 2manyTAs. I will go with the stock pump and return lines connected on first try at this fuel issue. Larrys set up if needed after that. The car was running an electric pump before resto, should have left it there...I will be changing it out this weekend if I can get the pump and will post results.

Lloyd-TX · 11-10-2006, 12:05 PM

2manyT/A's advice is good.

Though other's have issues running stock pumpson their HO/SD Firebirds, my blue Formula has run upper 12's @ 105 with the same 17054910 S/R '73 SD Q-Jet and a completely stock fuel system and no fuel supply issues whatsoever.

One further piece of advice - make absolutely sure that you replace ALL of the flex hoses in the fuel system. Also, purchase a new and correct fuel tank cap.

BTW - here are PN's for the correct OEM '73 SD fuel pump:

AC-Delco: 40931
Airtex: 40931
Carter: M6405

Hope this helps!

sd4me · 11-10-2006, 04:22 PM

Lloyd-tx

Good advice. I purchased a carter #M6405 today, thanks for the p/n's. The next check if the pump isnt it, is to set the float level. Whats yours at? I know it sounds bass ackwards, but I need to get under the car for oil change anyway, and havent liked that holley pump set up w/no return line.

Thanks

Lloyd-TX · 11-10-2006, 04:53 PM

Quote:

Originally Posted by sd4me

Lloyd-tx

Good advice. I purchased a carter #M6405 today, thanks for the p/n's. The next check if the pump isnt it, is to set the float level. Whats yours at? I know it sounds bass ackwards, but I need to get under the car for oil change anyway, and havent liked that holley pump set up w/no return line.

Thanks

You're welcome!

I set my float level at 1/4". Should work fine, but if you experience hot fuel handling issues (pig rich @ HOT idle), try lowering it to 5/16".

You also need to be sure that you're using the correct nitrofil float - not brass. The brass floats are larger, hence wasting VERY valuable float bowl volume. I prefer AC-Delco floats, but they're getting hard to come by. AC-Delco # 7037316 or 7037705. Standard FL1 or Borg Warner CF271 will work as well.

Check with Cliff Ruggles for Q-Jet parts if you need any.
ruggles@ecr.net

Once again, good luck with it!

J GLASGO · 11-11-2006, 09:27 AM

Quote:

Originally Posted by 2manyT/A'S

Larry's got the fix for your fuel delivery problem,but if you want to stay "stock looking",you might want to try this FIRST.

Take the Holly fuel pump off & give it to somebody that's running a two barrel.
That's about all they are good for.
Go to your local parts store & order the CORRECT stock mechanical fuel pump for your application.

4bbl & a/c cars used a pump with a reservoir (small can) on the bottom.

This is the one you need.

Your "so called" high performance Holly pump can't keep up to the large round port motors fuel demands,but the factory style pump with the reservoir should do the trick.

I've experience the same problem with BOTH 455HO & SD engines & found the stock pump with quadrajet will take you into the mid 12's if you're set up properly.

It will also resolve your return line issue.

If you can still buy the correct stock pump,it shouldn't be any more than 35.00 & 1/2 hour to find out.
GOOD LUCK!

Good advice,my FAST T-37,SD Formula,went 116,and 111 with this same set up.Actualy had a pusher pump on the T-37 when i first put it together,and it gave me a spewing problem in first gear,took it off,ran fine. Make sure that your sock on your tank pick-up is new,this is the biggest problem on most of these old cars.

x-bird2 · 11-11-2006, 10:22 AM

all good advice above. i think your statement about having tank pressure when taking off the gas cap shows the problem. make sure you have a vented cap and that the tank vents are not blocked off. I too am running a no-return line setup and ran into the same problem at about the same rpm when i was running a q-jet with no pusher assist. bowl size (i.e. keeping them full) in the q-jet is sensitive to what's going on in the rest of the system when everything is stock or close to stock. i ran a piece of rubber fuel line up off one the tank's corner vents to the highest point i could get it to and secured it there. ( i have an indoor garage and there are no fume or slosh issues) i also use 2 of the standpipe lines with the others open. put a new sock filter on the tank pick-up if you haven't already and make sure there's as little rubber line in the system as possible. i hard-lined everything up front.

ry57pont · 11-11-2006, 11:14 AM

larry, your pump idea is a great one, i was going to put a switch on the carb so at WOT the pump is on. How much HP is your car and what times does it run?

Larry Navarro · 11-11-2006, 12:46 PM

I had that setup on a stock SD 455 with the exception being the H-O racing HC-63(enhanced Ram air 4 grind) over the stock. Everything else was original SD.
Horsepower unknown but the car ran high 12's at 108.

ry57pont · 11-11-2006, 06:19 PM

Do you think your fuel system would work on a 470hp motor? or should i just eliminate the mechanical pump? i really like the idea of not running a electric pump all of the time.

sd4me · 11-11-2006, 06:34 PM

x-bird2:

Good advice on the tank venting. I just installed the stock fuel pump, changed oil and checked everything underneath. Too late in the day to take this sled for a rip though. I will monitor the pressure in the tank, now with the return line connected Im hoping it resolved the pressure issue, not sure though. The gas cap is not vented. I will verify what Ive got for tank venting as that my be part of the problem. J Glasgo, the pick up and sock filter are new also.

Lloyd-TX Thanks, I will verify float level and float. Just got the carb back, hate to open it up so soon, but gotta get the gas...

Thanks for all the great ideas. I will post final results soon.

2manyT/A'S · 11-11-2006, 08:56 PM

sd4me

FYI: I've had a couple of premature "failures" with NEAR NEW / low mileage Carter F/pumps.
Most noteable was in the smogtest lineup in my 71 T/A,(thought I was out of gas) but ended up riding home on the wrecker.
So,if the mechanical pump DOES solve your "issues",I'd be putting a NEW A/C or Airtex on your Christmas List!

sd4me · 11-13-2006, 11:27 AM

Thanks 2manyt/a's. I will keep that in mind.

RASK · 11-13-2006, 05:40 PM

My $.02, I'm no engine expert but, I was told by my engine builder to remove the stock internal Q-jet gas filter and run an external 3/8" filter. I'm pushing 460hp at the dyno. I was also told that I could run the stock fuel pump and lines and I shouldn't run out of gas unless I was going down the autobahn or something. Looking stock was very important to me while increasing performance significantly. I just finished putting it all together and haven't got it legal yet but I've taken it around a 3 mi loop getting on and off it and it hasn't stumbled yet. I would like to find out if removing the stock filter was necessary or not since the external filter is non-stock and it's there for anyone to notice.

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