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Old 07-09-2011, 10:23 PM
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fuel pressure reg w/ Edel 650 carb?

So I've read on here that the stock fuel pump produces too much pressure for the Edelbrock 650 cfm carbs and they tend to load up (flood) at idle conditions. Is it necessary to use a fuel pressure regulator to have nice idle conditions or is the pressure regulator a "must have"? I have the 400 engine, Edelbrock Thunder Series AVS 650CFM on an Edelbrock Performer manifold. Any recommendations?
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Old 07-09-2011, 10:25 PM
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Yes you have to have a presure regulator or an internally regulated fuel pump.
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Old 07-09-2011, 10:34 PM
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thanks co425 - do you have this setup on your truck? if so, do you have a pic showing how you plumbed in the regulator?
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Old 07-09-2011, 11:03 PM
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I have a 750cfm but other than that yes. Right now I just have the hard fuel line to the regulator to an Edelbrock filter into the carb. It's all inline on top of the manifold until I order up my Edelbrock fuel
pump that's the way it's going to stay. After I get the pump it will go fuel filter to the pump to the carb. I shoot you a pick but it's all covered in heat shield.
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Old 07-10-2011, 10:58 AM
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joshjones.thewelder
The AFB carbs can handle a fair amount of pressure. 4-7 psi is more than enough and I wouldn't worry about a regulator unless your pump consistently produces more than 7 psi.

The "off-road" needle and seat available for the AFB/ Performer carbs can handle a little more pressure, plus the bouncing off-roads conditions as well.

Keep in mind hundreds of thousands of AFB carbs were installed from the factory on Mopars, Pontiacs and even some Lincolns. They could handle things without a regulator, so can yours.

Josh
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Old 07-10-2011, 02:33 PM
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Until you cant figure out why your carb keeps flooding at idle.
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Old 07-10-2011, 03:44 PM
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Bad floats, bad needle and seat, dirt etc.

How much pressure was the pump putting out? Its not like the Autolite/ Motorcraft carbs are special or any factory Holley for that matter.

Josh
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Old 07-10-2011, 04:04 PM
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Edelbrock themselves state that over 5.5-6 PSI can cause issues. Their recommendation is either use an FPR or the off-road needle/seats.
With a cheapo electric fuel pump, and the choke wired open on my 1405, it loads up during warmup. I have a PSI guage right before the carb. The PSI starts at 7-7.5, but once the engine has started to warmup, the fuel pump does too, so the PSI drops to below 6, and there is no more loading up.
The fuel system is run "deadheaded", or without a return line. I suspect that with a return line, the PSI would stay higher, as the pump wouldn't heat up as bad.
This is on a rotary engine, and since one of the worse things you can do to a rotary is hammer on it before it gets to temp, I always run it till warmed up fully before driving it. It's not used on the street, so "driving" it pretty much means "hammer" on it......


Take what you want from this info. But, as many have learned the hard way, exceeding 5.5-6 PSI *can* cause issues with the carb at idle. It may not happen to everyone, or all the time, but it's common enough to warrent the investment into a good FPR, in my opinion. I have one, but haven't installed it. The edelbrock carb is coming off that car, to be installed on a truck engine. A holley 650DP will go on the racecar, along with the carter fuel pump and mallory return style FPR. I'm tired of the flooding issues with the edelbrock in corners, caused by the 90* rotation mounting (front of carb faces driver side of car) and the G-loading in corners. Coming out of a right hander, it stumbles like crazy, and black smoke out the exhaust. All other times, it's instant response. And it is quite the response too.........
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Old 07-10-2011, 04:05 PM
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ya i'm not sure how much pressure the pump is putting out - i've not had it running yet (new engine rebuild). Just trying to set it up from the get go with the correct equipment without having all the headaches later when things aren't working right. The pump is just a standard aftermarket diaphragm pump, close to OEM. Edelbrock manual says to have ~5.5lbs pressure. I might go ahead and put the regulator on just to eliminate any problems.
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Old 07-10-2011, 05:02 PM
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My 460 has the 750 and a Holley mechanical would overload it. I cleaned it out twice and checked the float height but still ended up installing it in the end.

Mounted on rad support.

Click the image to open in full size.

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Old 07-10-2011, 08:36 PM
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YES, you do need a FPR with an Edelbrock or Carter Carb on a Ford with standard 7 psi fuel pump pressure.

The 351M and 400s factory spec 7 psi on a mechanical pump. My old mechanical pump pumps steady 7 psi unregulated. Those old Mopars and Pontiacs did not have 7 psi pumps. They pumped good volume, but they maxed a lower psi. I remember my '69 Dart 340 had somewhere around 4-5 psi and I supplied a 3310 Holley 780 with it.

The Edelbrock / Carter carbs have shorter float arms than a Holley, a Holley will handle higher pressure.

Edelbrock clearly sttes max of 6 psi and recommends a FPR at 5.5 psi.

Here's a Holley 12-803 FPR I just recently mounted on my old 351M after swapping from a Holley that's seen many years of service for an Edelbrock 1405 600 and finding the truck loading up at idle as the higher psi pumped fuel past the inlet needle in it's seat because the floats cannot apply adequate pressure to keep them shut.

I made an "ell" of some 1"x3/16" steel, welded two tabs to coincide with carb studs, and since I used long studs, mounted the mount attop the nuts holding the carb on and used two more nuts. I mounted the Holley FPR to the "ell". I used a fuel pump pressure tester gage and tee between the FPR and carb to monitor fuel pressure while setting. It started out at 7 psi as I knew it would and cranked down to 5.5 psi and removed the tester and tee.

Click the image to open in full size.

Click the image to open in full size.

Pardon the dirty air filter and old looking Moroso Valve Cover .... they'll be replaced soo enough with that 400 .... as will those 20+ year old blue spark plug wires that a squirrel chewed into years ago and that I wrapped with tubing.
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Old 07-10-2011, 08:51 PM
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YES, you do need a FPR with an Edelbrock or Carter Carb on a Ford with standard 7 psi fuel pump pressure.

The 351M and 400s factory spec 7 psi on a mechanical pump. My old mechanical pump pumps steady 7 psi unregulated. Those old Mopars and Pontiacs did not have 7 psi pumps. They pumped good volume, but they maxed a lower psi. I remember my '69 Dart 340 had somewhere around 4-5 psi and I supplied a 3310 Holley 780 with it.

Josh ... The Edelbrock / Carter carbs have shorter float arms and smaller floats than a Holley, and as a result a Holley will handle higher pressure.

I've rebuilt and modified many of both. It's not that one is special or not. It's a matter of leverage. You want to use a lever to lift a load. The load in this case is the float needle being forced away from the float needle seat by fuel coming in from the other side, push by a fuel pump with strength measured as PSI. Just like when you choose a longer pry bar to move or lift or tear open a crate, a longer float arm makes it easier for a float floating in gasoline to push the needle shut agaist that fuel pressure. A shorter float arm is going to require more strength used to do the same job, just like there are some guys who can lift, move, or open that crate with a short screw driver while you might need the longer pry bar.

Holleys have both bigger floats that will carry more weight when floating in gasoline ... hence more force available .... and the float arm is longer, thus applkying more leverage against the needle.

There is also the question of inlet needle / seat diameter as a inlet of double the area with same psi will apply 2x force. But the Holley and Edelbrock both are pretty close in this reguard, and both have two.



Edelbrock clearly sttes max of 6 psi and recommends a FPR at 5.5 psi.

Here's a Holley 12-803 FPR I just recently mounted on my old 351M after swapping from a Holley that's seen many years of service for an Edelbrock 1405 600 and finding the truck loading up at idle as the higher psi pumped fuel past the inlet needle in it's seat because the floats cannot apply adequate pressure to keep them shut.

I made an "ell" of some 1"x3/16" steel, welded two tabs to coincide with carb studs, and since I used long studs, mounted the mount attop the nuts holding the carb on and used two more nuts. I mounted the Holley FPR to the "ell". I used a fuel pump pressure tester gage and tee between the FPR and carb to monitor fuel pressure while setting. It started out at 7 psi as I knew it would and cranked down to 5.5 psi and removed the tester and tee.

Click the image to open in full size.

Click the image to open in full size.

Pardon the dirty air filter and old looking Moroso Valve Cover .... they'll be replaced soo enough with that 400.
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Old 07-10-2011, 08:51 PM
 
 
 
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