V8 w/ carburetor + eletric fuel, runs too rich. Do I need a fuel pressure regulator? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 10-21-2009, 07:23 AM
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V8 w/ carburetor + eletric fuel, runs too rich. Do I need a fuel pressure regulator?

Got a new project from my brother, 88 dodge pickup (5spd) 4x4 with a 97 5.2L Magnum 318. Edelbrock 1406 (600cfm) carb, and an electric fuel pump that's always on when the key is on.

I failed state carbon monoxide emissions. The standard was about 1.25 or so, and I ran a 4.45.

After some research I understand this typically happens when running too rich.

Do I need a fuel pressure regulator, and if so how do I know its the right one?

Any help appreciated, thanks!

Heres a pic for good measure since I haven't been around for a while since I sold the Camaro:




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Old 10-21-2009, 07:45 AM
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You can quickly check to see if your fuel pressure is excessive by either splicing a T fitting into the fuel line and hooking up a pressure gauge or, since your pump runs with the key on - just pull the fuel line off the carb and put in on a gauge. You don't want to go over 5 lbs.

You could be experiencing an ignition timing issue as well, if the spark is not timed correctly it can also increase emissions.
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Old 10-21-2009, 07:49 AM
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is that test done at idle or at some set rpm?

what is the initial timing set at?

have you made any adjustments to the carb (idle mixture or jets)?
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Old 10-21-2009, 08:00 AM
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A rubber fuel line feeds the carb, I can disconnect that and hook a gauge to it I'll go buy one.

The emissions test is donw between 2,000-2,500 rpms. They had mine at 2,300 rpms.

Brother says he set ignition timing at -12 degrees (advanced.)

Only adjustments to carburetor were the idle mixture screws which I messed with to get the highest possible vacuum at idle with out losing more than 40 rpms.. I got 21 in/Hg @ idle.

More features of this truck as as follows: Pertronix stand-alone distributor, and MSD blaster coil. Dunno if that matters?
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Old 10-21-2009, 08:19 AM
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An adj. vacuum fuel pressure regulator should do the trick. It will only pump the pressure you need regulated by engine demand.
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Old 10-21-2009, 08:40 AM
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Here's the Edelbrock Owner's Manual. Use it to do step by step tuning of your carb and you should fly through emissions testing......
http://www.edelbrock.com/automotive_...ers_manual.pdf
Here are 6 pages of jets....
http://www.summitracing.com/search/P...Edelbrock+jets
And 10 pages of metering rods. Be careful here, they have Quadrajet rods mixed in with Performer rods. There are also Summit brand rods for Performers....
http://www.summitracing.com/search/?...ng+Rods&page=1
And 4 different diameter needle and seat combos....
http://www.summitracing.com/search/?...e%20seat&dds=1
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Old 10-21-2009, 08:58 AM
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This is my second time dealing with a carbureted vehicle, so I'll have to do some research before I click the links to figure out how all of the parts work, but I do thank you for the links.

I just bought a fuel pressure gauge, and regulator 1-6 psi. I will go check the fuel pressure, and if it's over 5/6 I'll install the regulator and see how it runs / drives after that.

It is hesitant to accelerate now so maybe this will fix that too.. does flooding/ rich cause hesitation?
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Old 10-21-2009, 09:42 AM
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hmm, now I am stumped. I hooked up a fuel pressure gauge and all I was getting was 4.5 psi. just before the carburetor.

That doesn't make sense, because there is absolutely no inline regulator, and unless the fuel filter is that clogged up, I don't understand how they were able to do this.

Well, back to the drawing board I guess, is 4.5 psi ok for street driving?

Must be up to the pieces of the carburetor itself now?.. confused.
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Old 10-21-2009, 09:59 AM
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Your 4.5 psi is fine, no problem there. There is most likely a bypass regulator built in to the electric pump.

Your issue is not fuel pressure but carburetor and possibly ignition tuning - print off the Edelbrock tuning guide and read up on carburetor function and you'll be ahead.

I'm rather shocked that CO emissions was your only issue for the test - what with the open element air cleaner and modified ignition I would assume that would be a problem right there - apparently not.
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Old 10-21-2009, 10:31 AM
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In NJ if you swap an engine it must be by the same manufacturer as the original, and be of the same year, or newer. 88 dodge truck with dodge 97 was ok with them.

The truck has true dual exhaust, 1 cat-conv. per bank of cylinders - they were glad to see that.
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Old 10-21-2009, 10:40 AM
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600 cfm AFB

sounds like metering rod changes will help you pass. find out which one it's running and increase the cruise size and keep the power size. for example if you have 65-47, install a 68-47 or 70-47. another consideration would also check float levels of the carb just to make sure they're not too high. (specs should be in the owner's manual.) then, I would dial in the ignition timing.

ps 4.5 psi sounds fine for your setup
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Old 10-21-2009, 11:24 AM
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Another thought about the air cleaner. If there is insufficient filter area for the cubic inches of the motor, there will be a restriction there at the element that could cause additional vacuum and possible enrichment of the air/fuel ratio. I know from going through emissions testing here in Arizona that a high reading will be shown if the air filter element is clogged. It makes sense to me that a filter of insufficient area would do the same thing.

On a 350 for instance, I like to use a 14 x 3 filter (131.88 square inches of filter area). Using this seat-of-the-pants 0.377 square inches of filter area per each cubic inch rule of thumb would indicate that a 318 would like around 120 square inches of filter area.

I think I would be looking around for a larger filter housing that would work on the ebrock carb and allow you to fit more filter area onto the motor. Might work, might not, but I'd be looking at this change along with dialing in the jets/metering rods and float level.
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Old 10-25-2009, 06:48 AM
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I took the carburetor out, rebuilt it to learn what every part of it is and tuned it through and through. The truck runs great now, but as I looked at the exhaust having someone rev the engine for me to check the exhaust I realized I'm puffing a bit of smoke, especially from the left side (true dual exhaust.) They hook up to the left side to do the emissions test.

This engine has really been used, towing, racing etc. The valve stem seals are probably due to be replaced.

Could the burning oil have caused me to fail emissions for high carbon monoxide levels?
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Old 10-25-2009, 07:15 AM
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The air fluel ratio of the carb's idle /off idle transition circuit and mainjet/metering rod part throttle cruise circuit needs to be fine tuned.
First hook up the PCV so it is functional. When you eliminate the PCV the carb's idle circuit is forced way richer than nessessary.
Get and install a common 3 or 4 wire heated type O2 sensor on the the exhaust head pipe near the exhaust manifold. This will allow you to read the idle and off idle afr using a volt/ohm meter or AFR gauge off the O2 sensor.

The exhaust system/manifolds ahead and after the O2 sensor must be leak free for the O2 sonsor to read correctly. If there are any air leaks, the sensor woll read wrong.
You want the idle/off idle/low speed part throttle cruise AFR as close to 14.7:1 as possible (lowest emmisions, hottest exhaust temp, best cat converter function. Tuning with a AFR meter/volt meter/O2 sensor will allow you to do this.
Adjust the ignition timing to 4deg BTDC at idle for the emmissions test.
Install new spark plugs. Inspect the cap, rotor and wires.

If you have a open type carb spacer under the carb, remove it and bolt the carb directly to the manifold. (air fuel distribution at idle)

Once you have the idle/off idle/cruise afr corrected a catalytic converter will function properly to further reduce the emmisions.
If you do not correct the carb AFR a cat converter will have a short ineffective lifespan. (the cat converter works best and lasts longest when the AFR is held within a narrrow range at or near 14.7:1 at idle and cruise. this is critical)

The edelbrock carbs are not factory designed for low emmisions and need to be dialed in/fine tuned to your motor. They tend to be set up quite rich in the idle circuit to allow them to run on anything. "universal"
The fact that the PCV is disconnected is just adding to the over rich idle.
resulting in a high CO reading on the smog test.

Last edited by F-BIRD'88; 10-25-2009 at 07:46 AM.
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Old 10-25-2009, 07:35 AM
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In your second pic, was that the way you took it in for testing? or were you in the process of working on it? Reason I ask is I don't see any vacuum lines to the port's on the front of the carb, connected. Where you run your advance hose to, is your choice, but I would think about setting the initial timing to the spec's on the tag under the hood. This would include, having the vacuum adv. hose hooked up to the proper vacuum port (ported vacuum or manifold vacuum). I don't see a vacuum line going to your ported fitting on the front of the carb or the full maifold vacuum port. Then again, maybe you don't have vacuum adv and it's all electronic.
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