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  #41 (permalink)  
Old 06-24-2016, 07:08 PM
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It is a custom Q-series from Brent. Clear sight windows on both sides, front and rear. No choke. Mechanical secondaries, jets 74/82, PV 4.5 (now 6.5). No idea about the air bleeds or restrictors. It does have the jet extensions in the rear. Billet metering blocks.

It does tend to almost stall while going around tight corners or hard braking - if that helps anything. Also don't know if it matters but I have an open 3/4 inch spacer between the carb and the intake (Performer RPM). Gaskets are tight - no leaks, no vacuum draws(no PCV, no distributor advance, no brake booster).

Not sure what to do about the fuel pressure or why it is dropping. 110 gph pump with 3/8 lines. Guess I need to tear it all out and go with AN fittings - blah.

Going to jet up to see what happens first. Won't be able to until Monday....

Last edited by Texasdoc; 06-24-2016 at 07:20 PM..
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  #42 (permalink)  
Old 06-24-2016, 07:47 PM
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while not great, i believe you can live with as low as 4 psi into your carb. forgot that you blocked your rear pv. that is a mixed blessing sometimes. i wouldn't be afraid to jump to 92 in the rear to see how it behaves. if that doesnt work then try 95s. if that doesnt work then we would have to start thinking about changing your emulsion bleeds and high speed air bleeds.

would be good to know what you have in there before you start ordering stuff; so I recommend getting the settings from the custom guy that set the carb (blykins?); if he doesnt have then then you can check when you change the main jets on monday.
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  #43 (permalink)  
Old 06-24-2016, 07:51 PM
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wait - your at 82 now? that does sound small without a pv but 92 is too much to start...i think 86-88 to start, then 92 if you need to, then other jets if you still need to go further.
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  #44 (permalink)  
Old 06-25-2016, 12:41 AM
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Doing some study after work. Not looking forward to the 14 hour day tomorrow...

Anyway, I have the MSD Mallory 110gph fuel pump. I read thru the instructions and found that it has an internal bypass of 7psi. The instructions don't say how to adjust the internal bypass, even though there is an external nut and allen screw.

Continuing my search, I found that the Mallory bypass regulators include a plug that disables the internal bypass on the Mallory fuel pump. You have to buy the Mallory pressure regulator to get this fuel pump plug. I bought the Holley HP billet regulator. The instructions for their *regulator* say that the 110 unit was designed for use without a pressure regulator - it doesn't say this in the pump instructions!

What I think is happening with the fuel pressure is that the pump's bypass, set at 7, is not letting the pump put out enough pressure to push the fuel thru the lines, thru the Holley pressure regulator, up to the gauge/bowls. By the time the fuel gets up to the carb, it is less than the 7 the pump is putting out. I have the Holley set on 6.5 (per Quick Fuel's recommendation). My guess is the pressure at the Holley regulator is dropping at WOT since the pressure decreases due to friction/flow while the pump is only putting out 7. In essence the two pressure regulators are fighting each other.

No where does MSD/Mallory list how the internal bypass works. There is a spring that I am supposed to remove and replace with a plug. It doesn't list the size of the plug. Does the fuel run thru the spring and if you take it out and install a plug, the fuel cannot take the bypass circuit? OR, does the spring hold the bypass plunger in to a certain depth and putting in a plug prevents this from collapsing under pressure??? How big is this "plug" that I need? Will adjusting the current allen screw in 1/2 - 1 turns increase my pump output pressure enough so the fuel pressure at the Holley regulator doesn't drop below its set point?

Any thoughts?

Last edited by Texasdoc; 06-25-2016 at 12:44 AM..
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  #45 (permalink)  
Old 06-25-2016, 04:27 AM
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Sorry that you have a 14 hour day ahead.....I know it's rough when you have problems like this and you don't have time to focus on it. It wears on you.

I have never used that particular combination but you are probably onto something. Your logic seems good.

It still would be easy to jet up a couple numbers all the way around and take it for a drive. Lot easier than going through your fuel system.

To fastd, I wouldn't encourage throwing big numbers of jets at a carb in order to richen it up. Making huge jet adjustments is an indicator that the engine is not efficient or the carb is too big. If the engine can't suck hard enough to create a strong signal, you will find yourself adding more fuel to try and compensate.
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  #46 (permalink)  
Old 06-25-2016, 05:29 AM
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blykins,

but do you think a 88 rear jet without a power valve is too big? do recall if that carb has annualar boosters?

sounds like texasdoc needs to figure out his fuel regulator issues first anyway; he might not have to touch the carb if the fuel pressure issue gets worked out.
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  #47 (permalink)  
Old 06-25-2016, 05:33 AM
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I would be concerned about going all the way to an 88 with a 750 sized carb. This is the same carb I use on all of my engines this size (and the same carb I send out to replace the Holley Street Avenger on all the Roush 427R engines), same calibration, etc. I normally do not have to jet up on the dyno to achieve the correct A/F ratio and normally just have to open up the HSAB's very slightly. As a matter of fact, the restrictive air cleaners that are used on Cobras typically richen the mixture up just by themselves.
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  #48 (permalink)  
Old 06-25-2016, 12:52 PM
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Quote:
Originally Posted by blykins View Post
As a matter of fact, the restrictive air cleaners that are used on Cobras typically richen the mixture up just by themselves.
I have one of these but it has a K&N element. Don't know how much it actually improves airflow.

BTW, I can't find the Mallory bypass plug by itself. They ship them with their fuel pressure regulators but not with the pumps themselves. Does anyone have a Mallory pressure regulator who is not using the bypass plug?

Last edited by Texasdoc; 06-25-2016 at 07:08 PM..
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  #49 (permalink)  
Old 06-25-2016, 09:16 PM
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Does anyone have a Mallory Fuel Pressure regulator and is not using the included Mallory Fuel Pump Bypass block off spacer? I have the fuel pump and need the bypass spacer. They only sell the fuel pump spacer with the pressure regulator. I don't want to buy a new pressure regulator just to get the spacer.


Last edited by Texasdoc; 06-25-2016 at 09:21 PM..
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  #50 (permalink)  
Old 06-25-2016, 09:33 PM
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I've never liked that idea.

The factory internal bypass is way higher than any normal pressure setting for carbs.

You can wind it up a bit more, or fit a slightly heavier spring.

In a bypass regulator setup, the excess is returned to the tank, and the pump bypass will never operate operate while spring loaded.

But it is there in case your front regulator jammed for some reason.

How much fuel pressure would the pump produce without a spring loaded bypass?

Food for thought?
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  #51 (permalink)  
Old 06-25-2016, 10:04 PM
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Quote:
Originally Posted by Gaz64 View Post
I've never liked that idea.

The factory internal bypass is way higher than any normal pressure setting for carbs.

You can wind it up a bit more, or fit a slightly heavier spring.

In a bypass regulator setup, the excess is returned to the tank, and the pump bypass will never operate operate while spring loaded.

Food for thought?
I disagree with this statement: The factory internal bypass is way higher than any normal pressure setting for carbs

Only my pump is set at 7 pounds. It can pump out more but the pumps regulator sets the pressure at 7 pounds at the pump's output.

Now you take that 7 pounds, push it thru a 40 micron filter, along 8 feet of 3/8" hose plus connectors to the pressure regulator. The pressure drop is around 3 pounds, leaving me with maybe 4 pounds when at max flow.

If I had bought the 140 which is pre-set at 14, this would work since the pump's internal bypass would not get activated. But I don't have that pump.

So, I need to block my pump's bypass so it will go above the factories setting of 7, so I can actually get my desired 6.5 at the carb - letting the fuel pressure regulator control the final pressure.
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  #52 (permalink)  
Old 06-25-2016, 11:49 PM
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Quote:
Originally Posted by Texasdoc View Post
I disagree with this statement: The factory internal bypass is way higher than any normal pressure setting for carbs

Only my pump is set at 7 pounds. It can pump out more but the pumps regulator sets the pressure at 7 pounds at the pump's output.

Now you take that 7 pounds, push it thru a 40 micron filter, along 8 feet of 3/8" hose plus connectors to the pressure regulator. The pressure drop is around 3 pounds, leaving me with maybe 4 pounds when at max flow.

If I had bought the 140 which is pre-set at 14, this would work since the pump's internal bypass would not get activated. But I don't have that pump.

So, I need to block my pump's bypass so it will go above the factories setting of 7, so I can actually get my desired 6.5 at the carb - letting the fuel pressure regulator control the final pressure.
Ah yes, you are correct there.

You have Mallory's equal of Holley's Red pump.

If you can't get the spacer, you could make one, but I would be fitting a heavier spring.

I think it would a safer option to fit a heavier spring?
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  #53 (permalink)  
Old 06-26-2016, 04:21 AM
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btw, according to holley anywhere between 5-7 psi is ok but ive heard and experienced that close to 7 is too high. holley also says that 4 is the minimum at redline.

i run 5.75-6
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  #54 (permalink)  
Old 06-26-2016, 09:05 AM
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Doc, simply crank in on the adjusting nut to raise the relief pressure on the pump, this is just going to be a quick test to see if raising the fuel pressure is going to solve your stumble issue.
I have a sense that it is not going to help as your video clearly shows that you are maintaining a visible fuel bowl level even when the fuel pressure drops to 4.5 psi. 4 psi should suffice to keep you bowls full for your 450hp motor. Heck, us Weber guys are running 3psi fuel pressure with smaller float needles than you Holley guys.
I am surprised that no one has commented on your statement that the car nearly dies when taking hard corners, I am thinking these two issues may be related
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  #55 (permalink)  
Old 06-26-2016, 09:10 AM
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There are no instructions on how to adjust it. Just crank it in (or out?) until it bottoms out? Or just go in a turn or three? I'll give it a try.

I changed the secondary jets but haven't been able to test yet. Went from 82 to 86. Will try it tomorrow.

What I've read about corner or brake stumbling is the fuel bowl level. Mine are half way up on both front and rear windows.

Last edited by Texasdoc; 06-26-2016 at 09:13 AM..
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  #56 (permalink)  
Old 06-26-2016, 09:31 AM
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Crank it in (clockwise) to raise pressure, a few turns should do it. That spacer that you mention simply eliminates the spring and keeps the relief valve closed in the pump, thus, allowing all regulating to be handled by your Holley regulator. Cranking the screw all the way in would probably accomplish the same thing.

Last edited by wolf k; 06-27-2016 at 03:51 AM..
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  #57 (permalink)  
Old 06-26-2016, 12:28 PM
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keep that 4.5 pv handy - if the 6.5 feels good at wot but too rich before wot then the pv could be better, ie go back to 82s but add the pv - especially for street driving.
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  #58 (permalink)  
Old 06-26-2016, 12:30 PM
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i meant if the 86 jets feel good at wot
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  #59 (permalink)  
Old 06-26-2016, 07:25 PM
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Last Monday I changed the plug gap on a 408 from .045 to .050.
It would miss a little at 4500 rpms. Re-gaped the plugs to .045" and it would pull to 6,000 with missing.
This is a 10. to 1 cr motor.

I did not see what your plugs were gaps at.
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Old 06-27-2016, 05:25 PM
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I usually run them gapped at .040. Last week I put them at .035 just to check since that it what they are gapped from the factory (Autolite 3924). No change. Next time I have them out, I'll put them back at 40.
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