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PMO regulator

I recently finished the rebuild on my engine. 3.2 SS, 9.5:1, DC 40 cams, recurved Distributer, rebuilt heads with intakes bored to 38mm, SSI, M&k 2/2, MSD 6AL Digital, and 46mm PMO,s.
I did the initial 20 min. break-in run but could not dial down the fuel pressure to any less than 5.5psi. I'm reluctant to do any further carb tuning until I can get the pressure down to the recommended 3.5psi. Conversations I have had thus far have stated that the ONLY reason the pressure is that high is due to a kink or restriction in the return line. I have traced the fuel line from carb to tank and can find no kink. As far as a internal restriction I don't know of a practical way to determine that. So my question is, does anyone know of a simple solution to this pressure issue? At this point I am considering installing a Mallory low pressure fuel pump.

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Old 07-03-2011, 04:22 AM
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Well, what fuel pump are you using now?
It is no use setting the float levels without the final fuel pump in the car AND operating on the same input voltage you will see when the engine is running under load.
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Old 07-03-2011, 06:19 AM
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Which way are you turning the adjustment screw? Out should reduce the pressure. If you have done this, then you have some internal restriction.

Here is a test: take the return line off the regulator and plumb to an empty gas can. Then start the pump. You should see a lower pressure. If so, you have confirmed there is a issue with the tank line or tank inlet. If the pressure is still 5.5 then there is an issue with the regulator setup or internal passages.

Obviously fuel is being pumped open loop and will likely fill a gas can quickly. Have a helper ready to shut off the pump quickly!
Old 07-03-2011, 06:22 AM
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Currently there is a Bosch stock fuel pump. The PMO regulator is turned counterclockwise to its limit (out). I will try the fuel flow test next but have to wait until tomorrow when I have a helper.
Old 07-03-2011, 07:28 AM
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I had the same problem. Ended up being a restriction in the tank at the return fitting. You need to disconnect the return line at the tank and open end into a gas tank. Run fuel pump and check pressure. If good, your issue is in the tank. If no good, go back one connection and try again. You will find a restriction somewhere.
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Old 07-03-2011, 07:39 AM
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Just curious BK911, that restriction in the tank at the return fitting, what was the cause of it?
Old 07-03-2011, 08:51 AM
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I am not really sure. I used por-15 to coat the inside of the tank. Maybe some gunk was caked around the return fitting, then I por-15'd over it. Or maybe just a puddle formed in the fitting causing a restriction.

I used some 12 guage wire twisted together to ream out the return fitting. Then a long wire brush with lots of carb cleaner.
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Old 07-03-2011, 09:17 AM
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Today I resumed working on the fuel system and checked the pressure where the AN fitting joins the steel lines. It was at 0.5 psi. Just out of curiosity I rechecked the pressure with everything hooked back up and got 4.1 psi. So here's my question. Will a warm engine with a recirculating fuel system raise the fuel temp. enough to increase the pressure 1.5psi ? I could have sworn that with the engine warm I got 5.5psi, or maybe in the excitement of the first run I read the gauge wrong. If the pressure would stay at 4.1psi I think I would be inclined to leave the system as is.
Old 07-04-2011, 09:09 AM
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I see a variation in pressure day to day. 4.1 sounds close.
Old 07-04-2011, 05:17 PM
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Got back to work on the issue and removed the return line from the gas tank. I had 3.5 psi running the fuel pump. Obviously I have a restriction between the first fitting in the engine comp. and the inlet to the fuel tank.Tried blowing it out with compressed air. Got a small brown stain in the catch rag but not what I would think would cause a restriction. I also cleaned the fuel tank inlet per BK911 suggestion, it didnt seem to be restricted but if the fuel line hooked up is 5.5psi I guess I have to assume there is a 2psi restriction. In the end i've decided to replace the fuel line. Will let you know how it turns out.
Old 07-06-2011, 04:19 AM
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Check out this thread:

PMO fuel regulator

Especially the 2nd page.
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Last edited by BK911; 07-06-2011 at 09:22 AM..
Old 07-06-2011, 09:19 AM
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Well I have to admit that after looking at whats involved in replacing the fuel line it seemed prudent to give cleaning the existing one another try. This time I ran Gum Out through the return line, then compressed air, then a twisted copper wire (like BK911) and repeat numerous times. In the end I was able to lower the return pressure by 1.25psi. A little crude did come out but not near as much as I thought would be needed to lower the pressure that much. That still left me 0.5psi short of my minimum goal of 4psi. So with a lack of any other ideas and a dread of replacing the fuel line I replaced the braided stainless fuel line with 6AN fittings to barb fittings and rubber fuel line. Surprisingly the pressure dropped another 0.5psi and put me at my goal. Now its time to take a crack at tuning the carbs.
Old 07-07-2011, 03:53 AM
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The fuel line replacement is not bad when the motor is out but can be a pain with it installed. A little bit of crud at the fitting could restrict the flow quite a bit. I replaced mine with braided stainless and can get the pressure down to 2.5 at wide open. If you have a lift it will make the job much easier. The fact that you were able to get the line to flow more by cleaning it out tells me it needs to be replaced.
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Old 07-07-2011, 06:27 AM
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Well Lindy I see your point. However I'm not a particularly talented mechanic and this rebuild has dragged on for 8 months now. Time to get on the road! I think I will add the fuel lines to my list of future projects. There's always a list.
Old 07-08-2011, 04:38 AM
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Mines been dragging on since 1992!
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Old 07-08-2011, 06:26 AM
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