PMO pressure

[dipso]

I can't seem to get my pressure below 4.5. I have checked the lines and they seem O.K.
I had a kink in my feed line, where it went over the steering rack instead of under, but I fixed that yesterday.
I am still at 4.5.
It increases just fine, I can get the pressure up to 15. I just can't get it down to 3.5.

I am thinking about removing my return line, taking the cap off the gas tank and blowing air through the hose from the rear.
Maybe there is a blockage.

What do you think?

P.S. These are brand new PMO's, Right out of the box. They run great but I am just going through the fine tuning.
Also my float level seems a little low.
Do either of these things matter that much?

[James Brown]

Don't think there is any blockage, if it is the CIS fuel pump, I think the PMO regulator can't get that low. Mine reads 3.5 at the lowest setting. Also, most mechanical gages are not that accurate at the lower side. Give it a try. Or you might get a pre-regulator regulator but that might reduce fuel flow (gpm's).

[SCOTITUDE]

I have the CIS pump and the pmo reg and it gets down to 3.5. Is there a way to check the regulator? or hook up a different gauge to the supply line? just to rule out the reg gauge being defective.

[dipso]

James, mine reads 0 at the lowest setting. 3 to 4 is what they recommend.

Scott, I don't have another way to check the gauge.

How important is .5 pounds of pressure?

[James Brown]

Dipso, yeah your right not worth .5 psi. Mine runs great at 3.5, i bet it would also run great at 6 psi.
Scotitude, yeah you can hook up a really good gage in line in place of your fuel filter downstream of the regulator and set the pmo regulator to 3.5 psi. Now is that 3.5 psi set with the pump running static (no fuel flow) or during full throttle (max fuel flow)? It seams that the gage does not move from 0 fuel flow to max flow. Stays at 3.5 psi.

[dipso]

I'm about 5 beers into this tuning thing.
I tried the other day and made it worse, I had to go back to the original settings.

This is tough.

Runs great out of the box and if i didn't have all these tools and paperwork I would be satisfied.
When I checked it with my synchrometer it was all off.
I know it can get better.

[dipso]

I give up for tonight. It does seem better since I unkinked that supply line. doesn't seem to stumble at quick throttle.

[James Brown]

Don't spend too much time trying to sync the carbs, they never will be all the same. Once close, use your ear (and a sober mind) to fine tune. And if it runs great, don't touch it!

[RWebb]

you should contact Richard - see what he says

BTW - my CIS pump can be regulated down to 3 or 3.5 just fine with the PMO unit

[dipso]

Randy, didn't want to bother Richard unless a last resort. And James, tuning carbs by ear is a a way off for me. I like #s.

Yeah, it's weird. Right out of the box they ran great. I went through the instructions for fine tuning and boy did they get worse. I had to go back to the original settings, that's where they are now.
Tonight I was just doing linkage and throttle adjustments.
Glad they came with original setting #s. i think it was 2 out on the mixture and closed on the air.
I did back off the air 1 turn if I remember correctly, that was 2 days ago.

It does seem that since I unkinked that fuel supply line they are running better. I'll bet when I get back to it in a few days the float levels will be up to par.

Also when i first attempted my balancing I was getting readings of 6 all the way down to 3 on my synch. Tonight I checked after unkinking the line yesterday and they are all about 5 to 4.

I'll bet i wasn't getting proper fuel volume.
Oh well. Friday I am off, That gives me a day to attack these things.
I'm confident.

Oh yeah, tonight i tightened up my linkage, brought my pedal up about an inch and set the stop on the butterfly at about 11:45.
Full throttle baby!

[lindy 911]

Try removing the return line from the regulator. Attach a piece of line long enough to go into a five gallon fuel can. .375 fuel line is cheap. Make sure the line won't fall out of the can then start the motor and check the pressure. If it goes down from where you are now, you know you have a return problem.

If it doesn't change, you know the problem is in the regulator or gauge. Process of elimination will get to the root. I have a pump that is set at 3.5 and shuts off when it gets there so it doesn't run constantly. I mounted it in the left rear wheel well next to the old flapper box and ran a new stainless steel line through the tunnel. Also ran SS to the filter and eliminated the accumulator from the CIS system. I'm running secondary filters inline after the "T" and before the carb (46 Weber). Works well.

If you see there is a return problem, check the filter in the tank. The return line goes through this filter; it's the big allen head plug in the bottom of the tank.

Lindy

[dipso]

Lindy, that's a good idea. Maybe I will try that but I am not too concerned about 4.5 when 3 to 4 is the suggested amount of pressure.
What could be the harm in an extra .5 psi?
Would it flood? Would it over atomize? Would it blow out some seal? Would it just plain not run right?
I think it would be O.K. But I don't know for sure.


I am only using the in line filters that PMO sent. I tossed the old filter and accumulator, they were stinking up my garage. PMO says to not use the filter or accumulator.
Why do you think I need a filter, before the filter?

About the filter in the tank, I think I have a different set up than you. Under my tank near the steering rack I have 2 attached nipples. One on the right and one on the left.
If i remember correctly the one on the drivers side is a little larger and is for supply. That was the kinked one, I couldn't believe it was practically folded in half.
The one on the passenger side is a little smaller and is return.
Nothing is connected to the big plug in the bottom. I think that is just for draining on mine.

I have had the front end replaced after I smashed it up pretty good one night. Probably a different year tank than 75.

[James Brown]

No the filter is in the tank and you remove it via the large Allen nut at the bottom of the tank.

[Number1_dog]

I spoke with Paul Abbott from Performance Oriented and he uses an item called Colortune to fine tune his Webers. This tool replaces a sparkplug and you tune each barrel individually by checking the color of the combustion in the cylinder that is fed by that barrel. The tool has a translucent top and you get a periscope that allows you to see the combustion in the cylinder. He says he uses it every time even though he has vast experience with tuning Webers.

[dipso]

I would like to check that filter, but I am tired of getting gas all over me. Maybe when my tank empties I'll give it a look.
That F-N kinked hose required 2 showers to get all the stink off me.

That Colortune thing sounds cool.

[cfries]

I dont have a fuel regulator and the pressure is right at 3.5lbs. Now I'm wondering if I have a kinked fuel line up front. Just installed PMO's a few months ago, but having issues with the fine tuning. An MSD ignition did help, but not perfect....yet.

[lindy 911]

Dipso,

3.5 is recommended and 4.0 is max. The consequences are float needles being driven off their seats and too much fuel getting to the bowls and overflowing into the intake manifolds. I know it sounds silly but the .5# you say you have is really 1.0# if 3.5# is ideal. 1# is 28% more than the ideal setting.

cfries,

What pump are you using? If it's a stock CSI pump somethings amiss. They make way more than 3.5# and would have to be regulated down with a return line to the tank. I guess you have a pressure gauge installed?

Lindy

[cfries]

Hi Lindy,

Not sure, I will have to check and I will PM you. I dont want to hijack this thread. I can hear a distinctive clicking sound if that helps. . Thanks for the reply.

[RWebb]

the filter in the tank is a fine metal mesh (on most 911s) - just a pre-filter, really

I also use the in line filter that Richard supplied with my PMOs - I intend to put in a Racor filter/water separator when I get the chance

you need to get a look at your gas & check the return for obstructions

[dipso]

Is there any chance that I don't have to drain the tank to look at that filter?