PMO float level

[dipso]

Where is the right level in the window for the float level?
I have both balanced perfect and they are right at the dot.

I am still running rich. Would lowering the float level a tad help cure the rich condition?
That seems like an easy thing to try if anyone has tried it.

I don't think I am ready for re jetting and all those other fun things.

[TimT]

Would lowering the float level a tad help cure the rich condition?

No

[RWebb]

pressure?

[dipso]

Originally Posted by TimT

No

Damn!

[dipso]

Originally Posted by RWebb

pressure?

I'm at 3.5 with a pmo regulator.
I was hoping I just had to high float levels.

Here is my situation.
I have a stock 2.7 motor. It's old and worn and needs a rebuild but all I could afford right now was the top.( Carbs and ignition).
They are 40 PMOs with 34 Venturis, 135 mains , 55 idles, 130 idle airs,190 airs and F11 tubes.

I can't seem to stop running running rich. When I set them to a respectable 12.9 or12.5 they just wont run right.
I need to be in the 10s in order for it to perform properly. I can get away with an 11 AFR but that is about it.

What do you think I should change?
I know changing jets would be easy, but I was hoping for something even easier, like a float bowl adjustment.

[RWebb]

try 3.2 & see

[dipso]

That's interesting. I didn't know lowering the fuel pump pressure would lower the float bowl.
I don't think I have much more room for adjustment on the regulator but I'll take a look.

What do you think about those carb specs I listed.
Maybe I should try a lower #.
Maybe 130 mains and 50 idles.
Would that raise my AFRs or does it work opposite, where a larger jet lowers AFRs.

[ratpiper71T]

Perhaps your emulsion tubes are wrong for the set up. You should contact pmo to ask about jetting etc. Setups. Here's a chart that was posted here a while back..

Weber Jet Settings

[KTL]

Pressure shouldn't be a tool IMO to adjust your AFR. Pressure should be adequate to fill the wells and keep them full for you. If you're too rich at 3.5, its not on account of pressure. The well is being filled and the float is rising to your desired level to shut off the fuel supply at the needle valve. Lowering the pressure is simply going to make the float fall more often, thus opening the needle valve more frequently. If you choke the pressure far enough to starve the well and your mains, that would certainly lean it out, but that's a very inefficient way to adjust for your problem.

Carb fuel pressure should not be confused with how most people think in terms of fuel injection pressure. Carb fuel pressure needs to be sufficient to keep the wells properly filled and that's all. Since you have a reservoir of fuel ("zero" pressure) in the wells that is feeding the carbs mains, fuel pressure is not a major factor in terms of mixture. You just have to ensure that the well is full enough but not too full.

If you're too rich, you need bigger air correctors or smaller main fuel jets. And note that the air correctors are typically a 3X change as compared to mains. Meaning a larger air corrector (more air) gets your 3 times leaner than a single main jet decrease (less fuel). Emulsion tubes are sort of a black art and i'd stick with what many say is a proven choice. Looks like those charts say F11 is a good choice for 2.7, so i'd stick with that.

Also your AFR numbers are contrary to what you state is your problem- too rich. If you say it runs better at 10, you are RICHER at 10.

[dipso]

Thanks KTL, that helps. It certainly sounds like you know more about the inner workings of a carb than I do.
I wasn't planning on lowering my floats to adjust the AFR, but I was wondering where the right place in the window (PMOs) is. You even said 'full enough, but not too full'.
Do you think being right at the dot is too full. I was wondering if I was too full.
That was kind of my original question.

I understand the AFR and running that rich is not supposed to be good for the cylinder walls. I have read that the ideal AFR for carbs is about 12.5. Mine won't run properly at that ratio.
So I have to richen it up.

I think my rings are pretty worn (130,000 miles) so that might be where my rich readings are coming from.
I have 190 air correctors and 135 mains.
What would you do? Go bigger on the correctors or smaller on the mains?
Or leave it alone and it is what it is.

[ratpiper71T]

Emulsion tubes are sort of a black art and i'd stick with what many say is a proven choice. Looks like those charts say F11 is a good choice for 2.7, so i'd stick with that.



Also your AFR numbers are contrary to what you state is your problem- too rich. If you say it runs better at 10, you are RICHER at 10.

If it's the chart I posted does it not suggest that f3 or f26 is the ET for a 2.7?

[RWebb]

Originally Posted by KTL

Pressure shouldn't be a tool IMO to adjust your AFR. ...

I agree completely. It makes no sense that when I backed off a tad from 3.5 on my PMO regulator that my PMO carbs ran better. It makes no sense at all...


BTW - I have F3 tubes burned into my brain, but check it.

[KTL]

I don't have PMOs, I have 46 Webers. So I would be using PMO's bowl plug-in vial to set the levels. My understanding is the key is to have them same so that the main circuits' reaction times are nearly as close to each other as possible.

In terms of your current jetting, it sounds consistent with other jetting i've heard of. But do think about changing to the F3 since it shows up as the tube of choice for many people. My reference material doesn't list the F11 as "current" useage so i'm not sure what type of circumstances that tube is used for. F3 is described as two uses:

1. For mixture enrichment at low rpm or during slight acceleration (tube w/out orifices at top)

2. When mixture enrichment for slight accelerations is needed, the fuel reserve in emulsion well must be increased: this is obtained by fitting a tube having small outside dia., orifices located prevailiingly in the lower portion and a larger size air corrector jet to prevent excessive mixture richness at high rpm.

For reference, my 3.0L with race cams is jetted with 36mm venturis, 160 air correctors, 55 idles (too low for me and I plan to change to 60), 200 mains at 4psi. I have to re-check my AF to see where i'm at but I definitely got it richer. Previously I was overly lean 16.0 with my 42mm venturis, 160 air correctors, 55 idles, 200 mains at on 93 octane pump gas. Since I was already high on mains, and didn't have any lower air correctors to cut down the air, I put in the smaller venturis to pull more fuel (via higher incoming velocity).

I also had backed down the fuel pressure to 4 because my instruction from the shop that built/tuned it was to have it at 6 to 6.5 psi. I felt that was way too high based on most everyone I ask- overpressure pushes the floats off the valve and you get excessive fuel and possible overflow. I suspect that high pressure worked at WOT when the mains could suck the fuel out of the wells at a high rate. However at lower rpms I don't think that was good to be running that much pressure.

Originally Posted by ratpiper71T

If it's the chart I posted does it not suggest that f3 or f26 is the ET for a 2.7?

You are correct. My mistake. F26 is a choice for "very large main fuel jets" according to one of my text sources. So might not be a good choice in dipso's instance since he's running 135 mains which aren't necessarily considered "very large."

Originally Posted by RWebb

I agree completely. It makes no sense that when I backed off a tad from 3.5 on my PMO regulator that my PMO carbs ran better. It makes no sense at all...

I'm just saying that fuel pressure shouldn't be viewed as a tuning tool per se'. Typically it's a set-it-and-forget-it approach and you focus on other variables. Since there's a well of fuel the carbs are feeding off, i'm suprised a slight tweak in pressure would produce the result you had. You sure your pressure reading is correct? If the pressure is errantly high by a good bit, backing it down might have made it agreeable to the carbs?

[RWebb]

FWIW, I used the built in gauge on the PMO regulator - only thing I can think of is that it was reading low. It seemed odd to me - maybe it was just a spurious temporal correlation of events & not causal at all...

[RoninLB]

F-11 for PMOs w/2.7

sometimes Webers and PMOs are different

[911pcars]

Originally Posted by dipso

I'm at 3.5 with a pmo regulator.
I was hoping I just had to high float levels.

Here is my situation.
I have a stock 2.7 motor. It's old and worn and needs a rebuild but all I could afford right now was the top.( Carbs and ignition).
They are 40 PMOs with 34 Venturis, 135 mains , 55 idles, 130 idle airs,190 airs and F11 tubes.

I can't seem to stop running running rich. When I set them to a respectable 12.9 or12.5 they just wont run right.
I need to be in the 10s in order for it to perform properly. I can get away with an 11 AFR but that is about it.

What do you think I should change?
I know changing jets would be easy, but I was hoping for something even easier, like a float bowl adjustment.

You've posted some issues with your carb setup recently, yes? Remind us about that and perhaps a short summary of how you set them up.

As I recall, you ended up using the idle air jets to adjust idle mixture/speed. That right?

Sherwood

[1QuickS]

Do you take your AFR readings at idle and then take a test drive or is it rich throughout the power band from idle, through progression on up to redline?

[dipso]

Originally Posted by 911pcars

You've posted some issues with your carb setup recently, yes? Remind us about that and perhaps a short summary of how you set them up.

As I recall, you ended up using the idle air jets to adjust idle mixture/speed. That right?

Sherwood

Well, the main problem I am having is it just blows a lot of smoke. It didn't do that before the carbs.
I start it up, poof. Lots of smoke.
I decelerate and poof. Tons of smoke following me up to the light. It's kind of embarrassing.
It didn't do any of that before the carbs. I keep thinking my rings are bad and the carbs are sucking so much more air that that is the reason it is pushing so much out my tailpipe. That's just a guess.
I don't know.
Could be the valves?

Yeah I tried to add more air by opening up the air jets a bit but that didn't really do anything so I put them back.

Basically, I just put the carbs on the way they were shipped. The specs listed above are the way they came.
They are perfectly balanced at idle and at a higher RPM. I have checked all that.
My plugs are new and gapped at 60. NGK BP5es, I wanted a bigger spark to help ignite more fuel.

Im out about 3 turns on the screws. PMO says that if you have to go 3 1/2 out it means you probably need bigger idle jets, but I think I am cool with that. I'd say my idle jets are fine.

I think mains are small enough already at 135.
What would putting a larger air corrector in do? Add more air and help vaporize the fuel for better burning?
If I need bigger air correctors, are they the standard Weber ones that I could buy at any speed shop. Or are they special only available from PMO.

There is one thing about the carbs that I find strange though.
When I put the synchrometer on them, they are all balanced perfectly but cylinder #3 has to have the screw almost completely out in order to synch.
The others are all in range without even having to adjust the screw very much.
#3 is getting spark, I pulled the wire and checked that.

It runs and runs pretty good. It just smokes like some old jalopy.
It's embarrassing.

[RWebb]

did you send Richard Parr a fax yet?

is this on the stock 2.7L motor?

what cams? stock CIS cam & pistons or...?

[dipso]

No, not yet. I'm pretty sure it's rings.
I remember reading that a quart every 1000 miles or so is bad. I have never checked, I use the car so infrequently, but I would guess a quart every 500 miles for me.
Possibly less.

I think I'm just screwed until I get the new pistons, cams and cylinders. That's on the list but not until next year.
I might fax Richard and see what he says, but he did give me a couple of numbers for carb experts in my area.
Maybe I'll just give it to one those guys one day and see what they can do.
It's probably best left to an expert than me just poking around at it, hoping to change the right thing and not the wrong thing.