How rich are you guys running your carbs?

[dipso]

How rich are you guys running your carbs. I was just out messing with my PMOs and checked the AFR.
I was running about 10 at idle. That's 2 3/4 turns out for me. Too rich.
I turned em in to 2 1/4 and brought the AFR to 12.
It ran pretty good but I think I had a few lean pops so I opened em up another 1/8 th and I imagine it's about 11.5 AFR now.
My timing is 13 btdc at idle and 35 at 4000.
My injection pumps are closed and then opened 1 turn.
My LM2 synched at 20.4, not 20.9. So all those numbers might even be .5 lower.

I can't seem to get them to run right at 12.9, which is what I read is ideal.
I had them set at 12.9 one time and it just kept lean popping. It seems to run better rich.

What are your AFRs at? What is the downside to running rich?
I know if it is too rich (10) the fuel washes the oil off the cylinder walls, and that is not good.
It's a stock 2.7 if that matters.

Just curious what you guys are doing.

[Steve@Rennsport]

To offer any suggestions, one needs a lot more details,....

1) Webers or PMO's???

2) Fuel pressure at a regulated 3.5psi?

3) Float levels PERFECT?

4) Idle jets?

5) Venturi size?

6) Emulsion tube number?

7) Main jets?


Once I have all that, I can help,...

[dipso]

Hey Steve, How's it going.
We talked a few times on the phone. I just bought that JB Racing six pin distributor from you.

Anyways, here is what my spec sheet says.
First of all they are PMOs, Holley Red pump regulated to 3.5 with the PMO regulator.
Float levels are just below the dot and pretty even.
What do you mean by 'perfect'?

The idle jets are 55's.
The venturi says 40/34.
Emulsion tubes F11.
Main jets 135.


Thanks.

[dipso]

Before you start brainstorming, I haven't done much with the air screws.
I just used them to balance the carbs and they are all in synch.

Maybe I could open those up a bit and add more air. Does that make sense?
I never thought of that before.

Thanks again.

[JFG]

Interesting thread, I am facing the same situation. On Monday, fingers crossed, I will have this solved with the aide of a mechanic. I know my limitations and with this I need help!
I would like to go out on a limb and guess what Steve means by, PERFECT. Exact, not pretty close, not good enough, but DEAD ON!! After talking with Steve and reading many of his articles and posts. I realize he does not mix his words, he chooses what he has to say accurately and to the point. It is with great respect that I say this.
Good luck with this and please update your progress.

[dipso]

Here is what I am thinking.
I have never messed with the air screws. Tell you the truth I forgot all about them.
I have been trying to get this thing running right with timing and fuel mixture. I think that is why I am always running too rich or too lean.

I think if I put the AFR back down to where it runs right, usually at about 10 something or currently 11. And then lean it out with more air, instead of less fuel.
I might get it right.
That sounds like the way to get all the fuel you need but without making it too wet in there.

I have been screwing with the injection quantity, fuel screws, timing and whatever else I could think of.
I never thought about the adding more air.

I have my fingers crossed, but that makes sense.

[James Brown]

I have Zenith's, anyone want to know about them? Totally different than Weber's but AFR is around 13. Any less at idle and they pop a little.

[911pcars]

There's a complete procedure for setting up the base idle speed. Please find them and start from a reference point instead of trying to shot gun this. You might get lucky or you might go off on a tangent.

Many procedures suggest adjusting the air bleed screws to initially balance the air flow through all six throats. Thereafter, the idle speed screws (2) determine the idle air flow and thus idle speed via the position of the throttle plates.

The idle mixture is important because even minor mixture screw adjustments can affect the part throttle mixture and thus overall fuel consumption. There's no point in wasting fuel if you don't have to. I've adjusted my Webers to about 3% CO (approx. 13.38 A/F) using an inexpensive Gunson CO meter.

In addition, rich idle mixtures don't burn completely. The resultant excess fuel can foul plugs and dilute valve guide and/or cylinder wall lube and thus increase valve stem, piston and ring wear, respectively.

Sherwood

[Steve@Rennsport]

Originally Posted by dipso

Hey Steve, How's it going.
We talked a few times on the phone. I just bought that JB Racing six pin distributor from you.

Anyways, here is what my spec sheet says.
First of all they are PMOs, Holley Red pump regulated to 3.5 with the PMO regulator.
Float levels are just below the dot and pretty even.
What do you mean by 'perfect'?

The idle jets are 55's.
The venturi says 40/34.
Emulsion tubes F11.
Main jets 135.


Thanks.

Oh yesss,....

Float levels MUST be perfect, not "pretty close or even" but perfect. If they are not, then your idle, pickup, part & full throttle and overall jetting suffers.

135 mains are small for 34mm venturies on a 2.7. I would run 145's to start.

Do you have 180 air correctors?

[Steve@Rennsport]

Originally Posted by dipso

Before you start brainstorming, I haven't done much with the air screws.
I just used them to balance the carbs and they are all in synch.

Maybe I could open those up a bit and add more air. Does that make sense?
I never thought of that before.

Thanks again.

Good man,......the air corrector screws are simply to allow you to make sure each throat passes the same amount of air at idle when the throttles are closed.

Don't touch them if they are all balanced.

[dipso]

Originally Posted by Steve@Rennsport

Oh yesss,....

Float levels MUST be perfect, not "pretty close or even" but perfect. If they are not, then your idle, pickup, part & full throttle and overall jetting suffers.

135 mains are small for 34mm venturies on a 2.7. I would run 145's to start.

Do you have 180 air correctors?

I adjusted the float levels just like it says in the instructions that come with the PMOs. I used a little mm ruler, I think they are good

I have 190 air correctors.

So you think opening up the air at idle a little is a bad idea. The PMO instructions say "Some engines run rich at idle, in these cases it is worthwhile to set the air screws one or two turns open for initial setting."
(I'm re-reading all the instructions 'after' I started the post. Duh.)

I don't remember, because like I said," I forgot completely about those screws". But I can guarantee they are nowhere near an initial 1 or 2 turns out on the air adjusters.

I'm not too worried about screwing anything up with adjustments. I am pretty good with putting things back where I found them. If I back them up 3/4 turn and it doesn't work. I'll put them back 3/4 turn.

Do you think I can reach the 12.9 by running rich at idle and adding air?
And , how important is it that I reach 12.9?

I'll probably give it a shot over the weekend. It couldn't hurt. (Famous last words).

[Trackrash]

Steve, using the glass vials on webers, can you explain what you consider perfect?

[RoninLB]

Originally Posted by dipso

How rich are you guys running your carbs.

It ran pretty good but I think I had a few lean pops so I opened em up another 1/8 th

I can't seem to get them to run right at 12.9, which is what I read is ideal.
I had them set at 12.9 one time and it just kept lean popping. .

I run for clean power and clean NGK BPR7ES/BPR8ES

my take on the adjustments is contrary to most on some things

I do have to live with a lean pop from a hot muffler when coming off the expressway into a ramp if I don't hit the pedal between downshifting to cool off combustion chambers and muffler. I can cool off EGTs by running richer and eliminate the occasional pop but power is sacrificed.

PMOs aren't Webers that seem to need rich to cover up carb deficiencies. Keep in mind that our carbs are only 3 circuits and not the 6 or 7 circuits other carbs may need to become doable.



I only live in Long Beach if you want a ride.............

[dipso]

Originally Posted by RoninLB

I only live in Long Beach if you want a ride.............

Oh yeah, I'm in Long Beach too. I'll be right over.
It's only a 3 or 4 thousand mile drive.

[911pcars]

Originally Posted by dipso

I adjusted the float levels just like it says in the instructions that come with the PMOs. I used a little mm ruler, I think they are good

I have 190 air correctors.

So you think opening up the air at idle a little is a bad idea. The PMO instructions say "Some engines run rich at idle, in these cases it is worthwhile to set the air screws one or two turns open for initial setting."
(I'm re-reading all the instructions 'after' I started the post. Duh.)

I don't remember, because like I said," I forgot completely about those screws". But I can guarantee they are nowhere near an initial 1 or 2 turns out on the air adjusters.

I'm not too worried about screwing anything up with adjustments. I am pretty good with putting things back where I found them. If I back them up 3/4 turn and it doesn't work. I'll put them back 3/4 turn.

Do you think I can reach the 12.9 by running rich at idle and adding air?
And , how important is it that I reach 12.9?

I'll probably give it a shot over the weekend. It couldn't hurt. (Famous last words).

Did you read nos. 8, 9 and 10? What effect are your mixture screws producing? They determine the A/F mixture at idle, they and idle jets. With the correct idle jets (and other baseline settings as suggested), the mixture and idle speed screws should provide enough adjustment to change the overall mixture.

Sherwood

[dipso]

I think I got it.
I went out there this morning and opened all 6 air adjustment screws 1 full turn. Then took it for a drive to warm it up.
Came back and synched the LM2 and got lucky, it hit 20.9 first try. Stuck it in the tailpipe and it read 12.9.

Once I saw how everything worked with each other I fiddled with it.
Went through the whole procedure. Turned all the mixture screws in to stop and then backed them all out equally. I think 2 1/2 to 3. Turned them in until it started to sound funny and backed them up again. Then messed with the air screws to bring everything to 12.9 again.

All barrels are pulling an equal 3.25 on the synch and everything is good. I think I finally got rid of that rich idle.
Damn, I wish I remembered about those stupid air mixture screws a long time ago.
I'm afraid to look at my plugs.

One problem, the #3 cylinder air screw is almost all the way out just to get to 3.25.
Other than that I think everything is good.

[911pcar]

Why not use the results given you by the LM1 instead of listening? It seems O2 sensor feedback would be more accurate, yes?

Sherwood

[James Brown]

I can't beleave you guys from California are even allowed to talk about carbs! Don't you have to sell or dispose of them?

[dipso]

Originally Posted by 911pcar

Why not use the results given you by the LM1 instead of listening? It seems O2 sensor feedback would be more accurate, yes?

Sherwood

I did eventually. But on initial set up for the carbs you back all the screws out to 2 1/2 or 3 and then turn in until engine feels it. Then back them up a 1/4 or so.

Then I double checked with the LM2 and the settings were good.

[dipso]

Originally Posted by James Brown

I can't beleave you guys from California are even allowed to talk about carbs! Don't you have to sell or dispose of them?

Yeah. I hear there is a guy in Bellingham, Washington who will take them off our hands, cheap.