Weber settings, almost stock 2.2

[mskala]

Hi all,
Yes I've searched and found tons of answers, but not for my exact engine,
and a lot of conflicting settings.

I'd appreciate some guidance, I just am getting my LM-1 set up so all I know
is really poor gas mileage and seems to be rich everywhere.

I have a 2.2E engine but with DC-30 (mod-solex) cams, and some porting
of the heads. And my 40IDTP's that came from original 914-6.
Current settings (as originally recommended by PMO):
vent: 32
main: 135
idle: 55
emulsion: F1
air corr: 180

I am planning to check with the LM-1 the 'cruising' and full-throttle from
about 3000-7100 with this setup and others, but don't want to blind guess.
Other parts I already have lying around to use are F26, 125 main, 170 air,
and 30 vents.

Thanks,
Mark S.

[mskala]

Also, forgot to say that overall running has been smooth with these
settings.

[Grady Clay]

Mark,

You will not find an ‘exact’ answer as every engine is different.
The Porsche Factory settings were a compromise and could be improved on.
You have a good starting point (too rich) and eventually may end up there again.
I assume your engine is sufficiently ‘broken in’ (and exhaust is clean).

You need a big sign for inside the rear window saying “EMMISSIONS TESTING”.
“Yes officer, here are my mixture test results at 102 mph.”


Seriously, develop a test plan with your LM-1.
You need more ‘spare part’ jets.
You want to first find a good balance between the main gas jet (now 1.35 mm) and the main air jet (now 1.80 mm).
Use ‘slightly-too-lean’ idle gas jets (50 or smaller).
You will need a range (generally smaller) of idle gas jets (the idle air jets are pressed into the carb top and not replaceable).
Be sure and measure every jet.
I recommend you use high octane race fuel for your full-power, high-speed testing. Using race fuel will not affect the jetting.
You don’t want any detonation causing mis-reading of the mixture or damaging anything when you close to the lean limit.

You will want to use ‘colder-than-usual’ sparkplugs with an extended tip. Something like NGK BP8ES or (colder yet) BP9ES. Have several sets available.
You will get very handy with your sparkplug wrench, correlating plug color to LM-1 readings.
Be careful with your sparkplugs into the heads – no ‘testing induced’ problems there.
The tailpipe color requires some distance for a valid reading.


The main gas jet has more effect at ‘lower’ rpm (say 4000 @ full throttle) and the main air jet has more effect at high rpm (say 7000 @ full throttle).
It is the combination that determines the mixture when running (mostly) on the ‘main’ circuit.
You will easily find a ‘good-running’ lean mixture here. It will be too lean but useful for setting the idle gas jet.

Here you will engage in a back-and-forth adjustment of the main gas jet and the idle gas jet.
Develop a ‘throttle-position-stop’ so you can repeat the throttle position, rpm and very light cruising speed (in 2nd gear).
This is a good ‘test situation’ for setting the idle gas jet as it is close to its ‘limit-of-flow’.
Keep in mind that the main gas jet is just starting to have effect.
You can get a sense of when (throttle position & rpm) that is occurring by looking down the carb throat with a timing light and observing the beginning of fuel coming out the auxiliary venturi.


Don’t let the accelerator pump function fool you.
Even a little movement of the throttle (when almost closed) and add 10X the idle fuel.
You can disable the pump if you want.


The most difficult part of all this are the transitions.
There are two:
The first is transition from the mixture and idle speed set at idle.
These are drilled into the carb body behind the screw-plug.
As the throttle butterfly opens, these ports are progressively uncovered, regulating the amount of mixture.
Typically anything you attempt here results in worse performance.

Another transition is from the idle circuit to the main circuit.
This is done with the ‘emulsion tube’ but the relative size of the idle gas jet and main gas jet has most influence.
Don’t worry about transitions until you have the main and idle circuits correct.

Your choice of cams, venture size, etc. are close to Factory settings.
Aside from the IDT transfer ports, you should be able to get these ‘perfect’.
When you think you are finished, it is the light-throttle transition from the idle circuit to the main circuit that will affect the ‘feel’ of your driving. Too lean is unpleasant.
You may also find you want one-size smaller main air correction jet to protect your engine at sustained high speed.

Lean to perfection but rich covers a myriad of sins.

Best,
Grady

PS: If someone finds flaw with my procedure or description, please chime in.
It has been a while since I have done this.
Most of my experience was on my engine dyno where I could ‘hug’ the engine, even at full power.
G.

EDIT
Here is a good link:
http://www.performanceoriented.com/technical.htm#PerformanceTuning

[1QuickS]

F1 tubes were OEM for 69 911T 2.0; F26's were OEM original 2.0 Normal. F26s are more commonly used in engines of your specification, you might want to give these a try.

Your carbs were designed to be more emissions compliant than the earlier IDA, IDS and IDAP carbs. They have an idle air correction jet size of 140 where the others used 110. The idle air jet works like the air correction jet for the main circuit in that it supplies air to the fuel to emulsify it; more air delivery equals leaner fuel mixture. The larger idle air jet contribtes to the "lean transition" issue along with the revised progression circuit holes used in the IDTP (69 911T) and IDTP13 (914/6) carbs. These later carbs had a progression hole location that delivered fuel earlier in the throttle opening sequence and provided nothing later, the earlier carbs had progression holes that were more evenly spaced; check out the photos on my site:

Weber Carbs Technical

The idle air correction jets may be replaced with tune-able ones to help enrich this transition if needed; contact me via my web site for info.

Otherwise your jetting looks good, you may want to enrich top end a bit with a 170 air corrector for full throttle runs.

Disclaimer statement: I remanufacture the Webers so they are tuneable; people like Grady and Steve Weiner know how to tune them.

[mskala]

Thanks guys. I will update on the (possibly slow) progress.

[911pcars]

"I am planning to check with the LM-1 the 'cruising' and full-throttle from
about 3000-7100 with this setup and others, but don't want to blind guess."

Using an A/F meter will remove the blind guess factor, yes? Anything up to that point will be a calculated estimate based on other owner experiences. And unless others have the exact same spec engine, it'll be close, but they're still educated estimates.

Sherwood

[mskala]

Hi, back after a long down time for the car. Just started playing
with the LM-1 but see something very unusual.

Look at the graph where I run up 3K-7K in 3rd gear. The AFR
gets very lean very fast at high rpm. I haven't seen this with
anyone else's graphs with Webers, could this show an
exhaust leak or something?



I'm using a small air corrector jet here because it didn't feel
right at high rpm with the usual 180. But LM-1 was not
hooked up at that time.

Thanks

[Eagledriver]

That looks about like my car's AFR curve. I think if you went above 7k, you'd find the mixture would richen back up as the engine's volumetric efficiency dropped. Mine goes from 10.5 to 13.5 and then back down to 11.5 when going from 4k to 7.3k RPM. This is with stock SC cams. From what I can gather there is really nothing you can do to alter the shape of this curve. All you can do is raise or lower the whole thing. You only get to 13.5 by 7k RPM. That seems like a reasonable setting for your car. By all means try some other settings and see what you can do.

-Andy

[1QuickS]

Weird...are your auxiliary venturis well seated and are their keeper springs holding them in intimate contact with the throttle body where the fuel is transferred from the emulsion tube well? If you have tall aux venturis that are loose (typical with time) then this could lead to an issue of fuel dribbling down the throttle body bores without being properly atomized.

Otherwise I'm empty.

[mskala]

From what I can gather there is really nothing you can do to alter the shape of this curve. All you can do is raise or lower the whole thing.

I'm sure it's never going to be perfect, but it doesn't have to remain the same
shape. Made some progress. Sorry the graphs out of LM-1 are not easy to
scale to each other and haven't had time to use excel on them.

4 graphs below. First is copy of earlier but clarified.
Cases:
32 vent, 140 main, F1 tube, 170 Air
32 vent, 135 main, F1 tube, 150 Air
30 vent, 135 main, F1 tube, 150 Air
30 vent, 130 main, F1 tube, 150 Air

Changing to slightly smaller venturi definitely affects the slope of the high
RPM rising AFR for the better.

[1QuickS]

I offer a comparative photo of F26 and F1 E-tubes for your benefit. The E-tube takes air from the air corrector jet and delivers it to the fuel which surrounds the OD of the E-tube. The air passes through the holes in the wall of the E-tube and emulsifies the fuel before it is drawn into the auxiliary venturi. In a simple comparison between E-tubes of comparable length and diameters like these two it is rather easy to see that more holes (F26 - on the right) will add more air to the fuel than the one with fewer holes (F1 - on the left.)

Try the F26 E-tube.

[mskala]

Originally Posted by 1QuickS

I offer a comparative photo of F26 and F1 E-tubes for your benefit. The E-tube takes air from the air corrector jet and delivers it to the fuel which surrounds the OD of the E-tube. The air passes through the holes in the wall of the E-tube and emulsifies the fuel before it is drawn into the auxiliary venturi. In a simple comparison between E-tubes of comparable length and diameters like these two it is rather easy to see that more holes (F26 - on the right) will add more air to the fuel than the one with fewer holes (F1 - on the left.)

Try the F26 E-tube.

Thanks Paul
F26 is the other type I actually have in the pile of parts. I'll be trying that tonight.
Trying to change one variable at a time. Relatively more holes and higher up than
F1 should be better.

[mskala]

Three more test cases:

30 vent, 130 main, F26 tube, 150 Air
30 vent, 130 main, F26 tube, 170 Air
30 vent, 125 main, F26 tube, 150 Air





I'm driving with the last case right now.

[ratpiper71T]

I thought S cam or S cam like setups called for F3 emulsion tubes-richer at WOT??

[1QuickS]

F3 is the next step as it looks like you got leaner with the F26s. The very first 911S engines were supplied with F26 tubes but later received the IDS carbs and F3s which tend to be THE popular choice for performance cammed engines. Those carbs were identical to IDAs but included a high speed enrichment feature for mixture enrichment at VERY high RPM operation. Jetting was: 32mm main venturis, 125 mains, 185 air corrections, F3 E-tubes and 55 idles.

[mskala]

Will have F3 to test soon.

With the current setup, very low throttle cruising on
the highway gave the following (not smoothed). It seems
like between 3 and 4K, flat ground is okay, but either a
slight hill or speeding up slowly with very light throttle
makes it close to lean. Should I worry about this if it
is only at low power?


Drove it on the highway for 50 miles twice already and
didn't notice any increased oil temp or weird feel.

[1QuickS]

I don't believe slightly lean at low power levels will get you into trouble.

You are running mostly on the progression circuit during your level ground 3K to 4K operation; you could open up the mixture screws a bit or you could increase the idle jet size to enrich the fuel delivery.

When you perform your idle adjustments you should keep the idle adjustment screw set so the first progression hole is covered by the edge of the throttle plate. This is equal to about a 3/4 turn open from fully closed for fresh carbs and even more closed on worn carbs. (Worn carbs bypass more air than fresh ones do.) You can only be sure of this throttle plate position at idle by adjusting them when the carbs are off the engine and then adjusting idle air balance and idle RPM (drop links disconnected) using idle air adjusting screws. The reason why I mention this is IF the first progression hole is partially exposed at idle THEN the idle mixture screw will be closed more to compensate for the fuel flow at idle while trying to achieve "lean best" mixture adjustment. Then, while driving on the progression circuit, you will not have all the fuel that would be available if the mixture screw was more open. (Fuel delivered during progression is the summation of fuel from the three progression holes PLUS the fuel from the mixture screw.) This would lead one to install a larger idle jet to compensate for a possible lean transition.

[bodde911sc]

Paul
Your expertise in the theory and application of carburetors continues to always amaze me. This forum should be grateful that you share this information. Thanks from this user that you continue to supply useful solutions to people with frustrating carb issues.

[Bob Ashlock]

Amen to that! Paul is the "Weber Whisperer"

[1QuickS]

I thank you for the kind comments.