Need help tuning L20 -running too lean on throttle

[bertvorgon]

That is correct.


It is NO problem that we go lean on lift off (NO load). My idle and part throttle cruise keeps me in the high 12's, then, when getting on it I go through a transition of a quick ramp to the 11's as boost comes up, and then, for me, a natural richening up at the very top end, due to the carb just not being able to flow anymore air regardless of boost.

This for me is SAFE as I head to 8,000 RPM and 16 lbs of boost, so, I have seen a drop into the 9.s also. The AEM wide band I got reads into the 8's, so that is a good range for me.

With all that, I usually get between 23 and 25 mpg depending on how much wide open or heavy throttle usage happens.

[Button]

I think you can calibrate the AEM sensor and I believe I did that but I will investigate if I can do that again to be safe. Below is an image of the #1 plug with ~40 miles on it. I was doing normal driving for the last 5 miles or so before I pulled it.

On another note I have been working on this car on and off for ~5 years and just got it insured and on the road about 2 weeks ago. On Thursday when I went for a drive I was sitting at a light and the lady in front of me decided to put her car in reverse and she backed right in to me, messing up my grill, hood, and bending the radiator support. Fortunately it still drives but I could not believe it. I'm in the middle of dealing with insurance now.

[bertvorgon]

To me that plug is not looking too bad. In reality it is the BASE of the insulator you look down into, to determine mixture.

The insulator is NOT glazed nor does it look like it is on the edge.

If you have NO sound of pinging....or.... detonation when you jump on it, I'd say you are close if not there. Maybe one more jet size but I would maybe live with that for a few drives and see what you think.

So sorry that happened to you, that is like what happened to FUNWITHMONKEYS on here, chimp backed into him in the ferry lineup.

[datzenmike]

My A/F ratio is bout 12-13 at idle and it idles well. The problem is that as soon as I give it any throttle while driving it goes extremely lean (17-18 A/F range). My plugs are way too clean and tell the same story that I am running way too lean.

Won't be an air leak. If it were bad enough to force a 17-18 a/f when driving, it wouldn't idle.

The weber is a progressive carburetor with the secondary pulled in around half throttle. What are your a/f readings when not using the secondary? If reasonable, maybe the secondary jet is partly plugged? if not too small. If lean right away on the primary maybe it has a blockage?

[Button]

Thanks guys. I checked for leaks with propane and didn't notice anything. I will check for blockages to be sure. It's hard for me to tell exactly when the secondary is kicking in. If the secondary's are kicking in at half throttle then it seems like it gets to about 14-15 when really giving it throttle but the drops down to mid 12's at WOT. I think I will drop the primary air corrector to 145. and live with that. I also have the Sync kit that I got from Pegasus racing to make it synced like the 38/38. I may try that soon too.

[datzenmike]

Just look at the throttle linkage to see where it starts pulling the secondary in. I see no advantage to opening both throttles together. That's a problem with the 38/38 too much opening too soon. It's more of a 6 cylinder or small V8 carburetor that has lots of displacement pulling in air. A small 2 liter will fall on it's face, balk or stumble.

I thought you said in an earlier post it goes 17-18 lean when giving it the throttle but now you say 14-15 dropping to mid 12s.

[bertvorgon]

I so agree with Mike on the dual throttle opening, not a good idea on our small motors really seeing street duty.

It would kill your fuel economy and make tuning the engine a bit of a bear.

[bertvorgon]

Morning World, wet day here on the West Coast and TONS of snow in the mountains now!

I thought I would give an explanation of why having a 32/36 have synchronous opening is not a good idea.

The accelerator pump for the secondary is not functional and the progression circuitry is not designed to cover the opening of the secondary, IF it opens at the same time as the primary. So while the primary circuit starts up from the idle circuit, there is not any "pump shot" into the secondary at the same time as you go from idle.

I have tried a dozen different things on my carb, to obviously go from idle to full kill under boost. Getting the secondary to work smoothly is so very important to smooth power flow.

Its one thing if you are high up in the rpm range where the fuel flow is at max on the primary and then the secondary opens. To do that from idle, say to do an acceleration, then lift, then get back on it, could give you quite the bog or stumble as the primary accelerator pump MAY not have completely re-filled the pump well, thus giving you an even more lean condition when BOTH throttles open at the same time.

I too am a bit confused when you have said what the A/f's are.

It would also KILL any fuel economy big time that the carb was designed to do, coupled with getting your vacuum advance hooked back up.

[RMS]

and get that intermittent "air bleed" from the kinked pcv hose sorted as it is contributing to the wondering numbers your seeing on your a/f gauge



crank case gasses added to the a/f mixture help with propagation of a turbulent flame wall and growth of the kernel at the point of combustion.

[Button]

Thanks again guys for the feedback. I was having those A/F numbers "17-18 lean when giving it the throttle but now you say 14-15 dropping to mid 12s" but I have been pulling it in to range as I tweak jetting. I just went for a drive and things are looking pretty good across the board and it seems to be running really well. I may drop the primary air corrector a bit but for now I am going to live with the current settings for awhile. Your guys feedback has been invaluable to help me get here and I appreciate it. Thank you for the diagram RMS, I will get that sorted, good catch, hopefully that catches the last of the inconsistency.

For the progressive kit, it came with a new accelerator jet that put's gas in both barrels. I guess I should have done a bit more research but it seems like it's mainly made for race applications where you are at WOT more often than not. I guess some guys used it to for racing where they limit carb sizes. There are some 2002 guys out there that have put them on for street use and liked them, but for the reason you guys mentioned it's probably not worth it, especially since it seems to already be running so well. I guess I will see if Pegasus takes returns.

https://www.pegasusautoracing.com/produ ... RecID=6942

[bertvorgon]

Thanks for that link, I knew some of the FFord guys were using that, as I had talked to some of them at the track.

As I was having my morning coffee I remembered that the Ford 5200 carb is basically a Weber under licence. It came of the Ford Pinto and a few other cars of that vintage. So, if you are ever stuck sometimes for parts or whatever, remember the 5200 is the same.

The 5200 came with a Nitrofil float, which is a direct replacement for the brass float, should yours ever die. The Nitrofil will last FOREVER, mine has been in there for 40+years.

Here is a quick link to a discussion of the 5200 but what is great are the cutaway diagrams of each circuit, so you can both see and get a better understanding of how it works visually...I'm a see type of guy!

https://www.thesamba.com/vw/archives/ma ... uretor.pdf

Also, if you are going for a long higher speed cruise or trip on the highway, you can put 1 heat range colder plug in...NGK BPR7ES. I run these for light duty with a lot of traffic...then for me....I go to a BPR8ES for harder driving and for a long mountain trip with good blasts, I go to a BPR9ES. You would never go there but it gives you an idea of a tuning point.

Here is a picture of mine at 4,200 RPM and my A/F is 12.5

[datzenmike]

I notice that the a/f is like a bell curve with a broad peak so there is little difference in running from 13.7 through 15.7, in fact a little lean is a good thing as all the gas is being used and there is no danger at cruise speeds. At 9.6 it ran as well as in the mid 10s so why dump all that gas?. Richer is better than too lean under power but I would like to see high 12s

Here's what I have...

Home made intake.


zx air filter and home made box.


$2 aluminum serving try for heat shield.

[bertvorgon]

To add to what Mike is alluding to;

Just to give an idea of my "bell curve" on a driving cycle with my wide band.

When I first start the car, where my intake manifold has NO heat and well insulated from my exhaust manifold, my A/F will be down in the 10's as the fuel has a tougher time evaporating.

After the engine has run for 10 to 15 minutes, my A/F comes up to the 12's at an 1,100 RPM idle. My idle is set high from my racing days and I have not touched it.

Then as I accelerate at a normal pace the A/F will bounce up and down between the 12's and the teen's as I shift.

Now, as I start to say head up a hill that is steep, as the primary throttle is ALMOST ready to open the secondary, my A/F will lean to maybe into the 13's to 14's, as the air corrector jet as at it's limit. In this scenario I have to be careful because at this stage of "leanness" the exhaust temp is starting to really get up there.

Then when the secondary cracks all hell breaks loose, the A/F drops for a fraction of a second to slightly leaner, then goes to low 12's or even into the 11's.

Then in my case, as the RPM build towards max, my A/F, again due to the air corrector jet size, and that it is quite small relatively speaking, I will head into the 9"s. Even at that I have to watch my exhaust temp..not your issue...but...this is where sustained throttle and load in any motor, see's the heat building, no matter what the A/F.

As I come to a stop the A/f goes really lean, into the 15's or 16's and sometimes if my motor is not fully up to temp..or more the case the intake manifold, my car will stumble and possibly die. This is something I am going to address in the New Year. I have not touched that carb for a LONG time so it too may need some fine tuning.

[Button]

Great info guys. Keith I saved that PDF about the 5200 carbs, i am a visual learner as well so seeing the diagrams is super helpful. Understanding what the carb is doing makes it seems less like voodoo magic. It's good to know about the spark plug heat ranges as that's something I didn't know much about. It's also good to hear the ranges your A/F goes through as you drive as it gives me a reference point, mine seems similar to what yours is doing.

Hey Mike, really cool set up, how are you liking those R1 carbs? Did you buy the carbs off ebay? Did it take a lot of tweaking and tuning to get them to work? I have been thinking about ordering the Bogg Brothers intake for the R1 carbs.

[bertvorgon]

Here is a NGK plug chart to understand what all those numbers mean:

A BP5ES plug was stock in the original 1600cc motor, then they came out with the BPR5ES, the R being for electrical interference suppression.

So, going from a 5 which is a "HOT" plug to a 9 which is a racing plug, being a "COLD" plug, gives us a HUGE range of plugs for our different driving conditions.

Many years ago I stupidly tried to run a 10 at the Hillclimb, so the damn things fouled like crazy, the things you learn.

The plug gap is set by the factory which of course we alter as needed for our motors and ignition systems, let alone compression and/or boost.

I'm lucky the motorcycle gang run the 9's so I have good supply.