A/F ratio- Tuning with the LM-1

[Zach Gomulka]

What is the ideal air fuel ratio range for a street engine? I'll be tuning my car with the LM-1 soon, and it's been so long since I've used one of those that I've forgotten. Thanks!

[GreenTom]

in theory is 14,7:1.
Go to innovate motorsport forum You'll get all answers.

[louisb]

Not for an aircooled. If you run it too lean it will run hot. Check aircooled.net's tuning recommendations for some starters.

--louis

[GreenTom]

Not for an aircooled. If you run it too lean it will run hot. Check aircooled.net's tuning recommendations for some starters.

--louis

oh yes that's true. too lean too hot

[Felix/DFL]

Hi,

you want to get in the regions from 11,7-12,5 A/F Ratio. That`s Lambda 0,8-0,85, there the ingnition speed is maximum, so the detonation is very fast and that`s good for the power output...
This region is on the rich side so there should be no problems with overheating.

A/F 14,7:1 is Lambda 1 where the 3 three-way catalytic converter has his best converting point, as said way to lean for an hot aircooled engine.

Greetz !

[Jim Ratto]

I set mine @

idle 11.6-12.2
cruise on idle/progression 12.8-13.2
cruise on main (freeway) 12.0-12.7
full open throttle 11.5-11.8

[Bruce]

Not for an aircooled. If you run it too lean it will run hot.

Ever tested that theory?

[louisb]

Have I ever run a VW lean? Yeah and it ran hot. Was it exactly 14.1, I have no idea since I don't have an LM1. I would just prefer to have a little cushion.

--louis

[Bruce]

My engine runs around 18:1 on the freeway.  No cooling issues.

[Zach Gomulka]

I finally got around to tuning my Zenith 32NDIX with the LM-1 yesterday Fruitcake and I started out with a baseline drive, and the jetting was very close as I expected- it drove very well so I knew it couldn't be too far off. But the idle and main circut could have still used a little leaning out- impossible to tell by just looking at the spark plugs. Instead of going straight to the jet box, I wanted to try out some larger Porsche 28mm venturies (up from 24mm), to see what the effect on A/F ratio was, and to see if there was a top end performance gain. Right off the bat, I noticed the idle circut was VERY lean, 19-20:1, and the engine was very unhappy- lots of bucking and kicking until I stepped on it and got on to the mains. But once it was floored, I was pleasantly surpirsed! It pulls MUCH stronger now up high!! Anyway, my  Zenith came with 50 idle fuels, and 140 idle airs. When I first installed the carb I swapped the 50's for 40's, thinking the stock engine wouldnt need that much fuel, and I guess I was right. But now with the 28mm vents, the idle circut was far too lean. So I went back to the 50 idle fuels, and the problem got quite a bit better. Now the A/F ratio is in the 16-17:1 range (and the engine still isn't happy), and of course still too lean.

SO.... My question for now is this: Do I drill out the idle fuels to 55 and give that a try, OR try a smaller idle air jet? Both would richen up the mixture, but how do I know which path to take?

Surprisingly, the main circut is still a little on the rich side (135 fuel, 220 air.... I think), and I would like to try leaning that out some. So once again, do I increase the air jet, or decrease the fuel jet to lean out the mixture??

THANKS!!!

[Zach Gomulka]

I robbed a pair of 60 idles out of another parts carb that I had lying around, but I havent had a chance to screw them in yet, I'll have to wait until after work.
Another question along the same lines... increasing the fuel jet size in order to richen the mixture woulld have a negative effect on mileage (right??)... Would decreasing the air jet not effect the mileage, yet also give me the richer mixture that I'm after??

[j-dub]

Zach,

Check out this thread on the Samba and notice what John@aircooled.net says:
http://www.thesamba.com/vw/forum/viewtopic.php?t=293837&start=0&postdays=0&postorder=asc

 He has a different approach on AFR, what runs hot and total timing. I just installed Travis's LM-1 on my oval this weekend and am just starting down the tuning road myself.

I have yet to find much helpfull information on Innovatives website, maybe I am not looking in the right place.

Let us know what you find out works best for you engine.

Jeremy

[Zach Gomulka]

Hey Jeremy good to see you here! I'll give that link a try...

I just got back from the trial run with the 60 idle fuel jets and it really didn't make much of a difference at all So I think the 50 idles are the ticket, but what I really need is some smaller idle airs. I know some Porsche Zenith 32's came with 120's, so I'd really like to find a pair of those, but I'll try anything smaller at this point. Anyone???

Once I get the idle where I want it, I'm going to start leaning out the mains a little...

[Zach Gomulka]

I set mine @

idle 11.6-12.2
cruise on idle/progression 12.8-13.2
cruise on main (freeway) 12.0-12.7
full open throttle 11.5-11.8

Jim, why do you run the idle so rich?? There is no load at idle, so it seems to me that you could run it as lean as possible

[Jim Ratto]

because that is where it runs well. The "numbers" don't make my car run correctly.
I tired "leaning" it out, but it runs very poorly.
So I can drive around watching the meter telling me "things are great" and the car runs poorly,
Or i can jet it so it rips the seat off the rails and forget the "numbers"
BTW I run a 60 idle jet in 120 holder and 7/8 turns out on mix screws

[Airspeed]

My engine runs around 18:1 on the freeway.  No cooling issues.

My hero!

I will definately give that a try with the EFI (was afraid to do that before..) 
I do however up the advance to 43 degrees at low trottle opening and cruise rpms 

Must give some awesome mph with such a high AFR (?)

Tnx for the encouragement!

[JS]

Jim, why do you run the idle so rich?? There is no load at idle, so it seems to me that you could run it as lean as possible
[/quote]

My IDA´s make the car undrivable if I put in idle jets under 60. The "blind-spot" between idle and main jet becomes bigger and bigger the more I lean it out. Running 65´s now, and it´s too rich of course, but very pleasant to drive. And when you rev it, it flies! 

[Zach Gomulka]

Thanks for the explanation. Silly me, I didn't take into account the fact that IDA's are a completely different beast

I've got some 120 idle airs on the way, if that doesn't do it, I don't know where to go next

[j-dub]

Hey Zach, Any update?

I have went down two sizes on my idle jets and am still idling in the range of 11.8 to 12.2, when i am at a light acceleration it is at 13.8 to 14.3. It dips into the 11s during full throttle pulls. I guess I am going to continue to go smaller idle jets until it protests. After that I will address the main jet and accelerator pump.

[Zach Gomulka]

I've got 2 120 idle air jets coming from a Zenith specialist in Sedona, hopefull they'll be here today. Hopefully that will do the trick. Once I get that dialed in I'll try leaning out the mains, but I think they may already be good to go. I've also got some 40 accelerator pump jets that I'll try in place of the 55's.

Once it cools down I'll make the drive down to Phoenix to flog it on the strip one more time- maybe 18's are in my future

[Zach Gomulka]

I screwed the smaller 120 idle airs in Friday after work. Still has a mid-range lean spot under light load/acceleration (gets up to about 16:1 at times) and the engine feels a little rough   It's a real pain in the ass driving around town because that is the range I'm always in. I havent had a chance to mess with the idle mixture screws yet, hopefully fattening them up some will help the problem?? Or are the 28mm venturi's simply too large for my stock(ish)engine??? I'd really appreciate some advise here guys!!!

[dirk zeyen]

the venturi's are not your problem. i run 45 dell's with 36 venturi's on a 2007cc engine with 35,5 inlet valves and it works!!!
i'm not happy with a lean runing engine.

dirk zeyen

[Zach Gomulka]

the venturi's are not your problem. i run 45 dell's with 36 venturi's on a 2007cc engine with 35,5 inlet valves and it works!!!
i'm not happy with a lean runing engine.

dirk zeyen

So what is the problem?? Operator error??

I ran dual 44idf's with 36mm venturies on a (well built) 1600, and it worked well... but I have heard tales of VW engines with single 2bbl carburetors like mine that work better with smaller venturies. Something to do with the long intake runners needing a small venturi to keep airspeed up. Does anyone have a similar experience? I would prefer to keep the larger venturi's in the engine, because after 3,000rpm it really woke it up! What else can I do??
BTW, I am using a Bosch 010 w/ Pertronix, 35 degrees total advance, if it matters...

[Mike Lawless]

If you have the smaller vents, it's only a little work to try it Zach. Give it a shot!

[Zach Gomulka]

I love the 28mm vents.... above 3,000 rpm! The 24's ran out of steam very early, passing power with the 28's was also increased noticably.

I'll check the float level.. good idea!

[dirk zeyen]

float level checked? any news? my opinion is that a engine with bigger vents needs a mixture more on the rich side

dirk zeyen

[Zach Gomulka]

Float level is good

I'm about to throw in the towel on these larger venturis

[Zach Gomulka]

I'm getting somewhere!!!

I talked to Steve Hollingsworth last week about my problem. He suggested raising the floats and putting in a larger main jet (from a 135 to a 140), to get the main circut to come on sooner, going larger on the air correction jets to lean out the full throttle A/F ratio (from a 180 to a 200), and going back to the 50 idle fuels since the 60's didnt make a difference.... So I did. I know you arent supposed to make 4 changes at once, but I was getting impatient!! I fired up the motor, and it was running extremely rich. So rich in fact, that it completely flooded out the motor in less than 30 seconds of idling, and it wouldn't restart Frustrated, I waited until the next morning and started it again. It does the same thing. I swapped out the raised float for a standard one, and the motor runs great! Except that it was running really fat under full throttle, and a bit rich everywhere else... but at least it was smooth!! So I pulled the 120 idle airs and went back to the 140s, and also took the air correction jets from 200, to 220, and now at 230- they bearly made a difference, still rich under full throttle long story short, I gauged the main jets and found out that the main jets that were first in the carb, stamped 135, were actually 125s! So last night I leaned it back down to a true 135, and it still runs great, about .5 leaner under full throttle. So tonight I'm going to screw in a pair of 130's and see what happens. Right now my full throttle A/F ratio is hovering around the high 10's...

[dirk zeyen]

hello zach,

like i said: small valves with  "big" vents need a rich mixture!!!
the air correction jets comes in at a rpm range a stock engine comes not in so easy so your changes makes no big difference!
good to hear your engine runs!!!

dirk zeyen

[John Rayburn]

If you ignore all of it and just spend the time jetting and test driving, you'll get it done alot faster and the engine will run way better than listening to some computer.