Weber tuning for high altitude/fuel economy

[TominMO]

Here is a jet kit for Weber 32/36 carbs, specifically for tuning for high altitude and/or fuel economy:

http://www.lceperformance.com/Weber-32-36-Jet-Kit-High-Elevation-Fuel-Economy-p/1035002.htm

They also sell individual jets in any size you might need, for $5.95 each:

http://www.lceperformance.com/Jets-Jet-Kits-s/1345.htm

And here is guidance for how to go about it:

http://www.racetep.com/weberaltitude.html

Note that by tuning for economy or higher altitude, you get both!
Personally I might not buy the kit, just note the leanest primary barrel setting they have (130 main, 150 air correction, 50 idle) and go leaner from there. But it would be nice to have the range of jets to play with, to lean out the secondary too.

[TominMO]

Also, if you are looking at drumnerd's posts about how his primary main is 100, bear in mind that he lives in Colorado Springs, which is at an elevation slightly above 6000 feet. So just copying what jets he is using might be a bad idea for someone at sea level. But his data is valuable, especially since he is dialing it in with a wideband, so you can use his numbers as a starting point and then if needed go a little richer.

From the jetting how-to article in the previous post, you could use drumnerd's figures once he gets it all dialed in (presumably ideal for 6000 feet), and figure how much richer you might want to go, if you are at or near sea level. As a rule of thumb you might try jetting for 4000 feet, and then see if you want to go leaner.

Drumnerd, here are some jetting calculations I have extrapolated from the jetting article, based on a primary main jetting of 100. See how they agree with your observations:
......................Primary.....Secondary
Idle.................35............30
Main................100..........115
Air Correction....240..........270

I'm not sure how much secondary values matter, since cruising will be in the primary only. I could see using the same values in both the primary and secondary circuits, or going leaner in the secondary, or richer. Keep us updated on your experiments. For carby people, this work is as valuable as my MPG testing. Not to mention getting our cars to run right.

[drumnerd33]

Glad you started this thread. I have been tweaking my tuning since i installed my weber, now bear in mind i installed my weber before i built my stage 3 dickmeyer motor. Pre dickmeyer stage 3 build i used a narrow band o2 sensor and it was basically worthless.... i ended up tuning the old school way by dropping the main jet size till i had a noticeable loss in power, then went back up one step. Now according to what i have learned about tuning webers (this is my first time tuning a carb let alone a weber) it seems the main jet sizes are adjusted for the size of engines, and then the air correctors are what you dial in for an adjustment of altitude (kinda makes sense because high altitude is thinner air so you need a larger air corrector for more air mixture to lean it out some)

Another big thing to remember is that your idle jets are feed off of the main jets, for example lets say you have the mains at 100 primary and 115 secondary, and the idles are 50 main and 60 secondary, if you raise the mains to 110 and 120 then that will cause your idle jets to be giving more fuel also so you may need to reduce the idle jets to compensate.

So lets review:
-Primary main jet tuning- lower primary main till noticeable loss of power, then back up one step.
-Secondary main jet tuning- you should have a noticeable gain in power when you open the secondary, start at maybe 2 steps larger then primary and increase until you dont seem to be gaining any more power when opening the secondary, then back one step.
-Primary idle jet tuning- A 50 is a good start for idle jet, if you have a stumble when you hit the throttle from a stand still you need a larger idle jet, increase idle jet until stumble goes away. Also the air to fuel mixture knob is affected from the idle jet, the book will tell you 2.5 turns out to 4 turns out is optimal but i found that to be not entirely true, but if you are backing out the mixture screw too far that means your idle jet is too small, if your turning in so far that its almost closed then its too large.
-Secondary idle jet tuning- This is basically the same as the primary idle tuning only it is the transition from primary to secondary, so if you have a stumble when you open the secondary then you need to increase the secondary idle jet. And easiest way to see if its too big is to decrease it until you have a stumble then increase one step.
-Primary air corrector- This is where it can get tricky.... best thing to have is a wideband afr and you increase jet size if your too rich and decrease jet size if your too lean.
-Secondary air corrector- This is the same process as primary only watching the wideband afr when you open the secondary, one thing to remember is to get your primary dialed in first cuz it will affect your secondary readings.

Ok now as for your afr readings at cruise you want around 14:1 but when you are under hard acceleration you want closer to 12:1 this is where i struggled the most after building my stage 3 dickmeyer motor, right now im sticking with what i got until matt can build my custom intake cuz he is pretty damn sure that is why im having trouble getting it dialed in better.

[drumnerd33]

Maybe this thread should be renamed because from the experience i have of tuning the weber, high altitude is just adjusting the air correction jets. Also when my uncle (who is a 30+ year mechanic) moved here to colorado springs from california had to tune his weber on his fiat, he had never done high altitude tuning so called weber directly and they told him to increase the air corrector jet size.... thats it, so he did and has been perfect, he didnt touch any of the other jets. He lived at around 4000 feet and colorado springs is around 6000 feet so thats a pretty good increase. Im not 100% positive on this but that is just from my experience so please chime in if anybody knows differently.

[TominMO]

Drumnerd, I take it you are tuning your Weber for performance, since that is what your motor build is all about. Once you get that dialed in satisfactorily, could you do some carb tuning for fuel economy, i.e. going a little leaner to see the effect on MPGs?

[drumnerd33]

Well for mpg you could keep the same mains and adjust the air correctors to get closer to 14:1

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[Spike]

Okay. I was about to buy jets, but I'm having a hard time seeing exactly what I'm supposed to get.

.100 Main jet, .120 Secondary. I've got that panned out.

Idle? .050 Main and .060 Secondary? I'll be leaving my airs alone for now, as it seems the nice gentleman in the Rocketman Adapter thread left his alone (and he's only about 200 feet elevation difference compared to me, 310ft vs about 500).

Thanks,

-Joe

[drumnerd33]

That's a good start but it can vary, that's why I did the weber drill bits and solder. Or you buy a while jet kit that has the options

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