L20b tune up.

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Cars: 69 Datsun 521 1300

L20b tune up.


Post by Rocketpanda » Mon Feb 17, 2014 3:49 pm

I have a 69 521 with a L20b swap. I'm running a weber 32/36 and I would like to know what are the proper ways to tune these carbs.
it's running really rich making my spark plugs pitch black.

On top of it all, any tips to tuning up a L20B? it has the Weber, Mr. Gasket electic fuel pump with a 5spd swap. L20b block/W58 Head.
-Thank you all!

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Re: L20b tune up.


Post by bonvo » Fri Mar 28, 2014 12:44 am

we need to know what jets you are currently running in the carb

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Re: L20b tune up.


Post by izzo » Sat Mar 29, 2014 7:55 pm

It shouldn't run that rich, jeez lol.

start car and let that thing heat all the way up to normal op temp. turn air screw in till its damn near killing the motor, use your other hand to jazz the throttle to keep it from dying. then start backing it out. once it smooths out, do one more half turn. that generally is the way its done. a properly jetted weber tho, shouldn't be any more than 2 1/2 turns out from seated according to weber. Pretty much what i've done on every weber and it's always ran tits, even if it came off a smaller or bigger L series motor.
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Re: L20b tune up.


Post by Jester » Fri Dec 26, 2014 10:21 pm

Izzo's description is pretty good. I'll post my method just for arguments sake. :fu:

Before you start the truck, turn the air screw in all the way till it JUST STARTS to seat. Keep track of the turns. Now you know exactly where your baseline is. Now put the air screw back and proceed to start the truck.Now, turn the screw air screw in till you notice it starting to run like crap. That's far enough. Now, since you have been keeping track of the turns your making, start slowly turning the air screw till you notice that the RPM's are no longer climbing. Do this a couple times till you know think you know where that sweat spot is. If you have an old tack sitting in the garage, it woulds great for this.
Once I find that spot where the RPM's stop climbing, I turn air screw BACK IN 1/4 turn. This sets it just to the lean side. All said and done you want to be close to 2 turns out. If you are needing more than 2 turns, your too lean. If you have less than 2 turns, you need to fatten that girl up a couple digits.

Hope this helps.

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