Weber 38 jetting
Apr 25, 2016 | 12:18 AM
#1
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From: 40 miles North of Atlanta
Weber 38 jetting
When you installed 38's did you have to change Idle Jets? I have freshly rebuilt 20R, header, 32/36 and wanted little more umph, so I purchased new Redline Weber 38, and the 45's were too small. I had to have mixture scews out 3+ turns for it to run. This is with idle screw less than 1/2 turn in after contact.
(I recently watched a video from Pierce Manifolds, and he confirmed idle screw has no purpose other than keeping accelerator plates from slapping casting of carb. anything more then 1/2turn in after contact you are releasing extra fuel @ idle. and this isn't a science you really need to look with carb off truck to see exactly when you expose the holes for that extra gas. On my 32/36 it was just 3/4 of a turn in after contact.
how Weber words it in instructions are misleading 1.5 turns 32/36 and 1 turn 38. these are not starting points but a worst case @ end of tune. true starting point would be the moment set screw makes contact, then note how far you turn before you see bottom of the "enrichening progression holes" that's the only adjustment window that you have on a 32/36 or a 38 idle speed screw.)
I kept mains and air corrector stock @ 145main, and 185aircorrectors. But bumped idle jets from 45 to 60. (60 was only matching set I had larger than 45 on hand) the 60's did the trick i'm idling at 750 and mixture screws are both matched at 1 turn out. idle speed screw just touches the stop before flap slaps aluminum in throat.
Just curious on what you guys did.
Michael
Looks like some come with 50 idle jets reading LCE's spec sheets on theirs. mine had 45's in it.
(I recently watched a video from Pierce Manifolds, and he confirmed idle screw has no purpose other than keeping accelerator plates from slapping casting of carb. anything more then 1/2turn in after contact you are releasing extra fuel @ idle. and this isn't a science you really need to look with carb off truck to see exactly when you expose the holes for that extra gas. On my 32/36 it was just 3/4 of a turn in after contact.
how Weber words it in instructions are misleading 1.5 turns 32/36 and 1 turn 38. these are not starting points but a worst case @ end of tune. true starting point would be the moment set screw makes contact, then note how far you turn before you see bottom of the "enrichening progression holes" that's the only adjustment window that you have on a 32/36 or a 38 idle speed screw.)
I kept mains and air corrector stock @ 145main, and 185aircorrectors. But bumped idle jets from 45 to 60. (60 was only matching set I had larger than 45 on hand) the 60's did the trick i'm idling at 750 and mixture screws are both matched at 1 turn out. idle speed screw just touches the stop before flap slaps aluminum in throat.
Just curious on what you guys did.
Michael
Looks like some come with 50 idle jets reading LCE's spec sheets on theirs. mine had 45's in it.
Last edited by msane99; Apr 25, 2016 at 05:09 AM.
Apr 25, 2016 | 01:10 PM
#2
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Joined: Sep 2014
Posts: 184
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From: South Georgia
It has been several years since I installed the Weber on my 1980 20R. All I did was install the carb and adjust the air screw until it quit running too rich using the instructions from Weber. I also added a header and completely desmogged the engine all at the same time. It has the same jets it came with. i did not change any of the jets.
Apr 25, 2016 | 05:32 PM
#3
on my 22r/20r hybrid with o/s 20r valves, 4-2-1 header, I felt the stock idle and main jets were a tad too rich, but the block was not in great shape and there are some intake manifold mods I want to do for better mixture distribution which may help, so many things I want to try!
