Weber Carb Jetting

Engine, Transmission and related drivetrain.
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abisel
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Location: St. Charles, Missouri

Re: Weber Carb Jetting

Postby abisel » 27 Jan 2016 15:29

The engine is an L20B and as far as I know, the lower end is stock. So CR would be stock.
The WebCam 91 is:
    valve lift - 0.450 for both I and E.
    Duration is - 260 for both I and E.
    Duration @ 0.050 - 238 for both I and E.
    Lobe center - 108 for I and 111 for E.
    Intake opens 11 BTDC / closes 47 ABDC
    Exhaust opens 50 BBDC / closes 8 ATDC
The head has all new components with 43mm intakes instead of 42 as stated in the first post. Cam timing is spot on.

I have tried to get the engine to idle with the first progression hole covered by the throttle plate and it won't do it. Even with the mixture screws backed out 1 to 1.5 turns. The engine rocks a whole lot and to the point it sloshes fuel out the main venturie into the carb bore. To get a half way smooth idle, I have to screw down the idle speed screws to just open the first progression hole and the mixture screws either seated or 1/8 turn out. This is with timing at 15 and idle at 1K rpm.

With 50F8 the hesitation is minimal. I tried 50F4 and 50F2 and the hesitation is much worse. If it put in 50F9 the hesitation is gone, but it is way too rich at idle.

So the current setup is:
    33mm venturie
    50F8 idle jet
    140 main with 190 air on F16 emul tube
    45 accel pump jet
    medium weight accel pump spring
    accel pump duration is 14mm.
    55 pump exhaust valve.
When I rebuilt the carbs, there was a very thin light ring around the plates when held up to a light. Maybe I need 79.5 degree plates instead of 78 degree? Or drill the hole in the plates. I could drill holes in the old plates since they are still usable.

I did a compression check with a warm engine and got 170 on 2,3 and 4 and 172 on 1. So the compression is good.
Last edited by abisel on 28 Jan 2016 05:40, edited 1 time in total.

Chickenman
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Location: Coquitlam

Re: Weber Carb Jetting

Postby Chickenman » 27 Jan 2016 17:52

With the current set up, can you kill the engine by turning the mixture screws in all the way? I'm thinking not...

F9's are a pretty common idle jet. The " F " in the numbering is the air bleed size. But just like Weber Emulsion tubes, they are not numbered numerically in size, but rather by chronological order of manufacture. Arrrggghhhhh!!! However there are charts available to decipher things.

Here is the proper order if DCOE Idle jets from Rich to Lean.

Table No.4
Idle jet air correction or bleed holes arranged from rich to lean.
Rich - F6 F12 F9 F8 F11 F13 F2 F4 F5 F7 Fl F3 - Lean


Here is a very good article on Weber jetting. Will make some things clearer.

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0ahUKEwjh4Pius8vKAhUILmMKHX68DwwQFggzMAY&url=http%3A%2F%2Fwww.lotus-europa.com%2Fnewsletters%2Flotus_west%2F00FU038.PDF&usg=AFQjCNHOTS46gJs5hAwW6AaE8F0SCMoUXA&sig2=Q_0_bidI6QymRTjI7KJXVg&cad=rja

Chickenman
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Location: Coquitlam

Re: Weber Carb Jetting

Postby Chickenman » 27 Jan 2016 18:12

Can you post a video of engine idling with best setup? Engine fully warmed up and give it a couple of " Snap" accelerations.

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defdes
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Re: Weber Carb Jetting

Postby defdes » 27 Jan 2016 19:22

Get yourself one of these, no more guessing. http://www.carbtune.com/colortune.html

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abisel
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Joined: 29 May 2014 14:30
Location: St. Charles, Missouri

Re: Weber Carb Jetting

Postby abisel » 27 Jan 2016 19:49

^^^ that looks pretty cool. I have heard of those before and it isn't all that expensive. But can you use it when driving down the road to see the flame color under load. I suppose you could mount your GoPro to watch the flame color.

With my current setup, seating the mixture screws will not kill the engine. Currently installed are the older style mixture screws which are not a continuous cone shape. I could install the newer style mixture screws and see what that does.

I found this earlier on the wonderful internet. A pdf of the Weber Tuning Manual
http://www.lainefamily.com/images/WeberTuningManual.pdf

I'll see about making a video.

Chickenman
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Re: Weber Carb Jetting

Postby Chickenman » 27 Jan 2016 20:11

Wide Band AFR are the only way to go IMHO. But they're only instruments. The tuner still has to interpret the Data. And with things like Transition tuning, AFR alone doesn't tell the whole story.

That being said, old timers like me didn't have WB AFR meters...or even Narrow Band ones back in the 70's and 80's. We learned to tune with Plug readings, vacuum gauge readings and a well tuned ear.

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defdes
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Re: Weber Carb Jetting

Postby defdes » 28 Jan 2016 09:16

You can't do it while driving and you wouldn't be able to see with a camera. I bought one when I was having no luck tuning my side drafts 15 years ago (ended up being sealant I had used on the air horns being drawn into the carbs). I bring it up just because it will eliminate a lot of the guessing that you are doing, Colortune will get you to a good AFR through the rev range transitions, then under load you can start reading the plugs.
Good luck, I know how frustrating it an be.

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bertvorgon
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Re: Weber Carb Jetting

Postby bertvorgon » 28 Jan 2016 10:15

What Richard said,....

When I think of how much TIME would have been saved with a wide band A/F meter that is available now...
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

Idoxlr8
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Location: Burnaby

Re: Weber Carb Jetting

Postby Idoxlr8 » 28 Jan 2016 12:04

X10 on the AFR meter.
I used the Innovate to tune the triples in my car and got it tweaked well enough to pass our infamous aircare here in BC.

Then immediately went home and tuned it properly. :mrgreen:
260z owner
510 wannabe

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bertvorgon
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Re: Weber Carb Jetting

Postby bertvorgon » 28 Jan 2016 12:20

That's funny, exactly what I did with my Toyota AE86, tune it like crap to pass Airscare, the re-tune to run RIGHT!
"Racing makes heroin addiction look like a vague wish for something salty" - Peter Egan

1973 2Door Slalom/hill climb/road race / canyon carver /Giant Killer 510
1968 Vintage 3HP Mini Bike
1971 Vintage 13' BOLER trailer

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abisel
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Location: St. Charles, Missouri

Re: Weber Carb Jetting

Postby abisel » 28 Jan 2016 13:59

Lets see if this video works:
http://vid481.photobucket.com/albums/rr179/ajbisel/datsooon_zpsiyxqxuhz.mp4
Not a very good video. the sound level isn't right. Idle sounds high in the engine bay, but it is at 1K.

I decided to adjust the valves 'cause they were a bit noisy and I pulled the plugs.
Here are a couple pics of the plugs after driving around the neighborhood, pulling into the garage and shut-down.
Left to right is 1, 2, 3 and 4.
Without flash, color is light brown, not tan.
IMG_20160129_102941942-1.jpg
IMG_20160129_102941942-1.jpg (336.93 KiB) Viewed 1204 times

With flash:
IMG_20160129_103002451-1.jpg
IMG_20160129_103002451-1.jpg (358.73 KiB) Viewed 1204 times

So with driving around mostly on the idle and progressive circuit, the plugs look just a little on the rich side with no.1 being the richest.

I need to take it out on the highway and drive a while on the main circuit, shut off the engine, pull over and pull the plugs.

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Byron510
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Re: Weber Carb Jetting

Postby Byron510 » 04 Jul 2016 09:20

This thread was just linked from another thread, and I agree this is great information Richard.

viewtopic.php?f=6&t=29079

Thank you for sharing this.
My twin carbs have been sitting on the shelf now for over 10 years, and although mine are all Mikuni carbs, the theory is very similar - for the most part. One day I hope to have these back on a car. Now that emissions testing has come to an end for us here in BC, I can think about a project when I can install them again.
And I'll need to eventually recall them back from the "loaner" state that they have been in for the past number of years (Chad, where are you these days anyways?).

Again, thanks Richard, maybe we should make this a carb tuning sticky!

Byron
Love people and use things,
because the opposite never works.

Chickenman
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Joined: 06 Sep 2010 15:10
Location: Coquitlam

Re: Weber Carb Jetting

Postby Chickenman » 20 Sep 2016 12:09

I link to this thread quite often from other Forums. Maybe it should be a sticky. Lots of good info here from all members.Image


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