TheSamba.com :: View topic - I need help on Weber IDA jetting tuning any info guys?

Fri Dec 07, 2007 2:20 am

Speedy wrote: AC.net rents them for $75, check in the pricing options when you're in his site. If you're really keeping it the $ is nothing compared to the outcome.

thanks speedy I know tuning with a wideband going make my car run much better and save more gas and all the headache of trial and error but I just trying to tune the carbs with what I have for now and drive pretty decent for now until I can save for a wideband. cost of living in hawaii is crazy everything has to be shipped we are in the middle of the ocean. thanks again.

Fri Dec 07, 2007 8:56 am

If you treat it (wideband) like it's yours you won't have a problem. The worst that ever happened was a couple guys running leaded fuel, we made him buy a new O2 sensor.

But sometimes guys like them so much they buy it instead of returning it. :D

Using a wideband really opens your eyes to how off your "perfect" tune actually is.

If the engine "cleans up" with a bigger idle fuel, instead try a smaller idle air with the smaller idle fuel. Try a 100 or 110 instead of the 120. You have to find out what the engine wants. But again, without a wideband it's like reading tea leaves.

John
Aircooled.Net Inc.

Mon Oct 02, 2017 7:20 pm

Backfires through carb during steady state Rpms between 1,500-3K. Current setup:

2016cc
42x37
CB 2246 cam
1 5/8 merged header
9.5:1 compression
050 dizzy...igniter 3 on order
Msd blaster 2 coil
.028 spark plug gap
30 degrees @ 3K

48 IDA
3rd progression
70 idle/120 holder
F7 tube/160 main/200 air
1 1/4 turns on mixture

Have got F2 tubes, 60 idle, and 115 holder on order. Here's link to 1st-3rd pull...later in video popping is noticeable at cruising speed.

https://youtu.be/IFQL3PFWzS8

Mon Oct 02, 2017 7:24 pm

this is more often than not a linkage sync issue. Carbs not synced at specific throttle positions, despite being synced at idle.

And 70 idles are too rich 98% of the time. Your spark plugs will be black.

Mon Oct 02, 2017 7:53 pm

Thanks for the quick response John. If that's the case, how do I sync the throttle linkage at different positions. Or is it a matter of the throttle plates being misaligned themselves. Sorry for being the novice, but how does slight difference in throttle position between carbs cause it to backfire through carb?

Mon Oct 02, 2017 8:20 pm

when one carb is open more than the other, the one which is more open lets in more air (more power) than the lesser one. So one side is pulling the other one.

Using the snail gauge, with the bypass port open, allows you to compare the 2 sides at different throttle settings.

It's far more common for this to be a linkage issue than a throttle shaft issue.

If the linkage holes are SLIGHTLY different on the 2 sides, the same linear motion will create 2 different angular openings. This is especially common with stamped steel (bent) throttle arms.

Tue Oct 03, 2017 4:30 am

Try a 37mm venturi if you only have 2 progression holes. 60 idles and 155 - 160 main.

Sun Oct 15, 2017 7:02 pm

Update...installed new wires and Pertronix igniter 3 distributor, so got awesome spark now. Car idles at 1K. I made a discovery...with the pedal to the floor the butterflys were only partly open. No wonder the car felt like it was struggling to pull. Drilled hole higher on the roller pedal to achieve WOT. Linkage is synced throughout the throttle movement. Installed F-2 emulsion tubes. Switched out the idle jets to 65’s still with 120 idle holder. Carbs pop more at 2,500 rpm cruising speed. Gonna try 115 holders next with 65 jets.

40 vents
65 jet/115 holder
160 main/200 air
F-2 emulsion
Mixture screws 1 1/2...lean is at 1/2 turn.

Timing: 30 degrees total
Spark plugs: .028

If it still pops, gonna try turning mixture screws out to mask the lean hole. Then I’ll order smaller idle holders to help carry it past the lean hole

Mon Oct 16, 2017 5:59 am

Smaller venturi and F11. I went through all the same fun and games.

Mon Oct 16, 2017 4:15 pm

Thanks for the recommendation...might have to go with 37’s. The 37’s would surely smooth things out with the increased velocity and turbulence. Still not cooperating with the 115 holder. I’m trying to keep the 40’s in...car ran great before the 3rd progression mod with 70/120 combo. It’s crazy that I can’t even get it to run smooth with 70 idle. Popping is less noticeable with 70s though. I’m gonna try 100 holders next. Today the popping was quick to come on at 1,500rpm steady state with 65/115. Also the flow is set at 5.

Mon Oct 16, 2017 4:34 pm

you added 50% more fuel with the 3rd progression hole, yet you think you still need 65 and 70 idle fuel jets? Your plugs are fouled. Get down to 55-60 range and re-tune.

Fri Nov 03, 2017 11:36 am

Update to the popping...was able to get rid of the popping. Adjusted springs on pertronix billet distributor to 1 silver/1 copper spring, essentially bringing more timing in earlier. Idle set @ 10/total @ 32. Started with 60/120 idle circuit...would pop between 1,500-3k. Next tried 65/120 idle circuit...less popping. 70/120 idle circuit...popping gone, but #2 plug is white at 2 turns mixture. #4 is tan with some white. Next, installed 60/100 idle circuit...no popping or hesitation, definitely can smell the added richness ratio. #2 plug is still white. #4 plug is now black...mixture screws are at 2 turns all around. As far as #3 & #1...#3 has always been leaner/white and #1 has been blacker than most and a little wet...probably due to worn rings. I’m thinking #2 has a stronger vacuum causing it to suck more air...also it is more responsive on the snail gauge. Car drives smoothly at cruising speed with no popping.

Compression test:
3: 105
1: 90
4: 95
2: 100

My question is, would it be advisable to tune each individual cylinder according to plug readings by using different jet/holder combos? Or should I use the mixture screws to individually adjust the lean issue? Don’t have a wide band. I understand the compression readings are a bit low and spread out. My plan is to get the engine running smoothly without running too lean and burning parts. In the future, when I bring the car down for paint I’ll rebuild the engine.

Fri Nov 03, 2017 11:57 am

Your compression being as low as it is is affecting your tune, it will never be perfect, I would get it in a drivable state and wait for your rebuild to spend your time on tuneing it.

Sat Nov 04, 2017 12:28 pm

I live on Maui and from Oahu and anything less than f10 70 idles no work for me. I would try f2 and maybe a little smaller main and air and keep the 40 vents. Us guys from the islands get a different way of jetting that work for us so I don’t know about you but hope it close enough. Aloha. Kehau

Sun Mar 25, 2018 6:16 pm

Back at it again. After a lot of research decided to change the vents to 37mm. Since the CB 2246 cam w/1.25 rockers floats at 7k, figured I would increase intake velocity to bring the powerband in earlier. Driving on the street 6.4k is the highest ill go. After the swap, still had 65/100, F2/160/200...definitely more rich, black cloud at higher rpm. Went for a cruise, car pulled stronger but felt like there was more to offer. Since the F2s have no holes on bottom, I swapped it with F7s...everything else the same. Car frrrking rips now! I may try go down on the mains to get better mixture. Got spare 150 mains, a little richness doesn’t hurt though keep the heads cool.

As for the lean hole, it’ll seldom pop below 2.4k...so try to stay out of that range.

Here’s a video of a quick rev:

https://m.youtube.com/watch?v=iyJAkXYyymw

Mon Jan 20, 2020 10:31 pm

[email protected] wrote: you can't quote an idle fuel you are using without also the idle air. On most weber carbs, the idle air is FIXED, but it's changable on the IDA.

I can give you a jetting combo where the 55 idle fuel is too rich, and another where a 70 idle fuel is too lean, DEPENDING ON THE IDLE AIR JET.

Without knowing your idle air you (and others) are wasting their time. Start with a 120 idle air and 60 idle fuel. I'd also try a 100 or 110 idle air and smaller idle fuel.

If you have 3 progression holes you'll need a smaller idle fuel than if you only have 2 progression holes.

and without a wideband to guide you it will be "not easy". In fact you'll NEVER get a perfect tune by "seat of the pants" tuning, you need a wideband for it. If you just want it to drive smooth, just jet it fat and enjoy the 15-20mpg. A perfect tune will get you 30+ MPG, but you need a wideband and a few hours of tuning.

Hopefully you'll have learned more in the past 45 seconds of reading this than the last several hours of "carb tuning".

John
Aircooled.Net Inc.

Good Stuff! Without that kinda info we would just be chasing our tails...

Tue Jan 21, 2020 7:13 am

99% of light load driving issues with any dual carb setup (especially IDA's) are related to proper syncronizing.
Esepcially with IDA's that have big butterflies, a small tweak the idle rpm screw or a pushrod makes a HUGE difference it lead/lag of a carb and will make driving a very On/off experience.

When syncronizing IDA's, I like to get the idle first, then adjust one pushrod in/out until I can hold a stead 2,000rpm with light pedal pressure and the motor runs smoothly on all 4 cyls. I get there by adjusting a pushrod in 1/16th turn increments.

Yes, 1/16th of a turn makes a difference in IDA's.

Having them properly sync'd at 2,000rpm makes them drive like dream.
Pay attention to this.
You can mess with all the jetting in the world and it won't cover up a 1/16th of a turn error in syncronizing.

This is why I HATE Berg linkages as they don't have any ability to fine tune the pushrods. That stupid "Z" bend pushrod is useless.