Dual Weber IDF 40s, Carb Rookie question... Options

[malcolm2]

Maybe a good measurement. But I don’t hear or feel anything. Sounds good and drives good. You guys have gotten me here. Might as well go all the way.

On the snail video, give me a time marker of what you hear.

So just to understand and maybe learn this tune by sound, i am gonna do the best lean process once more.

[rfinegan]

post another video of how its running, after you best lean tune

[Superhawk996]

On the snail video, give me a time marker of what you hear.

Original video - 9 seconds and 58 seconds

When you open the throttle you can immediately hear the engine stumble or bog down a little bit. Tone changes (lower pitch) and engine doesn’t immediately pick up RPMs. Essentially a stumble or time delay before the engine responds to your input and the engine is momentarily slowing down for those milliseconds before it recovers.

Based on that black plug, it’s running rich when idling. Then you hit the throttle and dump in even more fuel via the accelerator pump. It then takes a little bit of time for the air flow to catch up enough to lean the mix out a bit (but still rich overall) and then the RPMs can pick up.

[malcolm2]

Wouldn’t the original video be worthless now that i have changed settings? I guess it could help with BAD sounds.

I would be more curious about the sounds on the SNAIL video. That is current state.


Might have time to get to a full re-do this evening. You asked about the plugs. I will pull them all and and pix before i head to my real job today.

[Superhawk996]

Sorry, was late for me and I was tired. Those time stamps were from the video with the snail.

Yes, agree a little irrelevant if you’re readjusted and just a general comment on the what I was hearing in the early videos.

The 1st original video was worse with the engine shaking visibly much more due to poor tune and lack of synch & air balance. It got much better in the snail video but was still bogging when you initially open the throttle. Those are the time stamps I referenced.

[malcolm2]

Rich as expected. 1 & 2 do look better, but still have the a bit of very black non-shiney, dusty look on the edge. Kinda strange, but maybe not since each barrel is adjustable, but they all have a bit of difference.

I think 1 is best, 3 is worst, in terms of BLACK-ness.

Again, this was about an hour idling when I was adjusting, then maybe 10 miles of driving.

Can this be cleaned off to review again when I have attempted BEST LEAN IDLE?

[rhodyguy]

3-4 are running really fat.

[r_towle]

Reading plugs happens two ways
One at idle….
Then, after you super clean them start and drive immediately, with little to no idling
Go run it up and down the gears
When you are coming into the driveway, shut it down
Try for no idle during this phase ( not easy)
I start it and rev immediately to 2500 ish

After you stop, let it cool down
Check the plugs again
You should see a different condition

Idle is typically much richer
You want perfect color under load, when driving

Rich

[r_towle]

Reading plugs happens two ways
One at idle….
Then, after you super clean them start and drive immediately, with little to no idling
Go run it up and down the gears
When you are coming into the driveway, shut it down
Try for no idle during this phase ( not easy)
I start it and rev immediately to 2500 ish

After you stop, let it cool down
Check the plugs again
You should see a different condition

Idle is typically much richer
You want perfect color under load, when driving

Rich

[930cabman]

If I am checking plugs, I will run WOT for a short time, cut the ignition, coast to a stop and look at the plugs. Idling is a small portion of the picture, I want to know the mixture under load.

[gnomefabtech]

Big transition bogging is often caused by not enough timing advance. I couldn't see if you are using a vacuum advance but you should. Idea is that under low load and high vacuum there's a lot of advance to burn clean and under big load, less, so you don't get knock. For performance, vacuum advance should be connected to manifold vacuum NOT venturi vacuum. Set your total advance (above 4k rpm) to about 36deg with vacuum capped then let the idle advance fall where it does once the vacuum is connected.

I don't think you can read the plugs to set the idle mixture. For me the best results come from just turning in each idle screw until it starts to miss on that cylinder and then backing it out until it runs solidly. This will take a couple of rounds because as the whole engine starts running faster due to correct idle mixture you need to turn down the idle a bit and then reset the mixture a tad.

For the main jet you can get an idea of how you are doing by giving full throttle up a slight hill in a high gear and then lifting like 10%. If the car feels like it picks up power when you close the throttle slightly then it's too lean. This is only for the main jet though.

The idle jets are the most important and I generally start lean and see what I can get away with. You can have a pretty lean mixture at partial load and you should so the plugs stay nice and clean. You'll feel hesitation at like quarter throttle if the idle jets are too lean.

Lastly, I've seen some examples of dual carb setups having problems because the linkage isn't matched throughout the travel. You get all synched at idle but they are off at mid throttle. Try and check to see that the linkage is parallel and you hit WOT on both sides at the same time.

[Superhawk996]

I’d start with a fresh set of plugs - once they get carbon’ed up like that they start getting misfire. Carbon conducts electricity. Almost impossible to get them cleaned properly when running that rich on 3/4

[nditiz1]

2 things you need to understand for carb jetting.

1. How do you know if you are running rich or lean? Nose, ear, plug? Maybe plug, but an AFR. Unless you know what is happening while driving you are shooting in the dark regarding changing jets.

2. When does your idle jet circuit stop and your main take over? Hard to say, but you can get a feel for it by driving around with the main stack removed. You can literally drive a car up to 55+ mph only on the idles. Don't go up any large hills as you will find out fast where the transition zone is. That is when your mains would start to kick in. If you have your stacks in place and the car starts to miss and hesitate while moving through this zone you know that either you need bigger idles ( which in your case 50s will be fine) OR you need to bring the mains in sooner with either bigger mains, air corrector, emulsion tubes.

[malcolm2]

https://www.youtube.com/watch?v=kCXB0GVAgBA


Tomorrow i will balance with the bypass screws to get front barrels on each side to match the back barrels.

I don’t have this tune by ear down yet. So this is were i stopped.

Crazy fuel pressure gauge is still wonky. I got a new gauge to install, but it is bigger diameter than this one and has larger npt.

[nditiz1]

Going good. If the front to back is within a 1/2 point then the school of thought is just leave it, no need to adjust the bypass screws.

I might be on an island with my next comment, but I dont really like idling around 900 - 950. I really like 1000 - 1050. The car just seems to run smoother, but every application is different. The key is to make the engine happy. In your vid the engine seems to be running well. The drive will determine if those settings are just good at idle or under load. Also, do your same vac measurement at different RPM. So hold the engine speed at 1100 and see if both sides are the same. Do this at various points all the way up to 3000. If they are then your linkage is sync'd no need to touch it again.

One thing I did hear and maybe it was just the sound quality, but it almost seemed like a delay when you blipped the throttle for the engine to pick up. If your vac line is disconnected from the Dizzy right now then this would make sense to me. If not that then maybe I have been messing with triples too much and have forgotten the sound of duals (IMG:style_emoticons/default/rolleyes.gif)

Mine sounds a little different, but also the end of the tuning journey
2056 dual carbs

[Fahren Cars]

"You can convince yourself of this truth by driving the car with the main jets and emulsion tubes removed."

This is something that all carb owners should experience even triple owners. Get a feel for how the engine responds and where the drop off actually happens. Try not to perform this drive over any real big hills as it may require higher RPM/butterfly opening which will throw you into the Main and the car will want to die.

I'm going to assume that he is running a 28 venturi, 115 main, 50 idle, and 200 air if John set them up from ACN, but always good to double check.

I did see a video on youtube with a guy, IDFs and a 912. Running around a parking lot with the mains out. Very interesting. Discussion starts at about 16 minutes....

https://youtu.be/2uDY1wcx6mo

ACN sheet confirms, with one exception.

Jack and I are also running 40 IDFs, and we are going through the same process as the OP here. I noticed that some of the online VW tuners suggest setting float level at 10mm but the Redline rebuild kit instruction say 12mm, and then Aircooled.Net says 12mm. Can someone share insights on float levels?

[Superhawk996]

Can someone share insights on float levels?

Already covered within this thread - page 2

[Jack Standz]

https://www.youtube.com/watch?v=kCXB0GVAgBA


Tomorrow i will balance with the bypass screws to get front barrels on each side to match the back barrels.

I don’t have this tune by ear down yet. So this is were i stopped.

Crazy fuel pressure gauge is still wonky. I got a new gauge to install, but it is bigger diameter than this one and has larger npt.

As previously discussed, I chased a similar fuel pressure problem until I discovered a restriction (or two) in the fuel line. So maybe there's a restriction in the fuel line or tank (crud build-up), fuel filter loaded up with crud, etc.?

[malcolm2]

gonna get the BIG gauge on there today and see if it is more accurate. If that fails, I can pull the hoses and the filter to determine about that. I doubt CRUD is an issue as EVERYTHING is new except the gas cap.

Will drive it a bit today, maybe not too far, just around the hood and up some steep hills.

I also bought another fuel pump, I can try that if issues arise. But when the car is running and I see zero on the gauge, I can feel the pump running.

Yeah, float level measurement is a mystery still. But someone said the variation in specs comes from ethanol usage. Float sits higher I guess.

[malcolm2]

Here is a note about the plate and covering the small holes inside the barrel. I ended up taking one carb off yesterday, so I decided to check the plate situation.

There are 4 zig zag holes and I measured the speed screw all the way til it had fully mashed the spring.

so even at the Best Lean Idle preset, the btm hole is partially visible. Bad drawing, but here is an example.