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

[malcolm2]

Hello everyone. I will preface by saying that this is an engine from a 914. (IMG:style_emoticons/default/piratenanner.gif)

But it is in my VW Bus. Just now getting it moving down the road. Everything is new.

Carbs are new and I am a carb rookie, as well. Bought them from Aircooled.net and had them cleaned and set-up for the bus. My 914 has L-Jet FI, this group has taught me enough about that system to be dangerous.

So here is my question for the carb experts. What should the Pump Valve spray look like? It seems erratic and drippy. It kicks in 1st as I open the throttle, not a spray but pore, really. I will say that I see that in all 4.

[malcolm2]

Maybe the video will help. Close to the end, not very good lite, but the pump jets seem to really be flowing..... Is that normal. All 4 are doing it.

The purpose of the video was about the idle dropping, hence the name, but I got distracted by what seemed to be excess fuel.


https://www.youtube.com/watch?v=_4lPU2DNt44

[nditiz1]

So John from ACN is a master with carbs. Buying his clean and tune service is very valuable as well as his knowledge with IDFs.

It looks like either the accel pump linkage is not set properly, a blockage, OR missing parts. You should have a good steady stream squirt when you activate the throttle. I would pull the carbs off and check the stream on the bench. Also, pull open the pump on the side and make sure the spring is in there. It's been so long I cannot remember the base setting for the pump rod, but I want to say 3 threads showing after the lock nut.

[r_towle]

Sounds like they are not synced.
One cylinder sounds off, with valve noise also.

Even at revving it still sounds off.

I believe these are new carbs, you stated you just bought them?
Start with remove and verify all settings.
Sadly, they won’t be the same
Check and fix float level
Check and fix accel pump settings.

You should not see fuel at idle
Yes you will see the pumps squirt when you blip the throttle…they is their job
You should not see them at constant higher rpm’s ( to a point)

Get the book on how to tune webers.
Syncing them , once you get it right, will make the engine purr

[r_towle]

What carb linkage are you using?
Have you adjusted valves recently ( it does not sound like it)

You can tune each barrel to really be perfect.

[Superhawk996]

Sounds like they are not synced.

(IMG:style_emoticons/default/agree.gif)

To answer your question on the second carb it seems more normal. You should get a pretty steady stream. It will not be any sort of “spray” that is atomized coming out of the nozzle.

The first view the engine is shaking around too much (sign of not being synched) that I can’t see it terrible clearly but it does sort of look like too many drops and not enough stream

I agree with Nditiz - probably want to check them and figure out why you’re not getting a stronger stream.

Both the nozzle and the check valve are tunable to get the volume of accelerator pump discharge you need. However, you need that accelerator pump spring adjusted correctly and you need to make sure the pump diaphrams are in good shape 1st.

[malcolm2]

What carb linkage are you using?
Have you adjusted valves recently ( it does not sound like it)

You can tune each barrel to really be perfect.

I did adjust the valves while the engine was on the stand, and after some test running. but It would not hurt to check that again. I do have the SNAIL tester and have used it a few times.

The linkage is Sync-Link with cables and pulleys. I struggled with the hex bar and gave up on that.

[malcolm2]

Get the book on how to tune webers.
Syncing them , once you get it right, will make the engine purr

Do you have a book in mind? I checked the normal sources and it seems that the reviews are generic.

Very detailed instructions came with these carbs stating how to sync them which I have been thru a few times. Planned on doing that once more.

But you and others are suggesting a bit of a deeper dive with more detail settings and measurements etc... I would prefer a book that was for these IDFs or IDF 40s specifically.

Any thoughts here?

[Superhawk996]

Don’t worry about IDF specific book. I personally like the Dellorto book but it is now out of print.

The import part is understanding:

Weber IDFs run on the idle circuit and transition ports most
Of the time at light cruise and light tip in. You really only run on the mains when RPM is high and creating lots of vacuum at the Venturi neck. You can convince yourself of this truth by driving the car with the main jets and emulsion tubes removed.

As a result, the idle circuit tuning is critical. Note: Your motor isn’t idling well based on the video. Likewise it doesn’t transition off idle well.

You need to know what size Venturi and jets you’re working with as your baseline. You won’t get a decent snappy throttle response until you get down to 28mm venturis. Most
Carb kits come with venturis that are 30-32mm (too large) for top end HP - not good driveability.

Make sure your transition ports aren’t partially uncovered at idle. I used to see this all the time. Make sure your idle speed set screw isn’t holding the throttle blades too far open and uncovering the transition ports.

You need to balance airflow between each individual barrel before synching the carbs. Each time you adjust airflow - you’ll have to go back and tweek idle mix and also idle speed.

Look around for a used copy - Amazon, Ebay, post in forum, etc

[nditiz1]

"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.

[malcolm2]

"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.

[rhodyguy]

FWIW, AC.net is out of biz. Doors closed. The website did not reflect the change. The FB page is more up to date.

On the bottom of the Webers note the threaded rod. If the adj is too tight the pump jet can dribble.

Thomlinson’s Weber book is first rate. I found the Dell manual lacking.

[malcolm2]

ACN website does leave a bit of the door open for them to return, but I think it has been more than 6mths that it has been closed.

Yes, someone mentioned the pump rod adjustment. They could not remember the setting. But is was to count the threads (probably above the nut). I think he said, like 3 threads??? This one has quite a few more.

That book is very popular, and out of stock, even on ebay. I found a HAYNES on ebay for $15. I got that coming. and a PDF version of Dellorto Tuning Manual by John Savage that I downloaded.

[rhodyguy]

Can you compare the exposed threads side to side? Match the side that does not dribble.

Does the jet in ? dribble when the pump is energized and the engine is not running? If so, you might try backing the nut on the offending side off a bit.

Every time you adj something on the carbs, wait a moment for the adj to take affect. They don’t respond like FI.

What flavor of fuel pump are you using?

[malcolm2]

Can you compare the exposed threads side to side? Match the side that does not dribble.


What flavor of fuel pump are you using?

Just a quick fuzzy picture yielded similar threads on both carbs. 11 to 12 threads on each.

Pump is also from ACN. Do not think ROTARY is a brand. I believe Carter is a similar design. But I mounted it under the tank on the frame of the Drivers side.

[rhodyguy]

2 filters? The middle canister is a filter. I got rid of it. I went with a FI filter, same sized inlet and outlet. Perfect fuel line fit. Use shouldered clamps. Easier to see when the filter is fouled. The metal can? Not so much.

[rhodyguy]

Does the jet dribble when the fuel pump is energized? Have someone turn the key while you watch. Your engine oil may be contaminated with fuel. I would change the oil after you fix the dribble

[sportlicherFahrer]

The Tomlinson book is on the CB Performance site as well. Currently it shows available for adding to cart, but also has the link for notify when back in stock so I'm not sure what their stock really is.

https://www.cbperformance.com/product-p/0103.htm


Also, the repackaged Carter pump retailers sell (CB, PP, AC.net, and others) is available on Amazon for about half the cost. Not sure why there's such a big markup on these from the average car sites. Carter part number P90091.

https://www.amazon.com/gp/product/B07BBDSZP...=UTF8&psc=1

[rhodyguy]

‘Email notification when back in stock’. Could be a long wait. Post a WTB in the classifieds.

[930cabman]

I would bet on either the pump stroke is insufficient or the pump jet is (#12) is clogged, assuming the floats are at the correct setting and the float bowls are near full.