IDF idle mixture across cyclinders

[grrrdot]

Hi,
Just installed my first set of IDFs and spent the weekend getting them setup. I'm a little confused about where I'm ending up with the idle mixture settings so figured I would ask.

Some background:
The engine is a 1608 AFAIK US stock spec. internals. It has an EDIS ignition, Allison’s Snake headers and free flow exhaust. I did a compression check before installing the carbs and all cylinders are within 5% of each other.
When setting up the carbs I warmed up the engine and balanced the carbs ( checked the balance a few times actually )
I can get the car to idle around 850 but its a little rough.
I looked down the carb throats at idle and the tops of the throttle plates are dry.

Where I'm ending up:
Cylinders 2 and 4 idle best a little less than 1/4 turn out from seated.
Cylinders 1 and 3 idle best ~1 turn out from seated.

Any ideas why 1 and 3 would need more fuel? Is it something to do with the crankcase fume vacuum lines allowing more air in to those cylinders?
With these settings seems like the idle jets are too rich.. They are 55 jets which I believe is what Fiat paired with the original 1608. Is there anything other than the idle jet that could cause the rich condition? Could it have something to do with the slight miss at idle?

Thanks for any ideas,
-G

[sptcoupe]

Each cylinder will be different based on how it flows. Cylinders wear differently over time. So the goal is not to have each idle mixture screw turned in or out the same number of turns, but to adjust each cylinder to its optimal idle mixture. That mixture is what is referred to as "best lean". Turn the idle screw out until the cylinder stumbles, then turn it in slowly. The idle should smooth out and increase, and then fall off as you continue to turn it in, because the mixture gets too lean. From the point that it falls off, back it out until it is smooth and idling at its fastest. That will be the optimal mixture for that cylinder.

It may be a bit rough at 850 because it sounds like your idle jets are too rich. The idle mixture screws should be between 1.25t and 1.5 turns out at optimal idle mixture.

Can you tell us what your jetting is?

[grrrdot]

Hi,
Thanks for the response my current jetting is set to:
55 idle
125 main
210 air
F11 emulsion
080 bleedbacks.

-G

[sptcoupe]

That jetting sounds like it should work, assuming your cabs have 32mm chokes in them.

Try adjusting the idle mixture again. As you are turning them in, be sure to stop right when the cylinder falls off, and then back it out about 1/16th of turn. You may have them turned in too far and therefore too lean.

[sptcoupe]

That jetting sounds like it should work, assuming your cabs have 32mm chokes in them.

Try adjusting the idle mixture again. As you are turning them in, be sure to stop right when the cylinder falls off, and then back it out about 1/16th of turn. You may have them turned in too far and therefore too lean.

[engineerted]

Few questions: 1. are you using a synchronizer to balance between carbs?
2. Air bleed screws, turn them all the way in and use it to balance the port flow on each carb, then balance carb to carb with the center balancing screw.
3. What is the advance at idle, I find that the idf like more advance at idle 10-15degrees
4. 55 idle jet should work, but you can get 52.5
5. are these the 13/15 idf's for the later 70series? the idle screws are different and thus the number of turns are not the same between the two types.

[grrrdot]

Yup these are 13/15s
I’m using a synchronizer
Idle advance is 10 deg

I went through the balance then idle mixture adjustment process again. I’m ending up in about the same place.
1 and 3 are actually about 1 turn out.
2 and 4 are 1/4 turn out.

Emissions ports are capped.
These carbs still have the enrichment circuit. I don’t have a cable attached to it so it seems like it’s off. Could there be something wrong with the enrichment?

-G

[grrrdot]

Went for a drive with it setup like this and there’s a flat spot off idle, seems to be at one specific throttle position it’s bad enough that I’m getting popping through the carbs.
Looking at the plugs 2 and 4 look very rich and 1 and 3 look lean to just right...

Once past the flat spot the engine screams, have not gone to WOT yet.

1 and 3 also have the emissions port, it’s plugged but not sure if that would make a difference?

-G

[grrrdot]

So poking around I found this article:
https://www.thesamba.com/vw/forum/viewt ... eefdfdc1af

Which makes me suspect the enrichment circuit. I pulled the enrichment covers and everything looked sane, both valves went up and down correctly. Guess the next step is to take the top off the carb and pull the valves to see if there’s anything in there.
-G

[grrrdot]

Cleaned and checked the seating of the cold start. No real change so guess that wasn’t it.
I pulled the idle mixture screws just to see what they look like:

Is this right? I thought they were supposed to be pencil shaped.

Only other thing I can think of is that the throttle blades are installed wrong or mis-aligned and exposing another circuit.

-G

[grrrdot]

After some more experimentation the 1 and 3 cylinders are also backfiring through the carb during transition.
As I understand things that means they are going lean, maybe me having to turn out the idle screw on them more is the real issue.
I'll pull the carbs next weekend and give the idle circuit a good cleaning and inspection.

-G

[grrrdot]

After numerous hours of testing I’m confident that cylinders 1 and 3 both have a vacuum leak. This makes the synchrometer pretty much useless.
With some guess work I can get things close at idle by using the air bypass on 2 and 4. With those bypass open I can get every cylinder contributing about the same but I have to back the idle speed screw out all the way out to get 950RPM.

I pulled both carbs and it seems like the crankcase vent ports are the problem. With the external lines capped and my vacuum pump connected to the port under the carb I can’t get my hand pump going fast enough to build any vacuum. Spraying some WD-40 around it seems to be leaking air from the throttle shaft both on the inside and outside.

So... looking for advice where do I go from here? Complete teardown? Plug the interior port and hope the shaft does not leak too much? Other?