How to make a progressive work properly on a VW engine.

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I may edit this as needed, if I've overlooked anything, or need to make a change. If you have a question, ask in the reply and I'll edit the Original Post to clarify.

MAKING PROGRESSIVES WORK

If you have an EMPI progressive, you got hosed. Get a real Weber DFAV/DFEV.

Don't run a 009 or other centrifugal only distributor. They suck! Run our SVDA, it will make your tuning job MUCH easier. Good progressive carbs HAVE the proper port for the SVDA, if they do not you got a chinese copy or an old (ie: obsolete) progressive, and you will HAVE no other choice but to run a 009/010, but you will NOT have optimal tuning results like you would if you had a SVDA.

Centermount Progressives NEED intake heat, and lots of it. This is why a progressive on a T4 WILL NOT WORK. It's so bad and unfixable, we do not even sell the kits that are available for the T4. It will not work, do not ask, because the answer is "get dual carbs". Nuff' Said.

On a T1, the stock muffler is setup perfect, just make sure they are clear. But if you have an aftermarket header with the flanges on #2 and #4 primaries, you must relocate one of them to the collector (like the stock muffler!) to get good preheat. Don't be a lazy ass and think you are special and that these rules don't apply to you. Just relocate one to the collector, with some small steel tubing, and weld/braze it in place. Or have the guy at the muffler shop do it, it's an easy job for him.

If you don't do this relocation modification, don't bitch about the flat spot and poor MPG, along with needing "wack" jetting (like a richer primary than what I use). The intake preheat keeps the fuel that is metered at the carburetor (by the idle and main jets) VAPORIZED (Google "Latent Heat of Vaporization"). Your intake heat is of a fixed amount. The richer it is, the colder the intake is going to be. Don't be any richer than you have to! If the intake is cold, you have to jet rich to make sure that the air/fuel reaching the cylinder is rich enough, because a lot of the metered fuel condensed on the way to the cylinder because it's cold (not vaporized), and a long ways from the carb to the cylinder. So you have fun stuff like when you rev it up, all that condensed liquid fuel puddled in the intake makes it's way into the cylinders and now you are way rich. Intake heat IS A GOOD THING for centermounts! Even if it's 120F in the desert, the intake heat is a good thing! The more heat you route to the intake, the leaner you will be able to jet the carb, and keep the A/F the same. If you have a wideband, you'll see that as you add heat to the intake, it will run richer, since you are keeping fuel vaporized and it will combust properly!

I've even recommended to some guys that didn't want to hack their exhaust to have simply routed their hot engine oil thru the preheat tubes, which has the double benefit of heating the intake and cooling the oil AT THE SAME TIME. If you have a porous intake (ie: CHEAP) you are SOL on this one, it will leak.

http://vwparts.aircooled.net/Deluxe-Center-Mount-Intake-Manifold-Kit-Weber-DFEV-p/99004-410b.htm is a good intake.

Also, good intakes route the heat to the carb base, NOT just along the bottom tube. If you see a bottom tube only preheat model, walk away from it, it sucks. PERIOD. A good intake is not that much, and solves the progression linkage issue also (the carb doesn't line up with the throttle cable. Cheap kits have a ghetto connection from cable to carb, that doesn't even open the carb all the way up at WOT. The good intake will fix the linkage issue, with a McGyver like arrangement on the manifold. It works very well.

I will also say that hot air intake also helps your cause. Figure a way to get hot air from under the engine, to the air intake on the carb.

All Webers also need 3-3.5psi fuel pressure, and the floats set to spec. They are NOT SET when new, so learn to work on the carburetor! These 4 things (fuel pressure, float level, intake heat, hot air intake) are NOT done by 99% of progressive owners, and the cause of the bad rap.

The next issue is jetting. I have not once, in 30 years of working on these things, seen a progressive properly jetted, not even CLOSE, if I haven't worked on it first. I have also never seen a store that properly jet a progressive. Their "charts and guidelines" are horrible. HORRIBLE. It's like they want you to blow up your engine and wear out your rings/pistons from fuel washdown, in 5k miles. So, on we go.

Here are my guidelines for progressive jetting.

Primary idle, 45-50 at sea level, 40-45 @ 5k'. Secondary idle 10-15 larger than primary idle. Weber supplies them with the primary idle larger than the secondary, WHICH IS STUPID. It runs too rich on the primary, then leans out when the secondary opens.

The more intake preheat you have, the smaller your idle jetting will need to be, since the fuel metered by the jet actually stays vaporized, it's not puddling and condensing.

Main jet. 125 primary. 180-190 secondary (not a misprint). I've even seen some engines need 210 secondary mains. If you do not stagger your secondary jetting, you WILL have the same problem of severe lean out when the secondary opens up, since airspeed drops so much due to air flowing thru 2 bbls. You want to be lean on the primary (for mpg and cool running), but richen up to 13:1 when the secondary opens. Most clowns jet the primary and secondary the same. So when airspeed drops to <1/2 when the secondary opens, the vac signal the main circuit sees is also < halved, and your pride and joy leans out like crazy. This is why the secondary main MUST be much larger than the primary main. I'd like to slap the morons that recommends square jetting on the main jets. They are clueless.

Air jets. 160-180 will work, I generally use 160 on primary, and 180 on secondary. If you use a 180 secondary air, you may need to go up 10 more on the main, to a 190-200 secondary main. Do NOT be scared of the "huge" secondary jet, it WILL WORK PROPERLY. I've setup hundreds of these carbs, and know what works and why.

If you are at elevation, for every 4k'

drop both idles 5
drop both mains 5
increase airs 10-15.

These guidelines will work for a heated intake, properly setup carb (float, fuel pressure), with no ignition "issues".

Sea Level, run 45/60, 125/190, 160/180
@4-5K', run 45/55, 120/180, 175/190
@8k', run 40/55, 115/175, 190/205.

I even saw one guy at 8'k that needed a 37.5 primary idle.

If you do not have the intake heated, your jetting will have to be much richer than this, for reasons mentioned previously.

These guidelines are not exact, but VERY close.

I hope this helps. E-mail me directly (please do NOT use PMs, I do not check these) and I'll help further. Please have the basics covered first (fuel pressure, floats, ignition, etc), because that's the first thing I'm going to address, and if you do not I cannot help you.

John
Aircooled.Net Inc.
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[modok]

Thank you, truly. I just learned something.

I do have two questions for the sake of the................historical record.

Some type 1 manifolds have individual riser passages from the
butterflies to the cross tube, while others have a sort of plenum. Which is preferred?

Also, while there are many variants of this carb, most that I have seen, have a power valve. Is there anything a person needs to know about the power valve?

[busman78]

The best mod that can be done for the Power Valve is to drill the factory port from the outside, install a fitting which will block the passage the power valve currently gets a signal from and run ported vacuum to it. Wildthings came up with this, it is an easy modification.

The tube used was VW vacuum/vent tube, 5mm (4.78mm), a #12 drill and a smidge of JB although the epoxy was not really needed. Drilled hole just past the carb internal passage for the power valve, allowing the new tube to block it. Then ran a vacuum line from the ported vac outlet on the carb to the new power valve port.

[Jimmy111]

Photos

[IMG]

http://i269.photobucket.com/albums/jj53/jhmartin/progressive003.jpg[/IMG]

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Why? I will argue that when the carb is setup properly this modification is unnecessary.

[busman78]

My progressive are set up quite nice, were smooth and functional prior to trying this mod, although not a necessity, this simple mod just adds a little smoother transition a little sooner than the original set up. Try it.

Just for the record here is my progressive set up on 2.0L 39X34, 7.7:1, Raby 9550 cam at 5,000 feet with a .120 orifice direct bleed of crankcase vapors into the intake manifold. Mileage is 20-22, plugs are a nice light choc/tan.

Idle 60/50
Main 150/159
AC 170/180
Pump 55

Primary throttle plate was set with the carb off the engine so that it blocks the progression port, idle was then established with idle jet and idle mixture screw only.

[grimace007]

dont worry kirk, i have one as it stands it runs alright youve seen it

granted it runs a bit rich it runs great... but im still swapping to dual dells as soon as i can afford it
_________________
Brian
68 sedan

Dallas Air Coolers

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Busman, I think your hesitation was the idle jet setup. With a smaller secondary idle, when the secondary begins to open up it leans out (remember, there is no pump on the secondary). That's why the secondary should ALWAYS be richer than the primary, to prevent this lean out. You'll probably also pick up some mpg by adjusting the idle jet stagger.

It's important to note that you are not supposed to tune the primary idle jet for max response and power, it is SUPPOSED to be lean/lazy. If you need more power, open the throttle more. This also makes it easier to drive and less "jerky".

[modok]

John, I think you should re-think what Busman's mod does.

It keeps the power valve open at idle.

This will bring the mains in stronger during transition because the level of fuel in the main well will be higher at the moment the throttle opens.

Only change I see is mains kick stronger during transition.

[busman78]

The secondary idle jet is smaller cause it does not do idle, it is there to assist in progression of the secondary only, since the main jet is larger on the secondary, air flow (pressure) in the throat is already high the need for a larger secondary idle jet is not required unless you have a stumble when initial opening of the secondary, of which I have none.

The primary idle jet was tuned for best lean idle, instead of using the throttle plate as most do, I did it at the ideal setting for the throttle plate which is in the position of blocking the progression port, unfortunately you can not see this by looking down the throat of the carb when installed, if the throttle plate is below the progression port you will have hesitation before getting to progression, if you are past the progression port you obviously have too small of an idle jet and if a vac distributor is being used ported vacuum will be advancing the distributor. So the best, although a pain the ass way to set ideal idle is to set the throttle plate with the carb off the engine, install it then jet. There is a little wiggle room up or down, maybe a 1/4 turn but I have found the idle falls in the 850 to 950 range quite easlily doing it this way and provides a smooth idle that is none to rich or too lean.

[[email protected]]

A power valve exposes more "jet" to the main circuit. So it's only ON when the main is, which is not transition. You can have the power jet open at idle, it won't make it richer. Transition is handled by the progression holes. You can make the primary main 200 and it won't change transition. A main jet is a restriction only when main jet flow increases. It will have minimal restriction at low flows, and maximum restriction at high flows. So arguing that the power valve increases fuel at transition makes no sense.

The problem with having the smaller jet in the sec is when the secondary opens, it leans out (it has to, the jet is smaller). It already has a problem with lean out since the airflow is just beginning to move thru the secondary, which means less air is moving thru the primary. So, it leans out. Notice a pattern? With "square" jetting you'll have problems with main jet lean out, and progression lean out, on the secondary. Both are not good.

By having the secondary idle larger, the secondary progression gradually richens things, until the secondary main turns on. After all, when the secondary is on, you do not care for MPG, you need MORE POWER. If you did you wouldn't be on the secondary in the first place. So why use a smaller jet on the secondary then? It's even more important because the secondary is a larger throttle plate than the primary (32mm vs 36mm). So this is why the secondary main should be MUCH larger than the primary main. First because it's a larger throttle plate, and secondly because you'll get automatic lean out due to the decreased airspeed in BOTH barrels.

With jetting that most people use, it's too rich on the primary, and too lean on the secondary.

My jetting will result in a slightly "lazier" primary, but this is much easier to drive, and runs MUCH cooler engine temps, not to mention plugs/rings last a lot longer.

Idle A/F is irrelevant. You can get the same A/F with a 40 idle jet, or a 100 idle jet. Since you adjust it with the idle mixture screw. The jet should be sized based on how it drives OFF IDLE, since the idle jet is what affects tuning via the progression holes.
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[modok]

If raising the float level richens transition, so will a larger main jet, or opening the power valve.

Most carbs have what is called a compensated idle circuit, the idle jet draws fuel from the main well. That is it steals fuel from the main circuit. It lowers the level of fuel in the main well. When the idle circuit stops pulling fuel from the main well the level in the well can rise high enough to start the main circuit. This keeps both circuits from working at the same time. Get it? It transitions from the transfer ports to the main circuit. All this prevents both circuits from feeding fuel at the same time and fouling your cruise.

The opposite is called a divorced idle circuit, I believe dcoe's are an example.

Transition is when the main circuit starts working and the transfer ports stop working, right? If it is not, then what is it called?

[busman78]

The idle mixture screws are only good for one or two jets sizes up or down at best. If the throttle plate is not blocking the progression port when setting/selecting the jets for idle then you will really never get the correct idle jet, if you do then it is by luck. Verification of correct transition to progression can be tested, and should, so far the way I have been doing it has yielded excellent results with little (one jet size) to no changes. Also trying to adjust the idle mixture screw to compensate for bad transition is useless, best way is to test and change the primary idle jet.

You are giving the secondary idle jet too much credit. The only way to pick the proper secondary idle jet is to run the vehicle, a hesitation means a larger idle jet, start small, work your way up till the hesitation is gone. If you start out large you will never know. Weber was not wrong. Try it you may find that you do not need a larger secondary idle, or extremely large secondary main jet for that matter.

[[email protected]]

The idle jet mixes air and fuel together. This mixture is fed to the idle mixture screw. The mixture also feeds the progression holes directly. You are supposed to select your idle jet size based on how it runs ON THE PROGRESSION CIRCUIT. This is because the idle mixture is set with the idle mixture screws. And you can get 10:1 A/F with a 40 idle jet, or a 100 idle jet, or anything in between. You can also get 20:1 with a 100 idle jet. That's because the idle jet sizing should be done by how it operates on the progression circuit. This is because the idle A/F will be adjusted solely with the idle mixture screw. I never said to adjust the idle mixture screw to change transition. It ONLY affects idle A/F.

A larger main jet WILL NOT RICHEN TRANSITION. You can put in a 300 main and it won't change transition, since as mentioned before the jet is not a restriction until flow moves to a significant amount (which is not transition, when flow is ~0)

The problem with your tuning method of selecting the sec idle jet, is if you are too rich on the primary circuit, you have to go too small on the secondary. While transition may be ok, I guarantee you are too rich on primary progression. Why would you need a smaller idle jet on a barrel with a bigger throttle plate? With EVERY weber carb, as the throttle plate size increases, you up the idle jet size to keep the ratio intact. The #s are so consistent there is a formula to calculate the idle jet, when you know the size of the throttle plate.

I have hundreds of hours with wideband tuning on these things. When you jet it like I recommend you'll have idea tuning. If you put the big idle jet in the primary, the A/F curve will look like the Sierras, too rich on primary, then swinging way lean on secondary.

The most common error of progression tuning is just this. People select a "too big" primary idle jet. While it is true that you can get a smooth progression with the 50 sec idle, it's only correct because it's too rich on primary, and it's leaning out, but there's so much fuel from primary you don't hesitate.

When you go to small primary and bigger secondary, it will tune and drive properly. You can get it to drive super smooth, by just tuning it super rich. But the Butt Dyno isn't nearly as accurate as a wideband, which tells the whole story.

Float adjustment changes tip in of the main circuit, due to a change in the fuel level in the emulsion well. Main jet changes do NOT change this.

[modok]

John, I have no doubt your jetting advice is spot on for the dfav. You have done the work and are nice enough to share your experience.

But I cannot agree with your blanket statement; that main jet changes don't effect the strength of the main circuit as it begins to operate.

What experience do you have to demonstrate this?

My experiences with carbs with divorced idle circuits shows the idle jet pulling on the main well does influence the strength of the mains.
I have "divorced" a few myself, several Lawson toy carbs and also a pair of drla's, (which I regret deeply, made the mains come in earlier but in the end I'd rather undrill the holes).

In 99.9% of carbs, the Idle jets have been married to the main jet since ww2 at least, I found no mention of ""divorced" or "married" or "compensating" idle circuit" on Google. No one knows any different.
This terminology is as old as updraft carbs, but I am not making this stuff up. And DCOEs are divorced. It makes a difference.

I maintain the power jet mod should enrichen transition.
You will not see it with an Ox sensor because the difference will only exist for less than a half second.
It may only make a trivial difference. It may be of useless on a type 1....
Until I try it, I can't say for sure. Neither should you.
Don't knock it till you tried it.

Edit: I still feel we have a difference of terminology. "Transition" should be any time the throttle opens and vacuum drops enough to switch in the main circuit. This can be at 1500rpm, 2000, 3000 ect. Really any rpm high enough to work the mains. If you are cruising and then push the gas pedal you "transition" from the idle system to the main system.

[[email protected]]

the main jet is not a restriction when main circuit fuel flow is minimal or 0. Once you grasp this concept it will make sense.

Your main jet can be a 100, 200, 250, or even 300, it won't change when the mains come in. WHEN they come in IS controlled by the strength of the vacuum signal, which is related to airflow through the venturi and aux venturi. It's also related to the construction of the emulsion tube (hole placement, and hole angle). It's also related to the fuel level, since this sets the relationship with the emulsion tube holes. And it's related to the air jet size. But not the main jet.

This is why when I instruct people to figure out when the main jets come in, I tell them to put a HUGE main jet in. So when they are using the wideband, when the main jet comes in, it is very obvious on the gauge, since the gauge all of a sudden goes way rich.

Then you tune your air jet and fuel level to make the mains come in when the progression is going away. Once you have THAT right, then you SIZE the main jet to produce the A/F you desire. The main jet is the last thing you select when tuning. It has nothing to do with when the mains come in.
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[modok]

Since this is your thread John I'll go ahead and say for all practical purposes, that you are absolutely correct.
I think we are debating apples vs oranges here.
This thread should be titled "how to setup progressive on a small type 1 engine"
Busman is talking about a different manifold and a much larger engine.
I am talking about plenum type carbs in general.
Now it sounds like your talking about tuning IDFs?

I admit defeat.
Do you have any answers for my initial questions?

[[email protected]]

I have said you can't get a progressive to work PROPERLY on a T4 at all, due to the huge intake volume and no intake preheat. It's very possible he has to run a huge primary idle because of this.

Please restate your questions and I'll answer them ASAP
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[busman78]

John, the idle jet is larger cause the crankcase is being evacuated into the intake manifold, the larger idle jet is to compensate for that air. The eventual plan is to suck the crankcase fumes into the exhaust, in which case the idle jet will drop in size, and adjustments will be made to the other jets. I have found with this current set up that cold weather does not effect the runners due to the warm air coming from inside the engine.

[[email protected]]

this makes no sense, here's why. The blowby is not "air" (it's blowby), it should be from combustion and should not have O2 in it in the first place, hence no leaning (no O2=no leaning). If it does have O2 in it because it didn't combust, then that means it also has FUEL in it that didn't combust, right?

Why not port the blowby to the air filter and allow the carb to work properly? That's how they've been doing it for decades. It's also more likely to distribute evenly to all 4 cylinders, instead of favoring 1 or 2, being so dependent on where you are bringing it in.

The hot blowby would help heat the carb anyways, which is a good thing, especially on a T4.