TheSamba.com :: View topic - How to make a progressive work properly on a VW engine.

Thu Jul 14, 2022 2:21 pm

Thanks for that! Good to know.

Sat Jul 01, 2023 2:03 pm

My engine 1904.
Didn't do any jetting yet
who can advice for the best jetting and emulsion tube to use. the bus won't go more than 75 mph?

Sat Jul 01, 2023 2:59 pm

ManFromNapa wrote: Gonna port a weber progressive I have in the garage to use on an engine I'm building for my 64 bus until I have the $$ to go dual weber 40's. Going to use the guidelines listed by AirCooled.net for sea level, with some consideration for that fact that I like to go to the mountains (camping in Lake Tahoe). My engine build:

90.5mm Pistons
78.8 Crank
110 Cam
heater boxes w/ 1 1/2"

AirCooled.net recommends:
Sea Level:
45 Primary and 55 Secondary Idle Jet
125 Primary and 175 Secondary Main Jet
160 Primary and 180 Secondary Air Jet

Any tips? I'd prefer MPG over raw power.

Thanks

Hi,

Can you let me know what you end up with your settings? I have the same combo

Tue Aug 06, 2024 3:47 am

Fri Aug 16, 2024 6:23 am

[email protected] wrote: 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. :D

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.

Hi,

I followed your jetting method at sea level, but the spark plugs became carbon fouled at idle. What do you suggest?