TheSamba.com :: View topic - Center mount, progressive, 2BBl carb on Type IV doesn't suck FAQ

Sun Jan 22, 2017 1:34 pm

Wildthings wrote: The air correction jets operate in an opposite manner to the main jets. Going larger will lean the mixture and going smaller will enrich the mixture. The effect of the air correction jets increases progressively as the air flow increases, so a change in AC jet size will have less effect when the throttle is barely opened and more effect at full throttle.

If you haven't done so you should get a Weber or Holley book that explains how all the systems of the carburetor work.

Thanks! I have a weber Haynes book and it never mentioned the air corrector jets and their function.

Thanks for the help and info!

Tim

Tue Mar 07, 2017 3:34 pm

Have read through the entire thread. Haven't addressed my issues, exactly, but from the looks of things I'm in the right place.

Have had my T4 Bus ('72) for 3 months now. 1700 w/ Weber DFEV 32/36 and SVDA, stock fuel pump. Driving it 100 miles home it was okay for the first 45 minutes but after that it started to bog down badly, usually in 3rd or 4th, especially (but not always) under load. Engine would not quit completely but suddlenly power would die off badly, and I'd have to pull over. Engine would sputter a bit, then idle nicely after a few seconds. Then I'd drive off and it would start doing it again shortly.

When I finally got home, as soon as I could I did a basic tune-up: valves, points, condenser, cap, rotor, timing, even a new coil. Have since replaced all fuel lines and filters, including the one under the tank. In the meantime drove it around town and it ran great. Still does, around town. But it's only when I've been driving hard for a good 30-40 minutes does it start to act up.

My main question is: What does carb icing look like, when it happens? I hear a lot about it with these carbs. Does it happen early on, or once the engine is warm? What are the actual symptoms? I realize it can happen even in warmer weather. Usually, when I'm having the problem, by the time I get to the side of the road the Bus is idling nicely. I check in the engine room, it doesn't seem especially hot, and the base of the carb and the runners are cool, but not like ice cold. Nothing seems amiss.

Of course, I could check fuel pressure but by the time I get back there, things are running good again, so .... ?

And of course, a carb rebuild might be a good place to start. Just trying to narrow down whether this is an icing issue, or something else. I'm unfamiliar with the progressives but I've rebuilt 1BBL Solexes before. Just trying to narrow down what to do next.

Tue Mar 07, 2017 5:25 pm

Icing can happen during prolonged cruising. You may see frost on the outside near the base of the carb, but it is in the main venturi that the worrisome ice builds up and causes problems.

You could be drawing a vacuum on the fuel tank. The venting for the tank gets hacked as part of the progressive install and someone may have just plugged the vent line. Try driving with the cap loose.

Could be a fuel supply problem, maybe once the fuel in the pump gets hot the pump vapor locks and the output pressure drops. There are many ways that people install electric pumps when they do a progressive install and not all work all that well. For example some electric pumps will not work correctly if laid on their side.

There could be other explanations as well.

Tue Mar 07, 2017 6:38 pm

Wildthings wrote: Icing can happen during prolonged cruising. You may see frost on the outside near the base of the carb, but it is in the main venturi that the worrisome ice builds up and causes problems.

You could be drawing a vacuum on the fuel tank. The venting for the tank gets hacked as part of the progressive install and someone may have just plugged the vent line. Try driving with the cap loose.

Could be a fuel supply problem, maybe once the fuel in the pump gets hot the pump vapor locks and the output pressure drops. There are many ways that people install electric pumps when they do a progressive install and not all work all that well. For example some electric pumps will not work correctly if laid on their side.

There could be other explanations as well.

^ Venting, yeah, I could see that now that you mention it. Not sure how it originally would have been set up for my Bus but I'll research that. Would a vented gas cap be something to try?

I've never seen ice or frost anywhere. Just cold, maybe damp too.

Am currently running the OG fuel pump. Pretty sure the diaphragm is intact as there is no fuel smell in the oil. Might still need a rebuild anyway.

Actually, I have a line on a pair of IDFs, but it will be a while. In the meantime I'm having fun trying to figure out how to make this thing work. When it runs well (like around town, short trips) I actually like the way it feels. I can definitely feel it when the secondary kicks in.

Thanks!

Tue Mar 07, 2017 9:03 pm

There isn't a big selection of gas caps for these old rigs, so you are stuck with what is available. I would just check to see how much of the original tank venting is still there and figure out how to make it work again. The European models just vented the tank to the upstream side of the air cleaner and used no carbon canister.

Tue Mar 28, 2017 2:52 pm

Update: it was the fuel pump. The valve above the diaphragm had become dislodged. I cleaned it all up, peened the retainer that holds the little aluminum disc and spring into place, and reassembled. Just got back from a 25-mile cruise, 60+ the whole way, no issues. In spite of the lack of a functional valve, it must have been able to put out enough pressure to keep the fires lit at lower RPMs, but higher revs were slowly draining the bowl in the carb.

Thu Oct 26, 2017 5:20 pm

So, how much heat to the runners/carb is too much?...I rigged up heat to the carb from the original connection for carb heat ('73 dual carb), and made a sort of intake runner blanket from reflectix insulation that hopefully retains some of the heat from the area close to the end of the runners where they bolt to the heads...after a 7 mile test run the runners and carb base were hot to the touch, but not hot enough to burn skin....oil temp was fine at about 180...bus seemed to run very well, and is was kinda cool 60 degrees or so, and damp....assume I need to allow some cool air into the carb?

Rod

Thu Oct 26, 2017 6:06 pm

Rodmullet wrote: So, how much heat to the runners/carb is too much?...I rigged up heat to the carb from the original connection for carb heat ('73 dual carb), and made a sort of intake runner blanket from reflectix insulation that hopefully retains some of the heat from the area close to the end of the runners where they bolt to the heads...after a 7 mile test run the runners and carb base were hot to the touch, but not hot enough to burn skin....oil temp was fine at about 180...bus seemed to run very well, and is was kinda cool 60 degrees or so, and damp....assume I need to allow some cool air into the carb?

Rod
Not this time of year, your system sounds like it's working fairly well right now.
Most automatic (thermostat controlled) systems regulate the temp of the air entering the carb at ~90*f, a litttle hotter for those long runners won't hurt.
If you feel it's too hot or stick a thermometer in there to confirm consider a sliding door on the side of your cookie tin to let in a little cool air, or maybe one of those circular vents from the lid of a ball shaped charcoal BBQ?, the thing that looks like a nuke symbol.

You may have to rejet the slow circuit, or at least adjust the idle mixture leaner now that the fuel is actually vaporizing a bit on it's way to the cylinders.

Thu Oct 26, 2017 6:35 pm

Thanks busdaddy...previous to my modifications I did adjust the carb as best I could to "best lean idle"....and even that was an improvement. I may try to allow some cool air in and see how that goes. Thanks for the input, I need all the help I can get! It will be nice to be able to drive the bus a bit later into the fall...

Rod

Sun Jul 11, 2021 1:58 pm

Hey guys! I'm seeing if i can revive this thread a little. :D I have a webber progressive on my 1700cc type 4 engine and im having an issue that i think comes down to the distributor and timing. If you want to see the thread i started, heres a link (Link: https://www.thesamba.com/vw/forum/viewtopic.php?p=9671175#9671175 ) That also gives a little more backstory to whats going on. I'm here because this seems to be where all the Progressive Type 4 pros hung out.

My question is, what is the best distributor to run? I currently have what i believe to be a Bosch 009 with vacuum advance and retard, though i currently have both capped because it seemed to be closer to idling that way. I've seen a lot of stuff about Pertronix SVDAs and stuff, but i figured that i'd put it out here to see what people have to say.

Also if you get a chance to read through the thread that i started (the one linked above) and think its something else, please let me know. I know as much about tuning carbs as a submarine knows about flying.

Wed Feb 15, 2023 11:58 pm

So typical progressive issues with a non vac dizzy.on a 1800

It will idle really well lots.

But I mainly wanted to check the Jetting numbers with you guys

Primary secondary
Main 183 / 231
Idle 50 / 60
Air cor 175 / 195
Air 05 / 16

Is this very far off for jetting a 1800?

It idles nice... but its behaviour is a bit like an on or off switch... she basically wont go at all of idle... untill engaging primaries and then she is all go!

Read through this thread but still at a loss.

Thu Feb 16, 2023 12:44 am

so anyone running one of those new "egas" center mount Type 4 setups with the pre-heat and electric choke? i heard they actually don't suck

Tue Feb 28, 2023 1:46 pm

So typical progressive issues with a non vac dizzy.on a 1800

It will idle really well lots.

But I mainly wanted to check the Jetting numbers with you guys

Primary secondary
Main 183 / 231
Idle 50 / 60
Air cor 175 / 195
Air 05 / 16

Is this very far off for jetting a 1800?

It idles nice... but its behaviour is a bit like an on or off switch... she basically wont go at all of idle... untill engaging primaries and then she is all go!

Read through this thread but still at a loss.

Tue Feb 28, 2023 5:26 pm

I played around with the progressive that was in my bus (project) when I bought it. Got it to run, not bad.
Something to check, but make sure the secondary butterfly is not completely closed at idle.
Good luck

Tue Feb 28, 2023 9:52 pm

krisbeetle wrote: So typical progressive issues with a non vac dizzy.on a 1800

It will idle really well lots.

But I mainly wanted to check the Jetting numbers with you guys

Primary secondary
Main 183 / 231
Idle 50 / 60
Air cor 175 / 195
Air 05 / 16

Is this very far off for jetting a 1800?

It idles nice... but its behaviour is a bit like an on or off switch... she basically wont go at all of idle... untill engaging primaries and then she is all go!

Read through this thread but still at a loss.

Your main jets are Holley numbers and not actual sizes like Weber uses, somewhere there is an interchange chart. The jetting will also be different between carbs with a single booster venturi (typical of Weber) and a double booster venturi (typical of Holley).

Mon Apr 03, 2023 11:44 am

does anyone know how to quantify those numbers vs weber? I dont know the range that is too rich or lean?
Just trying to see if its in the ballpark or not.

has zero drivability on primary and then when secondary it takes off... so its like driving with an on or off switch.

Mon Apr 03, 2023 12:05 pm

metahacker wrote: so anyone running one of those new "egas" center mount Type 4 setups with the pre-heat and electric choke? i heard they actually don't suck

I picked a new one up a few years back for almost nothing, but have never tried it. Maybe this year.

Mon Apr 03, 2023 12:48 pm

krisbeetle wrote: does anyone know how to quantify those numbers vs weber? I dont know the range that is too rich or lean?
Just trying to see if its in the ballpark or not.

has zero drivability on primary and then when secondary it takes off... so its like driving with an on or off switch.

You might be able to get an idea of what jets you have using a tip cleaner for an oxy-act torch. Just carefully use the smooth end of the cleaner and don't run the ribbed part into the jets or you will ruin them.

Fri May 05, 2023 1:31 pm

krisbeetle wrote: So typical progressive issues with a non vac dizzy.on a 1800

It will idle really well lots.

But I mainly wanted to check the Jetting numbers with you guys

Primary secondary
Main 183 / 231
Idle 50 / 60
Air cor 175 / 195
Air 05 / 16

Is this very far off for jetting a 1800?

It idles nice... but its behaviour is a bit like an on or off switch... she basically wont go at all of idle... untill engaging primaries and then she is all go!

Read through this thread but still at a loss.

Here are the numbers I'm using on a 32/36 Progressive on a 2.0L T4 engine mounted in a 1970 T2 (Bought it like this, all hacked, I know it is not the best carb set up, I know!)

Idle 50/60
Gas 125/180
Air 160/180

Aircooled dot net has a very good article and gives good jet combinations for sea level and altitude numbers that are a good starting point. I tried the 45/60 idle they recommended but it resulted in one cylinder (#2) popping at idle. Spark plug check showed too lean of a mixture. Changed the 45 to 50 and problem was solved. Now I need to hook the motor to a wideband AFR/Lamda gauge to actually check if any more adjustments are needed but bus runs ok.

Wed Aug 02, 2023 10:25 pm

Hello Chaps,

I have a Spanish made Weber Progressive Kit I am tempted to fit on my 1980 Westy Joker Vanagon, aka :van_green: Beryl. She is currently equipped with twin Weber 34ICT's which work fine. Spanish made too :)
She passed her MOT test this week, ( She is MOT test exempt being over 40 years old but I like to know all is well with Beryl's health ). Her emissions levels were,
CO:2.5% & HC: 103ppm. (FWIW The UK limits for such a vehicle of Beryl's age are CO3.5% & HC:1200ppm).
I have to ask the Bay Window Bus team what CO & HC levels could I expect if I did fit the Weber Progressive kit?

Thank you's