Progressive carb preheat modification

[Smilespergallon]

Type 4 engine with a progressive carb. I understand that this isn’t the stock or most ideal setup, but I’m working with what I have for now. Planning to build a box around the air filter and plumb in warm air to heat it faster. Do I plumb the air from location 1 or 2? I believe 1 is where the stock preheat “toilet” was but the hole in my tin looks different. Does the warm air come off of off the number 1 cylinder? Lastly, what size are my fuel lines? Any advice from those who’ve made this modification welcome!

[airschooled]

Howdy,

Location 1 is the correct spot; location 2 is for the heater booster fan for helping defrost at idle. Cap off #2 and its corresponding round hole on the left side of the engine compartment well, or it's a cooling leak. On that note, you'll want a set of spark plug wires that actively seal the holes in the tin, preventing another coolant leak. Chances are you're missing the oil pressure switch boot too. You guess it, another coolant leak. All those are more important than the foam seal.

The preheated air intake requires more matching tin down below, as well as an optional "donut" shaped intake piece in the engine compartment.

Below the starter, near the original mechanical fuel pump location, there should be a square opening just like your location number 1, but 6-8" lower. Make sure you have this hole*

(Left piece in the photo)

I think someone ran a wire through your engine hole #1, so it's unlikely you have this piece, but you'll want it to connect the engine compartment hole to the hot cylinder head area down low without letting dirt in the engine bay:

Once you have all the factory bits reinstalled, your fuel line replaced with something newer and safer, a paper hose is all that's needed to get most progressives to smooth out in the summer. In winter it's nice to wrap the whole filter so only preheated air comes in.

Good luck,
Robbie
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[Wildthings]

You can't see the piece very well, but I made a flange that fit the holes and then welded a piece of thinwall tubing to it and use a somewhat flexible hose to make the connection. I also adapted the aircleaner from a circa 1975 Datsun-Nissan pickup to serve as an aircleaner, doing so allows the inlet air temperature to be lessened during hot weather.

I also dump the crankcase fumes into the lid of the air cleaner directly above the throat of the carburetor which keeps the oily mist from getting all over the inside of the aircleaner housing and making a mess. Going into the top gives the PCV hose addition slope so it drains well instead of clogging up with engine snot during cold weather.

[aeromech]

Good luck with your science project. I’d love to see this carburetor icing issue defeated in a cleanly installed and well thought out way.
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Lead Mechanic: San Diego Air and Space Museum
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Boeing 727,737-200-300-400,757,767
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Fokker F28/F100
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VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
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[orwell84]

I ran this carb for a couple years without doing much to set it up. I think it can be made workable with preheat and some other mods. I like its simplicity. The stock dual carbs are wonderful, but it’s tough keeping up with all the hoses, elbows and wires. Hard to get that stuff to stay put and remain intact.

The part about preheat is how you would turn it off so it wouldn’t suck hot air when the engine no longer needed it.

[Wildthings]

[aeromech]

Carb ice doesn’t care what season it is
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Bobs67vwagen]

I am glad to see this carb getting some discussion as to how to solve one of the issues with it. I have read a number of posts on here just dismissing this carb as unsuitable for an air cooled VW. This carb has been used with very good results on numerous vehicles around the world .

[aeromech]

I’ll bet those vehicles had some sort of ducted warm air going down the carb throat.

We had a type 4 on my run stand with this carb. After it warmed up it began having a rough idle. You could grab any of the four intake runners and see that they were ice cold. We took a heat gun and warmed the runners. Surprise, the idle smoothed out. Take the heat away and very soon the poor idle returned. This was on a 70 degree day in San Diego. This is what we did on the test stand

_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Bobs67vwagen]

Aeromech did you find that once the warm air was introduced to the air cleaner that the carb performed well overall, or were their other problems that surfaced with it?. Nice work thanks Bob

[aeromech]

Yup.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[NASkeet]

[airschooled]

Woah, I didn’t know that part existed. Super cool buy for anyone doing this on a progressive. Thanks Nigel!

Robbie
_________________
WTB: 215mm Type 4 flywheel. Cash in hand.

One-on-one tech help for your vintage Volkswagen:
www.airschooled.com

Road trip reports and tech blog:
https://www.patreon.com/airschooled

[aeromech]

Question? By the time you’ve purchased a single progressive and now gone to great lengths to search the world for the above tinware, I’m thinking some dual Webers might be much easier.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[TomWesty]

[aeromech]

Kads, I agree.

They ran well on this newly rebuilt engine in a 1974 bus

On display at the San Diego Automotive Museum
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[TomWesty]

Damn! Nice looking bus!
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[aeromech]

Thanks but I can’t claim all of the credit. It was already very nice before it got to me.
_________________
Lead Mechanic: San Diego Air and Space Museum
Licensed Airframe and Powerplant Mechanic
Licensed Pilot (Single engine Land)
Boeing 727,737-200-300-400,757,767
Airbus A319,320,321
DC9/MD80
BAe146
Fokker F28/F100
VW type 1 1962,63,65,69,72
VW Type 2 1971 (3 ea.) 1978, 1969
VW Jetta
VW Passat
Capable of leaping tall buildings in a single bound

[Wildthings]