Please Explain Stove Pipe & Pre-Heat Hose For Carb

[71surfbumsbus]

Howdy Gents,

Can someone explain the science or reason to have the stock "stove pipe" and pre heat hose to the oil bath air filter?

Is there an advantage/disadvantage to running a stock motor with it?

Why wouldn't running dual carbs need a pre-heat hose & stove pipe?

Besides blocking off the hole in the front tin to prevent exhaust heat entering the engine compartment, is there an aftermarket air cleaner you would recommend that is not the stock oil bath air filter for the carb?


Sorry for sounding like a "newbie", just looking to learn/get schooled from the vw community....
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SOLD - 1971 Bus 1600 dual port http://www.thesamba.com/vw/forum/viewtopic.php?t=322767&highlight=

1968 Beetle 1679cc single port http://www.thesamba.com/vw/forum/viewtopic.php?t=4...highlight=

[Boble]

Simle answer: VW put it there for a reason, so leave it there . Not one single uneccesary part in a VW engine.

Better answer: The pre-heat hose directs warm air from the cylinders up to the air intake. Reduces risk of carburetor icing and gives better air/fuel mixture. On later models the air filter has a flap (either mechanically or vacuum operated) that closes off the warm air when the outside temperature is higher. Engine runs better with the stock air filter.

[evilphoton]

I'm working on getting this system reinstalled currently...

I can tell you that the diaphragm that controls the red flap in Boble's pics can be rotted away. Mine is, and I'm trying to either find a replacement or somehow fix the diaphragm. So, don't assume that this part is just working, test it first.

I'm trying to fix a really cold intake manifold that causes rough acceleration if it's cool and humid enough.

If you have these parts in place, I'd leave them and/or hook them back up.
_________________
'71 SB - 08/1970
[s]34/3 (70/75/75z/135) - 26MPG[/s]
A pair of Kadrons
VW 028 DVDA, stock 1600 DP
'00 VFR
'01 Blazer

[gt1953]

The stove pipe and preheat keep the engine from carb icing...it does not have to be cold for your carb to ice up.
_________________
Volkswagen: We tune what we drive.
Numbers Matching VW's are getting harder to find. Source out the most Stock vehicle and keep that way. You will be glad you did.

72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold})

[airschooled]

[75smith]

[61SNRF]

In 1968 the US Congress introduced auto emission standards, and the air cleaner pre-heat system was part of that. It is generically referenced as TAC, or Thermostatic Air Cleaner. It was a Federal requirement for the car to be sold here new, and by the letter of the Law it is still a "required" devise, although there is no testing or inspection currently being done.

The Science is that in cold temperatures, fuel does not atomize or vaporize as easily as it does when warm. The cold fuel forms as droplets on the inside of the intake manifold and doesn't reach the cylinder quick enough, thus causing a lean condition. This is why carburetor cars have a choke, and fuel injected cars have a cold start injector and/or a cold start program written into the control unit program that enriches the mixture.
Without it, the engine takes longer to warm up, the excess fuel enrichment can lead to washing the oil out of the cylinders, and a cold engine can produce more friction and wear as well as sludging.

The advantage on a stock engine is by inducing hot air from the exhaust system it speeds the engine warm up, saves fuel, reduces emissions, reduces engine wear and improves driveability when cold.


Dual carbs as said are not as susceptible due to there close proximity to the intake valves and their overall richer fuel mixtures. They often mask any poor cold running symptoms by simply being able to dump more raw fuel in when cold. Aftermarket dual carb kits were never put through any Federal testing nor do they even try to meet the standards. When you buy a set, the seller usually releases their liability by simply stating "For Off-Road use only", otherwise they would benefit from a TAC system for the same reasons as a single carb. Note that '72-'74 dual carb Type II's do have a TAC system.
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-Bruce

An ounce of prevention is worth a pound of cure.

[71surfbumsbus]

Thanks for the answers everyone.

I'm running an oil bath in my 71 type II with 1600 dual port engine and never knew the specific function so I appreciate all the useful info.

Those pics were great! Going to bookmark this page.
_________________
SOLD - 1971 Bus 1600 dual port http://www.thesamba.com/vw/forum/viewtopic.php?t=322767&highlight=

1968 Beetle 1679cc single port http://www.thesamba.com/vw/forum/viewtopic.php?t=4...highlight=

[airschooled]

[71surfbumsbus]

[gargamel]

Interesting topic. My 68 bug had that oil bath for it's year but missing that little flap at the end.it seems to run well so far. Is it possible to swap it for a later model and work fine? I happen to have one restored of a 73