type 1 throttle valve positioner

skin daddio · Post by **skin daddio** » Fri Aug 31, 2007 5:17 pm

is anybody running one on their early bay?

i recently picked up a nice 30pict2 carb with the postioner attached.

i thought i'd remove the TVP to get an idea that the carb is running fine, then reinstall and adjust it. i'm still in the last cleaning phases on the carb which gives some time to think about the next move. anybody have any thoughts, should i just chuck the throttle positioner, or be glad to have it

vwlover77 · Post by **vwlover77** » Fri Aug 31, 2007 5:48 pm

IIRC, the throttle positioner serves only as a pollution control device. It does not impact the performance of the engine in any way. It is designed to prevent the throttle plate from snapping quickly shut when you release the accelerator, thereby reducing emissions.

So, if you want to minimize the pollution from your Bus, go ahead and use it. (But, based on today's emissions standards, the difference between using it and not may not be worth discussing!)

skin daddio · Post by **skin daddio** » Fri Aug 31, 2007 8:24 pm

cool, sounds simple enough. inside the positioner is supposed to be a filter. does anybody know the material that is used for that, and its appoximate dimensions?

Post by **Amskeptic** » Sun Sep 16, 2007 8:24 pm

skin daddio wrote:cool, sounds simple enough. inside the positioner is supposed to be a filter. does anybody know the material that is used for that, and its appoximate dimensions?

That thing is a marvel of precise engineering, replete with an aneroid bellows to adjust its action according to altitude. VW has the adjustment procedure in the fuel section. You can tweak it a bit to get the rpms to idle sooner when you snap the throttle closed, or you can stretch the interval a bit to get nice smooth double-clutch downshifts.

Colin

skin daddio · Post by **skin daddio** » Fri Oct 12, 2007 9:36 pm

aneroid |?an??roid| adjective relating to or denoting a barometer that measures air pressure by the action of the air in deforming the elastic lid of an evacuated box or chamber. noun a barometer of this type. ORIGIN mid 19th cent.: coined in French from Greek a- ‘without’ + n?ros ‘water.’

cannot wait to experiment. i think that before i run this device i might want to fig out the filter. mine came to me all dusted. suggestions?

Post by **Amskeptic** » Sat Oct 13, 2007 1:29 pm

skin daddio wrote:aneroid |?an??roid| adjective relating to or denoting a barometer that measures air pressure by the action of the air in deforming the elastic lid of an evacuated box or chamber. noun a barometer of this type. ORIGIN mid 19th cent.: coined in French from Greek a- ‘without’ + n?ros ‘water.’

cannot wait to experiment. i think that before i run this device i might want to fig out the filter. mine came to me all dusted. suggestions?

ANEROID, Baby, aneroid. Yeah, don't get all worried about that aneroid bellows-controlled throttle positioner "filter". Just clean it cursorily and slap it in there. Adjust towards "inactive" if you need a little specification room.
Colin

satchmo · Post by **satchmo** » Sat Oct 13, 2007 5:25 pm

Why didn't VW use a dashpot for this function like they did with the 72-74 bus? Maybe the dashpot is advanced techology unavailable at the time they use the TVP

Tim

hambone · Post by **hambone** » Sun Oct 14, 2007 8:17 am

Interesting, I've seen these on old carbs on occasion and was wondering how it worked.

skin daddio · Post by **skin daddio** » Sun Oct 14, 2007 8:23 am

Amskeptic wrote:
skin daddio wrote:aneroid |?an??roid| adjective relating to or denoting a barometer that measures air pressure by the action of the air in deforming the elastic lid of an evacuated box or chamber. noun a barometer of this type. ORIGIN mid 19th cent.: coined in French from Greek a- ‘without’ + n?ros ‘water.’

cannot wait to experiment. i think that before i run this device i might want to fig out the filter. mine came to me all dusted. suggestions?
ANEROID, Baby, aneroid. Yeah, don't get all worried about that aneroid bellows-controlled throttle positioner "filter". Just clean it cursorily and slap it in there. Adjust towards "inactive" if you need a little specification room.
Colin

do i got you that the filter was literally dried out dust and i should not worry about replacing it with anything?

Post by **Amskeptic** » Mon Oct 15, 2007 10:13 am

satchmo wrote:Why didn't VW use a dashpot for this function like they did with the 72-74 bus? Maybe the dashpot is advanced techology unavailable at the time they use the TVP

Tim

It was because VW was between a rock and a hard place before they happened across the vacuum retard/idle air dilution stunt of 1971.
In 1968/69/early 70, they were still using the throttle plate as the sole airflow control at idle. They had to close the thing so carefully that they had to establish the rate-of-closing within extremely tight confines. The throttle positioner is the far more accurate "closing time" device. When the vacuum retard/dedicated high air speed idle circuit came along, they could let the throttle close more sloppily, no HC spikes to flunk the Federal Clean Air standards. When the air-pump buses came along, the dashpot was less of an actual emissions reduction device and more of a driveability device to prevent that rpm dip that occurs when you hit then back off the accelerator (dip is caused by having two accelerator pump squirts wanting to flood the engine if you abort your demand for acceleration). Though the dashpot did indeed help reduce HCs on throttle closing snaps, the gulp valve was introducing huge quantities of air very quickly at the same time to help prevent backfires in the exhaust manifolds, that was the more important HC reducing device.
Colin

dingo · Post by **dingo** » Mon Oct 15, 2007 2:24 pm

Interesting stuff there Colin. By the way...why is the decel valve on the F.I. needed ? I dont have one..but im wondering what im missing.

Post by **Amskeptic** » Mon Oct 15, 2007 3:09 pm

dingo wrote:Interesting stuff there Colin. By the way...why is the decel valve on the F.I. needed ? I dont have one..but im wondering what im missing.

Same law of physics.
If you punch the throttle and the AFM wiper swings wide due to inertia (that is your acceleration enrichment device by the way), then abort your intersection jump or whatever, the sudden airflow restriction when you lift off the gas has an immediate effect at the intake valve (think finger over a straw), but the ECU and injectors are still processing your initial request. The decel valve allows the engine to digest the extra fuel within a second or so, thus helping to keep HC spikes down. I showed a number of IAC customers the reaction at the wiper in the AFM with the decel valve active and disabled. You can also hear/feel a difference with a rich engine, snap the throttle and release without the decel valve on an L-Jet engine and the revs will drop as much as 200 RPM below idle before recovering. With the decel valve, the engine merely returns to idle with perhaps a slight osccilation.
Colin
[some cars like a decel valve for smoother shifting (i.e. the engine speed drops in concert with your upshift), others are irritated by a decel valve(i.e. the engine rpm doesn't drop fast enough when you are upshifting)]

dingo · Post by **dingo** » Mon Oct 15, 2007 7:35 pm

snap the throttle and release without the decel valve on an L-Jet engine and the revs will drop as much as 200 RPM below idle before recovering

thanks for the explanation...thats precisely what i get.....ill have to find me a decel gizmo

dingo · Post by **dingo** » Wed Oct 17, 2007 7:30 pm

I was looking for a decel valve at the jukyard but didnt find any Busses, only a carbed 914. So i looked into a Wasser and found what looked like a plastic decel. valve....according to Bentleys its vacuum valve thats hooked up to the charcoal cannister...what function does this serve ?

Same arrangement as decel. valve..when vac. applied to small nipple, the two bigger pipes get thru-flow, then when vac. released, flow is plugged. Is this essentially what a D.V. does ?

also i noticed the Wasser has some elctrically triggered valves..possibly decel. or emmisions ? also all the 80's euro-Bosch cars have some sort of electrically triggered variations too. Interesting.

Post by **Amskeptic** » Thu Oct 18, 2007 7:38 am

dingo wrote:
Wasser plastic decel. valve....according to Bentleys its vacuum valve thats hooked up to the charcoal cannister...what function does this serve ?

That valve allows the engine to purge the vapors in the charcoal canister at low HC moments, like partial throttle and overrun particularly.

dingo wrote: Same arrangement as decel. valve..when vac. applied to small nipple, the two bigger pipes get thru-flow, then when vac. released, flow is plugged. Is this essentially what a D.V. does?

Give it a try, what the heck, have fun young Frankenstein. The only difference between the two may be rate of airflow, and the activation points are different only by virtue of their vacuum signal. The bay decel valve signal is sourced from the intake manifold, the wasser purge valve is likely sourced from the throttle body area.
Let me know how it works!
Colin

Itinerant Air-Cooled

Itinerant Air-Cooled

type 1 throttle valve positioner

type 1 throttle valve positioner