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Author Topic: Thema now dedra  (Read 6283 times)
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St Volumex
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« Reply #15 on: 07 June, 2010, 07:30:23 AM »

The device pictured is the Auxiliary air bypass valve. It has a bi-metallic strip that rotates a circular disc with a "pie slice" cut out section that slowly closes the opening that allows extra air past the throttle flap during cold starts. Hence it is effectively an auto choke.

It moves very slowly so you may not see any movement upon the appliance of a current. If you put it in the freezer you should see the opening get larger and then it will gradually close as the valve warms up. Since it is mounted above the thermostat, it also will close slowly with the heat off the engine.

Mike, I put it in the freezer, and it closed completely, but in the sunshine of the verandah, it opened only about one quarter max?  Still gotta test other things today...
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Guy McDougall
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Rare Parts for Rare Machines
Appia Coupé S3 (Rosina), Appia Berlina S3 (La Giaconda), Fulvia 1.3S 5 spd coupé (Tigger, belongs to Carol), Beta Spyder S2 (Vivaldi), Montecarlo Spyder S2, HPE VX (Pugsly) etc
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« Reply #16 on: 07 June, 2010, 10:56:44 PM »

Unless I'm losing it  Huh?, your Auxiliary Air Bypass Valve is operating the wrong way round.

When the engine is cold it needs extra fuel in the air/fuel mix. To do this the valve is open when the engine is cold. This means that when the throttle butterfly is closed (as in the idle position) there is an increased flow of air bypassing the throttle butterfly and therefore causing the Air Flow Meter to record more air intake (and hence more fuel required) for any given throttle position.

When the engine is warmed up, the Bypass Valve should be fully (or almost fully shut) so that all air into the engine is regulated by the throttle position and the setting of the idle screw.

One of the manual tests for the valve is to run the engine up to operating temp and then clamp the rubber pipes on one side of the valve. Clamping a pipe should not cause the revs to dip by more than ~50rpm. In other words, the valve should be as good as closed at full engine temp.

Or else I was very very drunk when I worked that all out!?  Roll Eyes

P.S. I can give you a spare when you are over!
« Last Edit: 07 June, 2010, 11:00:19 PM by Angle Grinder » Logged

Current Cars: 1994 2.0 VIS Thema Station Wagon, 1967 Flavia 1.8 PF Coupe.

Previous cars:
1983 Prisma 1600
1991 Thema 16v i.e. SE
1988 Thema 8v Turbo
1992 Thema 16v i.e.
1983 Gamma Coupe (manual)
1993 Thema VIS
1994 Thema VIS LE
1990 Thema 2.8
St Volumex
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« Reply #17 on: 25 August, 2010, 06:46:43 AM »

Tried everything under the sun and finally replaced the HT leads (I had successfully tested for spark previously) and hey, presto...  Huh?

It's running but I'm not entirely convinced.  Roll Eyes
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Guy McDougall
www.facebook.com/RetroPart
Rare Parts for Rare Machines
Appia Coupé S3 (Rosina), Appia Berlina S3 (La Giaconda), Fulvia 1.3S 5 spd coupé (Tigger, belongs to Carol), Beta Spyder S2 (Vivaldi), Montecarlo Spyder S2, HPE VX (Pugsly) etc
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