Itinerant Air-Cooled

Amskeptic wrote:Decel valves (vacuum limiting valve) simply add air when you snap the throttle shut. This prevents the prior charge of fuel that was introduced before you changed your mind from having to burn with little to no air.

VW utilized a solenoid-controlled decel valve on the automatic transmission buses to keep the idle from dropping too dramatically when you selected a gear. Tommu wants to press one of those into service to perform the same task when he turns on his air-conditioner. The same power that energized the A/C clutch can also open the decel valve.
Colin

SlowLane wrote: ↑

Thu Aug 01, 2019 9:02 am

Check the operation of your deceleration valve with the Mity-Vac. On a CA-emission vehicle it should open at 15-17" Hg.

Could you expand upon this please?

tommu wrote: ↑

Thu Aug 01, 2019 3:48 pm

SlowLane wrote: ↑

Thu Aug 01, 2019 9:02 am

Check the operation of your deceleration valve with the Mity-Vac. On a CA-emission vehicle it should open at 15-17" Hg.

Could you expand upon this please?

Based purely on measurements I took on a (ie. sample size of one) CA-spec decel valve vs. a Federal spec decel valve with my Mity-Vac. The CA-spec valve opened at about 15-17" Hg, while the Federal-spec valve opened at ~22" Hg.

Since CA-spec vans have a lower idle vacuum (~12" Hg) because of their late idle timing (5 degrees ATDC) this normally shouldn't pose a problem. But if one were to unwittingly mount a CA-spec decel valve on an engine tuned per Federal specs (7.5 degrees BTDC), then one might see some unusual behaviors with the decel valve opening just from the normal idle vacuum of ~17" Hg on such an engine.

Do you have part numbers for the differences? I never knew there were multiple.
Robbie

asiab3 wrote: ↑

Thu Aug 01, 2019 7:12 pm

Do you have part numbers for the differences? I never knew there were multiple.
Robbie

Yes, but I'll need to dig through my parts stash to find the two articles. That will have to wait until the weekend.

IIRC, there are differences in the mounting brackets as well. I believe the CA valve has a shorter bracket.

SlowLane wrote: ↑

Fri Aug 02, 2019 6:00 am

asiab3 wrote: ↑

Thu Aug 01, 2019 7:12 pm

Do you have part numbers for the differences? I never knew there were multiple.
Robbie

Yes, but I'll need to dig through my parts stash to find the two articles. That will have to wait until the weekend.

IIRC, there are differences in the mounting brackets as well. I believe the CA valve has a shorter bracket.

There is our garden variety huge vacuum canister decel valve on all fuel injected buses.
0 280 160 303

There is a little weird looking decel valve for automatics with an electrical plug to open additional air when you select "Drive" in the 1975 003 transmission, and I think they got rid of the electrical switch in 1976 with the 010, but they share this sort of fuel pressure regulator look:
022 133 551 C

There is a high altitude decel valve which is designed to require lower vacuum signal to open sooner because it is already rich up there at high elevations.
0 280 162 102


One more decel valve for CA 1979.
0 280 160 313

The 1975 FI bus had 5* ATDC retarded timing too, and with an automatic, it needed a blast of air if you selected a gear from neutral.
Colin

Air-cooled CA-spec Vanagon decel valve in my possession has these part numbers:
Bosch: 0 280 160 319
VW: 071 133 551A

I also confirmed my recollection that this valve begins to open at 15" Hg, and is fully open at 17" Hg.

I'm afraid that I didn't make a note of whether the junked Vanagon I pulled it from was a manual or automatic.

Now I'm looking for an automatic Decel valve with the selector-activated air bypass. Would this be an option?
https://www.thesamba.com/vw/classifieds ... id=1758588

p/n 311 906 171 but very similar to the one on the right here:

The one on the left (022 133 551C) is a vacuum 761/2 -79 auto decel valve and the one on the right (022 906 047A) is a 75-761/2 auto electric decel valve.

Decel valves (vacuum limiting valve) simply add air when you snap the throttle shut. This prevents the prior charge of fuel that was introduced before you changed your mind from having to burn with little to no air.

VW utilized a solenoid-controlled decel valve on the automatic transmission buses to keep the idle from dropping too dramatically when you selected a gear. Tommu wants to press one of those into service to perform the same task when he turns on his air-conditioner. The same power that energized the A/C clutch can also open the decel valve.
Colin