[Seipgam]

"On a related note, I'm led to understand that some of the Indian home market Bullets had some extra sort of screw-type inlet thereabouts on the manifold to allow a bit of extra air in to lean out the air-fuel mixture a tad for work at very high elevations, like up in those Himilayans."

Yes my '95 Bullet had this setup before I bought it.  An air pipe from the top of the air box to the inlet manifold with a valve in line that could be adjusted to add more air to the mix when at high altitudes.
Removed and discarded, of no use here in Australia.

Geoff.

[cyrusb]

High altitude operation. Sometimes I don't know what I don't know. Any other bikes sport that option ?

[Bilgemaster]

High altitude operation. Sometimes I don't know what I don't know. Any other bikes sport that option ?

Well, we've all sadly (for my limited understanding, at least) moved on from the humble but reliable mechanical carburetor, but one DOES hear tell of some special new ECU mapping upgrade/update for the 650s available from Royal Enfield for better high altitude operation, at least in their home market: https://www.google.com/amp/s/www.rideapart.com/articles/355240/royal-enfield-continental-gt-650-interceptor-650-ecu-high-altitude-recall-coming/amp/

Whether this update may be available, or already incorporated on their export models, I cannot guess, but if you're choking and knocking on your 650 up in the Rockies, Andes, Alps or Mexico City (elevation 7,382 feet or 2,250 meters), it might be worth asking, Huh?

[cyrusb]

Ah, I should have asked were there any other carburetor bikes with that option?

[ace.cafe]

Passive water injection is easiest with an outboard float bowl and jet tube, eliminating much complexity.
But it must be set up on the mouth of the carb, and not on the engine side of the slide or butterfly. Otherwise when the throttle is closed, all the water will get sucked into the engine from the high manifold vacuum.
It should be set up more like a power jet system.

[tooseevee]

Passive water injection is easiest with an outboard float bowl and jet tube, eliminating much complexity.
But it must be set up on the mouth of the carb, and not on the engine side of the slide or butterfly. Otherwise when the throttle is closed, all the water will get sucked into the engine from the high manifold vacuum.
It should be set up more like a power jet system.

           The earliest JC Whitney water injectors had a thin plate that contained the little water input fitting that you installed between the carb & the manifold. I installed one of these on my mom's '47 Chevy Fleetline in 1949 or '50. I was 12 and had already been driving her '36 Chevy (and tractors) at 11.

            It "seemed" to run better, but I have no "official" evidence of that, of course. This was in Wyoming which has very low humidity.

            The "New Improved" model mounted the water Inlet on top of the carb beFORE the butterfly (butterflies).

[Paul W]

I’m totally serious. Not sure about letting goats ride a bike though. Having spend the last three days and nights next to a field full of them, I wouldn’t trust any of them not to try to eat it.

Still, I’m not bleating about it.

[cyrusb]

Correct, my bike has one. It can be used to help set up the idle, but has no further use.

Do you have a pic of it?

[tooseevee]

Correct, my bike has one. It can be used to help set up the idle, but has no further use.

         Has one What? Which Post are you referring to?

          Digital tach? Digital speedometer? Water injection?

          If it's one of those little $2 Chinese tachs, I agree. They're useless and twitchy at anything above idle. Drove me nuts watching it. They're OK for a generator or lawnmower with a fixed operating RPM.

[cyrusb]

2CV, Im hoping Paul W is referring to the magic air screw some Bullets were equipped with for high elevation operation. Spiegam also referred to having one. Anybody have a shot of this setup?

[Paul W]

Here is the auxiliary air screw connector on my 350.

Sorry about the photo being rotated anti clockwise by 90 degrees!

The screw has a pointed end and sits in a conical seat, just like a brake bleed valve. It just allows air to bypass the carburettor. There was originally a clear plastic tube to the air box, supplying filtered air. My 350 is an Indian home market Electra, so presumably the factory catered for the rarified air when riding up in the Himalayan mountains.

The PAV equipped bikes had a similar adapter with a second pipe stub. That was open to the inlet after the carburettor.

[cyrusb]

Well, there ya go. thanks Paul, I never would have guessed.

[Paul W]

My Watsonian Squire workshop manual explains how to check and adjust the idle mixture by cracking open the screw. The principle being that If the idle speed markedly increases when doing so, the mixture is setup too rich and the mixture screw needs further adjustment. If it just falters when the screw is opened, it’s about right.