amal 930's with the screw in idle jets on the underside of the carb body

I went through my parts bin and found some extra amal 930 carb bodies. I had previously removed the pressed in idle jets in them when doing some experimenting. I looked at them yesterday and they weren't worn at all, so I performed the back side port clean out modification on them which entails drilling out behind the idle jet on the non-adjuster side and threading it to mount a set screw to be able to clean out the port (and jet in the case when the jet is pressed in there) I had the old style screw in jets that thread into the underside of the carb body on older amals, so I installed both old style idle jets on the underside of the carb bodies and I sealed the clean out ports that I made with blue loctite on each set screw to return these 2 carb bodies to working status.

I was wondering if anyone here uses an amal carb with the screw in idle jets and if they work just as well mounted underneath the carb as when they pressed into the port as in later versions. Does anyone know for sure if the change was made to the pressed in idle jet because it worked better being positioned closer to the vacuum source?? (yes, I'm curious about all kinds of odd things)

Here's a picture of the idle jet clean out I install in all my amal carbs. (the black allen head screw)



The picture below is the mount position of the old style, screw-in idle jet which lines up with the "straw hole" in the float bowl. It's in position to meter the fuel, but further away from the vacuum source so I wonder if it is more temperamental being mounted here. The advantage of mounting it here if it works the same is that it would be easy to clean, change it's size, or even drill out a tiny bit to change the best working position of the idle air screw if the slide wear gets larger over time....

The screw in pilot jets were rapidly dropped on the Concentrics's introduction on 4 strokes and the pilot bush of 17 thou equivalent to a 25 pilot jet introduced. It was too far away from the inlet to respond quickly enough on the opening of the throttle ie vacuum as you guessed. Issue was found on the Triumph 500 twin. It was retained on 2 strokes hence the provision of the threaded hole even when a pilot bush was installed.

Thanks for that. At some point I'll just turn down the screw-in #25 jet on the lathe and seat it in the standard pressed in position instead of the underside position. Since I also have a clean out port, that wouldn't be hard to do on these carbs.

o0norton0o said:

Thanks for that. At some point I'll just turn down the screw-in #25 jet on the lathe and seat it in the standard pressed in position instead of the underside position. Since I also have a clean out port, that wouldn't be hard to do on these carbs.

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You can modify the mk1s to take the premier type pilot jet
And I have read but never seen that you can also modify and fit mikuni pilot jets

Conversion to Premier spec covered in this thread.

Early 68 Commandos had those types of carbs