Forum

[trophyvase]

Jetting a 928 for a 500 Bullet with free flowing air filter would normally result in a 200 – 220 main jet, 106 needle jet and 3½ slide. But there is no real ‘normal’ as configurations vary. The hesitation between idle and throttle opening suggest the need not for a change of jetting but for a richer slide – if 3½ go to 3, if 3 go to 2½ .

Starting with one kick is good – in fact couldn’t be better! If it takes a few more I’d be reluctant to alter much in the carburetion. As it’s been said already main jets have no impact on starting. Nor for that matter should needle jets.

Doesn’t sound to be a lot wrong with the carburation from what Jawa-Enfield has said. I’m not convinced that plug ‘chops’ tell us anything much except on a racing engine at full throttle runs. Overall plug colour does help. As does the appearance of the silencer tail pipe.

[jawa-enfield]

All thanks for reply, but the manifold is 28mm, is 30 mm not too big?
(ist the Micarb on the 500 also 30mm?)

[Daiwiskers]

If it's bogging down but running with a 240 main I wouldn't go less than a 220 in one step
If you need to go lower than a 200 I would look at the needle position then needle jet and or slide

[jawa-enfield]

Is there someone else riding with a BSA m20 muffler?
I am thinking the 220 main jet with the pancake filter might be too small?

Still in the process of derusting the tank.. did not try it yet.

[jawa-enfield]

just made a trip, it is impossible to get the bike idling normally.. No false air. Idle revving all over the place. mixture screw adjusting does not help )does influence' idling screw does from shutting down to 2000 rpm in half a turn..
Never had something like this..

[Adrian]

Throttle cable sticking open? I once had a problem with a mid-cable adjuster getting caught on another part of the bike, this would snag the cable open enough so that the engine would rev and not idle. Sounds like something is stopping the throttle slide from closing properly.

A.

[jawa-enfield]

No cable is not sticking,, advance system now should be (..)working fine but idling keeps being very unstable..
Ysterday evening in the dark i could not find the idling jet of the amal?

I feel stupid, such a simple bike, runs good but cannot get it to idle..
should i 'try' electr. ignition? (cost a lot, and some build it back to points?)

[windmill john]

No. What happens if you buy electronic and still have an issue!?....

Any chance you can grab a carb off someone? Silly suggestion if there’s no one close!

S/H carb from our hosts? Might still work out cheaper doing that plus a rebuild kit than going electric.

But if you are thinking electric, Double check wiring to and from coil... test coil; not always clear with results if it had an issue.
Have you tried simply replacing the condenser yet?


John

[Wheaters]

just made a trip, it is impossible to get the bike idling normally.. No false air. Idle revving all over the place. mixture screw adjusting does not help )does influence' idling screw does from shutting down to 2000 rpm in half a turn..
Never had something like this..

Could this be a badly fitting throttle slide?

[Adrian]

Ysterday evening in the dark i could not find the idling jet of the amal?

On most Amal Mk1 Concentrics, there is no detachable pilot jet, it's a teeny fixed brass bush pressed inside the idle passages drilled into the carburetor body. Many owners have marveled at how cr*p this is down the years.

This means that you can't simply replace jets with different size ones to experiment, and if it gets blocked by any weeny piece of dirt in the petrol it can be hard to reach for cleaning purposes. Here's a helpful video on cleaning out a blocked jet, should you need to. Thanks to Bullet Whisperer for this one. Read the note in the main description, though!

https://www.youtube.com/watch?v=jwDUplLn4Xg

The more recent Amal Premier range Concentric Mk1s DO have detachable pilot jets. They're somewhat lean, allegedly, but at least you can change them.

SOME Mk1s were set up for two-stroke engines and don't work well on four strokes, I believe the spray tube is different but there might be other things too. Was that a new carburetor, if not, where did it come from?

A.