Amal Mk1 pilot jet (2012)

Hello all - my Mk2A 920 is now run-in and running well.It's fitted with 2 x new Amal Concentric 32mm Mk1's - no air filter but 2 x Bellmouths with gauze filters. I have one issue - to enable the engine to 'pick-up' cleanly from idle (i.e. no misfiring etc.) I have to set the pilot jets to run rather rich - this means that the idle is rather lumpy (but reliable at 1000 RPM). If I weaken the pilot jets to give a nice smooth idle the bike misfires briefly when I open the throttle.

Any ideas ?

1. float level on low side d/t going by the book rather than diddling to 1.5 pilot turns out base line.
2. Timing set by book rather than diddling ease to start just short of kick backs or road load detonation.
3. Hotter cam than standard &/or not degree'd optimally for low down response.
4. Pilot jet too small for the air gulps of a 920.

Do you have pressed in or screw in pilot jetting?

mwoo said:

2 x Bellmouths with gauze filters. I have one issue - to enable the engine to 'pick-up' cleanly from idle (i.e. no misfiring etc.) I have to set the pilot jets to run rather rich - this means that the idle is rather lumpy (but reliable at 1000 RPM). If I weaken the pilot jets to give a nice smooth idle the bike misfires briefly when I open the throttle.

Click to expand...

What size are the throttle cutaways?

The mixture from the 1/8 - 1/4 throttle position is basically governed by the throttle slide cutaway.

AMAL Tuning Guide
http://www.amalcarb.co.uk/downloads.aspx

With a 920 kit and open bellmouths the standard 3 1/2 cutaway could perhaps be too lean?

Al of the above is relavent, but check your new Amals to see if the needle jet venturi is the stepped cut away type, peculiar to 850 Nortons. Also the needles are special for 850's. I found the setting the fuel levels to the recommended height of 4.3 to 6.3mm below the float bowl flange eliminated the need to richen up the pilots to get clean low end pick up. I made up some fittings to fit in the bottom of the float bowls and provide a nipple to put a piece of clear hose on. This allows you to visually see the fuel height prior to adjusting.
Cheers Richard

Thanks goodness Cdo's with Amals are rather insensitive to float level once close enough to run. After using the visual fuel tube level methods, by also compensating for the bowl tilt when mounted, I now just eye ball to adequate to run then when nothing else to fix after a season or more riding fine I diddle levels til pilot screws land ~1.5 turns out. Main thing I notice when float level ~right on is the better sound/feel of throttle let offs and low slow tooling around in villages and off road. New lean burn gas tends to like a tad rich slide cut outs and other settings.

Found this nice video from Paul Henshaw on doing the Amal MK1 Pilots:



Incidentally, this guy hasa HUGE list of videos he's uploaded doing all srots of classic bike work/test rides. Checkout/subscribe to his stuff: https://www.youtube.com/channel/UCcxcOWPcVIykzWG_lqWuRWg

Play around with needle setting, try raising needle one notch. Just realised this is an old thread, it’s late and I have had a few beers!!