maylar
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- Joined
- May 13, 2007
- Messages
- 4,213
Posting this as a FYI for the archives. Not a question, just a report on my recent experieces with Amal needles.
Background: '74 850 MKII, stock intake (paper filter), 750 head pipes, Wassell silencers. Amal 932 carbs, 260 mains, 3-1/2 slides, flat top spray tubes. Carbs were sleeved about 7,000 miles ago.
I did some work to the bike last season and somehow ended up with the long 4 band needles (928/104) in these carbs. With the needle in the top groove (needle all the way down) the engine ran much too lean and hot. Raised the needle to the middle groove and it was much better, although a bit lame in the lower revs and mid range. I also got an unrealistic 60 mpg cruising at 50 mph. This indicates it's still lean, though the plugs looked OK. I ran it that way for the last 3000 miles.
So recently with the discussion of needles here, I decided to put the correct shorter, 2 band needles (622/124) in there to see what would happen. With the needle all the way down, my midrange throttle response was much improved. But the motor would surge a bit just off idle, and sometimes backfire on throttle - off. These symptoms are very similar to what happens with a partially clogged pilot jet.
Raised the needles to the mid position yesterday and the surging went away. Still had an occasional pop on decel, but cured that with 1/8 turn more rich on the idle mix. Throtle response is now excellent across the band, like an 850 should have.
So, be aware that needle taper and position have a profound effect just off idle and through the mid range. Just FYI.
Will report back on the change in MPG after a tankful.
Background: '74 850 MKII, stock intake (paper filter), 750 head pipes, Wassell silencers. Amal 932 carbs, 260 mains, 3-1/2 slides, flat top spray tubes. Carbs were sleeved about 7,000 miles ago.
I did some work to the bike last season and somehow ended up with the long 4 band needles (928/104) in these carbs. With the needle in the top groove (needle all the way down) the engine ran much too lean and hot. Raised the needle to the middle groove and it was much better, although a bit lame in the lower revs and mid range. I also got an unrealistic 60 mpg cruising at 50 mph. This indicates it's still lean, though the plugs looked OK. I ran it that way for the last 3000 miles.
So recently with the discussion of needles here, I decided to put the correct shorter, 2 band needles (622/124) in there to see what would happen. With the needle all the way down, my midrange throttle response was much improved. But the motor would surge a bit just off idle, and sometimes backfire on throttle - off. These symptoms are very similar to what happens with a partially clogged pilot jet.
Raised the needles to the mid position yesterday and the surging went away. Still had an occasional pop on decel, but cured that with 1/8 turn more rich on the idle mix. Throtle response is now excellent across the band, like an 850 should have.
So, be aware that needle taper and position have a profound effect just off idle and through the mid range. Just FYI.
Will report back on the change in MPG after a tankful.