fine tuning needles
Posted: Thu Aug 27, 2009 9:11 pm
in the motorcycle world.........the dynojet kits are well known........basically these comprise of amongst other things tailored needles...........
in the lambretta/vespa scooter world........these are not of course available........but in some circumstances are needed.......
with some set ups/using certain pipes and carbs.........its quite impossible to obtain a perfect
air/fuel delivery ratio......despite the array of std carb parts available..........
typically this will show up on the dyno as a weak area at approx 5000 to 6500 revs......or thereabouts........usually just where the pipe starts to come on song...........
the more efficient the pipe is ,the more pronounced this appears...............jl4,s...for eg
with dellortos.....this can be worked around in most cases.......
but with say mikunis.........it can be a pain............
and so......when all else has been tried..........modifying /tailoring the needle can only be a good thing.........
i know for a fact that this has been done by many a scooter racer .............
with great results...........
and so again..........if this is what you think you need to do..........this is how we would now do it
firstley of course ......you need to identify exactly at which point in your rev range needs sorting.........
easily done using a dyno............
just hold it at the revs in the weakest air flow/ bar graph indicator.........red zone............
then quickly mark throttle opening on bars using tippex etc............
then turn off.........and open throttle to marked setting..............and then mark on needle.......................just above diffuser/etc........
its then the area below this mark on needle that needs relieving/reducing in diameter..........
in order to richen up...........
the best way probably to do this is to put needle in a drill chuck...........and hold on at the desired point some sand paper............removing only say .2mm at a time...........
then try again...........repeat process until lean spot is evened out..............
i know it all sounds a bit "heath robinson"...........but it can work out very well.............
in the lambretta/vespa scooter world........these are not of course available........but in some circumstances are needed.......
with some set ups/using certain pipes and carbs.........its quite impossible to obtain a perfect
air/fuel delivery ratio......despite the array of std carb parts available..........
typically this will show up on the dyno as a weak area at approx 5000 to 6500 revs......or thereabouts........usually just where the pipe starts to come on song...........
the more efficient the pipe is ,the more pronounced this appears...............jl4,s...for eg
with dellortos.....this can be worked around in most cases.......
but with say mikunis.........it can be a pain............
and so......when all else has been tried..........modifying /tailoring the needle can only be a good thing.........
i know for a fact that this has been done by many a scooter racer .............
with great results...........
and so again..........if this is what you think you need to do..........this is how we would now do it
firstley of course ......you need to identify exactly at which point in your rev range needs sorting.........
easily done using a dyno............
just hold it at the revs in the weakest air flow/ bar graph indicator.........red zone............
then quickly mark throttle opening on bars using tippex etc............
then turn off.........and open throttle to marked setting..............and then mark on needle.......................just above diffuser/etc........
its then the area below this mark on needle that needs relieving/reducing in diameter..........
in order to richen up...........
the best way probably to do this is to put needle in a drill chuck...........and hold on at the desired point some sand paper............removing only say .2mm at a time...........
then try again...........repeat process until lean spot is evened out..............
i know it all sounds a bit "heath robinson"...........but it can work out very well.............