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Discussion in 'Yamaha 250cc In-Line 4's' started by GreyImport, Jan 4, 2018.
To clarify/correct the settings table at the top for the 3LN1 - there are two possible needle combinations:
all four carbs with 5CT7 - the inner two carbs (2&3) having a 0.5mm shim to raise the needle - clip position 3rd (middle) on all 4
outer two carbs (1&4) 5CT7 - inner two carbs (2&3) 5CT9 - all four carbs clip position 3rd (middle) on all 4 - note no shim underneath the clip on the centre two carbs (2&3).
The reason for this difference is because the 5CT7 and 5CT9 both have the same tapers - 1 degree for the first taper and 5 degrees for the second taper. The difference is that the tapers begin 0.5mm earlier on the 5CT9 so the 0.5mm shim underneath the clip is not necessary for those needles when fitted on the centre carbs (2&3).
The other reason why I am mentioning this is because 5CT7 needles are only available as part of the keyster kits, so you have to purchase the whole kit for just the needles and emulsion tubes basically as these wear the most rapidly.
The good part is that 5CT9 needles are available on aliexpress and ebay.
Where this gets interesting is with a set of four new 5CT9 needles for all carbs you can get the equivalent of the stock 5CT7 needle for the two outer carbs (1&4).
New setting for 5CT9 needles only
For carbs (1&4) clip on the 2nd position (higher) and placing the 0.5mm shim underneath - which is equivalent to 5CT7 clip position 3 without shims
For carbs (2&3) clip on the 3rd (middle) position and no shims.
This is discussed in this post and elsewhere in this thread