Help FZR250 3LN3 carb problem.

I took the 5CT7 from the photocopied 3LN1 supplement in the resources section - yamaha-fzr250r-3ln1-service-manual-supplement.11

What's the chances that your 3LN1 had 3LN3 or 3LN5 carbs or carb internals fitted?

 

CSI Tamworth - who's got a gravelly voice? Can you take a shot to portray the world from the carburettors point of view? You're going to need some pretty coloured gels for the lights...

 

I just checked the difference between the 5CT7 and 5CT9 against the Excel sheet that @maelstrom has http://www.litetek.co/docs/Mikuni_Needles.xls

5CT7 5 53.5 2.6 18.00 37.50 50.90

5CT9 5 53.5 2.6 17.50 37.00 50.90

The 5CT9 begins it's taper 0.5mm earlier.
So a 5CT9 with the e-clip 1 higher (leaner) plus a 0.5mm shim should be equivalent to a 5CT7 in the important ranges where it counts at the two taper positions - there is a diameter difference at the tip between these two, but basically at that throttle opening it should be all main jet

 

@GreyImport OK thinking on this a little more perhaps your 3LN1 carbs were on the cusp of development of the 5CT9 needles.

The 5CT9 in the centre carbs on the middle clip without the shim is equivalent to the 5CT7 with the clip in the middle position plus the 0.5mm spacer which is the original spec for the 3LN1.

Nice to know the cross reference between those so we can gather 5CT9 needles and emulsion tubes on their own to be able to refurb

 

@G1D1 - if you don't have a JIS driver posidrive will also work effecively, just be sure not to use phillips as they will ride up out of the screw very easily

@GreyImport - that table is partially correct with the 5CT9 on the inners there doesn't need to be an extra shim below 2 & 3
So it should read
carbs 1 & 4 5CT7,
carbs 2 & 3 5CT9
all 4 with clip on 3rd notch no shim
or
carbs 1 & 4 5CT7 - clip on 3rd notch
carbs 2 & 3 5CT7 clip on 3rd notch plus metal shim - equivalent to clip 3.5

Both of those combinations are equivalent and this all now tallies perfectly with the Yamaha published 3LN1 supplement and other specs I have seen.

I'll do a writeup later which will allow us to do the reverse conversion using only 5CT9 needles, which are available, for all four carbs - would be nice to be able to just replace needles if they are wearing quickly

 

I've got 4 kits here for 3LN1 - not yet fitted, I will measure the needles and let you know if there is any difference between them.
It should be easy enough to see where the tapers begin, which is the only difference between them essentially

 

OK so I've done a visual between inner and outer carb needles from the keyster kits for 3LN1 and they are identical - the lower taper which is easy to identify comes in at exactly the same point in relation to the notches - so fair to assume they are 5CT7 equivalent.

So for correct fitting - the centre 2 carbs have the 0.5mm metal shim as per the 3LN1 supplement.