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Keihin FCR tuning (Read 80 times)
Serious Thumper

The more I learn the
less I know.

Posts: 2041
Gender: male
Keihin FCR tuning
04/08/07 at 05:28:41
The first mod I did on my FCR41 was lifting the needle 1 click from 4 to 5, this improved throttle responce so I went to 6 this didn't help so back to 5.

Next was to mess with the low speed air screw and low speed fuel screw starting a 1 turn out I went to 7/8th of a turn out on the air screw and 1.5 on the fuel screw, no good so went to 1 1/8th on the air screw and 7/8ths on the fuel, no good I ended up where I started at 1 and 1.

Top end tuning came next (the fun part) the carb was supplied with a 165 main jet and a 200 main air jet.
I tried a 195 Main air jet which worked at full throttle and high revs but not so good at full throttle and lower revs.
Next I dumped the 195 and went back to a 200 main air, this leaned the top end off a little, I compensated for this by fitting a 168 main jet this was good but still a little lean (If you back off from full throttle you get a slight increase in acceleration)so 170 main fitted and working (back off and lose power,this can work in either direction so try it and see).

After I'd gone to the 170 main I thought the needle would be richer so I went from click 5 to click 4 which went better, then to click 3 which produced a backfire (as I'm sure you're all familar with)so back to middle click 4 and I'm pretty happy with the whole thing.

I hope this might prove usefull to those of you with slide carbs.

Clive W  Cheesy
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