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FCR Tuning Battles


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My year long and maybe longer battles with tuning 33mm FCR carbs on a 1991 Bandit 400. I have learned much on the relationship between the air jet, air mix screw, and fuel mix. Still some tuning to go as I wait for a few different air jet sizes to come in. I never had such fine tuning issue with my 1994 GSXR 750! Smaller motor with big carbs; I guess.

 

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On 8/12/2022 at 7:52 PM, TJS said:

Frustrations never end! Flooding! Time to check floats and needle valves!

 

If your bandit has a vacuum membrane at the fuel tap like oilcooled gsxr has , check it to see if gas is leaking through that .

Thats a lot of leaking though .

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  • 2 weeks later...
16 minutes ago, Gixer1460 said:

Those 'filters' will lose you a few hp - Dyno proven. Might keep bugs out but do no good for airflow unfortunately!

+1. If you're trying to run a 33mm carb on a 100cc cylinder you're going to need every bit of help you can get and those "filters" will only make things worse. I think the root problem is a lack of gas speed through the carbs at low rpm leading to very little depression over the jets making it difficult for the engine to lift enough fuel.

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What angle did you have the carbs at when you set them ?  On my FCR39mx the carb has to be angled so the float tab is just touching, but not compressing, the sprung plunger on the float valve. Your carbs are slightly different but of the same "family" so it could be worth checking what the official method is for them.

 

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