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Carb size 650

Joined Aug 2023
5 Posts | 0+
Finland
Has anyone tried bigger carb in 650 berg? I know that some have bored fcr to 43mm, has that made noticeable difference? Or even tried bigger Mikunis, 45mm or 48mm HSR?
 
I did a 44mm conversion but couldn't get the price down for a new batch to be made.

I think you'll find the 48/50 Mikuni are very quick!

Taffy
 
Interestingly FI bikes use huge throttle bodies compared to carbed versions. eg. Ktm 660smc 41mm fcr vs 690smc 46mm TB while both being 654cc, and newer 693cc version has 50mm TB.

Maybe bigbore Bergs were fitted with 41mm only because Keihin didn't have anything better to offer at time?
 
You will not have better results with bigbore carb or blades inside the back horn. the bigger micuni 45 or anything else is to slow for this bike. the stock carb is very very fine for this bike . the big problem is the air restriction . put inside the carb more air and a bigger main jet and you see amazing results and better cold start with the first touch of your e start without choke . the older bergs knew this problem very well and had two air filters but co2 restrictions after 2000 changed this. the factory target was the sales not the performance .
 

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How it can be so restrictive when area in filter inlet is much bigger than inlet in the carb? I mean it could be, I just don't understand it.
Easy starting without choke is just telling that idle jetting is too rich, that I do understand.
 
Dont forgett , you have a seat on your filter . how can breath well a race bike with this ? the colar have almost 180 degrees turn so the air have not any speed . just a slow breath . all race bikes have huge straight ramairs to the airbox .. why ? are they fools ? OK i will help you with pictures because i am not so good with english . i have done many experiments from 2004 to 2023 Most important for me is to start with 60-65 hp and stay near to this and dont loose 15-20 hp from temperatures after 15 minutes.First step is to free out the crank vent oil fumes .Nobody wants 80-100c oil fumes on his carb . all they talk about cold air intake . there is not cold air at 100c .Second is to put an air pod with bigger main jet . if you need details lem me know to help you further .
 

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crank vent fume out . I forgot to tell you about the easy cold start . how do you find my sparkplug ? rich ? this is the results of a good carb settings with a lot of fresh cold air . PERFECT BURN
 

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