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Main Jet (Physical) Size

  • Thread starter Thread starter mokosai
  • Start date Start date
M

mokosai

Guest
So I ordered new main jets for my '80 GS250T (with BS30SS CV carbs) and when they arrived the head was physically smaller than what's installed on the bike.

I went back and checked, and a few places online that sell jets claim that the Mikuni "small round" main jets are for BS series carbs and that Mikuni "large round" main jets are for RS or HS series carbs. I can't seem to find much agreement on whether or not they are equivalent for a given size. The only difference is the head diameter: 6mm on the small, 8mm on the large.

When I opened up my carbs they definitely had the large jets installed. Is that correct? Do I need large or small? Does it even matter?

Thanks!
 
I have only replaced jets with similar ones, but I don't think it really matters in this case.

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as long as they are Mikuni jets the physical size wont matter, its the actual jet number that matters. different make jets will be a different size jet hole..........
 
I did the exact same thing, ordered small round mains for my '87 GS450L and got a nice surprise when I opened them up and found large round. Did a lot of searching at the time, came across this post where someone called Mikuni and was told that they were 'basically interchangeable', whatever that means. I ordered large rounds anyway, just because I'd be paranoid about tuning afterward and wondering if any persistent problems were due to the jet type.
 
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