BS40 Jetting Ballpark

[Old School]

I have a stock 76 GT750 with BS40 carbs, I am installing a set of JEMCO's and looking for a ballpark for jetting (mains and pilots). I understand that weather and conditions play a part, just wanting some input from guys that have been down this road.

I most likely will not be running filters. Any other tips for these carbs would be helpfull as well. Thanks.

[tz375]

What did you end up with? I'd suggest stock pilot jets and 120 or 125 mains. I have gone up a couple of steps from stock and Jemco seem to need larger mains than I have got to so far. I have two sets of carbs with different jetting to try on the dyno soon.

[Old School]

I got my pipes on Friday and a number of other small parts to actually get the bike running and rideable. I have worked with the carbs, mainly a good cleaning and setup (they had a number of issues). I have the bike running pretty good and strong with a good solid idle. It carburates good. I am a little limited as to parts on hand, I have stock pilots with the mixture screws 1 turn out. The stock needles in the lowest groove, and 114 main jets. It may take a little more main, but it doesn't run bad now.

[tz375]

I suspect that you will be lean at WOT at the top end.

[Old School]

You may be right, I plan to pickup some this week to try.

[tz375]

Use only genuine Mikuni jets and that way you know what you are getting. 114 sounds like a sigma size and I have no idea what that flows like compared to Mikuni reverse small round jets.