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What carbs are these?/ how to identify carbs
- Thread starter Noidea
- Start date
Let's post this chart again.
You've got linked BS38 carbs, dual chokes,
One with 3-hole, other with 5-hole intake horns...
You've got linked BS38 carbs, dual chokes,
One with 3-hole, other with 5-hole intake horns...
2 different year carbs.........5 hole could be from 78/79............3 hole could be from hole from 74 - 77, probably 76/77
Yes, that's a mismatched set, one '78-'79 and one '76-'77. The earlier carb can't be any older than '76 because those didn't have the casting on the bottom to mount that angle bracket to. They will probably work like that as long as the slides, needles, and needle jets are matched. A small issue will probably be mix screw settings. They won't match carb to carb. The '78-'79 carb calls for a setting of 2.25 turns out, the '76-'77 carb is 1.5 turns out.
There are so many different combinations of components for the 76-77 & 78-79 BS38 carbs that I would recommend you try and obtain a spare 78-79 body ( 5x venturi openings) so that you have a matched pair
It is difficult enough jetting, syncing and tuning these carbs as a matched pair ...........but trying to do it with 2x different carbs would be an absolute PITA nightmare.
The 2x charts below will help guide you to what you have already and what you may need to buy .
The slides for the 76-78 carbs (3x hole ) are completely different to the slides for the 78-79 carb (5x holes) although they should work in either 76-77 & 78-79 carbs but if you want to swop the slides between the 2 x different models you'll need to swop the entire slide assembly ie slide, needle jet, jet needle and jet needle fitting kit . Most of these parts are not interchangable between the 2 x carb types.
I'm sure that someone on your side of the pond will have a spare carb body they can let you have.
An excellent alternative would be to throw those carbs away and buy some used EZ500 or GPZ500 Keihin carbs. They are 10+ years younger , less than half the weight of the Mikunis and parts and jets are in plentiful supply. There is a great thread somewhere on here detailing the rejetting and performance.
It is difficult enough jetting, syncing and tuning these carbs as a matched pair ...........but trying to do it with 2x different carbs would be an absolute PITA nightmare.
The 2x charts below will help guide you to what you have already and what you may need to buy .
The slides for the 76-78 carbs (3x hole ) are completely different to the slides for the 78-79 carb (5x holes) although they should work in either 76-77 & 78-79 carbs but if you want to swop the slides between the 2 x different models you'll need to swop the entire slide assembly ie slide, needle jet, jet needle and jet needle fitting kit . Most of these parts are not interchangable between the 2 x carb types.
I'm sure that someone on your side of the pond will have a spare carb body they can let you have.
An excellent alternative would be to throw those carbs away and buy some used EZ500 or GPZ500 Keihin carbs. They are 10+ years younger , less than half the weight of the Mikunis and parts and jets are in plentiful supply. There is a great thread somewhere on here detailing the rejetting and performance.
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Noidea
XS650 Addict
@5twins was correct about the set of carbs and years. They both have the same jets and screws. Only problem with that is the idlescrew isn’t supposed to be the same for both so when its screwed in it’s all the way or not at all would have to buy the proper one or figure how to make that one work. This is @Robert Dell Aquila bike and carbs maybe he can chime in and say what he’s got going on.
