80 XS11 Standard Carb Kit

[rpgoerlich]

Hard to find a full kit for an 80/81, I opted to buy a full 80 MNS kit with 120 & 125 jets. When I got started with the replacement, I found 120's in 1 & 4 and 115's in 2 & 3, PO must have switched the 115's from 1&4 to 2&3. Jets were all in good shape. I'm thinking about just replacing the 120's and re-using the 115's in 1 & 4. But I had been reading and saw where a few had went 120 across the board. Wanted to know how this worked for you and the MPG difference if any.

Thanks,

[TopCatGr58]

Hey Richard,

The staggered jetting was Yamaha's ploy to try to cool the inner cylinders with a richer mixture since they didn't get as much wind cooling, same thing with the varied amount of metering holes in the main jet NOZZLE on the earlier model carbs, but apparently they realized it really wasn't necessary. And so with the later 81 year carbs, they just put in same size straight across. No differences in Mpg or performance.

As long as your plugs looked good, nice tan color, not heavily black carboned up on the cylinders that had the 120's, then you should be good to go with 120's straight across. I've got Indy filters, and 4-1 pipes, and only have 117.5's, but could possibly go up to 120's even thought it's not flat at 8krpm. If you are running stock intake/exhausts, 120's are probably max if not possibly too rich!?
T.C.

[Barnfresh]

Yeah - The factory put different jets on the inner carbs in 1980... I was wondering what they were thinking... Engineers gone wild? Read that in my NOS Clymer's manual that I keep under my pillow...

[rpgoerlich]

So with stock configuration Air box and pipes, 115's would be the better choice across all carbs probably. Unfortunately I dont have but 2 115''s. So I'll go back with the 115's on 1 & 4 and 120's on 2 & 3, and check the plugs from there.

Thanks,