carbs

[mack]

I've worked on three sets of 1980 carbs this past week or so and non of them had pilot tower plugs in them. All the other ones I've worked on did. Yamaha must have changed the design later that year to eliminate the plug requirement as I can't find a cross over hole in the tower either. Anyone else find this with 1980 carbs?

[red bandit]

Yep, early 80 carbs have the crossover hole, later 80 carbs don't.

[Bonz]

I wonder how soon into the '80 production run they swapped? Must have been pretty early on?

[dbeardslee]

The ones with the plugs in the pilot towers and the cross shaft are referred to as the bastardized 80 carbs. Kind of a cross between the 78/79 carbs and the later model 80 carbs. I've only ever run into one set of bastardized variety, and the non-plugged variety seem to be a lot more common. The main jets are going to be different because the bastardized variety is only drawing gas from the bowls out of the main jet tower, while the non-bastardized variety draw from both the main and pilot towers.

[bikerphil]

I have to disagree with that last statement about the 'bastardized' 80 carbs. I've rebuilt 3 sets and they all used the same smaller (ie: 120 main) as the rest of the 80 and up carbs.

[red bandit]

Yep, I've never seen 80 carbs have anything bigger than 120's. But not all 80's had 120's. Some had 115's. And I want to say some had as small as 110's but that might have been on a 81.

[dbeardslee]

I have to disagree with that last statement about the 'bastardized' 80 carbs. I've rebuilt 3 sets and they all used the same smaller (ie: 120 main) as the rest of the 80 and up carbs.

I thought 110's were the 'usual' jets for the later carbs, although Yamaha shows 115's on 1&4 and 120's on 2&3 as the stock sizes. And it shows them using the same needles, but I couldn't find any info specific to the bastardized variety.

[bikerphil]

I thought 110's were the 'usual' jets for the later carbs, although Yamaha shows 115's on 1&4 and 120's on 2&3 as the stock sizes

Yep, I was just clarifying not to use the larger size mains (ie: 137.5) that the earlier carbs use, in the 80 bastardized carbs.

[Bikes]

My 80 carbs have the plugs.....

[motoman]

Yep, I've never seen 80 carbs have anything bigger than 120's. But not all 80's had 120's. Some had 115's. And I want to say some had as small as 110's but that might have been on a 81.

metering rod differences in Specials and Standards ARE the detrmining factor. XJ's have even different configured metering rods.

[mack]

the

OEM parts fische show 120's on 1&4 with 125's on 2&3 for an SG. Surprised me too. One set I did had 132.5's across all four (K&L) Inspecting those jets leads me to believe they would be the equivalent of 125 mikuni's.

[dbeardslee]

OEM parts fische show 120's on 1&4 with 125's on 2&3 for an SG. Surprised me too. One set I did had 132.5's across all four (K&L) Inspecting those jets leads me to believe they would be the equivalent of 125 mikuni's.

Then if you look at the LG it shows 110's across the board. And the way these carbs have been swapped around from bike to bike over the decades, it's like some weird Forrest Gump parody. "XS carbs are like a box of chaw-klits. You never know what you're gonna get."

[motoman]

Then if you look at the LG it shows 110's across the board. And the way these carbs have been swapped around from bike to bike over the decades, it's like some weird Forrest Gump parody. "XS carbs are like a box of chaw-klits. You never know what you're gonna get."

Metering coding numbers/letters on top and side of them WILL tell the story whether 80Standard or Special. /..........and your correct, the 81Special carbs use 110maibs and 42.5pilot jets. Fuel levels and those leves beibg identical IS a huge key to smoothness and bo hiccups

[mack]

I've seen

different pilot numbers for the 78 as well. Some call for 42.5 but the OEM fische and my supplement called for 45's. I'm putting in 45's with 137.5 mains! seats,needles and all jets are mikuni. Getting excited to push the button as soon as the jets arrive.

[dbeardslee]

Metering coding numbers/letters on top and side of them WILL tell the story whether 80Standard or Special. /..........and your correct, the 81Special carbs use 110maibs and 42.5pilot jets. Fuel levels and those leves beibg identical IS a huge key to smoothness and bo hiccups

The LG is an '80, not an '81. On the 81's the H shows 115's and 120's, while the SH and LH show all 110's. My point was you can't always go by the model of the bike 'cause they don't always have the original carbs installed.

I never go to the trouble of hooking up lines and checking fuel levels. I just set the floats where they're supposed to be and have never had a problem that way. But I do make sure I set both sides of the floats. One side I adjust with the tab, and the other by bending the cross bar if it needs it.