mismatched jets

[userflame]

Hello from a newcomer.

I belived I purchased a 1980 XS1100SG (VIN is 3U9). It came with some other parts including a complete carburetor. I have been tearing them both down for cleaning and restoration. CARB#1 has been cleaned up previously and CARB#2 is in pretty rough shape.

1. RE main jets:

1. CARB#1 are all 115 (3 of them are Mikuni and 1 is a different brand)
2. CARB #2 has all 110.

2.RE pilot jets:

• [*=1]CARB#1 are all 37.5 (6 holes in side) [*=1]CARB#2 are all 45 (no holes in side)

3. RE rubber parts

• [*=1]some of the rubber (O-rings, plugs, needle tips) seem to be wearing. What causes this? Should I just expect to replace anything rubber throughout (diaphrams seem to be in good shape)

I understand these types of questions (jetting) get asked all the time. I have done a bunch of reading but still feel a little stumped. I lack the confidence that:

1. I have properly identified my bike
2. The carbs are for sure stock or from the same model (although I am pretty sure about this based on the guide given on the website)

Since I have everything apart now, I am really hoping to do this correct once and eliminate the carburetor as a variable ( <--- am I asking too much here? XD)

Thank you
CT

[DiverRay]

I can understand your problem, I think. The XS1100 is an inline four engine with four carbs. All the jets in the carbs NEED to be the same. You are talking about TWO carbs, though. By the VIN, you do have a 1980 Special. The FIRST thing you will need to do is make sure ALL the jets are Mikuni! Aftermarket jets DO NOT WORK and cause all kinds of problems.
Pilot jets are 42.4 MIKUNI only, Main jets need to be 115 for the outside carbs, 1 & 4, the inside carbs, 2 & 3, are 120. Yamaha did this to try and keep temps even. You can just put 120 jets across all four carbs and then tune with almost no problems. I've attached the parts manual for your bike. This should help you to at least understand what SHOULD be in the carbs.
Again, use ONLY Mikuni jets in the carbs. They are still available, and if you have the correct size in some of the carbs, they can be cleaned and re-used with no problems. You WILL need to sync the carbs after you are done. I use 4 vacuum gauges on my bike, but carb sticks with the mercury will work.

[userflame]

Thank you for your reply, and the parts manual!

I am still a little confused as the manual you provided specifies Main Jets; 125 - 2 and 120 - 2

Theres another document on this website (XS11 Carb Jet Chart.png) that lists "US 80(SG) - Main Jet - 110"

And also there is a "Supplementary Service Manual for the XS1100G / XS1100SG" which lists exactly what you are saying.

What am I missing here?

[DiverRay]

You have the 1980 model and need to use the supplement manual for it. The US EPA had tighter specs starting in 1980, and all the vehicles had to meet them. You can make changes, but you should know a bit about carbs before trying.
There are a LOT of differences between the 1979 and 1980 carbs, as a lot of the part numbers have changed. Best thing to do is keep the carbs the way they were built for now.. And again, use ONLY MIKUNI jets!! The jets in the rebuild kits are mostly junk and you will never get the carbs correct if you try to use them. I know, I've spent many days trying to get a bike running correctly, and the only fix was all Mikuni parts.

[cajun31]

Hello from a newcomer.

I belived I purchased a 1980 XS1100SG (VIN is 3U9). It came with some other parts including a complete carburetor. I have been tearing them both down for cleaning and restoration. CARB#1 has been cleaned up previously and CARB#2 is in pretty rough shape.

1. RE main jets:

1. CARB#1 are all 115 (3 of them are Mikuni and 1 is a different brand)
2. CARB #2 has all 110.

2.RE pilot jets:

• [*=1]CARB#1 are all 37.5 (6 holes in side) [*=1]CARB#2 are all 45 (no holes in side)

3. RE rubber parts

• [*=1]some of the rubber (O-rings, plugs, needle tips) seem to be wearing. What causes this? Should I just expect to replace anything rubber throughout (diaphrams seem to be in good shape)

I understand these types of questions (jetting) get asked all the time. I have done a bunch of reading but still feel a little stumped. I lack the confidence that:

1. I have properly identified my bike
2. The carbs are for sure stock or from the same model (although I am pretty sure about this based on the guide given on the website)

Since I have everything apart now, I am really hoping to do this correct once and eliminate the carburetor as a variable ( <--- am I asking too much here? XD)

Thank you
CT

Just to add to what Ray is saying and to try to clear up some confusion for you. First off here is the link you were referring to: Carburetor Facts - Models and Jetting - XS11.club Forums. The 1980 SG and LG (with G referring to 80 models, H was 81, F was 79 etc..) your carbs came with 110s and 115s. Like Ray said Yamaha did that and put different size jets. From some things I have read to make the inner two carbs run cooler. Who knows for sure. Some people have reported having all 110 mains and others a mix of 110 and 115s. From my handle you will see that i am the original owner of my 1980 LG and mine I know for sure had 110 in 2 and 115 in the other two. Still do with no problems. The main point is that you are better off with true Mikuni parts. Aftermarket are a pain and have been proven time and again to cause problems. Specifically it makes the carbs very hard to tune. The pilot jets from the factory on the specials were 42.5. Sounds like you have a mismatch in that area and also sounds like non Mikuni parts. You would be better off replacing with genuine Mikuni. By the way you can find all these at Genuine Mikuni jets for BS series carbs - Jets R Us. All the parts that show wear are due to many factors. Age being one and one of the biggest ones is Ethanol gas. If you have it available to you it is better for these bikes to run Ethanol free. Keep at it and keep asking questions. Folks on this forum are put simply awesome and always willing to share their vast expertise to help. No such thing as a stupid question. The only stupid question is the one you have and don't ask.

[jetmechmarty]

Niche Cycle also supplies Mikuni genuine brass.

https://www.nichecycle.com/categories/carburetor/mikuni-parts-by-category.html

You may find them a little less expensive than Jets-R-Us.

I’ve had good experience with both of them.