carb upgrade for xs 1100

[tgranelli]

Hi! first time post to this forum.
I own a 1979 xs 1100 and am racking my brain on how to get a set of mikuni flat slide carbs to work for my motorcycle. The stock carbs have been upgraded I think with a 140 main jet. My problem is I am not very motorcycle savvy as far as upgrades are concerned. Mechanically abled I am but not toward bikes. The diagnosis is during normal idle the motor runs super rich; smoke everywhere. However during high idle the motor seems to operate fine. The jet size on the mikunis are at 135 and im not sure where to get new jets or where to find the info on what would work well with this modification. If anyone out there knows something or has done a similar mod I would love some insight. It is beginning to get very frustrating relying on half brained mechanics that claim to know 'everything' but still are not able to get the motor running; with a hefty hourly cost as well. Any info would be helpful!! Thanks!!

[DGXSER]

First off, welcome to the site!! Sounds like you have owned your bike for a little while. Also, where were you when I needed advice on good eats in San Francisco last week!

To properly tune the carbs, some info is needed first. What method of air intake do you have. Individual "POD" filters? Factory air box? Is the air box drilled? What exhaust is on the bike? factory four into two? Four into one? What manufacturer if you know? These are the biggest contributors to determining if you need any changes from factory tuning.

You may also want to make sure you have the 78-79 model carbs on the bike. Look HERE. It is not unusual that carbs get swapped out on these. You mentioned two different main jet sizes, 137 and 140. Factory would be 137.5 for the 78-79 carbs.

Once we get a little more info, we can help you with better suggestions. As for upgraded carbs, some members have swapped over to ZRX-1200 carbs and like the results.

[TADracer]

I guess my first response would be that if your machine is idleing very rich but it clears up when you get off-idle then your pilot jets might be too big or you have those dreaded pilot jets that come in the K&L carb kits. Remove your pilots and see if they are 42.5's (which is stock). Then check to make sure they have six holes in the side not eight (like the K&L 42.5's do).

If you need new jets then Jets-R-Us.com is a good place to order them.

[bikerphil]

Hi! first time post to this forum.
I own a 1979 xs 1100 and am racking my brain on how to get a set of mikuni flat slide carbs to work for my motorcycle.

This carb bank is not the stock type as you may know, the XS uses the BS-34 CV type Mikuni's. To avoid any further confusion, a pic of your carb bank would be most helpful. A few members do use the flat side carbs IIRC.

[Bonz]

I'm gonna go out on a limb here and ask "why a set of flatslides?".

I guess if you had a set of them hanging on the wall in the garage and wanted really badly to use them?

The fuel mileage is gonna tank, and the XS is gonna be hard to improve upon power-wise, it's been tried and tried, with little result worthy of the time and expense, IMO.

How about a set of ZRX1100/1200 carbs? They are a more or less direct bolt in, improve response dramatically from all counts, and should be a ton easier to tune than flatslides.

[tgranelli]

Carbs

A friend of mine had the flat slides laying around and suggested I try them. In reality the carbs that are on the bike would work I just need gaskets and seals, I was just hoping to find some info on what would work best with my setup. I have pod style filters and a four into one exhaust, aftermarket but I'm not sure who the manufacturer is. I have some money to put into my machine and would love a little more if not a lot more power for it. First of all where aside from Craigslist and eBay would I look for new/new used carbs?

[DGXSER]

New is not an option, not made anymore. "New to you" carbs can be had by posting on the parts wanted section of this site, as well as ebay and maybe craigslist.

[Bonz]

+1 on that, it's a buy and rebuild propsition for the most part, but you can find what you need fairly easily.

[Schming]

A friend of mine had the flat slides laying around and suggested I try them. In reality the carbs that are on the bike would work I just need gaskets and seals, I was just hoping to find some info on what would work best with my setup. I have pod style filters and a four into one exhaust, aftermarket but I'm not sure who the manufacturer is. I have some money to put into my machine and would love a little more if not a lot more power for it. First of all where aside from Craigslist and eBay would I look for new/new used carbs?

IMHO and most likely others on the site, your best bet is to keep what you have if they are the original early carbs which are much more tunable than '80 on carbs and they can be adjusted to compensate all the mods you throw at them.
So with that said, the info and the members on this site can and will help you get your bike, with mentioned setup, to be SCARY FAST

If you are a little handy around the garage these "Original Superbikes" given new life with a little TLC will amaze you.

The XS 1100 is one of the engines that they broke the mold on 'cause it was made just that good.

[TopCatGr58]

Hey there Tgranelli,

Welcome to the site. As you have discovered Flatside carbs are more for racing applications...mostly ON or OFF, not much subtlety in the low rpm throttle response range. As has been stated, best to put your OEM carbs back on. There are several sites for sourcing the parts you need, ie. gaskets, but what "SEALS" are you speaking of? Are you talking about the butterfly shaft seals? They usually are okay unless someone soaked the carb bodies in caustic carb cleaner/dip solution!

GeorgeFix on ebay provides lots of parts at decent prices, but can also get them from www.mikesxs.net , partsnmore.com, z1enterprises.com, etc..

Hopefully you've found and looked at the carbs 101 tech tip/thread for info on how to R&R the carbs SAFELY without breaking delicate internal parts?

Also, take a look at the tech tips/mods section, carbs/fuel and review the mods for the POD filters. Recent discussions have produced a consensus that some form of velocity stack allows the XS11's engine and carbs to continue to provide the low rpm power/torque that they are reknowned for. It has been reported that aftermarket pipes, especially 4-1 style move the powerband up a bit in the rpm range and losses in low rpm grunt are common, moreso when combined with pods. Due to the poor design of the inexpensive EMGO pods....their prominent mounting lip obstructed the airflow thru the carbs intake bell ports causing overly rich conditions and even loss of power at the 5-6k rpm point...would not actualy rev higher! So..attempts to mount the pods thru a variety of methods...some using the OEM airbox rubber mounts helped act like velocity stacks straightening and smoothing the airflow which helped the low rpm responses.

So....just some things to think about or pursue when putting the OEM carbs back on.

T.C.

[triplechop]

79 parts in 80 carb bodies?

I'm rebuilding my carbs on my 1980 special. Going to use pod filters and I have to tune richer for them. Is it possible and would I benefit from using 79 internals (emulation tubes , jets, needles etc? I have the parts to go either way. Thoughts?

[bikerphil]

My thoughts are that you will be creating a great headache for yourself. The internal passages of the carbs differ somewhat. I would just increase the pilot and/or main sizes if necessary and leave the needles and emultion tubes be, JMHO

[natemoen]

Nope. Slides are different and not interchangable, needles are slide type specific so they cant be swapped. Jets are all the same but sized smaller due to internal (and unchangable)internal differences in the carb bodies. Emulsion tubes won't do much if you swapped them so what's the point.

Stick with the correct parts for the correct carb bodies.