Thinking of rejetting

[jacked_72]

I've got a '80 XS1100SG special, which runs pretty good, but it does have that huge surge of power until you get to about 4K rpms. It idles pretty well, and I've gone through cleaning the carbs and syncing them. I didn't clean the emulsion tube because I didn't realize what it was, so when I go back to rejet, I'll clean that too.

Anyway, the bike has an aftermarket 4 to 1 exhaust and a K&N filter in the factory air box. From the Jetting Recommendations page, it looks like I should go up two sizes (two for the exhaust, one for the filter and then subtract one).

I honestly didn't check the main jet size when I had the carbs out, but I know they were old and tarnished and I'm asuming stock jets. It loos like the '80 SG ran with 120 on the outside and 125 on the inside cylinders. Should I go up to 130 (Main Jet #130 - Large Round Mikuni Type) or should I use the 120s as the base and move up two sizes from there? Any problem running the same jet in all 4 cylinders?

[Dylano*]

If the stock mains for that bike are one bigger in the middle two cylinders, it is best to keep it that way. The reason for them running more rich, is to keep them cooler. It is an air cooled bike, and the two middle cylinders have about 10% the surface area for cooling.

[motoman]

I've got a '80 XS1100SG special, which runs pretty good, but it does have that huge surge of power until you get to about 4K rpms. It idles pretty well, and I've gone through cleaning the carbs and syncing them. I didn't clean the emulsion tube because I didn't realize what it was, so when I go back to rejet, I'll clean that too.

Anyway, the bike has an aftermarket 4 to 1 exhaust and a K&N filter in the factory air box. From the Jetting Recommendations page, it looks like I should go up two sizes (two for the exhaust, one for the filter and then subtract one).

I honestly didn't check the main jet size when I had the carbs out, but I know they were old and tarnished and I'm asuming stock jets. It loos like the '80 SG ran with 120 on the outside and 125 on the inside cylinders. Should I go up to 130 (Main Jet #130 - Large Round Mikuni Type) or should I use the 120s as the base and move up two sizes from there? Any problem running the same jet in all 4 cylinders?

The 80 Special has 110's across for main jetting stock. Anything else showing something different is bunk and an urban myth.

Having said that,
since you DIDN'T actually clean the carbs by not removing the emulsion tubes, you need to go back and do the carbs over again. Pay special attention to the cleaning internally of the pilot jets.
LEAVE the stock jetting as a baseline to go from, even tho bike has exhaust mods.
Any main jet changes need to be done with Genuine Mikunis, not aftermarket copies like K&L and such, or you'll have running issues.
Might wanna pay a bit more attention removing jetting, then you'd know what's in there to start with.

[motoman]

I've got a '80 XS1100SG special, which runs pretty good, but it does have that huge surge of power until you get to about 4K rpms. It idles pretty well, and I've gone through cleaning the carbs and syncing them. I didn't clean the emulsion tube because I didn't realize what it was, so when I go back to rejet, I'll clean that too.

Anyway, the bike has an aftermarket 4 to 1 exhaust and a K&N filter in the factory air box. From the Jetting Recommendations page, it looks like I should go up two sizes (two for the exhaust, one for the filter and then subtract one).

I honestly didn't check the main jet size when I had the carbs out, but I know they were old and tarnished and I'm asuming stock jets. It loos like the '80 SG ran with 120 on the outside and 125 on the inside cylinders. Should I go up to 130 (Main Jet #130 - Large Round Mikuni Type) or should I use the 120s as the base and move up two sizes from there? Any problem running the same jet in all 4 cylinders?

The 80 Special has 110's across for main jetting stock. Anything else showing something different is bunk and an urban myth.

Having said that,
since you DIDN'T actually clean the carbs by not removing the emulsion tubes, you need to go back and do the carbs over again. Pay special attention to the cleaning internally of the pilot jets.
LEAVE the stock jetting as a baseline to go from, even tho bike has exhaust mods.
Any main jet changes need to be done with Genuine Mikunis, not aftermarket copies like K&L and such, or you'll have running issues.
The stock 42.5 pilots need not changed, just better attention to cleaning, using a toothpic for cleanin' all the side holes in them and the emulsion tubes.

[motoman]

If the stock mains for that bike are one bigger in the middle two cylinders, it is best to keep it that way. The reason for them running more rich, is to keep them cooler. It is an air cooled bike, and the two middle cylinders have about 10% the surface area for cooling.

The only year model that had staggered main jetting was the 81Venturer. It also has different configured metering rods, which were all the same. Stock main jetting for it was 115 outside cyls./120 inside cyls. As the ONLY factory tour model, the staggered jetting was a result of its anticipated extra load and the oil cooler which supposedly reduced air flow to center two cyls.
Is really no issue, and the collective here run same jet sizing across all four cyls..

[cajun31]

Read this thread

I started this thread in March. http://www.xs11.com/forum/showthread.php?t=41631

I followed the advice and left my jetting alone. Someone in this thread talked about your exact setup.

[TopCatGr58]

Hey Jacked,

The later bikes/carbs are tuned leaner anyways due to EPA standards.

My 81SH had 110's across all 4 stock. Shortly after I got it back to the USA from USN base in Yokosuka, Japan, I got a set of MAC 4-1's and put on it. I didn't REJET, rode it for 9 years, a few LDRS of a few thousand miles, never put holes in pistons, had power to 8.5K rpm.

In 2000 I rebuilt it with little (1179cc) big bore kit, put on INDY/Pod filters and so I then decided to put in 45 pilots vs. 42.5's, and 117.5 mains. Runs great, nice tan plug color, etc.. Dyno run showed that I could possibly go up 1 more jet size.

So....as stated, AFTER recleaning the carbs/emulsion tubes, pilot jets, then get new plugs, do some test runs and see how the plugs look and how the bike behaves. IF bleach white, and or feeling of running out of power at top of rpm band, then you could probably add a couple of main jet sizes. YMMV

T.C.

[jacked_72]

Main jets turned out to be 110 across the board. There was also some build up of crud on the outside of the emulsion tubes, though the holes seemed to be open for the most part. It was late when I got the carbs back in last night, so no report on performance yet.

[Dylano*]

The only year model that had staggered main jetting was the 81Venturer. It also has different configured metering rods, which were all the same. Stock main jetting for it was 115 outside cyls./120 inside cyls. As the ONLY factory tour model, the staggered jetting was a result of its anticipated extra load and the oil cooler which supposedly reduced air flow to center two cyls.
Is really no issue, and the collective here run same jet sizing across all four cyls..

Early Kawasaki triples had staggered mains for the exact reason I stated.
I'm sure others had them too...
Not saying the 80 special DID, I'm sure you are right about that.
BUT, I do think there are many more bikes with that configuration than just the 80 venturer.

[TADracer]

Jacked, since the title of your thread is 'thinking of Re-jetting', read the signature at the bottom of my post. Re-jetting can be a can of worms and is not for the faint of heart.

I am not getting into the nuts and bolts of what jets go where or what models had what sizes because if you re-jet then none of that really matters. You will end up with what is needed for a proper tune. All I will tell you is stick to genuine Mikuni jets (especially the pilots) and make sure EVERYTHING ELSE IS RIGHT AND IN TUNE before you touch your jets. That means plugs, timing, fuel system, spark, valve clearances, everything. Keep a log book of your changes and the effects they have and do only one change at a time.

On top of that I recommend you tune from the top down. Go to http://www.factorypro.com/tech/carbtun.html and use the high RPM version. Said it a hundred times it is a PIA but it works.

Have Fun!!

[Cobia]

Hey Jacked,
FWIW, in my G I'm running a 4 X 1 Kerker, a K & N filter in the std airbox. Airbox has two 1" holes drilled in the bottom of it and a shortened snorkel.
I've never had to deviate from the factory jetting. It's all a matter of properly tuning the carbs. I have BikePhil to thank for that.