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GS1100 Jetting questions

  • Thread starter Thread starter skythian
  • Start date Start date
S

skythian

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Alright, I can do brake lines and oil changes, but I need help figuring out how to (or if I need to) rejet these carbs.

The bike is an '80 GS1100ET that has been overbored from 1078 to 1136, has RC Performace 4-1 exhaust, and individual K&Ns. Obviously the previous owner wanted better performance, but I'm looking to improve the gas mileage. I'm only getting about 30mpg right now.

After tearing into the carburetor, the needle jet has 261 and O-8 stamped on it. Is this an appropriate jetting for these mods? Should I rejet?

The bike runs great, but cuts out a bit at full throttle, and the spark plugs are sooty. Indications of running rich?

Thanks in advance for the help.
 
skythian said:
Alright, I can do brake lines and oil changes, but I need help figuring out how to (or if I need to) rejet these carbs.

The bike is an '80 GS1100ET that has been overbored from 1078 to 1136, has RC Performace 4-1 exhaust, and individual K&Ns. Obviously the previous owner wanted better performance, but I'm looking to improve the gas mileage. I'm only getting about 30mpg right now.

After tearing into the carburetor, the needle jet has 261 and O-8 stamped on it. Is this an appropriate jetting for these mods? Should I rejet?

The bike runs great, but cuts out a bit at full throttle, and the spark plugs are sooty. Indications of running rich?

Thanks in advance for the help.
Click to expand...
I've been told to tell you that it is not stock. Here is a link to carb specs.
http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html
Oh yeah welcome to the forum. Our welcome wagon will find you sooner or later with his wonder web site.
This will get you started. Introduce yourself in GS Owners forum and Basscliff will find you quicker.
 
Last edited:
skythian said:
Alright, I can do brake lines and oil changes, but I need help figuring out how to (or if I need to) rejet these carbs.

The bike is an '80 GS1100ET that has been overbored from 1078 to 1136, has RC Performace 4-1 exhaust, and individual K&Ns. Obviously the previous owner wanted better performance, but I'm looking to improve the gas mileage. I'm only getting about 30mpg right now.

After tearing into the carburetor, the needle jet has 261 and O-8 stamped on it. Is this an appropriate jetting for these mods? Should I rejet?

The bike runs great, but cuts out a bit at full throttle, and the spark plugs are sooty. Indications of running rich?

Thanks in advance for the help.
Click to expand...

Oversize pistons are 1166 cc

What size are the main jets?
What size are the pilot jets?

What size carbs? BS34's or BS36's??

Are there grooves on the needle for adjustment? Sound like a stock needle.

You should be getting between about 35 mpg depending upon what cams you are running.
 
Probably a stupid question, but how do you tell the size of the main and pilot jets?
 
There is a size engraved on the outer rim of the jets. You have to remove the float bowels to get to them.
Your setup is pretty standard upgraded 1100 very close in fact to mine . We can probably get you set correctly with a few more details as posted before. Unless you know what was done to the bike before it is best not to guess but verify for yourself.
 
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Ok thanks, I'll check out the other jets tonight.

The previous owner claimed it was 1136 with Yoshimura forged pistons, and Yoshimura Stage 1 cams and springs. It's a 36mm carb.

Thanks for the help.
 
Greetings and Salutations!!`

Greetings and Salutations!!`

Hi Mr. skythian,

You'll find tips and procedures for carb tuning on my website. Check out the "plug chop" procedure also. This will tell you which parts of the throttle range are running lean, rich, or right on. You've been given a link with the stock carb specs. You'll have to remove the jets to find the part number/size. Note that Mikuni and Dynojet use different criteria to number their jet sizes and are not interchangeable.

Once you modify the intake, exhaust, bore, etc, about all you can do is make it as efficient as possible. Those mods were for performance and not economy. Keep us informed. Here's your S.W.A.G. :)

If you are here you probably have a 30 year old motorcycle that needs about 20 years worth of maintenance. You'll find all kinds of helpful tips, procedures, manuals, diagrams, "how-to" guides, etc, in the links below. Let's get started.

Let me dump a TON of information on you and share some GS lovin'. :D

I just stopped by to welcome you to the forum in my own, special way.
big_hi.gif


If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....
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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...

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Please Click Here For Your Mega-Welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike! :D

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff
 
skythian said:
Ok thanks, I'll check out the other jets tonight.

The previous owner claimed it was 1136 with Yoshimura forged pistons, and Yoshimura Stage 1 cams and springs. It's a 36mm carb.

Thanks for the help.
Click to expand...

Generally the pistons are either +2 at 74 mm or +3 at 75 mm

You have 4:1 exhaust correct (not 4:2:1)

Based on what you are saying and assuming a 74 mm piston

I would figure a Mikuni 135-137.5 main with with 47.5 pilots and a DynoJet needle on the 3rd notch.

http://www.dynojet.com/pdf/3133.pdf

With a similar configuration but with stock bore I ran the DG 138's mains which equates to a Mikuni 128 main
Here you will see a summary of the difference between 4:1 and 4:2:1 for the 1166 kit.


When I bored out to 1166 I needs about a 140-142 main


http://www.thegsresources.com/_forum/showpost.php?p=1267319&postcount=1

Edit 5/20/2012
Bike is GS1100ED 1166, ported head, K&N pods, 36mm BS36, GSXR 4:2:1 Yoshi, 0.340 Webcams, Accel coils, coil mod
The final jet setting I arrived at are as follows. You can compare this with the various descriptions

Exhaust____4:1__________4:2:1
Type
Main jet_____140__________ 135
DJ needle__3 or higher_______ 2
Pilot jet_____47.5___________45
Pilot Air____stock?________stock?
Click to expand...
 
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upgrades like that hm.
I have a 4-1 and pods stage 3 to get it to run right,35mpg or so goin easy and 27mpg ridin hard.
i think with your setup it's good as it gets unless you go stock airbox 4-2-2 pipes.
,only way me thinx.
oh yah 16v 1100 beast.with 36mm carby's.
and personaly i think if i had 4-2-1 pipes,which i would love but not at that cost they go for.i really don't think it would make a whole lotta difference.
 
5150/gs said:
upgrades like that hm.
I have a 4-1 and pods stage 3 to get it to run right,35mpg or so goin easy and 27mpg ridin hard.
i think with your setup it's good as it gets unless you go stock airbox 4-2-2 pipes.
,only way me thinx.
oh yah 16v 1100 beast.with 36mm carby's.
and personaly i think if i had 4-2-1 pipes,which i would love but not at that cost they go for.i really don't think it would make a whole lotta difference.
Click to expand...

I used the Innovate LM-2/LMA-3 with WB O-2 sensor to dial in the AFR across the RPM band so I am very confident in the numbers and settings as being a good start if not right on.

My GS1100ED/1166 got noticeably more light on the front wheel (from low rpm) once it was set right. 4:2:1 gives better mid range for sure and is more linear v.s the ranging monster that comes unleashed at 6K and the 4:1.


To OP.
I would also recommend the NGK Iridium plugs as they will burn off any fouling much better than the standard NGK plus. Do that after you get the jetting sorted.
 
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