Gs850gn carb settings

[dlas]

is anybody running a GS850GN(79 model, Mikuni VM26SS carb} with KN filters and getting decent results ?.
could you tell us what jet sizes you are running on the pilot and main jet, and any changes to the jet needle position, pilot air screw and mix screw positions. cheers. just got the bike last week and want a starting point to work from.

[Octain]

Welcome to the forums!!

Do you know what jets are in the carbs now?
Did ya get the bike with the pods already on it?

[dlas]

its running standard jet sizes, the previous owner had adusted the mix screw and it was running far too rich, I have put everything back to stock and Im going to try tunning from there.

[Big T]

I'd go

Fuel screw - 1 turn
Air screw - 1 1/2 to 2 turns
Main jets - up 2 sizes
Needle - raise one notch

and see what you get

[BassCliff]

Greetings and Salutations!!

Hi Mr. dlas,

Nope, it's not going to run right with pod filters and stock jetting. It will take a little trial and error. Jets are cheap so you might want to buy 2, 3, and 4 sizes up for each (mains, pilots) so you can experiment. Use the "plug chop" method to read your plugs at each throttle opening to tune each circuit.

Always start with properly cleaned carbs. You'll find the procedures in the links below.

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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...



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!

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BassCliff

[SqDancerLynn1]

This is an old post from Keith that may help you Re tuning the VM CARBS
Keith’s post
Stock carbs (U.S.) are VM26SS. I don't know if Canada bikes got 26mm or possibly 28mm? I do know 33mm are not stock anywhere. Sounds like your bike is starving for fuel above 6,000 rpm's. The jet-needles need to be raised and the main jets increased and probably the pilot jets increased too as I posted.
Your jet-needles are inside your slides.
As for the screws...the PILOT screws are reached from underneath and are engine side of the floatbowls. Use a mirror too see and adjust them. Turning them OUT (counter-clockwise) richens the mixture. They can be tight if never moved before and it's easy to strip the head off. Use a good fitting tool. They are sensitive to adjustments and even 1/8 turn can change the sparkplug color. For a starting point regarding the pilot circuit, I would adjust each pilot screw out 1/4 turn and test. When plug reading for the pilot circuit, ride the bike a few miles in 4th or 5th gear at about 40 mph. Just have the throttle open just past "idle". Do what the plugs/performance tells you. If you find yourself adjusting these screws more than a full turn out further from where they are initially, then you most likely need a step up (2.5) in pilot jet size and of course turn the pilots back in to where you started. You may even have to try larger pilots and turning the pilots out a little. It's suggested you start with fresh plugs or at least clean yours well.
For the SIDE AIR screws...adjust as follows. Put the bike on the centerstand and warm it up first. Turn the screws on both carbs facing you in 1/4 to 1/2 turn increments until you achieve the highest possible rpm's. Fine tune these two screws. Do the other two screws the same way, until you achieve the highest rpm. Now re-set the idle to 1,100 rpm with the idle screwknob. They usually end up about 1 1/2 to 1 3/4 turns out. Turning these screws OUT leans the mixture. Careful, these screws strip easily too if never moved.
Do the pilot screws first and then the side air screws. Jet needle adjustments must be followed with a vacuum tool synch. Then test.
A good carb synch is important with these carbs and re-jetting is too difficult without a good synch. Raising the jet-needles is the most work.
Test for the jet-needles at 1/2 throttle and the mains at 7/8 or wide open throttle.
I forgot to mention, remove the two float bowl vent tubes so the bowls vent better. The increased air intake creates a vortex in the tubes and this cause fuel starvation. Removing the tubes helps the jets draw fuel easier. This is recommended by jet kit makers regarding stage 3 kits, especially with VM carbs.

[dlas]

thanks for all the good advice, in the next week or so I will do a couple of jobs on the old GS and hopefully get her running. I will post the results. cheers guys