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Carb Tuning Question

  • Thread starter Thread starter indyjoel
  • Start date Start date
I

indyjoel

Guest
Hi

I have bought a Carbtune and have been trying to follow the guides from http://www.bwringer.com/gs/carbsync.html

But as a simple person I have some questions.

I have used the guide from above and have added some questions in bold.

Are my assumptions in the document correct or have i made a mistake?

Step 2
Remove the screws in the balance ports on the carbs. On the GS1100, they were allen bolts; on the GS400: phillips head screws. Install the hose barbs in their place. Refer Picture 1.

balance_port.jpg

Picture 1


Step 3
Adjust cylinder #3 to best idle. You may have to remove the covers over the idle screws. Drill each carefully with a small diameter bit, and extract by turning a screw a few turns into the hole you bored, and pop it out with a tug on the screw with a pair of pliers. Refer Picture 2.

idle_mixture_screw.jpg

Picture 2

Once the idle mixture is correct, set the idle speed to 1200 RPM (or other speed as described in the shop manual) using the adjustment knob located between the air box and the carburettors. Refer Picture 3.

idle_speed_adj.jpg

Picture 3

Cylinder #3 should draw about 10 in Hg (24.5 cm Hg). Using the carbtune to measure, Picture 4?

This is your baseline measure. If the motor is not drawing this vacuum, double check that the idle RPM and mixture are correct; a rich cylinder will not create the full vacuum.

carbtune_2_before.jpg

Picture 4

Step 4
Fine tune the idle mixture on #2. Is this the Idle Jet Adjustment screw from Picture 2?

Loosen the locknut between #2 and #3 cylinders,
Is the locknut circled on picture 5?

picture5.jpg

Picture 5

and adjust the vacuum to 10 in Hg (25.5 cm Hg) for both cylinders.Using the carbtune to measure, Picture 4?

Tighten locknut being careful not to move the set screw. Is this the set screw from Picture 5 as circled?

You may have to re-adjust the idle to 1200 RPM if the cylinders were way out of sync. As Shown on Picture 3?

Step 5
Fine tune the idle mixture on #1. Using the Adjustment screw from Picture 2?

Loosen the locknut between #1 and #2 cylinders, Is this the locknut from Picture 5 as circled?

and adjust the vacuum to 11.25 in Hg (28.5 cm Hg) for #1 cylinder.Using the carbtune to measure, Picture 4?

Tighten locknut being careful not to move the set screw. Is the screw circled on picture 5?

Most Suzuki GS 4 cylinder bikes with stock airbox and exhaust draw greater vacuum on the two outboard cylinders vs. the inner two.

Step 6
Repeat the steps described in step #5 on the final cylinder. Your carbs should now be balanced.

Return idle speed to normal, remove the manometer barbs from the carbs, replace the balance port screws, and replace the gas tank.
 
Yes to all, sounds like you understand it perfectly.
It may seem tedious, but what you are doing is setting the mixture perfectly for each carb with each step, then balancing the vacum draw so the whole (all 4 carbs) work in harmony.
Remember the mixture required by each cylinder will be slightly different to another, depending on many factors.
 
Last edited:
I'm glad you asked those questions, Indyjoel. I'm gonna try to balance my carbs for the first time this weekend and had all the same questions!
 
Hi,

I just wanted to share a few more pictures. Here you see the idle mixture screw used to adjust the idle on each individual carb, and the vacuum adjustment screw used to adjust the butterfly opening on three of the carbs.

reassembly040410_01-1.jpg


Vacuum/sync ports.

reassembly040410_05.jpg


Using the carb adjust tool on the vacuum adjustment screws.

reassembly040410_11.jpg


reassembly040410_10.jpg



Thank you for your indulgence,

BassCliff
 
Mr Basscliff

excellent photos which helps.

I had originally used your excellent photos and Mr Bwringer excellent guides.
 
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