GK76 carb balancing queeries

[wullie3xv9]

Hi folks. Any long term GK76 owners on here do their own carb balancing? If so, I'd like to know what are the best rev's to run the engine at to get good, steady, accurate readings on my vacuum gauges, as this will be a "first" for me so am a little nervous as I don't know what to expect! I have read several on-line carb balancing articles & Tony Sleep's excellent & very informative GSX-R 400 GK76SP Mikuni carb saga, but know one gives the best rev's to aid accurate balancing on these bikes! (My GK76 is an ordinary RM model with the standard, (non-TPS), 32-33 mm carb's).

Tony Sleep mentions that as these engines have a short stroke & small bores they don't create much vacuum, but doesn't mention what the best rev's are for balancing!? Anyone got any hints, tips & advice please ?

Regards.

Wullie.

[dobbslc]

I would just turn the idle screw up a bit. Maybe 1700 rpm.

[donk]

Any good at reading japanese ......? These are the pictures from the 76a manual the only rpm that I understand on it is 1300-1400

[Marsbar]

Carb balancing is a right pain in the back side to do on these because of the angle the carbs sit. Have to make sure you get a really decent screwdriver for it that fits perfectly. I bought a morgan carbtune awhile ago and it has already really paid for itself, they state that you should balance your carbs about every 5k miles or every time that the carbs have been disturbed.
I did balance mine @3k RPM but that was only because it wasn't idling for poop but looking at the readings it was at it was no wounder why, once they were balanced it felt like a new bike.

The set-up i used;

It really helps in buying a separate auxiliary tank do to this, you will have to make a T piece though as there are two inputs to carb.

Before balancing;


After balancing;

[glimmer]

Any good at reading japanese ......? These are the pictures from the 76a manual the only rpm that I understand on it is 1300-1400

Motor

[ Measurement of compression pressure ]
Unplug all of spark plugs and attach compression gauge to the cylinder you are going to measure.
[ note ] Attach compression gauge and check pressure leak doesn’t occur.
[ equipment ] Compression gauge : 09915-64510
Adapter : 09915-63310

Open throttle completely and turn the cell motor on. Read the maximum value of compression gauge.

Compression pressure Rotation number 450 rpm
Standard 10.0 – 14.5 kg/cm2
Limit 8 kg/cm2
Difference between cylinders 2 kg/cm2

Check items below if compression pressure is lower than the limit.
Around the valves
Valve clearance
Abrasion and damage of pistons, cylinders, piston rings
Damage of cylinder head gasket
Deformation of cylinder head

[ Adjustment of idling ]
Adjust idling by turning throttle stop screw.
Number of idling rotation 1300-1400 rpm

[ note ] If you measure rotation with an engine tachometer, connect lead clip to the high tension cable of the 1st cylinder.
[ equipment ] Engine tachometer: 09900-26006

[ Adjustment of pilot screw ]
#Use special equipment to adjust pilot screws.
[ equipment ] carburettor adjust driver : 09913-10110
Turn pilot screw till it stops lightly and turn it back by the value below.
Turning pilot screw back Master adjustment (about a quarter of a turn)

[ Tuning of carburettor throttle opening ]
#Use special equipment to adjust pilot screws.
[ equipment ] vacuum tester : KEK-55-3 (Kowa Seiki)

Check
Put vacuum tester hose in negative pressure outlet A of carburettor. Check that inhalation negative pressure of all cylinders are at the same level with standard idling rotation number. Adjust it if the difference is significant.

Adjustment
Set vacuum tester hose to the negative pressure outlet at the top of the cap.
Set rotation until the engine stabilizes by turning throttle stop screw.
Adjust inhalation negative pressure of 1 and 2 by turning adjuster 1.
Adjust inhalation negative pressure of 3 and 4 by turning adjuster 2.
Set inhalation negative pressure of all cylinders to the same level by turning adjuster 3.
[ note ] If adjustment takes a long time, use a fan to cool the engine down.
Use a 12V battery for vacuum tester.
Put idling rotation number to the standard number once adjustment is completed.

[wullie3xv9]

Many thanks for the very informative replies guys. Unfortunately, after several abortive attempts, I haven't been able to get my set of carb's to balance properly so have had to split them apart to check the condition of the butterfly shaft seals which are all totally worn out !! See my "GK76 Winter service/Tidy-up project" thread elsewhere in here.

Thanks again guys.