How to repair hanson mechanical professional scales

The fuel mixture screw on a PZ26 Jing Ke carburetor is typically located on the side of the carburetor, near the bottom. It is used to adjust the air/fuel ratio in the carburetor, which can affect the engine's performance. It is usually a small, knurled knob that can be turned with a screwdriver. It is important to be very careful when adjusting this screw, as too much or too little fuel can cause the engine to run poorly or stall. It is recommended to consult the manufacturer instructions or a professional mechanic before making any adjustments.

Are these a vintage or a digital scales? Is this for general cooking and baking or is it for accurate measuring?
General cooking doesn't need serious accuracy so unless it is seriously inaccurate I wouldn't worry too much about it.
Digital scales can be difficult to accurately calibrate without specialist equipment. For accurate measuring there are companies out there that can calibrate scales to an industrial standard for a fee.
You can check the accuracy of any scale buy using something you know the EXACT weight of. (Bag of sugar or flour). Set up the scales as normal. Add the known weight and read the scale. If it is more than a gram or two out it needs calibrating. On digital scales you might need to press the 'TARE' button before you start to Zero the display.
Most old 'mechanical' scales use a spring as the resistance to the weight you put onto the scale. You can get some adjustment but as the spring gets old it weakens and gets less accurate. Somewhere on the scale there will be an adjuster wheel. Often positioned high up on the back of the scales. *Note* mechanical scales are often not very exact so there will always be some level of inaccuracy.
Set the scales up as you would normally use them. Look at where the needle sits near the '0' mark. Turn the adjuster wheel a few turns, (counting them), in one direction. Press the weight 'Plunger' all the way down two or three times. Check where the needle has moved to. If it has moved the 'wrong' direction wind the adjuster wheel back the number of turns you counted, (the start position), then continue in that direction the same number of turns. Press the plunger down like you did the first time.
This method will show you which way to turn the adjuster and how far to get it back to where the '0' mark is.

This unit does not have batteries. The adjustment causes the tension to change internally. If you are not able to change it with the adjustment to read zero, either the springs inside the unit are stretched or the adjustment screw is stripped or at the end of the motion range

Try stepping on it lightly and quickly to see if it indicates a zero reading. If that happens, then weigh yourself before the zero goes away.

Turn the scale upside down (assuming it's a bathroom scale) and look for a small knurled or serrated wheel. When you know where it is, usually on the lower portion of the scale, turn the scale back upright to its normal position and turn the small wheel. One direction will cause the weight shown to increase, the other direction to decrease. Adjust the wheel until you have the proper reading.

Make sure the chair is clean and there is nothing between the chair the sensors. Put the setting to zero. if it the arrow goes to center you are good. if not you have to adjust the screw on the other end of the beam. Make a quarter turn at a time. Don't go crazy with it. Try to get the arrow to zero as close as possible. push down on the chair a few times times to make sure it is consistently gets to zero. Get several different weights to check the linearity, 10 should equal 10. 20 should equal 20 and so forth.

Hi. Cldchasr is talking about an electronic scale, not your beam scale. Coachphil was helpful but inaccurate for this model. I have a 230. Use Coach's method but there is no screw on the left to adjust. Instead, use the black zero balance at the upper left. Move the black slide on the silver bar until the scale balances.

There is a small knurled knob to the rear base at centre of carbies, this turns a worm screw, actuating a bar for all 4 carbs. The site below provides an exploded view and name of carby parts.

Here's a tip...if the knurled knob (designed to turn by hand) is too hard to turn, a multi facet (not hexagon facet) socket or ring spanner is far easier than pliers or grippers.

Cheers.

http://www.cmsnl.com/yamaha-fz600s-19861987_model9219/partslist/B-04.html

line up the adjustment block and put the screw into the hole. then carefully snug it down and put the cover back.