Side Valve Adjustment Procedure: M72, K750

You'll need 2 14 mm. tappet or "thin cheek" wrenches (normal wrenches are generally too large to fit in the enclosed space you'll be working in), a feeler gauge, and a tube of high temperature gasket sealant. Now, here's a cutaway of the valves:

On each cylinder the intake valve is located on the right (nearest the carburetor) and the exhaust valve is next to the exhaust outlet.
the relevant parts in the above diagram are:

1) Valve Lifter
2) Lifter Guide
3) Lifter lock nut
4) Lifter Adjustment Bolt
5) Valve Spring
6) Valve Stem

Adjust the gap between the lifter adjustment bolt and the end of the valve stem: 0.15mm (0.005") for exhaust, 0.10mm (0.004") for intake.

1) Remove the spark plugs & valve cover plates, turn the starter over until the intake valve closes completely. At this point the lifter will be at it's furthest point into the engine and the valve spring will be extended.
2) On the exhaust valve on the same cylinder loosen the lock nut and adjust the lifter adjustment bolt to allow 0.15 mm gap between the valve stem & the end of the bolt. Holding the bolt in place with one wrench, tighten the lock nut.
3) Turn the crank over until the exhaust valve just begins to close.
4) On the intake valve, adjust the lifter bolt to allow 0.10 mm clearance

Repeat the same process on the opposite cylinder. Turn the crankshaft over completely and recheck the clearances, readjusting as necessary until the the required gaps are maintained.

Balancing Russian Carburetors

K37	K65	K68

If you suspect carb problems ...generally indicated by excessive backfiring, difficulty starting even with a good spark, or having your boots soaked with gasoline... there are a few things to check before you decide to start tearing things apart. First, make sure you do have good spark and that the points and plugs are gapped properly. Next check the color of your plugs: optimally they should be a nice brown color, but in my experience that only really occurs in other peoples fantasies. Realistically they'll usually be dark, but they shouldn't be caked with carbon. Next check your floats: cut the fuel off and drain the bowls by loosening the lower filter (7), then pull your float covers and make sure that the float is seated correctly and has plenty of free travel. Check the air intake tubes for leaks and check that the nuts holding the carb body to the cylinder are tight. Make sure you have good fuel flow from the tank and that it's even on both sides.

Now determine if you're running rich or lean: this is pretty much determined by your plug colors. There are at least two screen filters that need to be checked if you're lean: in the petcock (fuel tap) under the tank there will be one at the top of the bowl and / or another inside the bowl. In the carburetor body there's another wrapped around the fuel port in the lower filter plug (7).

If those are clean and the idle / throttle adjustments are good, then the mix should be adjusted. On this model you have a fuel control mixture screw, so CCW (out) is rich and CW (in) is lean. The rule of thumb is that if the mix adjustment is on the intake side of the carb (by the air tube) it's an air control screw and therefore CW = Rich, CCW = Lean. If the mix adjustment is on the outflow side (next to the cylinder) then it's a fuel control screw and CCW = rich and CW = lean.

Carburetor settings via FoilHedz:

Setting K-301/K-302/K-37 Carbs.

Setting K-68 Carbs.

1. Warm up the engine (make sure both sides get hot because many times bikes are only running off of one cylinder). Retard the engine if you have manual advance. If installed, disconnect the supercharger hose and plug up the carb holes or as my lazy arse would do, pinch off the tube with vise-grips so that absolutely ZERO air passes from one side to the other. Then, kill or ground out one cylinder; we'll set the carb on the other cylinder.
2. Loosen the carb neck screws so that there is slack between the end
of the cable casing and the carb neck.

3. Note that it is now VERTICAL (mixture) and HORIZONTAL (slide lift) adjustments.
4. Screw the VERTICAL screw 1.5 turns out from a softly seated, fully in position (if already idling at all, skip this step).
5. Set the HORIZONTAL screw for minimum steady operation.
6. Adjust the VERTICAL screw for maximum engine speed.
7. Set the HORIZONTAL screw for minimum steady operation again by backing it out.
8. N/A.
9. Repeat for the other side.
10. Note differences in engine speeds when operating on single cylinders. Plug up both cylinders HT cables. Adjust the HORIZONTAL screws equally in 1/8 turns for final low speed idle operation.
11. N/A.
12. Put it on the center stand (or jack up the drive wheels on an MT-16)
13. Fire it up,
14. Put it in 4th gear (might wanna chock it),
15. Rev it up to 30-40khp,
16. Clamp/hold the throttle in place, AND DO NOT CHANGE UNTIL THE PROCEDURE IS OVER
17. Disconnect (or ground) one cylinder wire,
18. Note exactly what the speedometer settles down to after 10 seconds
19. Now quickly re-connect that side disconnect the other (don't move the throttle even though it'll rev up some)
20. Adjust the carb cable ferrule on the running side to match the exact speed you noted while the first side was running.
21. Now let off the throttle and reconnect your supercharger.

Setting K-63/K-65 Carbs

1. Warm up the engine (make sure both sides get hot because many times bikes are only running off of one cylinder). Retard the engine if you have manual advance. If installed, disconnect the supercharger hose and plug up the carb holes or as my lazy arse would do, pinch off the tube with vise-grips so that absolutely ZERO air passes from one side to the other. Then, kill or ground out one cylinder; we'll set the carb on the other cylinder.
2. Loosen the carb neck screws so that there is slack between the end
of the cable casing and the carb neck.

3. Note that both adjustments are vertical screws. It's now LOWER (mixture) and UPPER (slide stop) adjustments.

4. Screw the LOWER screw 1.5 turns out from a softly seated, fully in position. (If the bike is already mostly running, it is not necessary to "pre-set" this screw, simply adjust when you get to Step 6.)
5. Set the UPPER screw for minimum steady operation.
6. Adjust the LOWER screw for maximum engine speed.
7. Set the UPPER screw for minimum steady operation again.
8. N/A.
9. Repeat for the other side.
10. Note differences in engine speeds when operating on single cylinders. Plug up both cylinders spark plug cables. Adjust the UPPER screws equally in 1/8 turns for final low speed idle operation.

11. N/A.

12. Put it on the center stand (or jack up the drive wheels on an MT-16)
13. Fire it up,
14. Put it in 4th gear (might wanna chock it),
15. Rev it up to 30-40khp,
16. Clamp/hold the throttle in place, AND DO NOT CHANGE UNTIL THE PROCEDURE IS OVER
17. Disconnect (or ground) one cylinder wire,
18. Note exactly what the speedometer settles down to after 10 seconds
19. Now quickly re-connect that side disconnect the other (don't move the throttle even though it'll rev up some)
20. Adjust the carb cable ferrule on the running side to match the exact speed you noted while the first side was running.
21. Now let off the throttle and reconnect your supercharger.

Notes & Misc. M72 Sidevalve Engine Settings:

Ignition Points Gap settings: 0.40 - 0.50mm (set with advance on)

Spark Plug Gap settings: 0.50 - 0.60mm

Piston Clearance: 0.077mm (Note: pistons are oval. See Piston, Rings and Cylinder Bore Tolerances Diagram)

Piston Ring Gap: bore diameter x .004" (0.11 mm)

SAE to EU Oil:

SAE30 = M10D
SAE40 = M16D
SAE50 = M20D