One of the drawbacks with dual carb setups is the need to properly adjust them so they feed equal amounts of fuel/air mixture to each cylinder. If one carb is set differently from the other, the bike will be hard to start, won't idle properly and suffer from poor performance and fuel economy (well, maybe that last one is a contradiction in terms for a Dnepr). There are a few tools out there that can greatly simplify the process of adjusting (AKA: synchronizing) the carb's; a Twinmax seems to be the popular choice from what I've seen on Soviet bike forums. There's also a way to make your own synching tool by using a length of clear tubing, some automatic transmission fluid and a piece of wood, but what if you don't have access to or lack the funds to purchase a Twinmax? And what if you really aren't keen on playing with tubing and ATF because, like me, you know it will only end up in a big mess all over the garage floor because your butterfingers can't process the commands from your brain on time?

I did some searching online for a quick and easy way to adjust the K68's that came with my Dnepr and finally found a post on the Russian Iron Forum that was pretty close to what I was looking for. Scooterbob, another legend in the Soviet bike community, was the author and he wrote it in response to someone who asked for help sorting out their K63 carb's. I've taken the liberty of copying it and adding a few changes based on the differences I found with the K68's construction. Keep in mind that before attempting any carb tweaking you must ensure that the ignition setup is correctly, there is fresh fuel in the gas tank and that the carb's are clean. Also, make sure the engine is cold so you will get a more accurate setting.

First, pull the air tubes off the carb's so you can access the throttle slides. Then loosen the throttle cable adjusters on the tops of both carb's and screw them all the way in (maximum free play). Using the left side carb as your start point, gently lift the slide and insert the plain end of a 1/4" drill bit underneath it and centered at the bottom of the carb mouth. Make sure the bit is kept as parallel to the bore as possible while gently letting the slide back down to rest on the drill bit.

Then slowly adjust the throttle stop screw in clockwise while gently tugging on the drill bit until it slides out with the slightest drag, much like when using a feeler gauge to adjust valve clearances. Then repeat the procedure on the right side carb. This sets both carb slides at the same position, which also sets up the proper idle speed. Take your time here - it is essential to your sanity that they are as close to each other in the "feel" of the drill bit gauge as possible.

Now adjust the majority of the slack out of the cables, being careful to leave just a bit of looseness so as not to lift the slides off their stop screws. Twist the throttle open enough to insert the plain end of a 3/8" drill bit under the left carb slide, then gently roll off the throttle until the slide contacts the drill bit. Wrap some electrical tape around the throttle grip and the handlebar to hold it steady (or whatever else you can come up with that acts as a throttle lock), then very gently and slowly twist the throttle while tugging on the drill bit until it slides out with a slight drag. The throttle should stay in place from the tape, so carefully re-insert the drill bit to make sure. Adjust and re-tape the throttle as necessary until you get a "feeler gauge" sliding fit on the drill bit without twisting the throttle.

Remove the slack from the left side throttle cable and lock the adjuster. Re-check the fit of the drill bit. If everything is okay, move to the right side carb and lift the slide place the 3/8" bit underneath. Slowly adjust the slack out of the right side throttle cable until it lifts the slide enough to get that feeler gauge fit. Lock the right side throttle cable adjuster.

Take the clamp off the throttle handle and check for smooth operation. Now that the idle stops and the cable pulls are synched, you can adjust the idle mixture screws. Screw both of them in till they lightly seat and then back them out 1 1/2 turns.

Re-install the air tubes and start the bike. Back each mixture screw out 1/4 turn at a time until the engine speed drops off. Do the same small adjustments to each carb - DO NOT twiddle one without the other or you will lose your "coarse adjustment" and have to start all over again. Take your time here and turn the screws slowly to give the engine time to react. When the engines slows and changes pitch, go back in 1/4 turn, or until the engine speed picks up a bit. Then go an additional 1/8 turn in.

If the engine is idling too fast, turn each idle stop screw counter-clockwise a small and equal amount until the speed suits you. Turn clockwise if the idle is too slow. The engine should now be warm so a 500-700rpm idle should be good. If the engine is getting hot, place a couple of box fans in front of the cylinders and turn them on high to help dissipate the heat while you continue with the procedure.

Slowly open the throttle off idle and see that it doesn't go "dut-dut-dut-dut-dut" on one cylinder as it accelerates. If it does, you'll need to re-synch the cables. Pull each cable out of it's cup in the cable adjuster a tiny amount until you locate the side that starts running better (easy to hear if you have an exhaust system without a crossover pipe). Then adjust the cable on that side only until the uneven acceleration is cured. Take the bike out for a short run to check performance and, if all goes well, pat yourself on the back for a job well done!

Compiled and translated 2006 by Curt http://www.curtperedina.com

Adjusting the Pekar K68 for your Dnepr or Ural

Adjustment section translated from Pekar K68

Adjusting the Pekar K68 carburetors on your Dnepr or Ural.

This document is intended to server as the primer for proper adjustment of the K68’s. It also contains the product specification sheet from Pekar for all of the K68 models. I will talk about the use of different tools used for the synchronization step, but will not go into detail on each tool. As part of this step, I will explain the “old timer” method of synchronizing the 2 carbs without the use of any special tools (placing the bike on the center stand and using the speedometer to determine carburetor flow). This is very interesting to say the least.

Pekar Specifications

The following is taken directly from Pekar (translated): K6 Å , K68D, K68I, K68M, K68R, K68T, K68U, K68CH

o Horizontal flow

o Elliptical diffuser

o Cylindrical slide

o Centrally located float chamber

o Lever type float mechanism and detachable fuel line

o Adjustable idle

o Adjustable mixture and needle valve

o Hands free choke operation

o Symmetrical choke and throttle cable

o Synchronization port

o Float vent system .Compiled and translated 2006 by Curt http://www.curtperedina.com

Carburetor Transportation means Engine

Conditional diameter of diffuser (mm)

Diameter of mixing chamber (mm)

The capacity of fuel jet (ml/min)

Mass, is not more (kg)

Overall sizes (mm)

Drive of the starter

Ê 68 À the motorcycle

IZH-6.113-03

IZH- 6.113-03  28 31,5 250 0,55 77,5*81*155 Manual

Ê 68 D the motorcycle "IJ- Jupiter"  28 31,5 IZH- Þ 5 250 0,55 77,5*81*155 Manual

Ê 68 I the motorcycle "the IJ- planet IZH -Ï 5,-7.107-10 32 35 280 0,55 77,5*81*157 Manual

Ê 68 Ì the motorcycle IZH-'.902 IZH -6.902 32 35 320 0,55 77,5*81*157 Manual

Ê 68 Ð “Lynx” 440.76, 440.93 32 35 370 0,55 77,5*81*144 Manual

Ê 68 Ò “Ural” Motorcycles

IMZ-8.128 28 31,5 220 0,55 77,5*81*189 Electric

Ê 68 U “Ural”  Motorcycles

IMZ- 8.123 28 31,5 190 0,55 77,5*81*189 Manual

Ê 68 H motorcycle "IJ-chopper"

IZH- 6.113-05 28 31,5 240 0,55 77,5*81*155

 Manual. Compiled and translated 2006 by Curt http://www.curtperedina.com

Specification Chart from www.russianiron.com 

K63Ø

'Dnepr-12'

K750

K63T

Dnepr 11/16

K63y

Ural K65T

Dnepr K65y

Ural K68y

Ural

Choke size 26 26 28 26 28 28

Bore at flange 28 28 30 28 30 30

Main jet size (cc/min.) 135 163 170 165 170 190

Needle jet size (mm) 2,78 2,78 2,78 2,65 2,65 2,67

Pilot jet (cc/min) 50 50 50 50 50 50

Choke jet (cc/min) 55 55 55 55 55 55

'Diameter opening idle' (note 1) 0,7 0,7 0,7 0,7 0,7 0,7

'Diameter transition opening' (note 2) 1,2 1,2 1,2 1,2 1,2 0,8

Slide type Flat Flat Flat Flat Flat Round. Compiled and translated 2006 by Curt http://www.curtperedina.com

Figure 1

K68.Compiled and translated 2006 by Curt http://www.curtperedina.com

From Figure 1

1. throttle cable;

2. shielding caps;

3. cable guide;

4. cover of choke well;

5. spring of choke;

6. ferrule;

7. housing;

8. slide;

9. cable catch;

10. cable stop;

11. needle of choke;

12. lock of needle;

13. spring of the compression of needle;

14. slide bevel;

15. air duct of main system;

16. padding of the cover of float chamber;

17. cover of float chamber;

18. sprayer;

19. main fuel jet;

20. dosing tube of the system of idling;

21. stopping washer;

22. drain hole;

23. float activator (tickler);

24. slide (idle) adjusting screw;

25. spring of screw;

26. fuel-feed nipple;

27. balancing port;

28. balancing channel of float chamber;

29. mixture adjustment screw;

30. spring of screw;

31. mixing chamber;

32,34. transitional openings of the system of idling;

33. air duct of idling;

35. saddle of fuel valve;

36. fuel valve in the collection;

37. regulation element;

38. float;

39. channel of starter;

40. axis of floats;

41. air duct;

42. plunger of starter in the collection;

43. ferrule;

44. jet;

45. needle of corrector- enricher;

46. opening dosing;

47. fuel well;

48. the fuel duct of starter;

49. needle of starter;

50. spring of plunger;

51. guide of spring;

52. Choke.

Preparation for K68 Adjustment

1. Make sure the ignition timing is correct

2. Adjust the valves as necessary to ensure proper operation

3. Run the engine to warm it up a bit

4. Adjust the float setting. To do this, remove the carburetors (leave the throttle cables

attached), remove the bowl and turn the carburetor upside down (fuel will spill). The float

should look like this:

Adjust as necessary by bending the float support (#37 in Figure 1). Reinstall. Compiled and translated 2006 by Curt http://www.curtperedina.com

Figure 2

Installation and idle adjustment

1. First you must adjust the idle. It is acceptable per the manual to adjust the idle by using

the idle adjust screws (11). This usually involves screwing them then backing out 1 to 1.5

turns. Or you can adjust looking at the sliders

2. If installing the carburetors:

a. Remove the cover (2)

b. Remove the slider (3)

c. Place the throttle cable through the guide (18) with the spring (4) on the cable.

d. Route the cable through the slide catch (6)

e. Insert the slide assembly into the chamber and make sure it easily slides up and

down. Direct the needle (8) into the opening of the diffuser (angled side visible).

f. Screw assembly together and verify via throttle movement that slide moves

freely. Attach fuel delivery lines to (12).

3. Using the idle set screw (11) raise the slider so the lower edge is 1-2 mm.

4. Assemble to engine using the proper gaskets (paper – felt – paper).

5. Using the locknut (26) adjust the free play of the throttle cable (2-3 mm)

6. Adjust the idle mixture screw – turn in completely then out 1 to 1.5 turns.

˜

Starting using the K68’s (cold weather)

1. Verify fuel flow. Apply choke (pull 52 in Fig1).

2. Using the ticklers (13) allow fuel to enter the bowl until fuel drains from (14)

3. With the ignition off, kick 1 or 2 times

4. Turn ignition on, and as soon as engine is warmed up (maybe sooner) push choke

mechanisms to open choke. Compiled and translated 2006 by Curt http://www.curtperedina.com

Idle Adjustment (engine running and warm)

1. Remove one of the spark plug caps, and with the cap shorted, adjust (11) to decrease

RPM’s to a point of being minimally steady.

2. Adjust the mixture (15) out until RPM’s decrease. Turn in until RPM’s increase slightly.

Then turn in screws ¼ to 1/3 revolution.

3. Do the same for the second carburetor with the first spark plug cap shorted.

4. With both cylinders, adjust each idle (11) on each carburetor the same amount each until

it’s at a steady, minimal RPM. Use small changes. (at this point you can use your airflow

tool to check).

5. Sharply increase, then decrease throttle. Then engine must return to low RPM's smoothly.

If the engine goes below limits, readjust (11) from step 4.

Synchronization of the K68

Note: Rather than using the opposite cylinder shorted to test the pull of the live cylinder

carburetor, you can use something like a Twinmax connected to the test ports (27 Fig 1). Or, if

you have a model without these ports, use a Synchrometer (Appendix 2) held against the face of

the carburetor. These tools merely show airflow passing through each carburetor (which is

dependent on the position and wear on the slide). If using these tools, it’s not necessary to do the

following steps. You will want to use a throttle guide (Appendix 1), to show airflow at various

throttle settings. Using the flow meter of your choice make sure each carburetor is the same at

the various throttle settings.

1. Place the motorcycle on the center stand ensuring the rear wheel is suspended

2. Make sure you have large area to work with (safety issues here)

3. Shift into the highest gear with the engine running

4. Short one spark plug cap to the cylinder (using a nail or something in the fins)

5. Increase the speed to 40-50 km/hr

6. Fix the throttle using the throttle (maybe using a throttle stop screw under the throttle

housing).

7. Reconnect other cylinder and using the opposite carburetor determine the speed which

should be the same as the first.

8. Adjust the position of this slide to achieve the referenced speed using the locknut at the

top of the carburetor.

Adjustment of the mixture due to climactic condition changes.

This involves changes to the needle vale (8 and 9 Fig 1) (11 and 12 Fig 2). With the needle

moved upward, the mixture is leaned, movement down and the mixture is enriched. Needle

movement occurs through removal of the lock and moving the needle to the next groove (coarse

adjustment). Fine adjustment occurs through transposition of regulation washer (9 Fig 1) (19 Fig

2)..Compiled and translated 2006 by Curt http://www.curtperedina.com

Special Operating Instructions

Disconnect the fuel before maintenance on K68’s. Must be used with a tightly connected air filter

of manufacturers specification only. A modification of filter or manufacturer is not allowed. Fuel

used must be cleaned and filtered of all impurities. Carburetor parts must be washed in gasoline

only. Washing is not allowed with solvents. After washing, blow with compressed air to dry.

Cleaning any of the metering holes (20,21 Fig 2) or nozzle holes (22, 23, 24 Fig 2) with metallic

objects (wire, needle, etc.) is not allowed.. Compiled and translated 2006 by Curt http://www.curtperedina.com

Appendix 1

Fixing the throttle and stages of operation. Compiled and translated 2006 by Curt http://www.curtperedina.com

Appendix 2

Synchrometer (an alternative to tuning)

Used this on my 912 and it works great.

Appendix 3

Cutaway K68.Compiled and translated 2006 by Curt http://www.curtperedina.com. Compiled and translated 2006 by Curt http://www.curtperedina.com

“For more complete information on the K-68 visit Curt Peredina’s site at
http://www.russiancycles.com/files/K68Adjustment.pdf