K-301 CARBURETOR

K-650 CARBURETOR K-301

A big thanks to John <cytop450@verizon.net> for all the pages from the manual on the K-301, and to Don Black for the nice color pics, I hope I got it right.

FUNCTION OF THE CARBURETOR

   Gas from the fuel tank is delivered via the petcock to the float chamber through the pipe union #1 which is pressed into the cover #3.  From the float chamber the gas passes through the fuel filter #5, flows through passage (a) and idle adjustment fuel passage (b) to the main jet atomizer #14, settling on the level of gasoline in the float chamber (B).

   Since the engine has been started, the throttle valve is in the lower position and is only raised a little by the throttle valve screw #9, air will flow at a great velocity through the slit opening.  Influenced by high vacuum beyond the throttle valve, fuel via idling jet #18 rises through passage (b) and, being mixed on the way with air that flows from the suction conduit inlet throat through passage (d) and air filter gauze #20, is directed in a form of emulsion to the atomizing orifice (e).  Here the emulsion is pulverized by air passing at high velocity through the slit between the throttle valve and the chamber wall.  The combustible mixture so prepared enters the engine cylinders.  During idling, the main jet atomizer is not working because of reduced vacuum above it.

   As the throttle is raised, more vacuum is formed above the atomizer.  The main system is brought into action.  It consists of main jet #8, atomizer #7 and metering needle #5.  

   Outflow of fuel is limited by the circular slit between the calibrated portion of the atomizer and the metering needle of the throttle valve.  

   When the engine is working at medium loads, vacuum at the atomizer is compensated partially with air flowing to the atomizer through passage (c) which connects the atomizer hollow with the suction conduit throat.

   With the throttle raised completely (the last quarter of travel), the quality of fuel passing through the atomizer is not limited by the metering needle and depends on the throughput of the main jet.

ADJUSTING THE K-301 CARBURETOR

   There are three main areas of adjustment for optimum operation of a carburetor.  These are the idle adjustment, (at low revolutions), during acceleration and for the functioning of the throttle controls.  Before you bin to do your adjustments you need to start the engine and bring it up to operating temperature.  If you do your adjustment at a cold temperature as soon as the engine warms up the adjustment will be out of kilter.  The proper idle adjustment is essential for optimum engine performance.  Each of the two K-301 carburetors should be adjusted independently.  You begin with the L.H. carburetor.

   First you disconnect the R.H. cylinder sparkplug.  On the L.H. carburetor slacken the locknut #26 of the throttle control cable armour thrust nipple #27 and screw in the nipple to create a gap between the cable armour and the nipple.  Slacken the locknut on the throttle valve screw #15.  Now slacken the locknut on the idle adjustment screw #18.  Snug down the idle adjustment screw #18.  Using the throttle valve screw #15, reduce the RPM of the engine until they are at a minimum without hesitations.  While turning the idle adjustment screw #18 out, set the maximum speed for the engine with the throttle valve screw in the given position.  Gradually release the throttle valve screw #15 to set the minimum steady RPM. 

   Having completed the adjustment, tighten up the locknuts on the screws.  Return the plug wire to the R.H sparkplug, and remove the L.H sparkplug wire and repeat the process on the R.H. carburetor.

   The engine should run at the same speed when idling when running on either cylinder.  The carburetors are checked after adjustment on a warm engine.  To do this remove first one, and then the other spark plug wire while listening for any variation in operating speed of the cylinder that is working alone.  If one cylinder is running faster than the other, readjust the carburetors by turning the throttle valve screws in or out until uniform speeds are obtained in both cylinders.  When you have achieved this, tighten up both the locknuts on the throttle valve screws.

   You can check to see whether you are running rich or lean by visually checking the color of the spark plug insulator and electrode, or by using an aide such as a Colortune.  To do this it is suggested that you find a nice straight stretch of road that is not too heavily traveled.  You should be able to have about 1.5 – 2 km to perform this check.  Bring the bike up to third gear and ride the distance at about 45 -50 km/hr.  When you reach the end of the run, stop the engine suddenly by turning off the ignition, and simultaneously release the clutch.  Pull over to the side of the road, and take your spark plugs out of the heads and examine them.  A black carbon deposit indicates that the mixture is too rich, which means you need to lower your throttle needle, while a yellow, sandy or whitish color indicates the mixture is too lean, and the throttle needles must be raised.  Once you have found the correct position of the needle and the mixture is burning properly, you will find that the plug electrode and insulator will be a nice even brown color. 

   The final determining factor in maintaining a properly adjusted carburetor is having the throttle cables properly lubricated and adjusted.  If the cable armours get stretched out, the carburetors will get out of synchronization and the cylinders will not work properly in all three ranges.  Therefore it is necessary to properly maintain your throttle cables to prevent them from stretching or hanging up in the cable housings.  See the section on handlebars and cables for proper cable lubing procedure.

   Carburetor’s, like everything else, require a periodical bit of maintenance.  You should take your carb’s apart and service them at least every 2,000 km’s or so.  You should clean and wash all the parts, along with fuel and air passages as part of this operation.  The best thing to use for this is plain old gasoline.  If you find that you have excessive gum residue then you can use a little thinner for nitrodyes.  Do not use a rag or cloth to dry the parts, but it is acceptable to air dry them but preferable to use compressed air.  If you don’t have a compressor you can buy canned air at a camera shop.  Never use wire or abrasives for cleaning the jets or calibrated holes of the carburetors.

   Whenever you take your bike out for a ride, you should keep an eye on your carburetors, as the darn things do tend to spring little leaks, and vibrate nut’s and bolt’s out of adjustment.  The gaskets tend to dry out as well, so as soon as you see something that is not 100% right, you should attend to it immediately. 

   The majority of these leaks are found in the fuel petcock shut off valve, the petcock sediment bowl or in the float chamber.  If you notice gasoline in your carburetor air filter, these are the first places to look.  If you are constantly maintaining your air filter, and are washing it regularly and blowing it out with compressed air like you are supposed to be doing, then you will notice something right away.

   Do not unscrew the main jet without a good reason, because it is really easy to damage its gasket.  If the jet gets dirty, undo the plugs #13 and #11, and blow the jet clear with compressed air through the passage from the plug #13 end. 

   If you must take your carburetor apart for some reason, take extra care with the throttle.  When you disconnect the body from the cheek, you need to apply a fair amount of pressure to overcome the expansion force of the spring, which serves as both a retainer to prevent spontaneous separation of the body and the cheek when the throttle is being removed from the carburetor body.  You really should not remove the spring out of the throttle body.

   Reassemble the throttle after the throttle needle and the control cable tip are set into their respective recesses in the throttle body.  Once again some effort must be applied to overcome the expansion spring force.  Fit the throttle into the carburetor body with its cheek (throttle cutout) facing the inlet branch.  Be sure that the carburetor cover salient is fitted properly into the carburetor body slot.

“For more complete information on the K-301 visit Curt Peredina’s site at
http://www.russiancycles.com/files/K301Carburetors.pdf