Though the OKO is similar in configuration to other round slide carburetors, there are some differences which will make trouble-shooting the OKO a little different as well. The main difference is that the OKO has a seperate jet block that is held in place with two screws which are "Loctited" in, and it has a gasket which seals it to the carburetor body. If this gasket is out of place, torn, or has gasket cement blocking a passageway, it will have an enormous effect on tuning. Having said that, I'll try to go over different problem areas and their fixes.
Bike won't start: So you've made sure you have spark and compression and you are now looking into carburetion. First check for a good seal between the carburetor and the manifold, making sure you have no air leaks. Also make sure there is no fuel coming out of the overflow vent at the bottom of the float bowl. Check the spark plug to see if it is wet or dry. If wet, you are getting fuel and are probably rich on the pilot circuit. First try adding a little throttle with full choke to start the engine. This will have a slight leaning effect. On Hondas in particular, the choke tends to be a little over rich. If this does not work, turn the air screw out about half a turn or more.
If the plug is dry, make sure you have fuel flow and fuel in the float bowl. Then try turning the air screw in about half a turn to richen the pilot or slow circuit. Also check to make sure the choke is up. Remember, the colder the weather, the more kicks it may take to get enough enriched fuel to the combustion chamber. If your bike still fails to start, the pilot circuit may be clogged. You will need to remove the bowl and check the pilot jet and the pilot circuit. This information can be found on the carb tuning page. At this time you can also check to see that the jet block gasket is in place. With the slide removed, look down into the body where the jet block is attached. The area where the perimeter of the slide sits at closed throttle is recessed. The jet block gasket sits just outside of this. If you can see the gasket it is probably out of place and can be causing an air and/or fuel leak. (Click to see photos of the jet block gasket) To check to see if in fact there is an air leak through the jet block, place your finger tips over the upper right side vent hole/tube and the bottom left vent hole tube while the engine is running. If the rpms drop you have a leak. Remove the jet block (impact driver for philipps screws may be needed) and check to see that the gasket is in place. At this time you can also check to see that the passageways are not blocked. Still can't get it started? Send me an e-mail or give me a call.
Starts, but won't idle: When the bike is started using the choke, as it warms up the idle should decrease as the engine starts to "load up". At this time, push the choke down (off). You may need to raise the choke and release it until the engine warms up further. If the bike stalls, turn the idle screw in until it will idle, then turn the air screw in and/or out to determine if the idle is rich or lean. Turn the air screw in the direction which increases the idle speed and turn the idle screw out as the rpms increase. Find the spot where the engine idles at the highest speed without faltering (air screw) and then turn down the idle screw to obtain the desired idle speed. If the engines idles the best with the air screw turned out between one and two turns, you have the right pilot jet and all is well. Let the engine idle for a few minutes and then blip the throttle to less than a quarter turn. If the engine is slow to return to idle, or with 2-strokes it searches upon return, the idle is lean and you should turn in the air screw slightly. If the engine bogs or 4-strokes, the idle is too rich and you should turn the air screw out a little. If this "sweet spot" of the air screw is more than two turns out, switch to a smaller pilot jet. If it is less than a turn out, switch to a larger pilot jet.
Note: It is very important that the idle is correct before checking the needle and main jet. Once the idle is right you will be able to determine if you have the right size of carburetor for your engine. With the idle dialed in, ride your bike, giving it just a little throttle. If the bike pulls strongly just off of ide you have the right carburetor. If the engine is lean at this point, the carburetor may be too large. Raise the needle a little and ride it again at just off of idle. If it is still lean at this point, e-mail or call me. Conversely, if the engine runs rich just off of idle, the carburetor may be too small. Try lowering the needle a little and reride. If it is still too rich e-mail or call me. Do not try to compensate for richness or leanness with the air screw as it will throw off your idle.
Idles, but bogs when given throttle: With the idle dialed in at operating temperature you can check the other circuits, the cutaway, needle and main jet. The positioning of the needle can be changed to tune mid-range and the main jet can be changed to tune 3/4 plus throttle, but the cutaway cannot be changed. If the engine runs well except just off of idle, you probably need to change the carburetor size. Leanness will be evidenced by weakness, a slow return to idle and the engine searching (ring, ding, ding ding). If this area is rich, the engine will bog, run "heavy" or 4-stroke (fire every other stroke). If this area is rich you may need to switch to a larger carburetor. If this area alone is lean, you probably need to switch to a smaller carburetor. However, if you are intent on sticking with a larger carburetor, we have had some success by thinning the upper portion of the needle by about a thousandth of an inch. This will richen this area just off of idle as well as the idle. You may then have to switch to a smaller pilot or slow jet.
Mid-range/half throttle is poor: If the idle is dialed in nicely, and just off of idle is good, but the engine is erratic at half throttle, the needle clip is in the wrong position. Again, indications of leanness are that the bike will lack power, perhaps "spit back" or search when the throttle is released. If this is the case you can either add a shim under the needle or lower the needle clip and see if performance improves. If this area is running rich, it will be slow to accelerate, run "heavy" or 4-stroke. To cure this, raise the clip on the needle one notch. If that takes it too far, place a shim under the needle.
