Set-up and Installation of OKO Carburetors
Though we believe OKO carburetor set-up and installation are easy, they are a little different from conventional round slide carburetors. They are "spigot mount" with a spigot outside diameter of 35mm. If your engine has a rubber manifold that accepts 35mm spigots, then it is a simple replacement. If your old carburetor was a "flange mount", then we have a few different adapters that attach to the flange to convert it to spigot mount. If the manifold spigot is larger than having a 35mm inside diameter, we have some step-down sleeves for OKO installation. Below is a photo of the different size OKOs and the dimensions of the body. Please note that all sizes from 19mm to 30mm share the same carburetor body. It is just the bores that are of different sizes or dimensions.
Spigot O.D. is 35mm, intake O.D. is 50mm, height is 130mm, length is 83mm and width is 65mm.
All OKOs have the air screw (small horizontal brass screw) and the idle screw (up angled w/spring) on the left side. At this time they do not make any carburetors that are considered "right handed" or with these screws on the right side. The most notable difference between these carburetors and typical round slide carburetors is the shape of the slide and consequently the manner of fixing the throttle cable to the slide. Below are photos of the attaching of the cable to the slide.
Click on thumbnails for larger photos.
To instal the throttle cable into the slide, insert the inner cable through the top and the spring. You may then need to compress the spring to add the white plastic needle holder. Make sure the smaller diameter end of the holder faces the spring as it is the spring tension on the holder that keeps the needle and throttle cable end in place. The notch opening in the holder should face the flat side of the slide. The cable will slide though the notch with the ferrule on the end sitting in the recessed disc in the slide. The spring will push the plastic needle holder down over the cable end, holding it as well as the needle in place. Make sure that the needle is installed before the cable and plastic holder or there will be nothing to hold it in place.
Note the positioning of the needle holder with notch towards the flat side of the slide.
Click the thumbnail for a larger photo.
Removing the bowl and setting the float height.
When removing the float bowl to check the float height or to change jets, first remove the two screws holding the bowl in place (four screws with the clear plastic bowl). With the carburetor upside down, lift the bowl about a quarter of an inch. Then, with the the float pin on the left, angle the bowl towards you some and lift it off (see photos). If you try to lift the bowl straight up you may bend the overflow tube in the bowl which can either bend or interfere with the float or make it impossible to replace the bowl.
To check and set the float height after removing the float bowl, with the carburetor upside down, angle it as in the photo on the left so that the tab on the float just touches the pin on the float needle without compressing it. The correct float height, as in the left photo should be 21mm from the carburetor body to the bottom of the float. When turned completely upside down, with the needle spring compressed, the float should be positioned as in the photo on the right. The line on the float should be almost parallel to the carb body. It should not dip past parallel or the engine will be subject to flooding when the bike is laid over. Some people suggest the float height should be set at 19mms, but experience has taught us that is too high and will cause overflow problems as well.
Changing the main jet and the slow or pilot jet
The main jet can be changed with the float bowl in place by removing the drain plug (17mm nut). We file a notch in the bowl on our carburetors so the pilot jet can be changed as well without removing the bowl (see photo). We use a 7/32" chain saw file to accomplish this, being careful to not go too far, past where the O ring seats. However, there are advantages to removing the bowl to change jets, since the main jet holder may come out with the main jet unless it is held in place with a 10mm socket or wrench. Care should be taken when removing or installing the main jets since they will break if too much force is applied. The slow or pilot jet can be given more force to replace as it is a snug fit for several turns of a screw driver.