Done correctly this will enable you to exert maximum downward pressure on the screws and you will be able to remove them. If you have to come in at an angle then grind a profile on the end of your support bar to match the angle of the throttle shaft. In the picture you can see how this would be done if you could rotate the butterfly sufficiently to enable your supporting rod to fit flushĪgainst the shaft. ImportantAfter grinding down the screw to be flush with the shaft, you have to support the back of the shaft with a piece of solid bar as you apply pressure and try to turn the screw. Use both hands on the Dremel to avoid it kicking back. Mount the carb securely in a vice or similar, place some sponge under the butterfly, position a strong light source on the top of the carb, and lock the butterfly into a useful position to use the Dremel. Some Mikunis may come loose without having to grind. As always, take lots of pictures.Įven if you do not wish to stake your screws you may need to use a Dremel to grind down the staked section of screw to make it possible to remove them. Now it will be possible to put it back in exactly the same position. In this image I have marked cyl 4 on the bottom half of the butterfly. We have used images and details from a Keihin carb to explain the process of removing the butterfly screws because they are the most difficult.īegin by marking the butterflies.Carbs are made of an alloy with a high zinc content and they are soft.Take photos before and as you disassemble.Lubricate the threads of brass jets and screws before fitting to avoid galling and seizing. Screws and throttle shafts will need to be washed in solvent to remove any traces of oil and dirt before using thread locker. You should also expect that small parts like springs, screws jets and washers may fall onto the floor area and that you will need to find them. You should have a clean, well lit and comfortable work area. All images in this guide follow this format, so left does not necessarily mean the left side of the image but rather the left side of the carburettor as described. Orientation, for the purpose of defining left, right, and carburettors one to four, is defined as if one was sitting on the motorcycle facing forward carburettor one, in that case, is the leftmost one. Never use the silicone jointing compound on a carburettor. We suggest either rubber grease or silicone (spray or grease). You cannot butcher your way through a carburettor.Īll rubber parts, with the exception of the throttle shaft seals, should be moistened with just enough lubricant to give a glossy finish. You must also have well fitting blade screwdrivers for the various jets. You must use a JIS (Japanese Industrial Standard) screwdriver. The screws are JIS Cross Recessed they are NOT phillips screws. There are no phillips screws on a Japanese motorcycle, none! If you use a phillips screwdriver it will cam out and damage the screw. Trying to force it out can damage the butterfly and the carburettor throat. Once the screws are removed the butterfly can be very carefully removed. If the butterfly screws are tight, usually because they have been staked, then first, seal the carburettor to ensure that no grit can fall into the throat, and use a Dremel or similar tool to grind away the staked section of the screw. Do not use the butterfly as a stop when loosening the nuts on the end of the shaft. Because they have a long slot to hold the butterfly, they can be easily twisted or bent. Removal of the throttle shafts needs to be done with great care. Most of them will show all of the internal jets and parts, but very little of the external fittings that are between the carbs, such as springs and throttle shafts.
Mikuni bs34 carburetor manuals#
Note that most parts books and manuals do not show the details of the parts and assembly of the carburettors when they are separated. When disassembling your carbs, take as many photos as necessary. However, it could be useful for other models that use these carburettors. This guide is for a set of Mikuni BDST carburettors from a Yamaha FZR400RR 3TJ1.