Mikuni bs34 carburetor diaphragm
For our purposes we need the BS34 with a 73mm groove. They offer 2 diaphragms for the Mikuni CV34 carbs. You can order on line with PayPal or call the owner at the phone number listed. I did notice the slides will set lower to the bottom of the carb throat than the stock diaphragms did with their plastic rings. If the seal is good, the slides won't come down on their own until you remove your thumb. I used a red Scotchbrite pad to smooth things down before assembly.Īfter you are done assembling the tops on the carbs, you can check for a good seal by blocking the diaphragm vent hole with your thumb after pushing the slide up. Before you put your new diaphragms in, it's a good idea to make sure there are no sharp edges where the diaphragm fits over the inside edges of the carbs. The outside seal ring fits nicely in the groove and doesn't try to squirm out when you put the carb tops on. You were stuck with whatever you got from the factory. Some stock slides have the vent offset one way or the other after they were assembled. If anything, the dot makes it easier to make the dot-vent-engine line up easier. The old diaphragm with the alignment tab showing the vent in relation to the engine side of the carb. The dot again shown facing the engine side of the carbs. It needs to be closely to lined up with your vent. The dot circled in red is your refence point for aligning the vent hole toward the engine side of the carb.
#Mikuni bs34 carburetor diaphragm full
Your full assembled slide with a new diaphragm. Start on one side of the slide and work your way around the slide body like mounting a tire. The side view shows the rubber ring that replaces the 2 plastic rings on the stock slide. The 73 at the top refers to the diameter of the outside sealing ring, the BS34 to the carb it fits in, and the small dot on the bottom lines up with the vent hole to give you a reference point to properly position the vent towards the engine side of the carb. You can see the identifying marks on the new part clearly. When the bottom ring is cut it comes off the same way as the top, leaving a bare slide. The first step is to cut the top retaining ring off the slide using a pair of wire cutting pliers.Īfter cutting the ring it comes off easily and the old diaphragm can be removed. Here you see the relationship of the vent hole to the tab sticking off the flange of the stock diaphragm. The following pictures show how simple the replacement is The later slides are 79mm where as the early slides are 78mm, but their INNER diameter is the same, and so these replacement diaphragms may be a slightly snugger fit ONTO the larger slides, but their outer groove diameter of 73mm is the same!
#Mikuni bs34 carburetor diaphragm install
The 80-81/82 series carbs use 1mm larger diameter slides and both the slides/diaphragms are obtainable as a single replacement from several sources:įurther investigation on the JBM site, reveals that folks with LATER model/styled BS34 carbs ie, 81 SR250 which uses the same diaphragm assembly as the 81 XS11 were able to install these replacement diaphragms onto the larger slide. These are the early model 78-79 model carbs with the smaller vacuum slides.