LeBouc
XS400 Enthusiast
Hi all. I am still having problems with the engine not being able to reach its redline, whatever gear I am running. First, I think that any air leak that would affect the fuel mixture must be after the needle jet because, otherwise, it would not change the quantity of air being drafted by the piston downtroke through the venturi of the carb, just the quality. I found that the boot that joins the carb to the cylinder was not sealing properly so I went with silicone joint maker on both side. The tube protuding from the right side boot could slide in so I glued it with enough glue to completely seal that as well. Those 2 corrective actions cleared the problem with the idle and the rpm not going back down when the throttle was closed. However, even after I had uncrewed the pilot jet 3 turns, the engine was backfiring while still in gear and coming to a stop. The engine was not able to rev past 6000 rpm and I had to close the throttle a little bit to reach that point. So I went on the highway and brought the bike to that point in 6th gear; the engine wasclearly sputtering; to verify my theory (lean mixture), I pulled the choke and, immediatly, the engine ran fine and would even accelerate a little bit more. All those informations led me to think that the mixture is lean; the spark plug was also showing a light tan. I had in hand a couple of 150 main jets so I went with them to verify if it would clear the problem. The engine is now pulling to 7000 rpm but I don't believe the real answer is going even bigger on the main jet. The only seals that I have not changed on the engine side of the carbs are the butterfly shaft ones. On the diagram, they don't show those parts but I read that the part number is 256-14997. My question is: how many of them do I need?
