dgrizzle

I also have a 1977 XS360 and the carbs have given me no end to frustration and trouble over the past year. I actually wore a set of carbs out after removing and reinstalling them about 25 times. I had to get a new set. Here is what I have found. First thing to check: leaky floats - this bike WILL NOT run correctly without floats in good condition. Get new ones if necessary. Set the floats to the factory recommendation of 26.6mm height. Do this with a caliper. Adjustments of as little as .25mm make a difference in how the bike runs. Second thing: air filters - it doesn't matter what you use to filter the air, it can be nothing, it can be a k&n, , foam pods, etc. whatever. BUT - it must be placed inside the stock airbox, and attatched with the stock plenum. Without these pieces, you will get good running up to 6k, or good running above 6k, but never both. Making these carbs work with no airbox would involve modifying the air correction jet and slide bleed hole - no thanks. Third thing: Vacuum leaks - You can't properly synchronize your carbs unless there are NO vacuum leaks. The slightest leak totally throw off the running and the vacuum reading. B/C the carbs on this bike are very large for the engine size, they are very sensitive at small throttle openings, where synch makes a big difference. The three main areas where these carbs leak air are the intake spigots, the throttle shaft, and the choke mechanism. Replace the spigots - they are all cracked - XS400 ones fit and can be purchased on eBay. The choke housing and piston can get leaky as well. Buy/make new gaskets for the housing and make sure that the choke piston seals against its stop properly. The throttle shaft o-rings are the most annoying, and were the most elusive and significant vacuum leak. Because they mount on a rotating shaft, they can seal at some throttle openings and leak at others. This makes the bike run all kinds of funny, with weird, untrackable problems, appearing and disappearing at random. They don't make the little seals that these use anymore, but a good set of viton o-rings will work if you can get just the right size. They need to be a good sung fit on both the shaft and inside the housing. You have to separate the carbs and remove the shafts to get at these. Make sure that you put the throttle plates back in with the numbers facing towards the engine and on the bottom. Put red loctite on the screws that secure the throttle shaft to the throttle plates. Also, before you tighten down the screws, open the throttle and snap it closed a few times to check for free movement and to let the plate center itself in the bore. Fourth thing: Sychronization - you gotta synch the carbs with gauges. Gotta. It makes a huge difference at idle, off-idle response, and smoothness of running. You probably don't realize it now, but your bike is idling on mostly one cylinder. Synch those carbs! My final settings: Stock exhaust, stock intake and air boxes, with UNI foam pod filters inside the airboxes. Valves adjusted to factory spec. Timing 4 degrees advanced (very important to match timing cylinder to cylinder) 112.5 Main Jet 15 Pilot Jet Needle 2nd clip from bottom 26.00mm float height Idle mixture screws 2.5 to 3 turns out Idle speed 1500RPM Results: Smooth running around town, good response everywhere except for a little dead spot at 6300-6600. Motor comes alive at 6600 revs clean and strong to 8800RPM. Top speed on the level, crouched in is 95 mph (indicated)