Idle creeps up, help appreciated.

JohnP

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Just finished getting an 82' XS400 ready for the road and the only issue is the idle. I took it down the road and all felt good but as I turned into my drive I realized the RPM's were about 4,000 without any throttle. The next day I started the bike and let it warm up. All seemed fine and the without anybody touching anything the Idle went from around 1,000 to 4,000 RPM's. If you put the bike in gear and let the clutch out you can pull the idle back down. Thank's, John.
 
Sounds like you have an air leak in the carbs or the carb holders on the cylinders. Sometimes they get worse ad the engine heats up. Warm up the bike and get it so that it idles at 4000rpm, then spray around the carbs and boots with brake cleaner or WD40 to see if you can find a leak (the idle will drop once you hit the leaking area with brake cleaner).
 
Sounds like you have an air leak in the carbs or the carb holders on the cylinders. Sometimes they get worse ad the engine heats up. Warm up the bike and get it so that it idles at 4000rpm, then spray around the carbs and boots with brake cleaner or WD40 to see if you can find a leak (the idle will drop once you hit the leaking area with brake cleaner).
Thanks, I'll give that a try but I have also decided to rebuild the carbs and check valve adjustment before my son takes it back with him. I know I pulled the carbs and disassembled and cleaned them but that was almost ten years ago after that I ran it about a mile drained and ran out the fuel and parked it until now.
 
Also check to make sure your throttle butterflies are both closed at idle
Thanks I will check once I fire it up again. I just got the new intake boot's and started to pull the carbs off yesterday. It's been tough thinking about the bike while dealing with ice snow and freezing pipes. I will take a day very soon to rebuild, carbs, adjust the valves, put it back together and see how it does. I will check in with results.
 
Each carb boot also has a vacuum nipple. One goes to the fuel petcock and the other is capped. The caps they have available these days seem to crack and leak vacuum after just a year or two. Check those to see if it's the cause.
 
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