QuestionBelow is a Q & A from Rich Johnston that would expire on 8/10 and his allexpert accout is on vacation till 8/11. I tried the suggestion he gave and it worked somewhat. The bike somewhat idles now however after it does for about a minute you hear a noise in what sounds like the carb and it sounds like it is a puff of too much air or something similar and it chokes itself out. Start it again, it will start off running kind of well you then hear that "puff" again and it kills out. Sure sounds like it could be coming from in the carb but I'm not 100%.
Question This was bought from a guy that said the carb was taken to a shop to be cleaned due to tarnish and couldn't get carb back in after 1 or 2 years. I got it in and ran it and it started idling funny (up and down to dieing out) repeatedly. I took carbs back out and disassembled and thoroughly cleaned with a carb cleaner and reassembled setting all screws and pilots exactly by the book. Placed the carb back in and started it and it starts easier however it still idles up and down till killing out and all adjustments I do with the idle screw end up doing the same thing.
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Answer Check the timing advance unit. Sometimes the springs get tired and allows it to stay in advance too long. When you twist the cam it should snap back to the fully closed poistion. If it doesn't, the spring have relaxed. You can either replace it or pinch the ends of the springs just enough to get it to return properly. If you put too much tension on the springs the timing won't advance properly and the bike will loose performance.
Regards
Rich
AnswerI don't have much experience with these bikes, but I will try.
The previous owner said the carbs were sent out for cleaning and he never put them back on (It does have 4 carbs, doesn't it?). I would have originally suspected that the shop missed something in one or more of the carbs (I have heard a lot of stories about carbs that were "cleaned" by shops), but Rich has more experience with these bikes his suggestion makes sense to me.
I wonder if the "puff" you are hearing is actually a small backfire? (If it fires back through the carbs it's a backfire. If it fires in the exhaust it's an afterfire.) According to http://en.wikipedia.org/wiki/Back-fire backfiring is usually caused by a lean fuel/air mixture, ignition timing or bad wiring in the ignition.
Lean mixture can be caused by carb settings, blocked or partially blocked carb passages, a torn or missing air filter or a leak where a carb is attached to the airbox (check both ends of the boot). Since it won't run long enough to warm up you can't adjust the carbs, but you can set them to the factory recommended starting points and see if that helps. This information should be in your shop manual.
Information on static ignition timing with a test light should also be in the shop manual.
If that doesn't help try these guys: http://www.cb750c.com/modules.php?name=Forums
It's a forum for DOHC Honda Customs, but they are a good group and they have a section for K models.
