Motorcycle Repair: 1979 Honda CB 750K, honda cb, timing advance

Question
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. 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.

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


---------- FOLLOW-UP ----------

QUESTION: Thanks for the assistance Rich. That took care of that issue and is running somewhat better however it now has a different issue. Now that it is running better I got the idle set just right while it sat there however I ran a test drive on it and it accelerates fine however when you pull the clutch in to shift (and to all gears it does this) the RPM stays at what it was before the pull in for the shift. For example, if it hits 2500 rpm to the top of the gear and you pull the clutch in it stays at that and does not drop then shifting into and releasing it stays high and does that all the way through all gears. Downshifting doesn't even want to pull the idle down if you try to like do an engine brake, for example. It still runs high. I adjust the idle and it then goes too low, like it is set too low when finally able to get it down and dies out with adjusting idle any lower. Do you know what may be causing this?

Answer
Sorry Corey, but I think it's still the advance unit.  Take a pair of needle nose pliers and close up the loops on the ends of the springs on advance unit just a little to increase the tension on the springs.  I think you'll find it, fixes that problem. The only other thing that can cause something like that is low compression.  If the bike has low compression, it will require a lot more idle air to keep it idling right and when the engine speed is increased, there's less leakage in the rings and it stays at the higher speed.

A compression check will confirm or eliminate compression leakage as the issue.


Regards
Rich