Tuneup

[William Aubin]

I have just installed a refurbished SU carb in my Herald 1200 and am now attempting to tune it.  With only one adjustment it should be easy.  But I have not found the "sweet spot" yet.  At about 25 mph the engine starts to hunt and throbs rather than purrs.  I have been playing with the carb, the timing and the idle speed but I cannot get the result I am looking for.  I have read about looking for white and black exhaust.  But I cannot see a difference.  Do you have any sage advice?

                                                                                                                           Bill

[bobwa...@verizon.net]

William,

   There are as many ways to solve this as there are mechanics.  I have personally found the best way to get the mixture right is by checking the color of the plugs.  I typically make an adjustment, and then take a quick test drive, maybe 2-3 miles.  The change shows up on the plugs very quickly.  You are looking for a color from tan to light brown.  Keep in mind, if the engine is older an oil is getting past the rings there will be some sootiness that won’t go away.  This is normal for an older engine.  The fact that it’s hunting around sounds like its running on the rich side.  There is a link to some great articles on the carbs on our website on the “Technical Ref’s” page.  This one relates to tuning.  Good luck!!

 

http://www.buckeyetriumphs.org/technical/Carbs/CarbsIII/CarbsIII.htm

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