Topic: erratic rpm on long trips?

[huili]

After reading a handfull of threads on rpm there is still no answer.  I have a 76 cb550k bought last year in july.  At the time of sale things were fine or at least seems that way since it was my first bike.  I then decided to do some mods got mini speedo and tach made sure the ratios were corrct. Since I never believe anything the ads say I evan ran the original equiptment made notes and then ran the new guages with the old ones and made sure the observations matched.  At this time I have not taken the bike out for a long ride just small 10-20mi rides.  When I took a 2 hour trip for the first time I noticed after 45min of so of riding the speedo and tach would jump irratically.  The tach ran between 6000-7000 at 75mph but when it started jumping it would go from 5000-8000 and the seedo from 65-80.  The thing is there was not much wind and I did not feel any change in acceleration or crusing speed it felt smooth.  I initialy thought  I had faulty guages or may be the mini guages did not work so welll at those speeds. So the day after I ran the bike and the guages worked fine at 70 and above and this would only happen after some time of riding.  Any clues to whats happening? 

[Bob Wessner]

Are the new gauges mechanically driven via cables like the stock gauges, or are they electronic??

[cb(r)]

if the gauges are mechanical check for splits and cracks if all good then clean cable and shoot some lube down the it.   that would be my first and probably easiest solution.

[huili]

the guages are mechanically driven, no cracks and I have tried lube

[cb(r)]

well if the bike is running fine then swap the original guages back in and recheck.  if all is fine then it would seem to me that the new speedo and tach are the problem. 

[scondon]

well if the bike is running fine then swap the original guages back in and recheck.  if all is fine then it would seem to me that the new speedo and tach are the problem. 

   Also, if you relocated the gauges, check that any bends in the cable routing are at a minimum. Friction in the cables will cause erratic gauges, either by being too dry(lube) or improper routing or both. This usually shows up after a bit of riding. Cables heat up, expand, lube breaks down, etc...

[huili]

scondon, that could be it I had also put drag bars on and I the cables were a little long as I remembered. thanks