QuestionSo, I've broken out my 1983 Honda CM450E, and noticed after I had replaced the battery (what an improvement on starting and night riding!) that the speedometer was doing something strange.
While first increasing speed, upshifting normally, I found the speedometer would eratically jump between 40 mph and 55 mph, almost as if it was reading RPMs and something was missing. After setting into 4th or 5th gear for a short while (30 seconds or so) it would settle down and speed would be constant. Is this a problem?
Normally when cruising at highway speed, the need is pretty constant, but fluctuates normally as I go up and down hills. On the flat straight-aways, the needle is very steady.
Also, After filling my 3.25 gallon tank with fresh gas this week, I was expecting to get 200 miles out of the tank. About 140 miles, the engine started missing at 60 mph... and I instinctively reached down to rotate the fuel petcock. That seemed to straighten things out. It ran smoothly, but I panicked as it meant I would only top out near 180 miles, at best, and I was currently 30 miles from a stop near a gas station. I made it 60 miles round trip and stopped to fill up... 3.40 gallons, so I know I cut it close.
What might have caused this drop in mileage? The bike is in good running condition. I'm just getting back into Springtime riding and don't abuse it.
Thanks!
AnswerWhen a speedo or tach jumps around it usually means that something needs to be lubricated.
If you are lucky it will just be the cable. To properly clean & lubricate the cable you need to remove the inner cable and wipe as much of the old lubricant off as you can before applying new grease.
While you have it out examine it and replace it if there are any signs of fraying or loose strands - remember that your trip odometer is your fuel gauge and it is driven by the speedo cable.
Before you put the cable back together flush the inner cable with any common spray can lubricant and blow air through it or hang it up to drain overnight.
If that doesns't solve the problem it may be a dry bearing in the speedometer itself. Sometimes all you ned to do is get some oil between the parts where the cable engages with the meter. It could also be a bearing inside the meter and you will need to open it up yo attempt a fix.
Information about opening up CX/GL500 speedometers is at the following links. Yours should be similar.
http://choppercharles.com/cs/forums/25012/ShowPost.aspx
http://choppercharles.com/cs/forums/28842/ShowPost.aspx
I wouldn't worry about one tank with poor mileage if the next tank's mileage returns to normal. Any number of things can mess up the mileage such as running into a lot of heavy headwinds or just running faster than you should. My sidecar machine (CX650/Velorex700) gets over 20% better mileage if I keep the speed between 80 & 90 Km/h (50-56 MPH) than it does if I run at 120 KPH (75 MPH).
If your mileage continues to be lower than normal you might check for a dragging brake. Come to a stop after a short trip using only one brake (front or rear) and then feel the brake you didn't use. If it is hot it is dragging. Repeat for the other brake. While you're at it, feel the bearings to see if one of them is heating up and causing drag.
