I have a carbed 12kmi M750 with a DP analogue-faced tachometer. It seems to hang around 3-4k rpm most of the time and occasionally jumps up high or to zero when the revs are over 8k. The rest of the time, at idle and in mid range, it stays around the 3-4k range. I traced the cable back to a box on top of the airbox and the connections look fine, as does the insulation. IIRC Bosch gauges have default settings when a connection or sensor fails is this true here?
I did some searching and came up with no diagnostics, but lots of non-oem replacement advise.
Are there any diagnostics to do or should I just shell out for a new tach?
Thanks a ton in advance!
I had a similar problem w/ my tach. I ended up switching where the tach connected to. There was a similar connector on the opposite side of the battery and when I switched it over it worked just fine.
Thanks for the reply erkishhorde. Do you mean the little ignition module box/relay thing? I checked the connections there and they seemed clean. Also, the DP tach seems to be patched into an existing line that goes back down on the right side of the bike. I'm not sure what that is.
I think I found the culprit last night. There seems to be a short in the cable running into the back of the tach housing. I can wiggle it and get it to jump around. Now to open it up...
If the tach is dropping out and the bike is running fine, I bet you will find a broken wire some place. either that or the tach is failing itself.
FYI your bike stops making power around 7500 rpm, no need to rev it higher usually.
Quote from: ducvet on January 19, 2009, 05:38:36 PM
If the tach is dropping out and the bike is running fine, I bet you will find a broken wire some place. either that or the tach is failing itself.
FYI your bike stops making power around 7500 rpm, no need to rev it higher usually.
Thanks ducvet. I actually don't rev that high often - I was more interested in seeing what the tach would do that high. It jumped up to 10 krpm and then back to zero. I'm guessing it's this shorted wire in the instrument housing. Wiggling it makes it go in and out of operation.
I do have an intermittent high idle that comes and goes at stoplights, though. I assumed it was due to dirty carbs since the bike did sit for a little while before I bought it. Could this be tied to the same problem? I assume that the engine speed is measured off of a line that goes to time the ignition, is this correct?
Step 1 will be fixing the wire I know is shorting or disconnecting in the tach housing.
Quote from: ducvet on January 19, 2009, 05:38:36 PM
If the tach is dropping out and the bike is running fine, I bet you will find a broken wire some place. either that or the tach is failing itself.
FYI your bike stops making power around 7500 rpm, no need to rev it higher usually.
I know its a bit off topic, but the power peaks. Its not like it goes from 60 to 0 hp after 7500. When you shift you go to a higher gear ratio, thus requiring more power to accelerate.
Unless I understand it totally wrong, shifting at peak power isn't necessarily the most efficient, rather a point past peak power where the gear ratio of your current gear and the loss in power equal the power and gear ratio in which the next gear becomes more efficient, for acceleration purposes.
Quote from: cbduke on January 21, 2009, 07:40:41 AM
Thanks ducvet. I actually don't rev that high often - I was more interested in seeing what the tach would do that high. It jumped up to 10 krpm and then back to zero. I'm guessing it's this shorted wire in the instrument housing. Wiggling it makes it go in and out of operation.
I do have an intermittent high idle that comes and goes at stoplights, though. I assumed it was due to dirty carbs since the bike did sit for a little while before I bought it. Could this be tied to the same problem? I assume that the engine speed is measured off of a line that goes to time the ignition, is this correct?
Step 1 will be fixing the wire I know is shorting or disconnecting in the tach housing.
Your intermittent high idle problem is probably due a slightly high idle or throttle synch.
"our intermittent high idle problem is probably due a slightly high idle"
+1
As long as you do not over rev to an extreme you will do no harm to over-rev, it will wear more on the components as they are not designed to run at a high rpm with quickly decreasing power to keep the motor from being over stressed. To make quick time convetionl wisdom is to shift between peak torque and peak horse power. You want the new gear ratio to land in the part of the powerband that is climbing or at least stable not decreasing as you would need to shift again and only get a small gain.
Some bikes (900 with long intake manifords ) do drop power quite quickly so past peak you really start to loose power. 750's not so fast but still not worth the effort usually.
I will be the first to admit that i over-rev in certain circumstances, some times when setting up for a corner rather than grabbing an upshift only to have to down shift a second later. Sometimes there are other things using up our attention, or we just get lazy.