Tachometer is showing very low revs

Hi folks. 

My tachometer is showing very low revs despite the engine revving as normal. Maximum 2k.

I’ve rebuilt the rev counter and when I attach a drill that revs at a max of 3k, the tachometer shows the same. It returns to 0 without sluggishness or delay. So I’m happy the tachometer and the cable are doing their job. 

When I remove the cable at the tachometer end and observe the inner cable turning as the engine turns, it does indeed turn at idle, and the turns increase as I apply the throttle. 

is there a possible issue within the engine, where the engine speed is translated to whatever turns the inner tachometer cable?

I did try reversing the inner cable in case that might be the problem, but it made no difference. 

My bike is a KZ440 LTD chain drive 1981. 

Any advice or guidance appreciated. 

Thanks. 

Tacho drive is a worm drive off the camshaft. Going to either work 100% or 0%.
As you said it works kinda then its not going to be the drive. You seam to have ruled out cable also. 
When you did the tacho refurb, what specifically did you do?

99% of tacho issues are cable related or damper cylinder related both of which can cause needle bounce. Your symptoms tend to indicate excess tension on the drive shaft. 

Does your tacho look like this internally? 
 

Has the cam been removed and reinstalled with the tacho drive in place? (if so I believe damage can occur to the tacho drive gear)

Hi Warren. 

Yes, it looks like that. 

I bought a replacement tachometer on eBay. It arrived with one of the two fixing bolts sheared off where the thread meets the wider securing shaft so I carefully removed its internals and transplanted those to the external housing. Now of course I wish I’d tested the internals first.
While transplanting, I cleaned up the internals and the externals per a YouTube video, I noted posted here some time ago. 

 

Hi Wookie. 

I’ve not been inside the engine since I got the bike so don’t know. 

Here’s a potentially dumb question:

Does the rotation of the internal cable between engine and tachometer equal the rev count of the engine?

it’s just occurred to me: when I detached the cable from the tachometer and watched it as I revved the engine, it was slowwwww! I mean, 10s of revs per minute up to v low hundreds by my observation. 

does that info help?

When I did a rev counter transplant on one of my builds at a 1000 rpm  the rev counter read 1400 rpm so I had to get it back down to 7:1 to get the rev counter to read the same as the engine revs. The rev counter used a 5:1 ratio. I did this by making an inline reduction gearbox. 
I think kawasaki are the only Japanese company to use 7:1 ratios. So to answer your question, 7 revolutions of the cam shaft is equal to 1 revolution of the dial drive shaft. 

Thanks Warren. 

Your guidance tells me my confidence in the tachometer rebuild and the subsequent check with my drill is misplaced. 

I assumed it was a 1:1 ratio so when I put the drill on full power, 3000 rpm, and the tachometer displayed the same, I thought, Bingo! In fact, were it able, it should have read 21,000 rpm. 

In that case, I guess the tachometer is extremely sluggish. 

Going back to my rebuild, in the absence of white grease, I applied a small amount of 3 in 1 oil to the shaft, both at the top through the pin hole in the oil cylinder, and near the base where the shaft disappears beneath the magnet. Could the oil’s viscosity slow it so significantly?

Or, could it be a cable fault? I removed, cleaned as well as possible, and lightly greased the internal cable. I squirted a lot of carb cleaner through the internal route of the external cable. The integrity of the square ends appeared intact. What is typically faulty if a cable is the cause?

 

From memory all the ratio reduction is done at the camshaft/worm drive end.
At the rev counter end the cable drives a magnetic "foot" plate contained in the Bell housing. On the base of the the main shaft there's a steel foot opposing the magnet but not touching it. They rotate via a magnetic field. A hair spring gives the needle shaft and needle its return to zero ability and to a certain amount must create a bit of damping. Further up the shaft there's an oil filled bucket that does the major needle bounce damping. 
On my build all I had to do was build a reduction gearbox that changed the cable drive from 5:1 to 7:1.
I used a 20 tooth cog on the worm gear output and a 28 tooth cog on the cable drive input with a rotation reverser 16 tooth cog between the two. 

Have you pulled the drive gear to check it's condition ?