Bouncing tach

[Cyborg]

Went for a ride yesterday and returned with the dreaded bouncing tach. When cruising on the highway it intermittently bounces up and down between 1 and about 4K. Everything else seems fine at this point, other than the high beam indicator bulb which didn't work when I bought the bike. I assume it's a poor ground on the tach. When I did a search on the forum, there were a few threads about this problem. Has anyone out there gone through this recently?

 

I'm unclear on whether or not I have to disassemble the tach (remove the bezel) to repair the ground to the stud on the housing.

How is the tach grounded internally ? Trying to determine if running a second ground to the other stud will help.

 

I haven't done any checks or disassembly yet. Figure I'll keep it for a winter project..... unless it starts to drive me off the deep end.

[Kiwi_Roy]

I believe the ground is all on the outside, hopefully it's just a loose connection, it might be easiest just to add an extra wire to the chassis.

You could also try changing out the headlight relay and Start relay just in-case it's starting to go bad.

 

Remember your Start relay must be a 5 pin

[BigBlock]

I had this same problem, did what KR mentioned (ground wire to the chassis and replaced all my relay's).  Problem solved, works great, no bouncing around anymore.

[Cyborg]

I believe the ground is all on the outside, hopefully it's just a loose connection, it might be easiest just to add an extra wire to the chassis.

You could also try changing out the headlight relay and Start relay just in-case it's starting to go bad.

 

Remember your Start relay must be a 5 pin

Thanks for that. Will add the ground wire. The relays are currently Siemens for the 4 pin and a Bosch for the 5 pin.  Have both brands been problematic? Are you able to expand on the relationship between the tach bouncing and the H/L relay and start relay?

 

Why do I feel like I need to blow up a copy of the wiring schematic and post it under bright lights on my shop wall and change my mantra to ohm's law?

 

At some point this winter I would like to pick your brain regarding the switching over to LED's for the idiot lights..... if I may. 

 

Thanks again.

[Cyborg]

Staring at the schematic. Starting to ( I think ) understand the relationship between those relays and the + to the tach.

 

Is MG in the sack with the relay people? I can tell the schematic wasn't developed by one of those fellows from Hamamatsu. Jeez!

[Chuck]

The Siemans relays were problematic from the start. That said, I've seen them go for years and 10s of thousands of miles. Just the same, I'd change them all out. Get new ones from Pryo Dan. DPGuzzi.com. Cheap. (Guzzi content)

[Kiwi_Roy]

The headlight relay powers up the tach.

The start relay Normally closed contact powers up the headlight relay

If either relay is starting to play up you may be losing power to the tach causing it to bounce.

Buy all 5 pin relays, that way any relay will work in any spot.

Another source is Digikey part No Z2247-ND  (Omron G8HN-1C2T-R-DC12)

 

Ok with the dash lights

[Stick]

I can't recall the reason I needed to dig into my instrument cluster, but I was appalled at how crappy the ground connection was made to both tach AND the speedo.  I ended up "installing my own" grounding wire to a real screw inside that area.  

 

If you've never been in there, I imagine Gino did a similar, crappy job on yours.

[Cyborg]

Decided to give it a go yesterday. The ground wire on mine was between the tach case and one of the studs that is used to mount the tack. It didn't appear festered at all and seemed snug.  Call me a pussy, but I didn't really want to unscrew the stud and clean the contact area. I read somewhere that the threads that it screws into can be problematic. I made up a copper ground strap and attached it to the opposite tach stud and then ran a wire to one of the allen bolts on the engine. Took it for a test drive and thought it was fixed, but on the return trip it started bouncing again. I'm reasonably sure the ground is sufficient, so next step was ordering some relays from DPGuzzi.com . Talk about fast service. Not that keen on where they are made, but he says they are the best that he has found. If that doesn't work, I'll remove the studs, clean the contact areas and run both the original and added ground. If that doesn't work, I assume I'll have to remove the bezel and have a look at the internal ground.

[footgoose]

". I read somewhere that the threads that it screws into can be problematic."

 

agreed. mine was buggered. wouldn't tighten up, wouldn't come out. just flops a bit. I left it, ground wire between two nuts. the tach works fine.

[Stick]

". I read somewhere that the threads that it screws into can be problematic."

 

agreed. mine was buggered. wouldn't tighten up, wouldn't come out. just flops a bit. I left it, ground wire between two nuts. the tach works fine.

 

Yes, very similar on mine.  The stud was a bit loose - hence gnd. lug loose.  Could not be tightened or removed.  I added another lug to a separate screw, and made sure it was grounded.  Worked for me.

[Cyborg]

Installed the relays and went for a spin. So far so good. No more bouncing tach, but didn't go all that far. Started getting a misfire on my way home and didn't think I was going to make it. It did have the decency to wait until I got in the driveway before it croaked completely. I had asked the PO about the fuel warning light and was told it worked, but was't all that bright. For fear of being saddled with the same label, I figured that checking for fuel might be a good first step. Looks mighty dry in there. Will head to the gas station with the truck and get some of the Shell premium (without the alcohol). Hopefully that's all it needs. This thing seems awfully thirsty and I really wasn't beating on it that hard.

 

Just wanted to mention that I did a search on here because I wanted to know which relay was which. Came across a post by Kiwi Roy that answered everything. We are lucky to have him here.... Thanks Roy.