I'll second all Scot's suggestions. I once had an 1988 RS that was extremely buzzy in the bars and foot pegs. I did a basic tune-up with timing and carb balance. It was dead smooth after that. If I had been blindfolded I'd have sworn it was a different bike.

Thanks for the advice. I've gone through most of that... Should have said this vibration can be felt on the center stand at RPMs over 2,500. Most pronounced over 3,000 RPMs. So I isolate this issue to the motor. Also did the transmission test to eliminate the tranny. Both clutch and transmission have been updated.

But I do need to test the timing - although I would think it would start hard and run poorly if the timing was off. Which is not the case. Starts fine and runs up the revs smoothly. But I'll check.

I also tried my local air marshal's 1987 R100GS. Not a PD but same size engine and layout. We both felt the 93 PD vibrated a lot more than the 87 (which had some of this). Different saddle? Stiffer frames? I really don't like riding it.

thanks

I really don't like riding it.

That's truly a shame. But motorcycles will vary like that from bike to bike. I thought my '78 RT was smooth until I test rode a friend's '81 RT.

But do look at the timing at full advance. When I set the timing on that '88, the bike was new to me and I was simply doing a check over/ preventative work. The fact it smoothed out was a complete surprise.

That is encouraging. Taking care of an aging parent right now, but when I get home I'll check for sure. It would be so great to solve this. The suspension on the PD is amazing. The upright position really nice. The bags and racks make it a great touring bike. But the vibration sucks!

I'm going to try and have a tech day in MA for this. Will report.

Thanks again.

Finally made it out to Maynard, MA to visit Duncan of Duncan's Beemers. He's our local guru. I think he's ridden more older GSs than anyone around. He felt the vibration. So I'm not totally nuts.

First we checked the carb sync. He thought it was out (I didn't really), but he tuned it up. The throttle uptake from low to mid is super smooth. Don't think that's an issue in the vibration.

Then we checked the timing. At low speed it was a little out, but at full advance it was right on. Duncan said he wouldn't mess with that.

Then he took a test ride and noted that it vibrated the most between 2500 and 2700 RPMs. I do tend to ride in slightly lower revs (my other bike is an R90) so I might be stuck in the worst spot.

Note there are three places that we feel the vibration. The back of the seat, the pedals, the grips (mirrors). It has a Corbin saddle, with a softer center insert. The back of saddle is original and transmits a lot of the vibration. If I sit forward that helps.

And, it's a 1,000 cc bike. Bigger bang. But I rode an R100Rs for a few years, didn't really do this.

So our final assessment. The bike has 73,000 miles. Duncan thinks it might be the pistons/con rods getting a little out of balance. He's seen worse and definitely seen not well balanced motors - even right from the factory. But it's not terrible and I should learn to mitigate the vibration by staying in the smoothest rev band. The bike does everything else so very well.

Down the road balance the engine, perhaps. I did order some vibration absorbing pad for the saddle and might have back of the seat softened. Mostly I need to ride it more.

As our local marshal said, on a dirt road you won't feel a thing.

Ever had the friction disc in the clutch replaced ??? There's a trick that is not self-evident. The paint marks on the 3 pieces each get offset by 120°. Some people might assume the painted parts all get aligned. That would certainly increase vibration. Here's a video explaining, advance to 2:45 for the details....

https://www.youtube.com/watch?v=u7NFhiC9lgk

Just came back from 300 miles over the weekend. feeling much better about this bike. Here's what I did.

- Softening up that Corbin. They are just too hard.
- I swapped out the metal pegs and it helped. They are great for dirt, very positive feel, but they transit a lot of vibration.
- The biggest thing was the tires. Yes, it vibrates on the center stand, but I think that’s different. With the less aggressive style Metzlers it’s much better on the road.
- And I really learned that as you accelerate you feel the motor. At certain RPMs it’s much more pronounced. But settle in and it likes certain RPMs more than others.
- It’s not very high end fast, but it has tons of torque. Pulls like mad off the line but you need to use really high revs to keep up on the highway. But 4,000 rpms is better than 3,500 once you get there.

Does it still vibrate? sure, but it's a big, stiff bike and I can make it work for me. There's quite a bit of technique, but that's part of the fun.

Took a while to really appreciate. Now I can’t get enough of it.

He's seen worse and definitely seen not well balanced motors - even right from the factory. But it's not terrible and I should learn to mitigate the vibration by staying in the smoothest rev band. The bike does everything else so very well. Down the road balance the engine, perhaps. I did order some vibration absorbing pad for the saddle and might have back of the seat softened. Mostly I need to ride it more.

I'd like to know more about that. Other than the previously explained flywheel balance, "engine balance" is a mechanical thing, actually a ratio of the weights of various engine parts. Unless the PO slung a rod and only install one, or changed the pistons, I'm not really sure how "engine balance" could change. Engine balance is not something that changes by simply riding the bike down the road.

He's seen worse and definitely seen not well balanced motors - even right from the factory. But it's not terrible and I should learn to mitigate the vibration by staying in the smoothest rev band. The bike does everything else so very well. Down the road balance the engine, perhaps. I did order some vibration absorbing pad for the saddle and might have back of the seat softened. Mostly I need to ride it more.

I'd like to know more about that. Other than the previously explained flywheel balance, "engine balance" is a mechanical thing, actually a ratio of the weights of various engine parts. Unless the PO slung a rod and only install one, or changed the pistons, I'm not really sure how "engine balance" could change. Engine balance is not something that changes by simply riding the bike down the road.

Thee balance will chang slightly as carbon builds up on the pistons. For all purposes the rods will not change. The rocking couple will not change. The torque on the engine mouning bolts can be a factor. Sometime more or less is best, but if anything they will loosen, not tighten. A 60/40 tire it will never be as smooth as a road tire. if the dirt pegs have been discarded the dirt tire might be good to ditch too.

There are better ways of tuning the carbs that yield a smoother engine but unless running road tires it's spitting hairs.

Engine vibration will be RPM dependent, tire and wheel roughness will be speed dependent.

The balance will change slightly as carbon builds up on the pistons.

This is out-dated information. Back in the 70's when there was leaded fuel and additives adhered themselves to piston crowns, owner's manuals stressed "de-coking" an engine. People devised all sorts of ways of squirting strange stuff into the running engine's carb to do the job without disassembly. These days, modern unleaded fuels (especially Top Tier Fuels ) leave hardly any deposits on the piston crown. "Carbon buildup" is now a moot point.

One of the biggest "kick myself" moments is realizing the R100 I just wrecked was the smoothest BMW I've ever owned. And I think it's Number 7 or such. This is a difference from the factory.