Windshields and tank slappers Definitely Guzzi content

[geoff in almonte]

Check the clearance between the headlight and the windscreen - you should allow a gap of at least an inch to allow air under the windscreen.

At speed, the screen creates a vacuum which in turn causes uneven airflow behind the screen which could result in a wobble.  The effect is similar to riding in the turbulence behind a transport.

G

[Bulldog9]

Simplest is to remove the WS and go for a test ride. 

Large Fork mounted screens can induce high speed wobbles and expose weaknesses in the chassis. Steering head bearings, imbalance in fork oil, misaligned fort tubes/triple trees/axle, steering stabilizer, sometimes rear suspension as well with things like swing arm bearings.

Tires can play a big role as well. I never replace only front or back tires, always a fresh set. Changing just the front and changing profile may play a part as well.

Don't discount a poorly aligned windscreen either. Is the screen adjustable? Can you move it up or down in height? Have you checked it for being square?

I had a series of WS on my XS11 from a frame mounted Windjammer to a fork mounted Rifle with different height clear shields. The Stock and tall shields were steady as a rock, but when I cut one down to 1/2 stock height, it became a wobble monster with no cure. Had a similar experience on my C10 Concours.

Because I am cheap, I adapted the large Norge Windscreen to the Stornello, using adapter plates to connect to the DART screen mount. I lucked out, after some adjustment of rake and angle, I ended up with no wobble to 90 MPH, even on the super light V7 chassis. The screen is large, but properly aligned you can tune out wobble.

As it is a new bike, I'd go over it all top to bottom, but $10 says taking the windscreen off for a series of high speed runs will eliminate the shake.

[s1120]

Bike just turned 10k so the bearings are fine and I have checked the tension and there’s no play. I’m thinking it’s Possibly the shields effect. I’ve eliminated any tire issue, New tire on the front, I did drop from a 110 to a 100 series.

I would have guessed the head bearings also. My 02 stone did the same thing, but on slower back road corners. It was worse with the sheld on... bit still there with it off. Once I got the front in the air I noticed the head bearings were REAL sloppy!!!!  WAY out of wack, and my bike was also under 10k miles.

[Ncdan]

Thanks for all the responses, suggestions and recommendations and I have taken every one of them in consideration and will address until the issues is solved. Also let me reiterate it’s not a great big issue because I seldom reach the speed of 80mph mainly because I don’t to have to explain to an officer why an old retiree is acting like a fool😂 Just funning. However the bike is very stable and solid displaying no issues at all until yesterday when I hit that 80mph zone. It then corrected itself when I backed off a bit which could have been a serious wobble if I had proceeded to increase my speed.
Today I will put some of the compression back on the rear shocks, as a couple of the knowledgeable guys suggested, which I had removed a couple days earlier. I had released all of the compression the heavy PO had torqued down and let’s see what that does.

[oldbike54]

 Have watched one '97 California do the "dance" at speed , and have had a 2002  model brought to me after the owner experienced a serious head shake . In both cases a fork seal on one side had been leaking , leaving one side almost empty of fluid . The '97 has that crazy barn door handlebar mounted fairing and 40 liter H&B bags , the '02 just had a very small turbulence generator that stuck up about 3 inches above the headlight and small stylized bags .

 Patrons at the truck stop in Missouri seemed amused watching as we disassembled the '97 California in the shade of the one lone tree on the property .

 Dusty

[Ncdan]

Have watched one '97 California do the "dance" at speed , and have had a 2002  model brought to me after the owner experienced a serious head shake . In both cases a fork seal on one side had been leaking , leaving one side almost empty of fluid . The '97 has that crazy barn door handlebar mounted fairing and 40 liter H&B bags , the '02 just had a very small turbulence generator that stuck up about 3 inches above the headlight and small stylized bags .

 Patrons at the truck stop in Missouri seemed amused watching as we disassembled the '97 California in the shade of the one lone tree on the property .

 Dusty

Thanks for that information Dusty. I think I can eliminate any fork or front end issues at this time. There are no signs of any leaks in the forks, I know any seal can start leaking but its obviously not leaking now or ever in its 10k miles. When the new tire was replaced Monday my mechanic checked the Head bearings and tension and all was fine.
Today I’m going to put some preload back on the rear shield which I had removed ALL of what the PO had added and see what that does 👍

[wirespokes]

Why not set the suspension properly with sag at 1/4 - 1/3 total travel?

Stock shocks don't tend to be quality items. Maybe one (or both) aren't doing so well.

Tires can have internal issues. I had a front tire that was maybe 50% worn, looked fine, but replacing it fixed a bad low speed wobble.

A worn rear tire can cause wobbles.

Swing arm bearings and adjustment also.

Considering others have had no issues with the fork mounted wind screens, I'm guessing it's not the issue. And even though the wobble is above your normal speed, it needs to get resolved. You'll be passing a semi at high speed one day and the change in wind speed, pressure and direction will bite you big time!

It's even possible the PO sold the bike because of this issue.

[Ncdan]

Why not set the suspension properly with sag at 1/4 - 1/3 total travel?

Stock shocks don't tend to be quality items. Maybe one (or both) aren't doing so well.

Tires can have internal issues. I had a front tire that was maybe 50% worn, looked fine, but replacing it fixed a bad low speed wobble.

A worn rear tire can cause wobbles.

Swing arm bearings and adjustment also.

Considering others have had no issues with the fork mounted wind screens, I'm guessing it's not the issue. And even though the wobble is above your normal speed, it needs to get resolved. You'll be passing a semi at high speed one day and the change in wind speed, pressure and direction will bite you big time!

It's even possible the PO sold the bike because of this issue.

Thanks WS for that info. In the “Sag Spec” is those numbers you stated measured when my weight only is on the Bike??

[Ncdan]

He was saying that the fork tube in question is not the FORK LOWER - he was basically saying the way you wrote it made us picture someone trying to attach the lower clamp/mounting bracket not the fork tube, but the larger diameter slider below it which some call a "fork lower". That is all. I'm staying out of the rest cause it seems to be covered.

No problem and thanks. I guess I figured that’s it’s obvious the latter could not happen. All is good and I appreciate everyone’s input. Now the next post will answer all the questions. Thanks Kev

[MMRanch]

 

Ncdan

Where do you live where the speed limit is Slightly above 80 ?

 

[Tkelly]

My 2cents,you are talking about a lot of work.What if you do all that stuff and still have the problem?You will have to remove the shield then. my eldo did this a couple times before I pulled the old widow.It was solid up to 100 then.Good luck but don’t do the speed test on the freeway.

[Ncdan]

Problem solved!!!!
First let me say thanks to everyone that took of their time to respond and a couple of you guys hit the proverbial “head on the nail”.
I probably need to start by asking all to look over my testing procedure as it’s probably considered reckless and irresponsible but some times drastic actions snd need to fix particularly drastic events.
When I took possession of the bike the PO had cranked the compression aspect of the rear shocks probably to 30% of full compress status. It road very ruff, so at my weight of 170 in full gear, I figured an uncompressed shock should be ok. After talking To one of the guys here Last night Who suggested putting at least half that preload back on.
So this morning I did just that. After making a pre run to check for energize LEO running radar, I got off the ramp and headed the other way, 4 lane but not interstate, Traffic was fast, around 80mph. I fell behind the line and backed off about a half mile, then let her go. From 80 to 100 MPH she was as steady and firm as a real mans handshake. Absolutely Stone solid!
I think one thing we can take from this is which shields and which positions they are mounted probably does not effect these issues of stability at higher speeds. I think the bikes suspension should be the place to start in fixing the issue.
Thanks again for the help guys and please overlook any weird or strange thing I may have said as sometime I slip.  👍

[wirespokes]

Here's the data on sag. The suspension has to be able to absorb bumps, but it also needs to track depressions or pot holes as well. So those are two opposite vectors.

Because of that the suspension has to be free to move both up and down.

It's been found that the best place to set the suspension is 1/4 to !/3 from the top. Bumps evidently need more travel than holes.

There are a few ways to determine what the 1/4 distance is. With the wheel off the ground, measure from the axle to the frame. That will get you full extension.

Look up the specs on the shock, or for the bike, for full suspension travel. Say it's 3".

Now take the bike off the stand, and sit on it. Have a friend measure the distance from the axle to the frame and it should be 3/4" to 1" less.

You can also put a zip tie on the shock piston rod at full extension, sit on the bike, then put it back on the stand. You'll be able to see how far the suspension moved.

Glad it did better this time and got rid of the shake. For now anyway. By increasing rear shock preload, ride height was increased. That in turn changed the steering head angle and the angle of attack of the wind screen. Hopefully the sag is correct. If it's stiff, then more work is needed and this is another data point to consider.

[Ncdan]

Here's the data on sag. The suspension has to be able to absorb bumps, but it also needs to track depressions or pot holes as well. So those are two opposite vectors.

Because of that the suspension has to be free to move both up and down.

It's been found that the best place to set the suspension is 1/4 to !/3 from the top. Bumps evidently need more travel than holes.

There are a few ways to determine what the 1/4 distance is. With the wheel off the ground, measure from the axle to the frame. That will get you full extension.

Look up the specs on the shock, or for the bike, for full suspension travel. Say it's 3".

Now take the bike off the stand, and sit on it. Have a friend measure the distance from the axle to the frame and it should be 3/4" to 1" less.

You can also put a zip tie on the shock piston rod at full extension, sit on the bike, then put it back on the stand. You'll be able to see how far the suspension moved.

Glad it did better this time and got rid of the shake. For now anyway. By increasing rear shock preload, ride height was increased. That in turn changed the steering head angle and the angle of attack of the wind screen. Hopefully the sag is correct. If it's stiff, then more work is needed and this is another data point to consider.

Thank you so much for taking the time to give me those specs and guide lines and I’ll definitely use it as a guide and reference. Thanks!!

[BrotherJim]

Last time I rode my '02 Stone with my Givi's attached and loaded and my Dart Marlin windscreen, I experienced a bit of wobble at, let's say 90mph.  Slowed down to closer to 80mph and the wobble went away.  Now, I put new shocks on it a while back before I got the notion that I'd be putting bags on it, and I set the sag at 220lb at that time.  I've got fresh-ish Metzeler 880's with about 3,000 miles on them.  I think that what I was experiencing was being overloaded for my chosen preload settings.  If any of the other suggestions don't yield favorable results, maybe get a buddy to help you set the suspension sag to your expected weight range.  I honestly don't think that the steering damper does much, except look kind of cool. 

[Ncdan]

Ncdan

Where do you live where the speed limit is Slightly above 80 ?

 

I didn’t say  the speed limit was 8o, MM, I said the traffic was collectively running around 80👍

[BrotherJim]

Ha!  Late to the party, I guess.  Glad you've got that sorted.  These really are great machines.