fine tuning - vibration at 1.5-2.5k rpm

[toomanybikes]

'81 GL1100 with 19k miles that generally starts, runs and idles very well. The valves are set, carbs clean&synced, new belts, etc. Oil is T4 15W-40

The only remaining thing I notice is a vibration felt in the faux tank at low rpm accel, typically 2nd or 3rd gear and ~2k rpm. It still pulls strong and the vibration clears up above 2.5 rpm.

All the engine bolts are well tightened. I didn't do any clutch work other than adjust the cable. I didn't dig into the drivetrain other than setting the valves and swapping the water pump.

Probably being obsessive, but is this vibration "normal" or is there something I should double check?

[Whiskerfish]

Does cold or hot engine make a difference?

[toomanybikes]

Does cold or hot engine make a difference?

Don't know. Def happens when cold, will try hot next ride. May take a few days as forecast has temps in the high-80's and this bike has a Vetter, so i don't ride it above 80.

[Whiskerfish]

Sounds like it could be a sticky slide. Engine Temp does seem to have an effect on them. If 3 are moving and one is not at low power settings that will cause an uneven pull. Just for troubleshooting you can add a couple ounces of MMO to your gas and see if that changes anything.

[toomanybikes]

Sounds like it could be a sticky slide. Engine Temp does seem to have an effect on them. If 3 are moving and one is not at low power settings that will cause an uneven pull. Just for troubleshooting you can add a couple ounces of MMO to your gas and see if that changes anything.

Good idea. I've done that exact remedy on a VX800 one time. Will add some today and report back next ride.

[toomanybikes]

UPDATE - MMO and a good warm-up didn't completely eliminate the vibration below 2500rpm.

Unless someone has magical insights, my assessment is:
1. Don't go below 2500 rpm
2. It's a 40 year old bike, deal with it.

Thanks all

[BlueThunder]

What do you mean by "vibration"? Are we talking about a buzz felt through the frame and/or handlebars or are we talking about frame shaking? Keep in mind that the motors are not rubber mounted so some vibration will be felt. And as you state... it is a 40 year motorcycle. It will not be as smooth as one from 2020.

If you believe that the vibration is excessive then I would suggest that the opposing cylinders are not in sync. The further out of sync the greater the vibration. I would check ignition timing. If the timing is not within specifications, especially if timing is too advanced, fuel detonation would "buck" piston movement. Bucking would also occur if carb synchronization is off as well. In both cases, the greater out of spec, the greater vibration.

[gltriker]

'81 GL1100 with 19k miles that generally starts, runs and idles very well. The valves are set,carbs clean&synced, new belts, etc. Oil is T4 15W-40

Probably being obsessive, but is this vibration "normal" or is there something I should double check?

"Bench synced" ? Or, all 4 carburetors were Dynamically engine idle speed synchronized with vacuum gauges or a manometer type device?

How many turns from their seat is each of the 4 pilot screws set at? No guesses.

vibration. Is this a new to you GL1100?

[toomanybikes]

"Bench synced" ? Or, all 4 carburetors were Dynamically engine idle speed synchronized with vacuum gauges or a manometer type device?

How many turns from their seat is each of the 4 pilot screws set at? No guesses.

vibration. Is this a new to you GL1100?

Bike is new to me after sitting for several years. Best I can tell it was last registered in 2013.
Carbs were bench synced to get them close, then engine idle synced with a Morgan carbtune
Pilot screws at 1.5 turns out. Spec is 1.25, but that would have put the grey turn caps to the wrong side of the bowl tab and restricted any further enrichening.
Re: scale of vibration, it's a very minor vibration felt through the tank. I was just trying to get it perfect, but it's a 40 year old bike

[gltriker]

Thanks for the additional specific details.

[Whiskerfish]

Just a long shot but lube your speedo and tach cables

[ob1quixote]

Even longer shot, bad or missing hinge bushings in the shelter sides.

[toomanybikes]

Even longer shot, bad or missing hinge bushings in the shelter sides.

Unlikely, the GL1100 shelter is different than the GL1000. Fewer hinges. But I did consider adding rubber dampeners to the mounting bolts.

[robin1731]

Remove the limit caps from the mixture screws. On 1100 carbs I always put them at 3 turns out.

[desertrefugee]

...Def happens when cold, will try hot next ride. May take a few days as forecast has temps in the high-80's and this bike has a Vetter, so i don't ride it above 80.

For sure let us know what you find.

But I couldn’t help making a comment on your criteria for riding during the summer. If I followed your rule here in Arizona, I wouldn’t ride very much.