Vibration through footpegs..4200rpm+

[moosehead]

Update...well Duane was right on the money...thank you sir.

After checking every nut and bolt, especially on rear sbframe, engine , tranny etc I went for test drive to see if anything happening....vibes still there at 4200rpm and not going away

I said to myself, "it has to be simple...it always is"...then I started adjusting cables for better sync at around 4000+ rpm. Riding in 3 and 4th gears and adjusting on the left carb while riding nothing happening but as I got to the vibration start around 4200 rpm some more fiddling then voila....smoothed right out

I locked the cable adjusting nut down finger tight while continue to ride...was damn nice and smooth right up to 7000rpm!

Bit dangerous but on a lonely back road I didn't kill myself!

When got back I was locking the nut down and ran my finger down the cable...ouch..huh?...was a minute burr in the cable so this may expalin why this imbalance was there at certain cable length. This burr would just be riding up the cable adjuster to the sheath at 3/4 throttle so maybe it was hanging up or stopping to pull there while the other carb kept on pulling. I don't know...but, that was a "new" cable...file it smoothed for now until can get replacement. Tried it out after the surgery and it was smooth as butter all the way through...yipee!

What gets me is this was literally by the seat of the pants and feet tuning! Damn it felt good...hell with the balance sticks

Thanks for the "old school" sync' lesson Duane...will be tuning differnetly in the future!

[Duane Ausherman]

Congratulations for finding and fixing it. Many worship at the alter of gimicks and they never will even try a suggestion.

Between myself and 4 very good BMW mechanics we tried every dial, gauge, stick, vacuum and other to find a scientific/objective way of doing it. Nada, by ear is the best and fastest by all 5 of us.

I also bet that the time taken to do it was less than any other method you tried.

[Deleted User 287]

I really liked gspd's modification where he put an adjuster collar on one of the cables up at the throttle control (retrofitted a two-cable system) so he could adjust it while keeping both hands topside and his eyes on the road (I know how important that can be!).

[moosehead]

Congratulations for finding and fixing it. Many worship at the alter of gimicks and they never will even try a suggestion.

Between myself and 4 very good BMW mechanics we tried every dial, gauge, stick, vacuum and other to find a scientific/objective way of doing it. Nada, by ear is the best and fastest by all 5 of us.

I also bet that the time taken to do it was less than any other method you tried.

Well adjusting balance while riding took me maybe a minute until I found the sweet spot

Took me half a day dickin' around with my $4 manomometer and then my buddies vacuum, dial guages he uses for his jap multi cylinder machines...and then it still wasn't on!

I've got a 78 R100/7 just about ready to go so I'll be trying to get it set up with my "ears" first then get her out for good run and see how it feels. Looking forward to the run.

[Duane Ausherman]

Adjusting the carbs while sitting still is an artificial condition. Usually, things are close enough to allow it to work fairly well. However, consider that the bike going down the road is under actual dynamic forces that are not present while sitting on the center stand.

Finding that "sweet spot" while riding at realistic road speeds is easy, but usually shows a drawback. The bottom end few hundred rpm can be less than smooth. You must decide which you prefer.
1. Smoothness at your touring speeds where you spend hours.
2. Smoothness while pulling it up from an idle where you are only spending a few seconds.

It might help to go to http://w6rec.com/duane/bmw/Tuning.htm and do a bit of reading on this issue.

I know that we all want a perfect world where everything works out nicely. Sorry, it just isn't like that.