Topic: My bike hates to run at 3000 rpm = max. vibration, yours ?

[Spanner 1]

My K1 750 hates 3K rpm in whatever gear...in 5th. it's like 45 mph. It seems like all the possible ' slackness' , wear and tear, drive chain slop and blacktop 'feedback' all converge into an unpleasant vibratory ride...speed-up ever 2 mph and it's gone ( or slow down ).
Anyone else have this ?......I'm beginning to think it's pandemic among old SOHC bikes ?

[JohnG]

A couple times over the life of mine I have been amazed at how much smoother it was with a new drive chain and sprockets.

Beyond  that, how old or worn are your tires??

Have you checked the various bolts that hold the engine in the frame for any loose, broken or missing?

Rich carburation can lead to vibration but you did not mention changing it.

[Spanner 1]

I'm not saying it's a bad, worn out motor vibe, but a noticable ' point' in the rpm scale that the bike doesn't like....just not happy at. No big deal, I'm totally happy with the state of tune ( at the moment ! ) but it's a node or harmonic of the workings of the motor/bike that appears at a certain rpm...yes ?

[mark]

The baffle is a bit loose and buzzes right at 4K.


3K in 5th? I'd almost call that lugging. Kick it down a gear or two.

 

[JohnG]

I would say your problem is the state of tune of your motor, not the fact it is an SOHC 750. Give it a really comprehensive tuneup, including carbs and see what happens.

[Spanner 1]

I think my post is being misunderstood..!  I'm not looking for help with my bike, just making an observation....I don't believe you guys who say your bikes are totally smooth through the rpm range from idle to 8k. No-one has noticed a particular rpm where these SOHC motors ( by their design ) produce more vibration than any other point on the rpm scale ??
On mine it's just under 3K. Again it's not bad, but it is noticeable for sure.

[Gordon]

No-one has noticed a particular rpm where these SOHC motors ( by their design ) produce more vibration than any other point on the rpm scale ??
On mine it's just under 3K. Again it's not bad, but it is noticeable for sure.

Haven't noticed it on mine, but I'll try to pay closer attention to the vibrations on the way to work today and see if I feel anything. 

[JohnG]

I apologize for misreading your original question...

I would say I have a slightly noticeable vibration peak at 4500 rpm.  I say that because with the original stock gearing, that would occur at highway speed.  I changed the gearing to lower the RPM and moved away from it.

If you have one at 3000  (which I will pay attention to in the future), that would make sense.  These things are all harmonics of a basic vibration and therefore their frequencies are all multiples of some base frequency.  Like one at 1500 rpm.  Mine is certainly no sewing machine at 1500 either...

The GL 1000 has much more symmetry and therefore less vibration peaks.

[Mdub]

It would be worth checking the engine mount bolts.
They do occasionally loosen.
Mike

[Kevin D]

My K1 750 hates 3K rpm in whatever gear...in 5th. it's like 45 mph.

My K1 absolutely loves 45-50 mph, about 3000-3500rpm and I believe it would run forever at that speed.

I like it best pulling gears through 6000-6500rpm.

[mystic_1]

3K in 5th? I'd almost call that lugging. Kick it down a gear or two.

+1



mystic_1

[Spanner 1]

So, I thought I would have a bunch of responses saying 'Yeah, my bike has a vibration ' node' at ( fill in the blank ) rpm......not evident so far, which got me to 'cogitating' about all the tuning I've done on my bike. Basically a full tune-up twice. However I have had an intermittent carb overflow problem for some time and got to investigate yesterday. I took the #1 carb apart ( the one overflowing ) to try polishing the needle valve into its seat as the seat is removable ( K1 7A carbs ). On the bench I rigged a short piece of tubing in the drill which contacted the valve sitting in it's seat and spun it for. and rev. with the drill for a few seconds and with toothpaste ( ! ) as a polish...saw it in tricks/tips.! Worked a treat!
Anyway , on putting the carb back together I happened to shake the floats....yep, gas in 1 float...dang..I can't believe it....O.K., so float will sink carb level too high, #1 way too rich...vibe prob ??, one cyl. running with different 'parameters' = vibration. The answer is YES...did away with the prob. when swapped-out a spare float. You never know with these old bikes......!

[JohnG]

I had a set of Mikunis for a while which I could never quite tune for the entire RPM range.  The rich area would cause the bike to shudder a bit, which is probably a more extreme version of what you were running into since it was all 4 cylinders being too rich.

Toothpaste!!  Neat!!    Someone suggested Brasso which worked well with QTips.  But you have to thank those Keihin design engineers for making the seats removable, and better yet, with the carbs in the bike!

[fmctm1sw]

Mine gets to a point where the spedo, tach or something else up front becomes very buzzy.  Around 5k if I recall, haven't ridden it in a while...

[Johnny5]

Mine's the most buzzy around 4-5000 rpm. Before and after that, it's pretty smooth. Who knows...