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Old 06-10-2010, 11:19 AM   #1
Redux
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Engine vibrations above 6k RPM

Recently I started to notice vibration in the engine.
Was barely noticeable at first, but now it feels like riding a 250cc twin.

Engine vibrations become evident at 6k RPM and amplify with RPM increase. This happens while stopped and on the freeway while riding. If I pull the clutch at high speed, the engine goes to idle and the ride is perfectly smooth. There is also an overall loss in power.

So I tried some test - 8k -10k rpm about 80mph I turned off the ignition via killswitch - vibrations were still there as the engine was gear braking. So I'm a little stumped.
If the ignition was somehow involved - in the above test it should have smoothed out. Would it be the same for carbs?

Bike has 61k miles, and there is a small leak from somewhere in the chain sprocket area (1-2 drops a week). Clutch is brand new (less than 4k miles).

Any ideas would be appreciated. 1992 VFR750
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Old 06-10-2010, 11:21 AM   #2
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Change your oil and check for metal in the oil with a flashlight.
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Old 06-10-2010, 07:24 PM   #3
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Change your oil and check for metal in the oil with a flashlight and magnet.
fixed it
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Old 06-17-2010, 11:44 PM   #4
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..
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Old 06-18-2010, 10:11 AM   #5
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Anyone?
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Old 06-18-2010, 01:25 PM   #6
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Timing chain stretched? I know this was the case years ago on my 95 zx6r
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Old 06-18-2010, 01:31 PM   #7
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Timing chain stretched? I know this was the case years ago on my 95 zx6r
VFR's don't have timing chains. The cams are driven by a gear connected directly to the crank.
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Old 06-18-2010, 01:50 PM   #8
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and the engine vibrates only when you're moving?
what about when you kill the engine and pull the clutch at speed?
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Old 06-18-2010, 01:56 PM   #9
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and the engine vibrates only when you're moving?
what about when you kill the engine and pull the clutch at speed?
No, the engine vibrates even when standing and revving the engine. When I pull the clutch in at speed, the engine goes to idle, and the ride is smooth.
Killing the engine while in gear and moving, the bike still vibrates.
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Old 06-18-2010, 02:13 PM   #10
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how are the vfr's mounted on the bike? check there.
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I got the hint and dropped to the back of the ranks just in front of Ares, who btw rocks the outta that 250.
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Old 06-18-2010, 02:36 PM   #11
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Well, this probably isnt it because you mention that it does it when stationary but I had a vibration issue that was chain alignment related. Originally I had the chain eyeballed on the marks (vibration), then I did digital caliper to the 1/10th of a millimeter from the back of the swingarm (vibration), then I got the chain alignment took that has the clamp that you put on the sprocket and the rod to visibly align it (less vibration). Well that tool was handy cause it showed me how far off my marks were and eventually I fine tuned the alignment by centering the sprocket on the chain with equal play on either side (no vibration). Moral of the story.. the marks can't be trusted.

This vibration was only UNDER accelleration and DECEL with clutch dis-engaged and pretty much all rpms but it got worse as RPM's increased. Clutch engaged and coasting it was smooth as glass.

Another suggestion

Re-torque your motor mount bolts especially if you have sliders or have recently put sliders on the bike and check your chain alignment. Maybe your engine shifted.

Another suggestion

Inspect Clutch basket.

Last edited by Mr. Evo IX; 06-18-2010 at 02:39 PM.
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Old 06-22-2010, 10:06 AM   #12
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Borrowed a gauge-type carb sync tool. The readings were all pretty close, but now I think I'm going to build a manometer, as the gauges measure the vaccum in 10's of inHG. And the allowed difference is 20mmHg. (20mmHG = 0.8inHG)
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