Another vibration post

oberling

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I know that the 650 has a reputation for vibrating a lot, but I'm not really sure what counts as a lot since my beater '80 special is the only motorcycle I have ever owned (so far lol). The vibrations at higher rpms seem really severe. I notice it when I am accelerating in town, and when I am riding around at normal country road speeds, but it really becomes a problem when I am on a state highway and trying to hold anything above 50-55 in 5th gear, because it's incredibly fatiguing. I get the worst of it through my seat, but the bars and mirror vibrate a lot too. It's tolerable for short periods at 60, but it's absolutely vicious at 70 and beyond. I rode to the next town over today and half way there the tail light went out which I presume was a solder joint fatiguing because that has happened in the past.

My carbs are not jetted quite right but they are (at least visually) synced with one another. (I adjusted until the slide position was exactly the same between both of my aftermarket flat slides) I did the valves recently and those are fine. Motor mounts are clamped down pretty tight. I never checked the cam chain tension but I will. Timing is set in stone as far as I am aware since the bike doesn't use points.

I've heard some people say that the vibrations aren't so bad on the '650, and other people say that all the bikes vibrate like crazy. It feels wrong to me though. The only comparable experience vibration wise that I have had is when my harbor freight powered minibike with a frame that has no bar across the top of the engine hits 5000 rpm with it's incredibly wobbly misshapen clutch and an unbalanced single that was designed to rev to only 3600. I would expect a production vehicle to be several orders of magnitude better so I'm pretty confident I have a problem somewhere.
 
+1 on carb sync. Make yourself a manometer and sync them. Tiny tweaks make a big difference and can really help reduce (not get rid of) vibrations. You might also consider going to a smaller rear sprocket to bring down the RPMs at highway speed.
Cleaned and properly jetted carbs will make syncing them easier. Check your cam chain tension, then your valve lash.
 
Carb jetting rich is better
And setting the Ignition later makes it run smoother.
Unless fex the crank has problems
Does it run OK other wise.
How does Spark Plugs look
Stock bike ? Saddle ? Handlebar ? there Softer grips can be used
 
Adjust the cam chain. Adjust the valves. Bad as you say it is. Start there.
Now sync the carburetors. Maybe you should clean them first. Check the slide diaphragm. There should be no holes.
 
OP, which "aftermarket flat slide" carbs are you using? If they're Chiwanese knockoffs, you're in for interesting times. One common source of vibration induced discomfort is loose motor mounts. They should be torqued to spec and in sequence. Download the factory service manual from https://www.biker.net (thanks, Jean Akers!) and do what Mama Yama says. If you don't mind her, your motorcycle will punish you.
 
OP, which "aftermarket flat slide" carbs are you using? If they're Chiwanese knockoffs, you're in for interesting times. One common source of vibration induced discomfort is loose motor mounts. They should be torqued to spec and in sequence. Download the factory service manual from https://www.biker.net (thanks, Jean Akers!) and do what Mama Yama says. If you don't mind her, your motorcycle will punish you.

YES Sir not pretending I know anything but nevertheless I do the Mexican wave upon reading that

and do what Mama Yama says. If you don't mind her, your motorcycle will punish you.

At least try factory setting if nothing else works ..Some people refuse that also.Not saying that it is so in this case
But it is refreshing to hear from a World class expert --Recommending follow the service manual
Mexican wave on that ....!!!
 
I get a vibration from 3-3200 rpm. I just try to stay outside of that engine speed range snd all is good. As said above, carb tuning and synchronization is important.
 
Here's an engine mounting bolt chart I put together. I like to use the '77D specs. DO NOT use that '78SE 65.1 ft/lb spec for the lower long #5 bolt. I don't know where Yamaha was coming from with that one. When I got my '78, that bolt had been broken and replaced, maybe because of using that too high torque value .....

oM64GW9.jpg
 
The 78-82 manual was corrected to show a sensible 36 foot pounds for the #5 bolt. I'd give odds that the metric torque numbers in the 78 manual were correct. The manuals had many conversion errors, but the metric specs can be trusted. The G-SG Supplement repeated the error in its list of torque recommendations for individual components. It would have been nice if the literature had received the same kind of QA that bikes and parts were given. Tip: When you see 40-plus foot pounds specified for torque on damper rod bolts, don't do it! That's an 8 mm. machine screw, folks. Yamaha's metric number converts to a sensible 14 foot pounds.
 
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