Excessive vibration while riding

[cmills83]

I am trying to track down an excessive vibration problem with an xs I just finished building. I tried syncing the carbs with a manometer, a digital manometer, re-jetting, replacing the carbs, I don't think it's the carbs. What else could cause this? The engine has good compression and starts right up.

I have a fiberglass tracker seat so I don't expect it to be perfect but I am getting blurred vision riding this bike.

 

[TwoManyXS1Bs]

These are always fun. Is it speed-related, or rpm-related?
Speed-related - Check wheels, drivechain and sprockets.
Rpm-related - Check engine mounts. Also, look for runout of rotor and shaft.

 

[cmills83]

Definitely rpm related, the engine sounds great but it seems like the mid range powerband is a bit weak, not sure if I need to adjust the jets/needle or something else is going on.

The mounts are all tight, how would I go about testing run out on the rotor?

Thanks for the reply.

 

[TwoManyXS1Bs]

Something to think about is the frequency of the vibration. The cam runs at half the crank rpms. The clutch runs at less than half of crank rpms. If you think the vibration is at crank rpms, then you may want to first rule-out crank problems. Here's some threads that have crank and rotor runout/balance issues (you'll have to dig deep into these):

http://www.xs650.com/forum/showthread.php?t=36211
http://www.xs650.com/forum/showthread.php?t=38420
http://www.xs650.com/forum/showpost.php?p=374864&postcount=498

Here's one with drivechain issues:

http://www.xs650.com/forum/showthread.php?t=27912

Some of the threads in the forum that question vibrations find solutions in carb tuning and balancing.
Then again, could be ignition timing scatter.
Let's hope it's that simple...

 

[XSLeo]

I might start with the steps in a tune up.
#1 adjust cam chain.
#2 adjust valves.
#3 if points set gaps and timing. TCI check timing.
#4 carbs, the carb guide will help with these.
If this helps then go onto other things. Like wheels, are they true and balanced?
Wheel bearings, swing arm bushings, Neck bearings. Tires.
Leo

 

[cmills83]

Thanks for the feedback. It seems like it's vibrating directly with the rpm's. I'll check the cam chain and valves and go from there.

It's happening at idle so definitely something with the engine, which sucks because this is the 2nd engine I've tried and the compression is great.

 

[TwoManyXS1Bs]

When you check the timing with a timing light, does the flashing image of the rotor mark appear stable, or does it skip/flicker or bounce around?

 

[hein weijers]

Hi Cmills,

An important question: is this your first XS650? You should know that all XS650 motorcycles vibrate. I had four XS650 bikes and still have one. Three of them were "moderate" shakers and one was a terrible vibrator. I have tried everything to improve the behaviour, but nothing worked: rephased crank, dynamically balanced crankshaft, big bore, other carbs, new drive chain, balanced clutch, nothing really helped.

I sold the bike, got a "new" project, a 1982 pile of rust. I did a top end restauration, left everything standard an to my surprise the engine ran smoothly and with much less vibrations than my first bike.

I discussed that with Jerry van der Heiden of "Heiden Tuning", who also assisted with the balancing of the crank. He had the same experience: some bikes just vibrate much more than others and nobody knows why.

Hein