650R Decomp Issues

9 replies to this topic
  • Thumpmeister

Posted June 17, 2006 - 08:09 PM


Okay, rebuilt the top-end last summer because of excessive valve noise. Replaced piston, rings, valves, guides, cam chain, and had the cylinder replated by millenium technologies.
The bike made this ticking going into it, partly caused by piston slap. And when I finished, there was still some ticking, just not as loud anymore.
Except lately, the ticking has become more intermittant, and its producing different tones in the ticks. Everything is in spec. Valves are adjusted, and manual decomp is adjusted.

My question is, has anyone had any issued w/ the manual or auto decomp on these bikes? I'm really leaning towards it, because if I pull the manual decomp lever in ever so slightly while the bike is idling, then the tones of the ticks are varyed w/ how much the lever will move at each pulse. Obviously kind of hard to explain this.

Mostly, anyone know of any decomp issues on these bikes? The shop manual is no help; it says nothing more than how to adjust the manual decomp.

  • needsprayer

Posted June 18, 2006 - 04:43 AM


Do you think is it related to engine temperature? Is it possible that exhaust valve seating changes are causing this intermittent noise?

  • Thumpmeister

Posted June 18, 2006 - 03:46 PM


Do you think is it related to engine temperature? Is it possible that exhaust valve seating changes are causing this intermittent noise?

I don't think so because when I did the rebuild last summer, I had the head machined, and the valves ground to match.

If it was the valve seating, wouldn't that cause a slight loss of power due to gasses leaking? Just wondering...

  • needsprayer

Posted June 18, 2006 - 04:08 PM


Since you had that done I would look elsewhere.

  • Thumpmeister

Posted June 20, 2006 - 02:07 AM


Man, all these years, I knew there has been something funky w/ that stupid auto decomp, and I finally found out that there IS an issue w/ it.

If anyone is interested, follow this link, and check the bullitin at the bottom of the page.


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  • HawkGT

Posted June 20, 2006 - 02:42 AM


Off topic, but the F3 front end on this thing is sick. Neat website--haven't seen it before.

Posted Image

  • Thumpmeister

Posted June 20, 2006 - 09:54 AM


Yeah, it is a sick bike. Actually, the way I found it was on ebay; he's selling the bike. Go unter ebay motors, and type in 'xr650r', and this will come up. Pretty cheap for what he's done to it.

  • weskc35k

Posted June 20, 2006 - 11:01 PM


I put risers with J Button high bend on my pig and in tight right handers it ticked and stopped till i reset the decomp cable.
That Honda Xr650 site is awesome,to raise some compression do you think i could add some weld to the centre left side(facing) of the squish dome in the head without warping the head if i went steady .

  • itsnotajeep

Posted June 21, 2006 - 10:53 AM


Okay......So after Soboba destroyed my 650 this year.....I did a top end....and had a simliar weird ticking noise.....Turned out the Auto Decomp. was throwing 180deg backwards....and making some pretty bad noises!! Best solution......HRC cam.....I opted for the HotCam....and wish I'd just done the HRC.....or have the oil-hole welded on the stocker.

Keep the shiny-side up!

  • Thumpmeister

Posted June 22, 2006 - 12:04 AM


Why do you prefer the HRC unit over the Hotcam unit? The HRC unit is over double the price, and what do you gain?

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