whats happening with my 85 xj700??

im out riding with my girl. evry thing is great. after about 50 miles i noticed a slight stutter upon take-off. no biggie. i head home on the interstate. around 75mph. i get home bike running great. the next morning i attempt to start my bike and there is this horrible tap/knock. the compression sounds different. strange. i start again it starts...barely. then bam runnin beautiful. sticky valve? been sittin a while. the next two days no prob. still small stutter at take off. then tonite i get off interstate park my bike and about 45 minutes later start it and horrible taps again. i keep cranking sounds like i tjhrew a rod bang bang then all of a sudden bike fires i here an intermiddent tap then that stops. WHAT HAPPENED any advice greatly appreciated thanx all...

 

Sounds like somethin may be up with your TCI. Firing at the wrong time or mis firing occasionally.

I'm sure more will come in with thoughts. My bike sounded the same just this week when i had messed up my TCI

 

Probe the Engine to isolate exactly where the noise is originating from.

Buy a Wooden Dowel, cut a length of Fiberglas Driveway Marker, a Broom or Mop Handle.
Hold the Probe like a Ski Pole. Place one end of the Probe on the Engine.
Put your fist around the opposite end. Apply pressure on the Probe with your thumb on the End of the Probe.
"Listen" to the Probe.
Place you ear on your thumbnail and actually listen to the Engine.
Make notes.
The noise is located at this spot.
Knock, vibration, rotational, scraping sound ...

Isolate where the noise is coming from.
Rule-out exhaust leaks.
Check Mounts.

 

the tap is coming off right side of engine. when i was turning it over you could actually feel the knock and hear it. definatly internal. not exhaust. wont start when tapping hard. when running its running good. just went to store run great.tho i did have to turn my idle up.

 

Also the Vapor from
http://www.trailtech.net/85-704.html and then get a dashboard
around 150 for everything you need

 

How many miles are on this bike, and when did you last check the valves?

It very well could be a sticky valve; I wouldn't keep running it until you figure it out.

 

Yeah, +1 for valves.
Pull the spark plugs on that side and you may find
some indication that a cylinder is not running as
it should.
Tiiming chains wearout but that would sound like a
rattle or marbles in a can and come from the top center
of the valve cover.
A long shot but.....while the valve cover is off check bolts
holding the cams down, they may not have been torqued
corretly.

 

my bike has 20000. ive never checked valves. bought it,cleaned carbs and running great since. i think it has to be a sticking valve. i wonder what caused that??

 

At 20,000 we can rule out a worn-out Cam Chain.
The working life expectancy of the Cam Chain is 55-60,00 miles.

Slack is possible.
Remove the Cam Cover and try lifting the Chain off the Bridge between Cams.
Do a Manual Resrt of the Cam Chain for "Insurance" ... peace of mind.

If the noise persists ... try Unplugging a Spark Plug Cap to each Valve in turn, to see if the Noise changes or stops.

A Big-end Bearing that has "Spun a half-shell" will guiet-down with No Spark to the Hole.
You'll be able to Probe the Crank area and detect a Spun Bearing or hear it ticking without a big loud knock.
Reattaching the Plug will make the Knock reappear.

 

The valves need to be checked and have their clearances adjusted if necessary every 5000 miles.

They tighten up as they wear. A dead-tight valve will open too soon and be in the exhaust stream way too long also. That can lead to sticking.

NEGLECTING regularly necessary maintenance would be what could have caused that.

 

thanx guys. i just removed my cover. nothing noticable. oiling real nice. clean. getting ready to read the valve threads and adjust. by the way, bike running good. im thinking my valve got hot and stuck upon cooldown on both occasions. also put my ear on yamaha side cover and could hear noise. probably normal. will keep evryone posted.

 

damn... where to get special valve tool?

 

chacal, Bike Bandit, chacal, Amazon, chacal, Old Bike Barn, chacal...

Actually just about anywhere that sells motorcycle stuff. I forget where I got mine.

You do realize you can't SEE the valve, even the top of it, in an XJ motor, right? The sticking part is right IN the combustion chamber, it's not a visual inspection.

You found this already, right? http://xjbikes.com/Forums/viewtopic/t=14827.html

 

yeah i knew that about the valve. just meant no metal shavings, etc... the noise was that bad. anyway i did the ol stethiscope trick and i have a tap in my far right exhaust valve. tap..tap..tap gotta get tool and do valves. just cant believe how good it runs after all the noise. i really thought i slung a rod at first