mysterious loss of compression

[paint it black]

i hadn't rode my '88 280 for 2 weeks,so thought i'd give it a little run today,

tried to kick it over and there was hardly any compression,it was like i had the

decompression lever pulled in,

my bike usually starts in 2 or 3 kicks but today it just wasnt happening,

first thought was there was a problem with the decompression mechanism,

ive got the kickstart cable removed but still got the manual lever,so disconnected

that as well which made no difference,then did the valve clearances,although

i only did them a couple of months back,that made no difference,still no compression,

and still not getting close to starting,then got my mate to push me up and down

the road until it eventually fired,after that it ran fine and the compression returned

to normal,so what could have caused that? not had a problem like that before,

was rebored less than 6 months back and usually got very good compression,

so what happened,any ideas,

[mcnutty]

Could it be that possibly a valve was stuck open from sitting for two weeks that way? I don't know if i'd worry too much about it...it's your bike's way of telling you you need to ride it more!

[ATJ_Number_1]

Could it be that possibly a valve was stuck open from sitting for two weeks that way? I don't know if i'd worry too much about it...it's your bike's way of telling you you need to ride it more!

Thought the same thing but he checked the valve clearances and one would have been way off if stuck open.

[Paul47]

Clutch stuck in the disengaged position? In other words, you weren't even turning the engine over? Might be telling you your clutch needs attention.

[ATJ_Number_1]

Clutch stuck in the disengaged position? In other words, you weren't even turning the engine over? Might be telling you your clutch needs attention.

lol, how does that work? A bad drive clutch would not stop the engine from turning over.

Edited April 4, 2010 by ATJ_Number_1

[Perc82]

I've heard of this a few times before. After setting up a while NO compression?

The suggestion from "creeky" has been to add a little oil to the cylinder to help the rings seat.

This has worked well in the past for me too!

Although… I do still wonder about the clutch sticking on the cam's auto decompressor, because I’ve had this happen to me while on a riding trip??

[Chuck.]

I've had this happen on other bikes. Oil helps the sealing of the rings and when an engine sits for a long time the oil drains off the rings and bore. Push starting or a little starting fluid will get them running. A good high quality MC dyno oil will reduce the tendency (dyno oil has more cling than syn).

[paint it black]

well it was back to itself this morning,second kick,

think i'll start it every week from now on,

with work and doing up the house spending "quality time" with the wife

and a riding buddy who has less spare time than me,i only get to use it about

once a month,every weekend would suit me better,but thats the way it goes,

thanks for all your input

im using 10/40 semi synthetic diesel oil,could that have caused the problem?

[taggkent]

im using 10/40 semi synthetic diesel oil,could that have caused the problem?

Uh-oh, que long and boring oil thread lol

[Paul47]

dyno oil has more cling than syn

I read it was the other way around, heh.

I don't believe the rings theory. To me Perc82 has the answer, the overly-complex auto-decompress cam mechanism. Something malfunctioned or stuck there.