I'm not a softy ... :-)

[JanBros]

Another from Stewart archives

I know for a fact he was running 15:1 then
so 35cc = 15:1. 


"am running a 35 cc cyl head volume  right now stock is 42 cc  i have tried down to 29 cc"

you wouldn't happen to know if that is with or wihtout the plug hole ?

even with it, gives my 32.7 already quite a high compression ratio, and if that's without the plug hole even more ?
would explain a lot ...

[Motorrad]

http://www.csgnetwork.com/compcalc.html
Playing around with this link. I'd venture to say your around 16.5-17:1
every engine builder I have ever known (including myself) always cc the head WITH the spark plug # you plan on running INSTALLED

[dave916]

what year is your engine?  looks like 86-87,  the 86 run a bit higher compression and wont have any decompression slots in exhausts sub ports, also a later dome piston may up the the compression a little , not sure how to accurately calculate the compression ratio with a dome piston and do u alllow for ur 1mm head gasket and 0.5 gap the piston usual has to TDC ,
if u are running a too high compression ratio u will get pinging at low revs

i think u have a problem  with decom valve , the valve is not beeding enough compression or the hole in the head is to small , [try kicking over with valve not instaled]

[JanBros]

what year is your engine?  looks like 86-87,  the 86 run a bit higher compression and wont have any decompression slots in exhausts sub ports,

I believe it is the very first watercooler (only 2 Kips, no middle one, and the front sprocket is hold in place with a nut as oposed to a circlips on all the later ones), so before 88 ? engine nr is KX500BE004221

 also a later dome piston may up the the compression a little , not sure how to accurately calculate the compression ratio with a dome piston and do u alllow for ur 1mm head gasket and 0.5 gap the piston usual has to TDC ,
if u are running a too high compression ratio u will get pinging at low revs

it has a flat piston. no headgasket, I putted an O-ring in it.

i think u have a problem  with decom valve , the valve is not bleeding enough compression or the hole in the head is to small , [try kicking over with valve not instaled]

without the valve it's a bit easier, allthough still very hard compared to my txin 250. Never had a 500 2-stroke before, so I have no reference as to what is normal and what isn't .

[dave916]

a 500 single  two stroke is going to be 10x harder to kick over than a 250 twin
the 86- 87 is going to be harder kick than  the later kx
i think the 86 came as with a single ring ,flat top piston , fitting a later 2ring [slight dome] piston will also make it harder to kick
fitting no head gasket is also going to make it alot harder, maybe try running a 1mm gasket if compression is too high
[do a compression test]

if it kick over easer with decom valve removed ,it  probable mean the valve is not bleeding enough compression, try a different valve
 a 500 single will needed to be kicked over from TDC to start, kick the bike over slowly on compression stroke stop around tdc and then one good kick, there is loads of info on how to start a kx http://www.kxriders.com/forums/index.php/topic,2169.0.html

[JanBros]

finaly she came to live today   

couldn't get more then some flames out off the exhaust, so started thincking the ignition timing was wrong, allthough set like in the owner's manual.
made a tool so I could spin the cranck with an electrical drill and with the stroboscope it was clear she fired too late . gave her a lot more advance and she fired up 

http://www.youtube.com/watch?v=YogBS5Er3Lg

from 30sec's on, you can see a special anti-wheely-device apparently build into the engine , didn't know off that, first time I've seen it ... 

so just checked if the woodruff key was still ok - it was - and only then I saw these ignition-marks (I thought it had to align with the mark on the cases)



with which one it is supposed to align ?
 

[dave916]

from 30sec's on, you can see a special anti-wheely-device apparently build into the engine , didn't know off that, first time I've seen it ... 
funny  , maybe you need a bit more preload on forks to compensate for lighter engine

http://www.youtube.com/watch?v=YogBS5Er3Lg  would like to know how  2 exhaust silencers will have on the power??

[JanBros]

  would like to know how  2 exhaust silencers will have on the power??

I don't know, and it's not my main concern at the moment. Power will already be a bit down with the cut-and-re-welded expansion. I made the twin silencers to try and keep the noise down