Maintenance & Technical > KX500 Original
I'm not a softy ... :-)
JanBros:
--- Quote from: Motorrad on April 22, 2010, 10:12:44 AM ---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"
--- End quote ---
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:
--- Quote from: dave916 on April 23, 2010, 09:12:53 AM ---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 .
--- End quote ---
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
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