87 KDX200 Help Needed

[Tomthesparky]

Morning gents,

 Have nearly finished the build up of my old KDX200, when i purchased this old girl someone had previously bored and sleeved the barrel for a 240 kit, there is no evidence of the head being modified in any way to suit this. My question is could this cause the compression to be to excessive to run properly/ start easily.

 in the long run i would prefer to go back to the standard plated barrel however the budget is not there at the moment

[80-85 husky]

Friend has lots of dx's inc 240's. he jetted his a bit richer and its running fine, others have issues and try head mods, its the shape which causes detonation...another solution i have heard is the exhaust stinger is too small causing overheating and possibly the detonation.. GMC has a pipe or is making one to suit? plenty of discussion on this one.

[Tomthesparky]

Cheers,

 Was a little concerned, only way to get it to start is to get towed and even then is locking up until i get it in 6th. Still yet to sort out the jetting properly it is currently very rich.The original carb was trash and for now have a fake air striker 35 on it so pretty much starting from nowhere (not quite have changed the jets to 88 specs which had a 35mm kiehin flat slide).

 As for the compression it feels distinctly harder to kick over than a mates TM300.

if anyone has a good/ replatable air cooled KDX cylinder give me a yell, not entirely keen on the big bore thing

[80-85 husky]

something is decidedly off there...they arent much different to kick than the 200...try a second head gasket in it. it should start 1st or second kick off the choke

[80-85 husky]

jump on to the ozvmx facebook page, all the knowledge there should help or a dedicated kdx page, there will be plenty of assistance past my limited experience.

[bazza]

Try 80-85 husky method with xtra head gasket, cheap way to see if less compression helps

[TT5 Matt]

is the piston crown touching the head?try kicking it over with the sparkplug out

[Hoony]

is the piston crown touching the head?try kicking it over with the sparkplug out

......................  only way to get it to start is to get towed and even then is locking up until i get it in 6th ........................

as TT5 Matt said Times 2 , i was thinking the same. is it an air or water cooled mode? if water cooled is water getting into cylinder causing a hydraulic lock ?

[Tomthesparky]

Thanks guys,

 TT5 Matt i had the plug out and she turns over freely, when i was assembling i did check i had clearance, i was a little cautious of that as i already had to take a couple of mm of the bottom of the piston skirt to clear the cases, have ordered another head gasket to drop the compression, but i think the long term solution will be to get the head machined to suit
 
 Have also ordered a genuine PWK to see if that sorts out the jetting issues, it currently runs very rich at idle which i have tried to fix by going smaller on the pilot (air screw seems to do nothing) but now have it running very lean once on the pilot. I am not sure if that is a symptom of the high compression or the junk Chinese carby.

 Will keep you posted on results

[Tomthesparky]

 OK so a genuine PWK was fitted and already have an improvement in idle quality. Will be fitting an extra head gasket and then on with the jetting saga.

[Tomthesparky]

SOOO,

 The headgaskets i bought are not the copper type and are for a standard bore. Bit the bullet and pulled out the dremel, and took some material off the head, basically laid back the original step/ radius from the quench area to the combustion chamber into a smoother transition, not great but has dropped the compression a bit. Unless someone knows more about 2 stroke quench to bore ratios and is willing to share i am not going to go any further.

 Will Having high compression make the bike not want to idle? I have the idle screw all the way in and still cannot get the  ###ing thing to idle? I am currently running a #42 Pilot in the carb would that be too lean?

[Momus]

If you are using composition head gaskets meant for a standard bore there is a good chance that the piston is hitting the gasket- possibly across the pin axis.

Have you measured the compression ratio?

[Tomthesparky]

Sorry, should have mentioned that it is currently running a copper gasket that is bore size. Have not measured the compression, it just feels very high by my foot.

[TT5 Matt]

to workout what comp ratio you have go to 49ccscoot.com and search calculating 2 stroke compression ratios.theres step by step guide to going it with little cost/equipment needed

[Momus]

Sorry, should have mentioned that it is currently running a copper gasket that is bore size. Have not measured the compression, it just feels very high by my foot.

Might be a good idea to check your copper head gasket. They are not always accurately made and if neat for the bore diameter only need a smidgen of misalignment in the studs for the piston to kiss it. This contact can be  soft and feel like big compression. A rule of thumb might be the gasket bore 0.5 mm larger than the cylinder.
I fairly often make copper head gaskets for the small Honda's I play with and have learnt that chasing max compression and mixture usage by tightening the dead space formed by the gasket crevice can catch you.