1985 mxc250

klrroo

klrroo

Member
I finally found the project I was looking for. 1985 KTM mxc 250. Rads are mint, inverted forks are mint and everything works. It also goes like a raped ape. I have a new seat coming for it and the rest is in excellent shape. I will need to pick some brains here for some info as I am a KTM newbie.
 

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klrroo

klrroo

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Actually I already have a question. What mix and ratio should I be using in this? I know, I know but I am a 2smoke newb. :hb:
 
klrroo

klrroo

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It is surely mixed gas, no oil injection :(, have to get used to mixing. I have heard 40:1 is a good start to see how it runs and go from there. I am getting 180psi in the cylinder so that seems high enough, surprising as it sure looks like the motor has never been open. If anyone can find me a skid plate you would be my hero. :hb:
 
O

old trials guy

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I don't think this bike is injected. The last injected dirt bikes I recall were the old Yamaha DT series, old Honda MT series and Suzuki TS series. As most manufacturers migrated to four stroke technololgy for dual purpose and recreational bikes the injected models disappeared. Most modern two strokes and especially competition two strokes use premix.

Opinions will vary but the manufacturer probably suggested a really low ratio of 20 or 25 to 1. With the oils available today you could run a high quality premix like Maxima K2 at 50:1. I run my trials bike a 80:1 and many run Optimal at 100:1.

I think you would be safe to start at 40:1 using a racing two stroke oil and if you are getting excessive plug fouling and carbon build up drop it to 50:1.

Also you might call the folks at Holeshot or Spunky's both of which are KTM dealers and I am sure they will give you good advice.

Keep in mind that oil ratio inverselyeffects the fuel air mixture ratio. More oil means less combustible fuel and as you reduce the amount of oil (higher gas to oil ratio) you are slightly richening your fuel air mixture. This might call for some minor jet changes if you radically alter the oil mixture.

I hope this help.....otg
 
klrroo

klrroo

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There are holeshot stickers on the bike so I guess that is where it came from, I will contact them and see if I can get some info/parts. I will try 40:1 and see how she blows. :hb:
 
250ccforme

250ccforme

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Didn't realize 2 smokes went from premixed to oil injection then back to premixed. :shock:
 
klrroo

klrroo

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Hello all, having a problem with the low end and idle on this bike. It runs fantastic on the mid to upper end, but it won't idle unlessI feather the choke. Any advice? Thanks
 
flyn

flyn

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Very common for the pilot jet to get clogged on bike that sit for extended periods of time, dismantle the carb and let it soak in some intake - emission cleaner, If you try to remove the pilot jet be very carefull, they are usually seized in. Do not try to put a wire or torch tip cleaner thru the pilot jet as the size is very critical, best to soak it and use compressed air.

Good luck ,

I had a 1975 KTM 250 GSback in the day, Great bike, I know yours will be to!
 
klrroo

klrroo

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I cleaned the carb, removed the pilot and soaked/cleaned it but still acting up. The bike spontaniously revs high so could that be an indication of alean condition? My carb boot to the motor is in bad shape and cracked up and siliconed, could air be leaking in and causing a lean condition and the problems with idle and reving? I have a new carb boot coming from fleabay so I am hoping that helps. I am sure learning a lot about 2 strokes, very simple bikes and you gotta love that powerband hit! :clap:
 
S

sagot

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You might also have a leak in you crank shaft seal on the dry side. This can sometimes cause problems down low.
If you can get to it try spraying some WD40 or ether at the seal while the bike is running and see if there is a change in RPM.
Sometimes the seal can be replaced by carefully hammering a sharp screw driver in and prying it out. You then need a big socket to tap it back in. The socket must contact the seal near the outer diameter.
 
klrroo

klrroo

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Interesting, I will check that too tonight. I think I am getting down to it as there is not much to these bikes. As soon as I get the idle and low grunt worked out I am doing the brakes front and back then putting the new seat on. She will be a pretty sweet bike after that, then I have to decide if I am keeping it or selling it! Thanks for the info! :hb:
 
klrroo

klrroo

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Thanks, I thought it was a good find and would be fun to work on.:hb:
 
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