1979 YZ250 Engine Rebuild

[baseballpro3112]

Hi,

I have a '79 YZ250 that I think needs new rings. I can get it to start on the first few kicks, but it smokes like crazy when it is running. I fogged up our whole valley with just a few minutes of riding. I haven't been able to do a compression test, but I think that the compression is a little low. If anyone could give me the regular compression for it in PSI, it would be greatly appreciated.

Thanks

[JUST ME!]

Hi,

I have a '79 YZ250 that I think needs new rings. I can get it to start on the first few kicks, but it smokes like crazy when it is running. I fogged up our whole valley with just a few minutes of riding. I haven't been able to do a compression test, but I think that the compression is a little low. If anyone could give me the regular compression for it in PSI, it would be greatly appreciated.

Thanks

Throw a set of rings at it if you like but does not sound like the problem! I use to mix my fuel at about a 25:1 ratio. Or 40 mls/litre. With this much smoke it has too much oil or the oil is seperating from the fuel whist bike is sitting.

Always a good idea to mix your fuel as you need it. Don,t leave mixed fuel sitting around. Oil and oil soaked carbon deposits may have collected in the expansion chamber.Remove exhaust system from bike.Remove silencer from exhaust. Have someone with oxy/acetylene gear heat the first inch or so of pipe, where it connects to the barrel, until metal begins to glow in a ring formation around end of pipe. Sit system on concrete floor. Turn acetylene off and oxygen on full. Hold oxy torch in glowing end of exhaust. You will see the glowing ring around pipe slowly continue to travel along the length of the exhaust. Takes 5-10 minutes to complete. Very impressive to watch if you have never seen it done before. Allow pipe to cool and DO NOT quench. Stand pipe on end and a masive amount of rubbish will fall out of it! First time you see it done you will think the pipe is going to gett hot enough to cave in,trust me it doesn't. Do this in a well ventilated area as it makes a large amount of smoke!

[JUST ME!]

Throw a set of rings at it if you like but does not sound like the problem! I use to mix my fuel at about a 25:1 ratio. Or 40 mls/litre. With this much smoke it has too much oil or the oil is seperating from the fuel whist bike is sitting.

Always a good idea to mix your fuel as you need it. Don,t leave mixed fuel sitting around. Oil and oil soaked carbon deposits may have collected in the expansion chamber.Remove exhaust system from bike.Remove silencer from exhaust. Have someone with oxy/acetylene gear heat the first inch or so of pipe, where it connects to the barrel, until metal begins to glow in a ring formation around end of pipe. Sit system on concrete floor. Turn acetylene off and oxygen on full. Hold oxy torch in glowing end of exhaust. You will see the glowing ring around pipe slowly continue to travel along the length of the exhaust. Takes 5-10 minutes to complete. Very impressive to watch if you have never seen it done before. Allow pipe to cool and DO NOT quench. Stand pipe on end and a masive amount of rubbish will fall out of it! First time you see it done you will think the pipe is going to gett hot enough to cave in,trust me it doesn't. Do this in a well ventilated area as it makes a large amount of smoke!

Further to this reply. You will now be surprised by how light the exhaust system is compared to when it was dirty.Whilst exhaust is off turn motor over with kick start until piston is high enough to cover exhaust ports. then clean buildup out of port. Don't scratch piston.Makes a very noticable difference to performance of bike. As far as compression checking nobody bothers. You can tell by the pressure required on kickstarter. Besides you say it starts easy. ALL THE BEST!