Two Stroke Motocross

Two Stroke Motocross Forum => Vintage Two Strokes => Topic started by: 1979YZ on September 08, 2011, 09:22:33 AM

Title: 1979 yz 125 wont start. Help?
Post by: 1979YZ on September 08, 2011, 09:22:33 AM

Hello everyone,

I just had my 1979 yz 125 rebuilt both bottom and top end

when i put the engine back in my bike it took MANY kicks to start it
-when it finally did it ran BACKWARDS
-i heard this is a timing problem to i have been playing around with it and cant get it to start still
-i matched the notches in the timing 2mm before TDC
-There is a spark
-compression
-fresh gas
-clean carb
-no start, doesnt even try

I tried tipping the bike over and emptying any excess fuel from the cylinder
-this worked and a good amount of fuel came out
-still wont start

does anyone have any ideas of what i should try?

thanks!!!!

Title: Re: 1979 yz 125 wont start. Help?
Post by: SachsGS on September 09, 2011, 07:03:22 AM

Check your compression - you should see 150+ PSI.

If you are certain your ignition timing is in the ballpark you may have a CDI that is failing.

Title: Re: 1979 yz 125 wont start. Help?
Post by: ford832 on September 09, 2011, 10:20:45 AM

What sachs said.Also,it's more likely to kick back and do this if the timing is too far advanced.Try it at TDC and go back some from there to see if you can start it.It's best to mark it before you take it apart.Once the deed is done,it's best to find TDC with a dial gauge as factory marks are notoriously inaccurate. 

Title: Re: 1979 yz 125 wont start. Help?
Post by: ridered125 on September 23, 2011, 09:33:50 AM

I have a 79 YZ. The stators on these bikes go out and they will act like you are describing. If the stator is stock, it may be bad. I bought an aftermarket stator and it worked fine. Also, if you install the stator backwards it will act like what you are describing.

I had to turn the bike upside down and pump it out like you are describing.