GoonSquadCDR

Member
Mar 28, 2016
2
0
Hey guys, I understand that I have only just joined your group, but I really need some help. I have an '03 YZ125 for my boy, 12, and it will not start. Back story...Seized the crank a while back running way too hot and way too lean. Split the cases, replaced the bottom and top ends. All new hardware, software, everything. Put it back together and it started right up, ran for a bit, around the block and died. Had some old gas residue in the bottom of the tank, gummed up the carb. Cleaned and cleaned and totally rebuilt and cleaned the carb, everything is in working order there. Thought that was the issue but slapped the carb on my RM250 and it ran. Unhappily, but it ran. Now the YZ won't even bump start, kick, nothing. Reeds are good, carb is good, plug is good(tried BR9EG and BR8EG), compression is 165#, even repacked the exhaust. I don't know what else to try. Kill switch is not stuck, stator is good with strong spark, everything is moving freely and by all accounts, should work. Really want to get my boy back on the bike, and I don't have money for another one. Any ideas would be appreciated. Thanks
 

truespode

Moderator / Wheelie King
Jun 30, 1999
7,945
242
Did you replace any fuel lines?

I once had a DT 100 and the vent hose on the gas cap came off so I replaced it with the first hose I could find. It was too small and didn't vent well so it held the gas like when you put your finger on top of a straw. The gas would trickle so it would fire up and use what was in the float bowl then die.

Check the hoses for any obstruction.

Also, have you tried putting some premix in the head, put the spark plug back and see if it fires? If it does then it is a fuel delivery issue of some sort. Even though you cleaned the carb it is good to check the movement of the floats to see if it is stuck and not letting fuel to the float bowl.

Ivan
 

GoonSquadCDR

Member
Mar 28, 2016
2
0
Did you replace any fuel lines?

I once had a DT 100 and the vent hose on the gas cap came off so I replaced it with the first hose I could find. It was too small and didn't vent well so it held the gas like when you put your finger on top of a straw. The gas would trickle so it would fire up and use what was in the float bowl then die.

Check the hoses for any obstruction.

Also, have you tried putting some premix in the head, put the spark plug back and see if it fires? If it does then it is a fuel delivery issue of some sort. Even though you cleaned the carb it is good to check the movement of the floats to see if it is stuck and not letting fuel to the float bowl.

Ivan
I didn't pull any fuel lines to begin with, but figured for a few bucks I could replace them all. So I ordered a new tank vent hose, carb overflow lines, and hoses to and from the petcock, all OEM from motosport.com. Every time I pull the carb, I end up dumping about a float bowl worth out, so I figure I am getting fuel to the bowl. Pulled the plug like you said and tried a little fuel in the head, nothing. Tried starting fluid (just once, just to see if it would fire) nothing. I really don't know what could be keeping this thing from starting besides some kind of voodoo magic. I got enough spark to light myself up, all the air I could want and I put fuel directly into the head... Checked compression again, just to make sure I wasn't hallucinating, 165#. I am truly at a loss. I'm no master mechanic by any means, but it's a single cylinder 2 stroke, not the most difficult engine work I've done. I'm just tired of disappointing my boy. I may just need to bite the bullet and take it to a shop. Thanks for the input.
 
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