Hi all, I am new to the forum. I have been searching through the threads here and can't seem to find an answer.

I have my sisters TB 250 I am going to fix. First with the problems... It starts very hard, i.e crank and crank and crank and crank. Once it starts it will not idle, warm or cold. Once running it feels underpowered from normal and very dawgy. It runs like a chainsaw with a split fuel line, if you've ever experienced that. Really only wants to start if you hold the throttle 1/2 to 3/4 open.

Possible contributing factors. Ever since my sister and grew up and moved out the four wheelers don't get ridden much, they usually sit close to 6 months (not stored properly) with only my dad occasionally moving them. When I first got on it after I heard it wasn't running right, the oil light was flickering. Of course i dumped some 2-stroke oil in it right away, although it wasn't empty I'm worried somebody might of been riding it and possibly starved it for oil.

Anyway after adding oil I rode it and confirmed the problem. I then checked for possible vacuum leaks from the carb to the crank case. everything was tight and I didn't see any splits or issues with the rubber. I then cleaned the carb and briefly checked the fuel line for flow. After all that the issue remained the same.

I think my next step will be to give it a compression test. I am thinking maybe it is time for a top end? or maybe it is the crank seals? ( I have heard these can dry out and crack, especially if not stored properly) Has anybody had a similar issue or have any ideas on what else to check?

Oh yeah, I also checked the spark with an actual spark checker (one of those spark plugs with a very large gap) and it seemed good.

 

id start with a compression check then move on to a good carb cleaning especially since u say it sits for months at a time...o and maybe new fuel and oil...maybe even eliminate the oil pump and pre mix

 

welcome to the forum. yes the first thing to do is a compression test. it needs to be at least 100 psi or you might as well planing on a rebuld.

 

Exactly what I was thinking. Is this typical behavior for a worn out top end?

 

Pretty typical. Hard starting,wont idle,sometimes may backfire,or may run good for awhile then bog down and die. When cooled down will restart.. Check compression,if 115 psi or less,time to check into at least a top and,possible crank seals,plus lower engine rebuild.

 

Thank you! I will post up compression numbers after I check it. Will probably be a few days.

 

Thought I'd give you guys an update. Turns out it was starved for oil. I didn't mention this before, but I work out of town for a couple weeks at a a time. When I came home all the expensive Polaris 2-stroke oil was on the floor of my shop. So pretty sure it was being ridden around without any oil in it. Anyway compression test showed low numbers so the cylinder is out getting measured for taper/out of round and will be bored if required. Just waiting to hear back from the machinist on his measurements. Oil was leaking from a damaged hose on the motor side (not from the oil tank).

 

While the cylinder is of I'd check for any up and down play on the rod and any bearing noise as you roll the rod around! Side to side play is ok,but NO up and down on the rod. If there is a new rod and lower bearing will be needed to be installed and the crank would have to trued up. This is just to keep you from spending money on a top end and have the rod go out next which can take a brand new piston and cylinder bore out with it.Especially since it was starved for oil.