Ok so we have this Baja Wilderness 250 ATV that has been sitting in the garage. We just moved to Alberta from Ontario and the ATV was not running when I got here. So a week ago I figured I would try to get it running. I have never tore apart an ATV before or worked on one, but I am not stupid and I do have some knowledge of how a motor works and am good with my hands.

So, the owner, which is my GF's mothers fiance, told me that it was getting blow back and popping out the carb. So when I was turning it over, sure enough it was blowing gas out of the carb. He said he tore it down and messed with it but still got the same results. After some messing around with it I decided to tear the head off.

After I got the head taken apart, I realized I didn't set it to TDC, so I had to take off the cover on the left side of the engine and also take off the stator or magneto thingy or whatever it is called to see the F/T marks. There is no visible marking or line to line up the line for the T mark on the casing or anywhere, so I just assumed it was supposed to be at 12 oclock directly straight up and the piston sitting at TDC confirmed this for me. So after I did this and inspecting the jug/piston/rings everything seemed to be in pretty good shape as far as I could tell so I put it all back together. At this point I had to put the cam sprocket back on and the only way I could line the sprocket up was at 12 oclock with both valves closed. I tried to line up the mark on the sprocket with the pointed mark on the casing but I could not get it to line up perfectly. So I just said whatever and put everything back together.

I tried to start it and it was still getting blow back through the carb. At this point I am thinking the exhaust valve is not opening all the way or something. I do not have a set of feeler gauges handy so I can't set it to proper specs, nor do I even know what they are. So I adjusted it and left a very small gap, a slight wiggle and tried to fire it up, no go. For the hell of it I just tightened it down so it is touching the valve spring all the time. Tried to start it and it fired right up. So I took it for a spin down the driveway and back and it had no ***** at all, full throttle and nothing just bogging along. It could barely make it up the driveway. So today I decided to double check the timing, and of course it was off. I think I screwed up and put the chain on wrong and had some slack on the exhaust valve side. So I re adjusted everything, put on the tensioner and tried to fire it. Won't start. Give it some throttle and it will start, barely, and only run if I give it some gas, as soon as I let off throttle it dies. Keep in mind when I do give it throttle, it is very poor, not revving high just sounds like crap and boggy.

At this point I don't know what to do. Last night it was actually moving, but with no guts at all, very sluggish and no power. And today it just won't even start lol. Anybody have any tips? I am sort of thinking timing is somehow off, even though I know it is as best as I can get it.

Pretty soon I am just going to give up on it. At least I know when I buy my own atv it won't be one of these chinese bikes.

 

Okay so I tightened down the exhaust valve more than it should be and it runs. Choke all the way to left, will not fire, choke all the way to the right and it will fire.

If I tighten it down too much and try to pull it is very easy to pull as if there is no compression, which is understandable, I am assuming the valve is open when it should be closed. If I back it off a bit I can find a sweet spot where it will fire up, If I back it off to the point where there is a bit of a wiggle and a very very small gap it will not fire and it is very hard to pull on the pull start. Would this be a bent valve or is my timing screwed up. I read that if a valve is bent it won't run, and it will run if it is tightened to the point the valve is almost being pushed open.

 

This makes no sense to me. How could pushing a valve open make it seal better? Where did you read this?

Keep in mind, I'm *not* and expert on engine rebuilding, but I do have some common sense, and this flies in the face of common sense... . If a valve it too tight you lose compression. If a valve is too loose you get valve clatter noise - but it still runs albeit a bit noisy.

I'm wondering if you've got your valve timing incorrect. A quad will run with the valve timing off one tooth - but just barely.

 

What I mean is I read if a valve is bent it won't run. But if I tighten the exhaust valve down so it is putting pressure on the valve but not tight that it is always open it will fire.

 

I had a CN250 which ran with the timing off a tooth. It would start, run, throttle up, but had no cajones. BUt, once I got it dialed in, it was a whole nother machine.

I recommend properly setting the valves. You should be able to google the appropriate settings and get yourself the feeler guage. YOu can't really eyeball that one.

What's your compression reading?