It has a carb issue - you had to hold the throttle open to start it because the crankcase was flooded with gas - gas pouring out of the carb was a sign that the carb was having a problem and not controlling the fuel level inside the float bowl.
1987 Trail Boss 250 4x4 Won’t Start!
Hello!
I recently purchased a 1987 Trail Boss 259 4x4, it had been used for plowing and then passed around and mostly sat for the last 20 + years.
PO said the oil injector was not working, so for a while I was prefixing. After much tweaking I got it running, really good too! Recently came across an issue where it was bogging when I hit higher rpms, thanks to this thread and some others, I was able to unplug the rev speed limiter and it ran better than it ever did for me! At the same time that I unplugged the wire for the speed limiter, I noticed the line for the oil to the carb was connected to nothing.. so I popped it onto the carb, filled the oil, and it was working.
Took it for one test ride, ran great. Maybe 10 minutes after I parked it I noticed gas just absolutely pouring out of it. It wouldn’t start until I held it wide open for a minute minimum, and then the second it dropped in rpms it would die, and now it won’t start at all.
I couldn’t help but feel like it had to be connected to something I did, but I don’t know how it could be. Took the head off, the bolts were looser than they should be, but the head gasket seemed fine.
Base gasket was obliterated, piston has play in the cylinder but no scores or marks and the ring gaps definitely out of size, the crank case had gas in it, and the exhaust pipe also leaked gas when I removed it and flipped it over.
so I’m getting the cylinder bored, and getting a new piston and rings.
My question is, does it seem like I’m on the right track? It feels so coincidental that this would randomly die in the blink of an eye but I know that’s how these things go sometimes.
Any help or insight would be much appreciated!
Also for extra info the crank seals are freshly replaced, carb is clean, can’t think of anything else relevant I’ve done to it.
Thanks!
I recently purchased a 1987 Trail Boss 259 4x4, it had been used for plowing and then passed around and mostly sat for the last 20 + years.
PO said the oil injector was not working, so for a while I was prefixing. After much tweaking I got it running, really good too! Recently came across an issue where it was bogging when I hit higher rpms, thanks to this thread and some others, I was able to unplug the rev speed limiter and it ran better than it ever did for me! At the same time that I unplugged the wire for the speed limiter, I noticed the line for the oil to the carb was connected to nothing.. so I popped it onto the carb, filled the oil, and it was working.
Took it for one test ride, ran great. Maybe 10 minutes after I parked it I noticed gas just absolutely pouring out of it. It wouldn’t start until I held it wide open for a minute minimum, and then the second it dropped in rpms it would die, and now it won’t start at all.
I couldn’t help but feel like it had to be connected to something I did, but I don’t know how it could be. Took the head off, the bolts were looser than they should be, but the head gasket seemed fine.
Base gasket was obliterated, piston has play in the cylinder but no scores or marks and the ring gaps definitely out of size, the crank case had gas in it, and the exhaust pipe also leaked gas when I removed it and flipped it over.
so I’m getting the cylinder bored, and getting a new piston and rings.
My question is, does it seem like I’m on the right track? It feels so coincidental that this would randomly die in the blink of an eye but I know that’s how these things go sometimes.
Any help or insight would be much appreciated!
Also for extra info the crank seals are freshly replaced, carb is clean, can’t think of anything else relevant I’ve done to it.
Thanks!
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That is what I thought at first, but even after draining the crank case, and checking that the carb was starting and stopping the flow of fuel, letting things air out/dry out, it still wouldn’t start. And didn’t sound like it wanted to at all. My next guess was that the base gasket was blown out which ended up being true when I got down to the cylinder, so again, I guessed the flooding did that?It has a carb issue - you had to hold the throttle open to start it because the crankcase was flooded with gas - gas pouring out of the carb was a sign that the carb was having a problem and not controlling the fuel level inside the float bowl.
I’m boring cylinder and replacing piston rings and gasket cuz I can see now that needs to happen. I’ll have to take another look at the carb and make sure there’s no issues there, hoping when it’s all back together it starts!
OK - well yeah, you had multiple problems - the head was under torqued, that didn't hurt anything, just needed re-torqued. The cylinder was under torqued or over torqued - if someone had removed the cylinder, installed it and didn't get it tight, then crankcase compression blew out the base gasket - if the cylinder was installed, the base gasket re-used and then the cylinder over tightened, the base of the cylinder may have been warped and installing with a new gasket could cause the base gasket to blow out again, but if the cylinder base was warped and the gasket loose between the bolts and the crankcase filled with gas, then it may have been gas that blew out the gasket. I have seen crank seals blow out from the crankcase being full of gas.
Since the cylinder is off being bored out, I would run it by a machine shop and have the cylinder base trued. A machinist would chuck it up in a lathe and take a few thousandths off the gasket surface to make it perfectly flat. That would eliminate the possibility of the ears where the base bolts tighten the cylinder to the crankcase being warped and assure a good seal.
Sounds like you have it under control.
Since the cylinder is off being bored out, I would run it by a machine shop and have the cylinder base trued. A machinist would chuck it up in a lathe and take a few thousandths off the gasket surface to make it perfectly flat. That would eliminate the possibility of the ears where the base bolts tighten the cylinder to the crankcase being warped and assure a good seal.
Sounds like you have it under control.
I’ll definitely get the base trued. That’s an excellent point.OK - well yeah, you had multiple problems - the head was under torqued, that didn't hurt anything, just needed re-torqued. The cylinder was under torqued or over torqued - if someone had removed the cylinder, installed it and didn't get it tight, then crankcase compression blew out the base gasket - if the cylinder was installed, the base gasket re-used and then the cylinder over tightened, the base of the cylinder may have been warped and installing with a new gasket could cause the base gasket to blow out again, but if the cylinder base was warped and the gasket loose between the bolts and the crankcase filled with gas, then it may have been gas that blew out the gasket. I have seen crank seals blow out from the crankcase being full of gas.
Since the cylinder is off being bored out, I would run it by a machine shop and have the cylinder base trued. A machinist would chuck it up in a lathe and take a few thousandths off the gasket surface to make it perfectly flat. That would eliminate the possibility of the ears where the base bolts tighten the cylinder to the crankcase being warped and assure a good seal.
Sounds like you have it under control.
Feels good to know I’m (hopefully) on the right track.
Thank you!
1 - 5 of 5 Posts
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