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Saturday evening I came across what appeared to be a good deal for a 1998 Trail Boss 250. The previous owner has had it since the showroom floor. It ran great for him from that point up until last fall. A family member was riding it down the trail and it up and died on her. Has not been able to get it to fire since. They replaced the top end, still could not get it to start. They threw it up on the local classifieds for $300. I was the first to respond, and now its mine.

Knowing the top end had been rebuilt, I brought it home thinking that it was something electrical, or fuel related. Got it home and immediately began to tear it apart. Pulled the plug out, ground it to the motor, and pulled the rope. Got spark.

Put my thumb over the spark plug hole, and turned the engine over, blowing my thumb off the spark plug hole. Appears to have enough compression to start.

Moved on to the gas tank and carb. The tank was all but empty, and the carb looked like it needed some TLC. Pulled it off, cleaned the main and pilot jets, cleaned the slide, the throat, and put it all back together. Drained the rest of the tank, cleaned it out and put fresh premium in it. Put it back together, pulled and pulled and pulled. Nothing. Hooked it up to my car to allow the starter do the work. Still nothing.

Checked the throttle cable for proper adjustment, unplugged the ETC, nothing. Key switch, and kill switch seem to work as normal.

After several minutes of holding the throttle wide open, full choke, half choke, feathering the throttle etc. I was at a loss. Pulled out the spark plug and poured a small amount of premix into the cylinder. Still nothing.

I decided to pull the pull rope for a while, one of those pulls, the engine stopped like it was seized. After a little persuasion, it finally turned freely again. It only took maybe a 1/4-1/2 rotation for it to spin freely again. I do not believe the engine to be seized because it now turns freely again.

I know this is a lot of info, but any ideas? Is it possible that a skirt or a ring is down in the bottom end banging around in there? Would that keep it from starting though? FullSizeRender (17).jpg ,
 

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Saturday evening I came across what appeared to be a good deal for a 1998 Trail Boss 250. The previous owner has had it since the showroom floor. It ran great for him from that point up until last fall. A family member was riding it down the trail and it up and died on her. Has not been able to get it to fire since. They replaced the top end, still could not get it to start. They threw it up on the local classifieds for $300. I was the first to respond, and now its mine.

Knowing the top end had been rebuilt, I brought it home thinking that it was something electrical, or fuel related. Got it home and immediately began to tear it apart. Pulled the plug out, ground it to the motor, and pulled the rope. Got spark.

Put my thumb over the spark plug hole, and turned the engine over, blowing my thumb off the spark plug hole. Appears to have enough compression to start.

Moved on to the gas tank and carb. The tank was all but empty, and the carb looked like it needed some TLC. Pulled it off, cleaned the main and pilot jets, cleaned the slide, the throat, and put it all back together. Drained the rest of the tank, cleaned it out and put fresh premium in it. Put it back together, pulled and pulled and pulled. Nothing. Hooked it up to my car to allow the starter do the work. Still nothing.

Checked the throttle cable for proper adjustment, unplugged the ETC, nothing. Key switch, and kill switch seem to work as normal.

After several minutes of holding the throttle wide open, full choke, half choke, feathering the throttle etc. I was at a loss. Pulled out the spark plug and poured a small amount of premix into the cylinder. Still nothing.

I decided to pull the pull rope for a while, one of those pulls, the engine stopped like it was seized. After a little persuasion, it finally turned freely again. It only took maybe a 1/4-1/2 rotation for it to spin freely again. I do not believe the engine to be seized because it now turns freely again.

I know this is a lot of info, but any ideas? Is it possible that a skirt or a ring is down in the bottom end banging around in there? Would that keep it from starting though? FullSizeRender (17).jpg ,
Pull the flywheel. Check the magnets and pickup coil. Crank hearing could be bad. Damage inside flywheel. Magnet came loose etc...
 

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Discussion Starter #3
Good call. I can pull the recoil starter without having it explode in my hands, right?

Additionally, would this cause no-run situation even if I am getting spark? Should I be looking for something else as well?
 

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Yes. I bought an 04 trailblazer. Motor was locked. Pulled flywheel and it was all mangled. Replaced pickup coil. Stator and flywheel. Pulled it and started right up. Soon as I hit the starter it did it again. But felt no crank play. The hearing on that side was bad. Had to rebuild lower end. But those magnets like to come loose too. Pull flywheel Check everything out. Not a huge task. Like 8 bolts and flywheel puller. Car harmonic balancer puller worked.
 

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Also, be sure to check your crankshaft seals. If they are worn or leak they will not allow the bottom end to create a vacuum to draw the fuel into the cylinder for combustion. If you replace the flywheel side seal be careful not to drive it in too far as there is no lip to stop it.

You can also do a leak-down test to check for bad seals/gaskets. To me these engines are finicky but seem very reliable once you get them right.
 

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I agree. But that wouldn't explain it catching and hanging up.
I'd guess by dumping the fuel in the cylinder you vapor locked it temporarily.... :dunno:
 

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Discussion Starter #10 (Edited)
Pulled the recoil starter off tonight. When I pulled it off, oil came running out. It wasn't 2-Stroke oil, that I do know for sure. It appeared to be some sort of 4 stroke oil. Probably something that the PO did. To my knowledge the flywheel should be bone dry. Accurate?

When I pulled the plug initially, there was fuel on the spark plug, it appears that it is getting fuel. Will still check seals when I get it apart.

I "attempted to get the flywheel off. Broke a bolt in the process. Long story. Any tips on getting it off? Are you supposed to get the puller tight, then hit it with a hammer like with a pitman arm puller? I was cranking on it with a breaker bar tonight with no success. Any ideas would be helpful. Will be hitting it again tomorrow.
 

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Yes. And there should be no oil in the lower end. None at all. These motors have no balance shaft or anything. Kinda like a weed eater motor. All lubed by the mixed fuel.
 

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There is a plug on the bottom of engine. Pull it and make sure it's empty. Clean and dry everything behind flywheel and in cover. Then retry.
 

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Flywheel removal can be a challenge on these. I have had better luck using an impact driver with the puller over a breaker bar if you have one. If it still won't budge, leave the puller tight and heat the flywheel around the shaft while trying to keep the heat off the shaft itself and try tapping the end of the puller with a hammer. Also, when warm, spray with penetrating fluid. Try to use grade 8 bolts with the puller as they don't tend to stretch as much.

Try not to get the flywheel too hot, you don't want it smoke'n.
 

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Discussion Starter #14
Will try that tonight. Thanks for the tip.

Here's a picture of how it sits now. Is the bendix supposed to look like this? At one point the outside gear was in contact with the flywheel gear and the machine was locked up solid. It could not be turned over. Now that the bendix is not "connected" to the flywheel the engine spins freely. I cannot slide the bendix back at this point. It is stuck or lodged in its current position.
 

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Looks ok but outer gear should be able to twist and move out. Once you get the flywheel off to inspect everything you'll be to mess with and see everything.
 

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Discussion Starter #16
Update: broke the screw extractor while trying to get out the remains of the broken bolt. This project isn't going as planned! Haha
 

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Discussion Starter #18
Update, got the Bendix back in, cleaned everything up, and nothing. Finally broke down and did a compression test, 30psi. I hope to be tearing the top end down on Monday. Does anyone recommend a good place to have the cylinder bored/honed? I do not know of any reputable machine shops around here.
 

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Just gonna hone and re-ring mine. Sounds like yours is a little worse. Mine ran. Just a freshening up. I have the dealer do mine. Charge about the same as everyone else. Just don't buy the parts from them.
 
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