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Discussion Starter #1
Long story, short, we were riding last saturday (27f) and after a very brief stop to make sure all riders were good to go, my friend started up my Trail 488, and went to accelerate, and it just wouldn't go. Engine bogged down, very sluggish throttle response, and wouldn't rev past 3200rpm. If the primary were even to start to engage, it would nearly stall the engine. It didn't sound normal to me, like it wasn't running on both cylinders evenly. Without much on the trail for extra parts and tools, I let my friend take my sled and ride with the group back home, so they could grab a vehicle and trailer to come rescue me.

Got the sled home, and started to try and diagnose. It ran fantastic for about 40 miles, and then without warning, would hardly run any more.

Things I've done:
Compression test (115pto/120mag).
Removed flywheel and checked for wiring damage at stator (still ohm checks at 154ohms on exciter coil).
Cleaned magnet surfaces on flywheel, and exciter coil magnet surfaces (they were rusty).
Engine has spark, seems to be pretty bright blue.
Pulled mag side case drain, some greyish oily liquid came out.
Checked both needles/seats on both carbs, made sure bowls were clean. Neither needles seemed to be sticking, but the two separated floats on the mag side carb didn't want to move on their stems really freely. Cleaned the stems with carb cleaner, and a light wire brush. Both seemed to be moving better when I put the carb back together.
Exhaust pipe pulled off to make sure there wasn't some sort of restriction.
Airbox checked for restriction as well.

There was a pebble stuck between the sealed side of the CDI and the fan housing, that maybe made a slight stress indent to the CDI case, but not 100% sure it did anything to the inside of the CDI box.

I have a few people I work with kinda stumped, but as they have not seen the sled yet, it's all based on things I've looked at.

Any ideas on something I'm missing here?
 

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Are the carb slides in sync, chokes set correctly also. I would tear the carbs completely down, clean jets and all passage ways, compressed air is important here, just to eliminate the issue of it being carb related. Clean the fuel pump, and check the pickup line and pulse line. This way you know the fuel system is 100%. The 5psi difference is almost the max difference in compression that you want to see. With the carbs off see if you can tell if there is scoring or anything on the pistons. I fought a bog in an xlt once that only occurred once it warmed up. Ended up being a bad crank bearing
 

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To keep things simple here.....did we swap plugs? A fouled plug can look ok but cause one to pull what is left of his hair out at times. I mention this because I haven't read that fresh plugs were installed. Starting and stopping/idleing is usually what kills plugs when carbs aren't set up 100%. Let us know what you find.
 

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Discussion Starter #4
I have not put new plugs in it yet. I tried a set of Champions out on the trail when it started having the issues, but to no avail.

Still need to pull the PTO drain and see if anything comes out of it, as I am wondering if one of the needles stuck when we stopped, and flooded the engine, which could have been the main cause all along?

If it was flooded, do the crank cases ever clean themselves out if the issue is resolved, or is it an issue until the drains are pulled?
 

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Long story, short, we were riding last saturday (27f) and after a very brief stop to make sure all riders were good to go, my friend started up my Trail 488, and went to accelerate, and it just wouldn't go. Engine bogged down, very sluggish throttle response, and wouldn't rev past 3200rpm. If the primary were even to start to engage, it would nearly stall the engine. It didn't sound normal to me, like it wasn't running on both cylinders evenly. Without much on the trail for extra parts and tools, I let my friend take my sled and ride with the group back home, so they could grab a vehicle and trailer to come rescue me.

Got the sled home, and started to try and diagnose. It ran fantastic for about 40 miles, and then without warning, would hardly run any more.

Things I've done:
Compression test (115pto/120mag).
Removed flywheel and checked for wiring damage at stator (still ohm checks at 154ohms on exciter coil).
Cleaned magnet surfaces on flywheel, and exciter coil magnet surfaces (they were rusty).
Engine has spark, seems to be pretty bright blue.
Pulled mag side case drain, some greyish oily liquid came out.
Checked both needles/seats on both carbs, made sure bowls were clean. Neither needles seemed to be sticking, but the two separated floats on the mag side carb didn't want to move on their stems really freely. Cleaned the stems with carb cleaner, and a light wire brush. Both seemed to be moving better when I put the carb back together.
Exhaust pipe pulled off to make sure there wasn't some sort of restriction.
Airbox checked for restriction as well.

There was a pebble stuck between the sealed side of the CDI and the fan housing, that maybe made a slight stress indent to the CDI case, but not 100% sure it did anything to the inside of the CDI box.

I have a few people I work with kinda stumped, but as they have not seen the sled yet, it's all based on things I've looked at.

Any ideas on something I'm missing here?
Check the throttle cable safety switch. It is designed to kill the engine if you release the throttle but the cable stays tight, keeping the engine running fast. I have a 1996 Indy Trail Touring w/488 cc engine and it was driving me nuts with stalling and starting issues. Sometimes it would run OK cold but not warm as if the engine heat was affecting the cable length. After the dealer replaced it it was like new again.
 

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Pull both case drains again and see if anything comes out....if so you are leaking by the needles and seats. Inspection by viewing means nothing on these things. If you do get more flowing out just shut the fuel off when stopped (all times) until you get it fixed correctly. I had an XLT that I had to turn the fuel off on the trail when stopped because it would flood out the cylinders.
 

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Discussion Starter #7
Did some further inspection today. Made sure both needle/seats were not sticking, and the floats were moving. All move freely. Noticed the carb boot on the MAG side gad some grayish oily crud in it, and after pulling the crank drain for the second time, more oily grayish liquid came out. Rotated the engine by hand, and looked at both piston skirts. Found the MAG side is fractured and a chunk of the skirt is missing.

Now the question is, what made it crack? Age? Engine has 2934 miles on it. Other side has vertical (very light) scoring marks. No signs of cracking.
 
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