Hello everyone.

I bought a used 96 Xplorer 400 a couple of months ago. It ran great for the first couple of weeks, but then the hot light started to come on, then it wouldn't start after that. The fan wasn't coming on, so I jumped the temp switch on the radiator and the fan works. I took it up to a 'mechanic' to get it running again and they said they replaced the needle valve and it runs now. They then told me that I need a new fan since the hot light comes on. At that point I realized they don't know what they are doing and just got the atv without them doing anything else.

Got it home ran good. Next morning there was gas all over under it. Was leaking from the overflow on the carb. They didn't replace the seat, just the needle.

I rebuilt and cleaned the carb, replaced all the jets, throttle needle, gasket. put new air cleaners on it, as well as a new air box to carb boot since it was ripped. Started right up and idled fine. Put a new temp sensor on the radiator as well. ran it around the yard for 15 - 20 minutes and the light didn't come on, the fan also didn't come on. I can hear coolant bubbling too (thinking air in there keeping it from circulating, maybe causing the temp switch to not close).

Next day I took it out again. was smoking pretty bad out of the exhaust, white-ish smoke, the throttle started bogging and it ended up stalling before I could get it back to the barn. Can't get it started now.

I set the air screw and idle to what it was previously, air is at 1 turn out, idle 2 turns. throttle needle clip is on the 3rd place down.

I honestly don't know what else to check now. There's gas getting to the carb, I've checked multiple times. Spark is good. I don't have a compression tester to check that though.

going to go through the service manual tonight again to check the throttle needle setting, but not sure why it would run good/normal and then have it bog down after a while. Not sure about the smoke/exhaust either.

Any suggestions are greatly appreciated, thanks!

 

Check compression. If it's below 115 psi,you've probably seized the piston/blown a head gasket.The sensor is at the top of the radiator that controls the fan. You can take this sensor to an auto house and match it up. Possibly you had air in the cooling system that was partially to blame for running hot also. There's a bleed screw on the top of the head to remove any air pockets.

 

Thanks for your reply opt. I've replaced the temp sensor already, trying to get it running before troubleshooting that/bleeding the air. It will start and run, but it does the same thing after about 15 minutes, with bogging down then stalling. I've got the service manual as well, so I'll make sure the throttle is adjusted correctly, but it makes me think it's something else since it seems to only do it after it's been running for some time.

 

Always bleed the air before cranking a 400 up. If it runs for a while and shuts off,then it's probably rings loosing seal against the cylinder when warm. Usually when it's cooled down,they'll run until it gets warm again. I'd tear the top end down and see where you stand.

 

Update, replaced the head gasket, was leaking. Coolant issue solved. Got the carb tuned well, good compression and correct rpms, and was running really well (had a mechanic friend help me out). Loaded it up, brought it home. Next morning I filled it up with gas (5 weeks old gas, at the most), started it to warm it up. It stalled before I could unload it, and will not start again. Starting fluid won't do anything, gas is getting to the carb. Carb is clean. Gas tank is venting, plug is wet, although it looks like oil. Checked the spark and it's blue/orange (checked it on a steering rod, not the frame though, not sure if that makes a difference).

Any ideas? Would reeds for a flywheel key be the issue? When it stalled it was just a normal stall, didn't seem to stop hard. Not sure how to check the reeds, just see how hard they move?

 

Again check compression,plus a compression check is just a general way of checking the condition of the top end.Even if it show 120 psi or more, I've had some 400s that had broken off small portions of piston skirts that would show fairly good compression,but wouldn't run worth a flip.Plus I've had partial seizures that would do the same thing. Reeds generally aren't a problem unless you have one that's brittle,broken off. Plus you can check the reeds and the intake side of the piston in one step. Just pull the intake block and pull the recoil,check the piston skirt/body for any broken pieces along with any scoring. Same for the exhaust side of the piston,pull the pipe and check the piston as you move it up and down. Having to replace a head gasket to begin with usually takes a toll on the piston itself in many cases.

 

update, calibrated the choke, ran well for a day, then started overheating and bogging. Turns out the water pump went on it, coolant/oil/metal shavings everywhere. exchanging the core for a newly rebuilt engine next week, as there's no telling what else is wrong in there, at the very least the cylinder is going to need to be honed, if not bored, new rings and piston...etc.

 

When you install the new engine run the first tank of fuel premixed 50-1 to help with break in. Don't forget to bleed the bolt on top of the head to remove any trapped air from the coolant or it can over heat very quickly and damage that new engine.