Hey guys,

Just bought a couple fixer uppers. A 95 and a 96 sportsman 400 2 stroke.
The 95 is brought up to speed and purring like a kitten. However I am having problems with the 96.

Here it is:
- machine won't start, every so often it will give a small kick as if trying to go, but never does.
- i did a carb rebuild, it's all good.
- new spark plug and checked for spark - good - plug is BR8ES. Plug is wet- although quite a bit of black oil. I'm sure this is normal with a 2 stroke that hasn't ran in a while.
- did a compression test. It's running 90 with the electric start and closer to 110 with the pull start. New battery, new starter.

I'm lost on this one. When I spray fuel into the carb, it sometimes gets a chug, but mostly a small ticking sound, which is strange to me.

Anybody have any suggestions?

PS- im mechanically inclined and familiar with small engines, but far from a genius. So I may have missed something obvious. Let's hear it.

Thanks

 

Think that's the problem,compression is too low.Pull the carb and look at the intake side of the piston and exhaust side of the cylinder. Piston/cylinder may be scored or may just be worn out. Needs at least 120psi or more to even run right.

 

Hard to tell from a picture. It doesn't look like there's any scoring or grooves. I'm not an engine guy. But looks like I'll be tackling this.

Where do I start? Top end gasket kit and piston seals?
Never torn one apart before so this should be good.

 

Hard to tell from the pics,but best to tear the top end down. If you have a set of cylinder bore snap gauges and a set of mics you can measure the piston and cylinder. If you don't have you can pull the rings,insert the piston in the cylinder,piston through the bottom of the cylinder flush with the sleeve. Hold the piston tight against one side and see what size feeler gauge can slide on the opposite side of the piston. If you have .005 or more time for a fresh bore and over size piston. If it still has the original piston,should have a 38 A or B marked on top. Possible it may have already been bored once,will show what over size it is. .25. .50,etc.Plus here's agood video on checking piston to cylinder clearance. They even show the "redneck" method using feeler gauges towards the end..
Plus manual calls for .0023 to .0037 max on the cylinder to piston clearance. I always aimed for a tad tighter clearance .0015-.002 and broke them in easy.

 

I have the identical issue on a cheap fixer-upper I just bought - low compression (~105 psi). I assumed the piston was original so I ordered a 0.020 over piston and top end kit. Hopefully, it hasn't already been done once. The question I've got is, how hard is it to remove the head, piston and cylinder with the motor in the bike? Pretty easy or does a lot of the bike have to be disassembled to get to it? I know I'll need to remove the exhaust and carb/intake. And most likely the fuel tank. I'm hoping that's about it to get to the cylinder.

 

Pretty much like you described as to what needs to be removed,but clutch cover also needs to be removed to make it easier to get to the right side cylinder nuts.Plus after assembly don't forget to open the small 10mm bleed bolt on top of the head to remove any trapped air from the cooling system.Always premix the first tank 50-1 to help in piston break in or 40-1 if you're not using the oil pump.

 

What about reeds?

 

You can check by pulling the reed block and check but very seldom are reeds the problem on the 400. Plus low compression is the tell tale sign and 90-110 psi isn't good. Another thing to do since you're going this far is to change the crank seals. They take a beating same as a piston and cylinder do. At least replace the seal behind the drive clutch if you don't want to pull the stator and right case as this is the one that leaks the most. Item#48. http://www.cyclepartswarehouse.com/f...1996&fveh=5412

 

Not to knock your info old Polaris tech, but 110 lbs of compression is good enough to run. I've had them run with as low as 90lbs they run like crap with lower than 100lbs but they do run. I would test the coil and stator to make sure they're within ohm specs. It could be just a simple weak spark, I've repaired plenty that had a weak spark, they just didn't have enough spark to fire the mixture in the cylinder. I would do this before cracking into the motor.