Just finished a top and bottom end rebuild on a 1996 polaris 400 sport 2 stroke and it's hard to turn on the compression stroke. I can't get more than one rotation out of every pull because it locks up before the second rotation. I only have the pull start at the moment so no electric start. When I take out the spark plug, it turns great. The engine was started once after the rebuild but some other stuff had to be done and put on. After replacing the old parts, a week or two later, it's now it's acting as described.

Before first startup:
The carb was rebuilt but seems to be leaking some fuel from the bowl flange. New spark plug, spark plug cap, new top and bottom rod bearing, all new crankcase bearing and seals, new namura piston and rings at 83.5mm(+0.5mm), all gaskets, waterpump bearing and seals, new stator/coil. I have disconnected the oil pump and premixed the fuel 40:1.

After first startup:
After the first start up, some coolant was leaking from head to the outside of the engine, I have since fixed this issue. The engine is getting spark but there's no igniting of the fuel. The reeds were also replaced with Boyesen power reeds. There is no fluid in the crankcase because I removed the drain plug and very little gas came out.

So to sum up, I would like to figure out why it's so difficult to turn after one rotation on the compression stroke. Thanks for any help.

Edit: I have checked the compression and it won't go over 93psi, I'm only using the recoil start so I am unsure if higher pressure can be achieved with the pull start.
I have tried a couple other CDI's I got with the atv but they may or may not be working.
I have tried pouring some fuel in the spark plug hole and there is still no combustion.

 

Have push started it with all that new compression

 

Hopefully you have the crank drain plug back in. Did you purge any trapped air from the bleed screw on the head? If fluid is leaking from the head to the outside of the engine that may be the biggest problem.The head or cylinder may be warped or you didn't torque the head down properly. 93 psi on a new top end isn't good. Have someone hold the throttle wide open and pull the engine over 3 or 4 times and see what the compression reading is. If it's still 93 or less than 100psi,problem may be in the head or cylinder or head gasket.

 

2007 Polaris Sportsman has no pressure on the thumb throttle control.

 

?? Thumb lever loose? No cable pressure or what?

 

I discovered the butterfly was stuck in the wide open position. Corrected that, so all is well.

Thanks

 

Understand now what you meant. Wouldn't hurt to use some Liquid Wrench or PB Blaster to penetrate through to the the shaft on the butterfly valve and open and close the throttle several times.Could have been a one time thing,but I wouldn't take any chances,plus make sure you have 1/8" slack at the thumb lever only.

 

To update my post, I bought and replaced the starter to get more starting power and now it starts. I'm guessing there was too much compression to use the pull start. I also switched around to another cdi I had. Thanks for all the help.
No thanks to the guy hijacking my post.

 

Don't sweat it. Both your problems are resolved..