I have finally worked most of the kinks out and got both my 2005 sportsman 90's running. Carbs cleaned, brakes done, etc. anyway I'm having a problem with both somewhat intermittently. After riding flat out for a short period then slowing each bogs upon acceleration like they are running out of fuel or something. I've changed fuel and air filters, air boxes are on etc. got out my compression gauge to check and one is 85psi and one is 90psi. I checked both with batteries charged and throttle full open. Could this cause the issue I'm describing?

 

Probably is as the manual says 115 psi is the minimum on the 90 youth model.Possibly time for a fresh top end.You can buy a complete top end kit cheaper than having the cylinder bored out,then a new over size piston,rings and gaskets. http://www.ebay.com/itm/POLARIS-SPORTSMAN-90-CYLINDER-PISTON-GASKET-TOP-END-KIT-SET-2001-2006-/330981605218?pt=Motors_ATV_Parts_Accessories&hash=item4d100a7f62&vxp=mtr

 

Thank you again polaris tech. I just looked up and ordered the kit. I figure ill do one at a time and see how if goes. As far as the top end, can I replace with the motor in the quad? Didn't know if there was enough room etc to remove and replace the cylinder.

 

Kinda cramped,but you can pull the head and cylinder off and replace with the new parts.Cylinder head nuts torque to 14 foot pounds.

 

Great ill get busy when he parts get here. I've read in several posts about the bottom end and crank seals causing compression problems? Is there a way I can check or make sure I don't have bottom end problems when doing the top end without pulling the entire motor out? I can do the top end but if there are other issues I don't want to waste my time and money. Thank you in advance

 

Crank seals can leak causing problems also,but you have to pull the flywheel and stator on the right side and the clutches on the left side to get to them.Try the top end kit first as it seems it needs it with the low compression you listed and see how it does.Running for awhile and then dies,sounds like after the engine is warm the piston rings start to loose pressure against the cylinder walls.This is another sign of low compression on engines.

 

Ok got her pretty much back together. Is there supposed to be a new gasket for the exhaust head pipe? I looked at what I could find in the manual and it said replace with gaskets and high temp rtv?

 

Ok, I double checked and it didn't have a gamer or anything when I pulled it apart. I read somewhere on here that a leak at the head pipe could cause issues. Maybe that was the source of some of my problems to start with. Any input will be appreciated so I'm not chasing shadows on this

 

Yes it has an exhaust pipe gasket and yes if leaking bad enough can cause problems.Item #17.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse

 

All back together with new gaskets and top end. When I first cranked it up it sounded real tight like the starter didn't want to spin it but it started any ran fine. I run it easy and let it cool several cycles to break in. Take it for a full test and after riding about 15 minutes all if the sudden it bogs and seizes. It will restart immediately or after it cools then run till it gets hot again. I have no idea what the deal is. The piston/cylinder kit were both new. Is there anything else that could cause it to be seizing? Plug looks grey but not white. It's getting oil from the injection plus I mixed in a little premix for the first tank. I'm about to part this thing out.