I have a 400 2x4 and it was running great!!! We took it out last weekend and came across some mud and water. Nothing deep, but the air filter hold down broke loose during my ride allowing mud in the carb. I have removed the carb and cleaned it. I did the same for the reeds. All it will do now is backfire when choked. Please help!!!

 

No need to post twice..

 

Thank you for the response!!!! The piston ring seizing up is what the oil in the cyl was for I read in the other thread Im guessing that it is not seized because it still turns over unless Im misunderstanding it. Do you know what the compression should be on that atv? Also i bought some new reeds for it but im afraid to install them with it backfiring so hard. I dont want to waist the $40 if they could get damaged, but if the reeds arent closing all the way I wont get good compression on the test........ Is that correct????

 

Yeah sorry about posting the same question twice. I didnt realize the first one went through until I posted the second one. I was still trying to navigate the site

 

Just check compression. Should be at least 115 psi or so for it to at least run. They can also show fairly good compression at times but still back fire like I mentioned if the rings are partially seized,piston cracked or even if a small part of the piston skirt has broken. Any of these can interrupt the proper intake of fuel/oil/air mixture,can affect lower end compression and mixture transfer through the ports for ignition.If enough water has entered the crank case,it could even cause the seal behind the drive clutch to push out or leak enough to where it wont get enough fuel and back fire. You can pull the intake manifold off,check for any reed petal that may have been broken when water entered and also look directly at the piston for any visible damage plus through the spark plug hole for any visible damage at the top of the piston. Even water that may have enter the recoil and stator area can cause problems also. You just have to eliminate one thing at a time.

 

Dang, I didn't realize it could have done that much damage . I will check the compression, carb, reeds, and stator after church today. I will post what I find. Thanks for your help!

 

Ok, I not getting any compression at all on the gauge. It just bounces from 0 to 5 and back down again. I can pull the pull start and there is no resistance at all. My Bayou 250 will rip your arm out of socket when I pull start it. Can the rings be that far gone after running so good prior to the water or am I looking at a possible bent or stuck exhaust valve?

 

No valves on the 400 2 stroke. Yes water can wash down a piston real fast,especially a 2 stroke that relies solely on the lubricating oil coming from the injector or premix unlike the 4 strokes that are bathed in oil. Just pull the head off,pull the recoil over and you can probably see the damage on the cylinder walls if the rings have seized bad enough.Very rare occasions(if the piston isn't damaged/clearance is still good) can you just install new rings if they've seized and hone out a cylinder.But I don't advise it! Most times takes the first over piston/rings and bore the cylinder.Dirt Cheap Yamaha, Honda & Polaris OEM Parts & Accessories – Cycle Parts Warehouse

 

Looks like im buying a top end kit. Thank you for the help. I will post more when I tear it down. Thanks again for the help

 

If finances are tight(as most people's are now days) Namura has good rated teflon coated piston kit in .020 and .040 over depending on what size need to clean the cylinder bore up.May not be as long wearing as Wiseco,which imo is the best,but within most people's financial reach. All you need is someone that can bore and finish hone the cylinder out to where the piston skirts to cylinder base clearance is NO greater than .002. http://www.ebay.com/itm/NAMURA-ATV-020-PISTON-TOP-END-KIT-POLARIS-400-2-STROKE-83-44-/371059888702?pt=Motors_ATV_Parts_Accessories&hash=item5664e4923e&vxp=mtr
Wiseco kits if you can swing it.Not really that much more.http://www.ebay.com/itm/Wiseco-Polaris-SCRAMBLER-400-2X4-4X4-Piston-Top-End-Kit-Gaskets-84mm-PK1109-/330870857201?pt=Motorcycles_Parts_Accessories&hash=item4d09709df1&vxp=mtr
Just have the cylinder measured as to what oversize is needed..