dummy piston question

[Jim417mx]

So I'm 99% sure its time for a rebuild on my suzuki.. its puffing white smoke every once in a while and hard to start. I'm from the world of 2 strokes and boring and all that work. If I'm correct the ltr is a nikasil cylinder, what all do I need? Just a piston kit with new rings? Or do I have to pull the cylinder off first to see if the walls are ok. I plan on getting an ATP 14:1, should that work, will that be ok for A-class national racing?

[kfx400rider03]

check cylinder wall. hone the cylinder so the rings seat properly and thats it pretty much

[TitanMotorworks]

to hone cylinder properly, you need a diamond hone, not just a ball hone!, check top lip of cylinder for plating coming off. which is caused by dirt. I reccomend not going high compression on a used crank with more than 75 hours. reason is crank is adapted to its compression, putting more compression to it will cause rod failure sooner. also check intake valves for the hard starting. specially if you run K&N air filter. Replace valve seals while you have your head off. check valves faces for cupping.

[bigbad400]

def has low compression, but your piston could be just fine, like stated check your valves, they are more apt to go and will cause hard starting, white smoke and its cheaper fix generally. i dont know if these motors have it or not but some small higher compression motors have a decompression mechanism on the cam or exhaust valve for easier starting, and with those motors that have one, the mechanism can stick and you could have an exhaust valve hanging open on you. i never saw the inside of these motors, so i dont know. just a thought. the honda 400ex is known for this problem and most aftermarket cams do not use the decompression, good excuse to upgrade ur cam if it is the issue. good luck

[Limited Z_400]

dont forget to check your valve guides for wear.

[Jim417mx]

Well I pulled my top end off... turns out I broke the top ring and it ate my cylinder wall too. I just finished putting a 13:1 CP piston and a new cylinder on. It it hard to start and will not idle at low RPMs as of right now. Before you guys say anything, I'm sure half my problem is my spark plug and fuel, its still the same one from the old piston and it's all carbon, and I am still running pump gas. I will be replacing the spark plug and getting race fuel after work and will be updating my post. I tried adjusting the idle screw and the throttle cable. I know I need a valve job but I do not have the money right now, I'm 21 and I literally work 6 days a week just to be able to afford racing, i love it, its my life. I just want to finish the rest of the season then send my head out for porting and valves, etc during winter. I'm just hoping my broken ring didnt eat my valves, they looked ok, just all carbon'd up just like the spark plug was.

[Jim417mx]

Well it turns out I still had low compression after the piston install. After further investigation I found out my valves were shot. I installed an ATP race head with cam, +1 valves, and porting. And the bike would start and idle but not rev. Upon having 10-15 hours to diagnose my problem, I checked my TPS and set it to 59.9, and it still did the same thing. About 5 hours later I re-checked the TPS. It turns out when I tightened the TPS bolt, the sensor moved just enough to throw it off... so I re-set it and my problem is fine. Hope this helps somebody in the future.