I have a 1999 400 EX. It puffs a bit a blue smoke when first started. I am guessing this is a ring problem. I would like to put a higher compression piston in along with a cam. Would anybody have some good suggestions:
What pistion type?
What compression?
What cam?

The bike has been piped, jetted and air box modified.

Thanks

 

im not a 400ex guy but my guess would be:

a 11:1 piston...otherwise you'll have to run race gas ot atleast a mix
im not sure about the cam...but for a piston...maybe a pro lite piston

anyone around to help this guy out?

 

i run a Wiseco 11:1 piston with a hotcam stage 2 cam and porting, i heard bad things about wiseco's compression ratings tho i have no complaints. from what i have heard, JE pistons are the best. as for the cam, i have heard web cams are the best, the hotcams are cheaper tho. thats what i un

 

i would go with a je or ross 10.8:1 compression piston and a hotcam. if your looking for a high revving bike, go with stage 2. if you are worried about lowend power go with stage 1. the web cams require hardened rockers. you can't run hardened rockers with a regrind like the hotcams. by the way, if your puffing a little smoke on start up, i would also replace the valve seals.

 

Thanks. I would rather have the bike be quick on short bursts. We ride mostly in tight areas except for when we travel out to Little Sahara. I would like to see it be responsive to the quick punch of the throttle. Would changing the carb be worth the investment?

David

 

If you only notice it when the 400 is first started then it is probably the valve seals. When they go bad they let a little oil seep down from head, not enough to notice unless the 4-wheeler has not been running and enough oil has gathered in the cylinder.

 

yeah, i was thinking it was probally the valve seals too. go with stage 1 if you just want short bursts of speed.

 

with a larger carb it is possible to lose a little power until you get the rpm's up a bit. however, you might be satisfied with a stock carb bored out.

 

mine was smoking then i changed the oil twice with 20-50 insted of 10-40 now it doesn't smoke at all, so try 20-50 honda oil

kc

 

Thanks again to everyone for the advise. I will try the oil remedy if I don't crack into the engine.