So after 7 years of hard riding Im about 99% sure its time for a rebuild with my z400 and am not really sure as to where to start looking for info on building this bike?

Right now the bike is lightly modded, jetted, full yosh pipe, and an air filter and moves. Its right next to 450's in the woods and ideally I would like to be able to pull on 450's but reliably. I know I could go all out with a high compression piston, headwork, carb, cdi box and do the whole 9 but know bikes of this caliber tend to get a bit "finiky" as far as reliability and all that good stuff.

I was hoping to really just rip the bike apart and just do a high compression piston and call it a day, this way the engine isnt super modified, Ill have a little bit more power and should still have reliability. I know if I do valves and all that fun stuff I need to worry about clearance with the piston and what not. Im looking for some decent info on what to do and how to do it so I have an idea on what im getting myself into. Any feedback would be appreciated
-Gary

 

You will probably need to check ptv clearance just with a high compression piston. You could always just get a ported and polished head with over size valves and cams to get more power out of it.. I am looking into ways for my 06 KFX400 to get some more nads to it...These are awesome machines and I have seen the smaller stroker kits kick 450 *** with less cc's..

 

IMO, you could just get your head worked on. No valves and such, just flowing it.
A higher comp piston will demand higher octane fuel.
I flowed the head on my boys 300ex and he felt a big difference in power. We went to a national for the fun of it and he took 2nd.
I've been told that big cc's and stroking reduces reliability because the head bolts are too fat apart (needed 1 more) ie: they'll blow gaskets. Really pump em up (high hp) and the bottom of the case will blow out.
Absolutely great machines when left sorta stock/minimally modified hp.

 

When you say "flowing" you are talking about a slight port and polish are you not? The term flowing usually refers to putting it on a bench and checking the airflow capability of the head/intake. A port and polish and even a stage one hotcam would work wonders on these machines..

 

Yes porting.

 

Wasnt trying to be a smart rear end, just didnt want to get them confused...

 

I need to freshen up my son Z400 also have no fear in big boring and/or installing hi comp piston. Already have done rev box,cams, edelbrock carb and porting and had a very reliable running quad that surprised quite a few 450 riders. Thinking of going with the weisco 440 kit just saving the money to do it.

 

I know! and thats why I love my Z soo much, it has NO problems keeping up with the 450's that I ride with in the woods. Being able to pull on them would make me soo happy PTV is piston to valve clearance right? I could run a similar to stock CR piston and do some head work to gain a little more power and that would more then likely be more reliable then a high comp motor correct?

Since I bought the bike back in 04/05 the original owner used to run a 2/3 mix with VP Red. (2 gallons of red to every 3 gallons of 93 oct). Im not against running a higher octane fuel that would cost $10+/gal, im not made of money but for the 1-2 days a month I ride the bike I can justify burning $20-30 a day in fuel. I have been told that the 440 kit would make it alot more less reliable also and is why I want to stay away from that, I might need to run an "oversized" piston and get a bigger bore/hone if my cyl wall is a little scored up. I dont wanna go too big and take alot of material away from that cyl wall also, but under decel I get alot of "piston slap" and can really feel it between my legs. Granite Im not going out of my way to downshift and decel to feel this but know I never used to feel this before I love how it sits now, jetted, full yoshi pipe and an airbox. The bike moves but I want just a little more power, and since im pulling the motor to rebuild it I figure why not get a little more power outta it now.

Do you think if I did the edelbrock carb, some porting and a set of hot cams I would notice a decent power gain over how my bike sits now? Im not looking for super amounts of power as I stated before, just a little more.

Thanks for all the input guys, I really got more responses then I expected and hopefully this thread will help any other in similar situations as I am.

-Gary

 

Do FCR 39 (like from a yfz 450) carb with some head work and you will see a big difference.
I would do the carb, the head work and a 434 kit from CW (affordable and reliable) and some cams. Then you will keep up with the 450 in ALL conditions.