250x engine project

[400thacker]

Ok I have tore down one of my engines and I have what looks toi be higher than stock compression piston and a unknown size overbore. motor ran real good before but started smoking a little.

since i found out it was bored and had a high comp piston, I figure it would be worth it to make an high flow exhaust and grind the inside of the flange down for more flow, plus maybe a slip on.

I am going to try to port and polish one of my heads and see if I can do that for more flow and use stock size valves

I think that a hot cam may be a good idea but what do you guys think about them and what would you suggest? will the CDI still limit it to stock RPM range?

also I am going to go with a 400ex carb and oil cooler that I have sitting around, what jets would you start with?

If anyone has any other mods to suggest please let me know. I am doing this on a budget so keep that in mind.

As far as the body and frame go, I am going all stock except grab bar, renthal bars and 400ex A-arms and front shocks.

this is going to be a woods quad and something to play around on.

Thanks for looking.

[dman66]

From what I've read on this site and other sites,do'nt install the 400ex carb due to it's a royle PAIN to keep jetting, tuning and dailing it in to your engine.Just my two cents from reading different articles - unless your racing it,I would'nt go 400ex carb.You can rejet your 250x/300ex carb to work just aas good.I have a Wiesco 75mm 12:1 piston,rejetted carb,and all else is bone stock.At 180lbs,my quad pulls damn good for a 250x. A stage 1 cam,stock valves,stock rockers,good piston - rings -fresh bore,K&N air filter,and a aftermarket exxhaust,would do your project good.While your in there,get a new cam chain and chain guides,maybe aa new oil pump,and clean the sump oil screen!!! You could keep going on and on with rerplacement parts.

[stroked 400ex]

A 12:1 piston helps alot, the 400ex front end is awesome but run the 300ex spindles and u need a shock relocater I bought diamound j's relocater or if u can cut and weld do it yourself, cdi is a good mod helps alot gives u that extra Rpms, ran a Curtis sparks cdi for a long time no problem. 400ex carb is a ticket it. I have a built 400ex And a parts 400 so I tried the carb it was great... 400ex plastics fit too... For the oil cooler buy the jaggs oil cover for 60$ it puts cool oil throughout the whole motor... Get a full exhaust and aftermatket airfilter... I run a full fmf, wiseco 12:1, k&n airfilter, the whole 400ex front end, 400ex plastics, and 5 inch rear and this quad is wider than my 400ex and feels just as good