Rebuild question

[Mattrick400ex]

Well my 400ex is starting to blow the white smoke, i think i washed the cylinder. It all started with a bad cdi box and every time i tryed starting it it would flood the bike from giving it gas. I would let it sit pull the plug clean it up, then it start sometimes. It did that about 2-3 times out. I realized it was the cdi box and bought white bros and put it on and it started up everytime without even giving it any gas.But now its james bonds when riding.

My question is i want go 440 or bigger in a few months, which size is the best for the money and who's kit? and How much?
I do alot of mx riding, some trails.

Right now where is the best place to find stock parts(rings,piston etc) to rebuild to ride during the winter.How much for them?

This is the first atv i have owned so all new to me, thanks for any help.

[AZ440ex]

EBAY!!! for parts.

A 440 built correctly with a stage two cam is probably the best choice dollar for dollar if you are wanting a bigbore for mx. I feel the stage three cam sacrifices too much bottom end for the track. The kits are readily available and pretty cheap.
As far as brand, I have run weisco for a long time without problems but have heard others have had issues.

460's and bigger can get expensive and if you race thats going to put you into the open class were to be honest our 4XX's have trouble keeping up (Riders being equal of course):devil:

[Mattrick400ex]

Originally posted by AZ440ex
EBAY!!! for parts.

A 440 built correctly with a stage two cam is probably the best choice dollar for dollar if you are wanting a bigbore for mx. I feel the stage three cam sacrifices too much bottom end for the track. The kits are readily available and pretty cheap.
As far as brand, I have run weisco for a long time without problems but have heard others have had issues.

460's and bigger can get expensive and if you race thats going to put you into the open class were to be honest our 4XX's have trouble keeping up (Riders being equal of course):devil:

Thanks that helps out, Now one question a friend of mine has a 08 lt450r and that thing is badass. Would a 440 with stage two cam be quick enough maybe to keep up with a stock lt450r with equal riders?

Thanks for the help again, i was just looking a some weisco ad ina magazine.

[400exstud]

The build up 440 MAYBE will keep up with the STOCK LTR however as soon as he takes out the spark arrester and adds the cherry bomb (about $50 cost for him) you have little to no chance of ever seeing him again.

[AZ440ex]

Originally posted by 400exstud
The build up 440 MAYBE will keep up with the STOCK LTR however as soon as he takes out the spark arrester and adds the cherry bomb (about $50 cost for him) you have little to no chance of ever seeing him again.

Agreed, if you two are the same class rider he will have to make very little mods to do to out power you.

A 440 on a good day is about 42-44HP.

A new 450 with little work gets about 52-54Hp.

Your best bet is to be a better rider and train harder so when your on the last few laps you have that little extra left.

It is about 80% rider 20% machine on the MX track

[AZ440ex]

You can get a 440 piston, sleeve, gasket set for about $200
Cam $120
HD head studs $70

Then depending on what labor you can do yourself you need the sleeve put in the cylinder and the head studs installed. About $150 for both.

Port job- I have no idea on the going rate (my engine builder does mine)

Valves, some go +1 on the size, I did not so I'm not sure on that cost.


In the end you have to put alot of work and money into it. IMO money is better spent on suspension first. Dollar for dollar it will improve your lap times more than anything else.

[Mattrick400ex]

thanks for all the help guys.

[AZ440ex]

Originally posted by Mattrick400ex
thanks for all the help guys.

No problem, unfortunately the old 4hundy just is not competitive in MX anymore. I rode a full mx 450r with 56 HP and it was a beast but I just didn't feel comfortable on it like I do on the 400.

After this season I'm pretty sure I am sending mine off to JB racing to convert it to a hybrid. That will rule out me running in any production class but I'm ok with that.

[9sec.Bird]

Matt doesnt want none of this!

I have a Full Yosh pipe, cherry bomb and air filter kit.
The Zuki gets up and runs away from his 400ex :devil:

[Mattrick400ex]

Originally posted by 9sec.Bird
Matt doesnt want none of this!

I have a Full Yosh pipe, cherry bomb and air filter kit.
The Zuki gets up and runs away from his 400ex :devil:

Ha ha not funny:D

[AZ440ex]

Originally posted by 9sec.Bird
Matt doesnt want none of this!

I have a Full Yosh pipe, cherry bomb and air filter kit.
The Zuki gets up and runs away from his 400ex :devil:

Until your transmission blows up like every other LTR ;) :blah:

Has it started to pop out of gear under a load yet? It's only time:(

[9sec.Bird]

Originally posted by AZ440ex
Until your transmission blows up like every other LTR ;) :blah:

Has it started to pop out of gear under a load yet? It's only time:(

I thought the 08's had a little better trans. ?

I havent rode it a whole lot yet.