hi im thinking about getting a 400ex and was wanting to know some of the common know issues. i own a 300ex and its a beast and runs very good and strong, ive always been a fan of honda products just want to know what to look out for, from what ive been told this 400ex im looking at has been bored over to a 426 and its setup for cross country/trail riding any advice would be great, im not new to any of this ive just never owned a 400ex

 

Think of your 300EX on steroids and with better suspension. You wont be disappointed.

That being said the thing I do not like about your machine or any used machine is for the guy to bore it out to 426 and is into racing I would walk unless its a give away deal.
There are just to many used 400ex out there that are being sold by people who just weekend trail ride and never fooled with a thing and left it stock.

I do that when buying used 4x4s ,as soon as I see big mud tires and a snorkel job on the ATV , I,m out of there.
There just to many used ATVs to chose from to risk it.

You think you would of had the same good luck with your 300 if it was bored out to a 325 all this time? Not so much.

 

The 400 itself is about as rock solid as they come. Once you start the mods, you also have to increase the maintenance. I wouldn't have an issue with it being bored over, but you have no real way of knowing if they took care of it. Once they bored it over, did they decide it would take those 25' jumps better? Maybe, but what did they do to the suspension or other parts?

And just because they spent the extra cash on doing that doesn't mean it's worth any more than a stock 400.

 

Ok well I know it has been taken care of the guy im getting from is a mechanic and his whole family races quads. ive seen all thier other toys and they run and look top notch. I waiting on pics and more info on this I just needed to what to look for when I go to buy it, im actually trading a completely biult 93 yz250 for it and my yz250 is prolly one of the cleanest running dirt bike out there

 

If the 400EX is good they have no weak spots in any years. Their as reliable as your 300ex.

 

Sweet I was hoping so, ive owened alot of different quads my 300ex was the best running quad ive had yet it doesnt look the prettiest but it gets the job done and then some

 

There are 2 things to look for. The upper motor mount goes through the rocker cover and is prone to cracking. You also want to make sure the swingarm is tight. If the pivot bolt is worn replacing it is a issue because they freeze up and have to be cut out.
Other than that they are a solid machine.

 

when bbk are installed alot of times the head bolts are reused. Since they are already stretched they can sometimes leak. when the owner tries to keep tightening over and over they eventually strip them out of the case. Replacing them with new factory bolts (or aftermarket) and give the holes a real good cleaning / tapping and using loctite ensures a good seal. I have 2 years on my 500cc bbk with no leaks using this method

 

This model is more strong and powerful than previous. Honda claims that it designed the 400ex engine to produce more torque and power, Everything is good except for the wires have been choped off.

 

You forgot about the clutch oiling problem the 99's had, but that's all I've ever really heard about.