Buying a modded 400EX - Need help

[Punkmaster Flex]

Hi,

I'm just about to buy a very well equiped 400EX. It has a lot of handling upgrades such as Houser +2 tables, Works suspension and a lot more.

The bike was rebuilt from the ground up this winter. It now has a 12:1 JE 416 piston in it. I heard the max compression that 91 octane fuel will handle is 11:1 but the bike was always run on 91 octane.

Is there a risk of overheating / damaging in not using high octane fuel with this setup? How reliable is it?

Thanks in advance!

[storms400ex]

i heard 416/426 are reliable engines, if anything i would mix it 91/110 that way its cheaper on your wallet, just listen to see if starts pinging if it does then more likely you'll need 110 straight gas

[Punkmaster Flex]

Is there any other solution apart from changing octane or switch to a 11:1 piston to avoid detonation?

I dont feel like paying huge bills for VP racing fuel or open the block to put a 416 11:1 piston in there. That would suck. :/

[ae13291]

416ex is a reliable motor, but unless you are getting a killer deal i would rarely buy a internally modded engine like that

[Punkmaster Flex]

Well the whole quad is fully modded. Everything is aftermarket except the rear axle and it's only a grand more expensive than the stock EXs around here.

I think that's pretty much a killer deal. :)

[jcs003]

if the guy has papers on the engine work and you can trust his maintainance practices then get it. but do not pay more than someone selling a stock bike. when you buy an previously built engine you are taking on a reliability risk that will cost you in the long run.

basically the stock engine is built with reliability in mind and that is a piece of mind for a buyer...

[Punkmaster Flex]

Ok here's the situation. Over here a 1999-2004 stock 400EX usually sells for 3000$.

The 2002 I found has +2 a-arms, three Works shocks, a +2 steering stem, a lot of wheels, bumpers and grab bars. On top of that it's 416. And for less than 4000$.

The motor itself costed 1500$ to get done and the guy has the papers to proove it. I think the deal is pretty good.

My tought is maybe this 426 isnt exactly 12:1 compression. The shop might've used thicker gaskets to take the compression down a bit just so it doesnt detonate all around.

I will have to talk with the guy and maybe call the shop that did the job to see if this 12:1 compression engine can handle 91 octane fuel.

[416exman21]

sounds good- i run 110 its better than low grade- with 12.1 you need 110

[ngates788]

Originally posted by Punkmaster Flex
Ok here's the situation. Over here a 1999-2004 stock 400EX usually sells for 3000$.


that is steep ... you can buy a used 450r for that where im from, unless your talking in canadian dollars and not USD?

[Punkmaster Flex]

First of all yes I'm talking about Canadian dollars, and here a 450R goes for about 5000$.

This is totally different from your guys in the states. Here a quad is almost as expensive as a car lol.

[Snipe]

hahaha love the last part I gave as much for my quad than my 2001 dodge ram lmao.

If you trust the guy or better yet trust the ppl that done the work then I say its worth it.

To do a 11:1 piston all they would do is pull your piston out and put a thicker sleeve and then put the piston there is a bit more to it than that but it wouldnt be to bad if your worried about that.

[Punkmaster Flex]

Ok I'm going to see the quad next weekend. Here's the engine setup:

2006 450R Carb
JE 12:1 Piston
MX Porting
Valve job
Barnett Clutch
Cometic gaskets all around
Crank and crank bering rebuilt

I heard that jetting my carb a bit on the rich side will avoid detonation so I can run of pump gaz. So, do you guys think I can run this setup for a couple of years without problem if I maintain it as it should be?

I got the money for the quad but I'm not rich enough to redo the engine 2 weeks after buying it...

Thanks!

[droppedmazda]

you dont have to do anything to the sleeve to lower the compression. all you have to do is change the piston to lower the compression. i've been running my bike for 2 years with a 12.1 compression piston in my trail bike. i run it on 93 octane which is suppose to be the same as the 91 that you all have. my piston still looks as good today as when i installed it. i dont see why everyone on here says you have to run 110 race gas with that compression but you don't. my bike does run a little on the rich side but i don't see how how that would help it any. just buy the bike if you want it and see how it runs on the 91 that you have and if it don't work change the piston or run a mix with race gas.

[Punkmaster Flex]

Oh well, I thought a lot about it and after trying a stock 400EX with a slip-on, I decided I'd go with a stoker bike that I will mod with time. The 416EX is truly a deal for the guy that likes mechanic but I'm the guy who would rather have a reliable machine than a 450 eater that's always broken.

I'll try to see the 1999 400EX that's for sale not so far from here tomorow. We'll see how it turns out. :)