400ex bbk question

[caseywoods5]

hey guys i recently bought a 2003 400ex... i was told it was rebuilt not long before i got it off of them and it had a 440 big bore kit... they gave me a number and said it was the mechanic's number and he said that it did have the 440 but i don't know whether to trust it or not. i have also been told that my 400ex sounds like it has the 440 and a cam but they were just going by sound. is there any way i can tell if it's a bbk without tearing down the engine? also it had a cobra pipe on it when i got it (i know, cobra is junk... i took it off and you can see through it, might as well be a straight pipe, very loud)... i need to know whether it's a 440 or not though that way i can get an idea on what size jets i need to get (it is very lean, pops like crazy on decel). any ideas? thanks in adance!

[caseywoods5]

here are a couple of vids i got of it...

http://www.youtube.com/watch?v=2HMcq0C0-FE&feature=channel_video_title

http://www.youtube.com/watch?v=nxRTo_YYbJc&feature=channel_video_title

[ish416]

It sounds like every 400 I've heard that's had a blown out exhaust.

Your going to have to pull the head off and measure the bore to find out what size it is. Also would be good to see if it has a stock cam or not.

Also, invest is some tires. Seriously.

Looks like it's in good shape from the vids.

Welcome to the forums.

[Stickman400]

You could take a borescope and see if there is a number on top of the piston. Should tell you what brand and size it is if it has a number on it.

[caseywoods5]

alright guys thanks, and what exactly is a borescope? also, i already know i need tires, but i don't have money for new tires just yet, and i know a cobra is seriously just a straight pipe with a piece of screen at the end. it's so loud it's not even funny, i'm getting a new exhaust soon so it will be quieter and sound better before too long haha... i really DO NOT want to have to pull off the head because i hate having to time a motor so i'd like to look into the borescope thing.

[crownandmonster]

A bore scope is a good idea on a fresh rebuild, but in all reality if it has some run time on it there will be carbon covering the top of the piston so any numbers would most likely be coverd in carbon. IF you have one laying around though its deff worth a shot.

[Stickman400]

It's basically just a camera on the end of a flexible tube and you have a small screen that you can look at whatever you're pointing it at. You can stick it into the plug hole and see inside the cylinder. They are quite expensive though. But you should be able to rent one at a local auto zone or a similar place.

[caseywoods5]

i found a borescope for 85 dollars so when i get some cash i'll be getting it... and as for my cobra exhaust, i found a good used white brothers e2 pipe on ebay, i'm trying to talk the guy into adding a buy it now, if he does then i'll be getting that pipe. and hopefully before too long i'll have that borescope to find out whether or not this really is a 440.

[crownandmonster]

I wouldn't waste 85 dollars on something you aren't sure will even work...I would try to rent one or borrow one first. Like I said odds are you wont be able to read the numbers anyway because of carbon build up.

[caseywoods5]

well when i met the people to look at it they let me ride it and told me to go easy on it and not ride it real hard because it was just rebuilt and wasn't broken in yet... so would there be carbon on it? i haven't rode it but a few times up the holler and back to my house, maybe a mile or so each ride.

[Stickman400]

Yea, I'm with crown on that one. I'd rent one because it won't take much riding on it to get it to build up. Plus unless you plan on needing it in the future, you'd be wasting $85.

[crownandmonster]

If thats the case then it shouldn't have any carbon on it...that is if they were telling the truth. Its you're money man you can do what you want with it. If it were me I would take the head off, that way you can look at the condition of the valvetrain also.

[caseywoods5]

honestly, the main reason i'm avoiding taking the motor apart is because i've only timed one rfvc motor before and i got it wrong and bent valves because i was rushing and trying to shorten the process... let me see if i've got it right though as i've rebuilt many motors and timed them before. i know you get the motor at tdc by taking the plugs out of the stator cover and turning the motor until that notch lines up, then line up the notches on the cam sprocket and put on the chain, is that all or is there more to it? also, how do you get some slack in the timing chain? is there a way to take some pressure from the tensioner so it's easier? most times i struggle trying to get the chain on up top at the cam.

[Stickman400]

When turning the motor to TDC there is a T mark that you line up instead of a notch. And the cam sprocket has 1 vertical mark that goes up and 2 marks on either side of it that line up with the surface of the head. And to get more slack in the cam chain take the tensioner off. Other than those 2 little things you're right about the rest.

[caseywoods5]

how do i take the tensioner off? and thanks for all the help so far man, i really appreciate it.

[dxcody]

tensioner is just 2 8mm hex bolts on the back of the cylinder, take the exhaust off to get to it.

And dont forget to replace those 2 crush gaskets or else you will never be able to jet it right, since that will cause an exhaust leak.

[caseywoods5]

^^^ alright man thanks, i hadn't even thought about those gaskets... would it be safe to reuse my head and valve cover gaskets?

[dxcody]

you cant reuse a headgasket ever, once it is pressed down onto the surface of the cylinder it needs to be replaced if takin back off.

The valve cover might be Ok, but it is probably just as cheap to go buy a full new top end gasket kit, as it is to buy just a headgasket. And I along with many others on here am going to reccomend, the cometic tripple layered steel gasket kit. Its hands down the best there is in my opinion.

this is a link to the right gasket kit:


http://www.ebay.com/itm/HONDA-TRX400EX-400EX-COMETIC-TOP-END-GASKET-KIT-99-08-/320801867463?pt=Motors_ATV_Parts_Accessories&vxp=mtr&hash=item4ab14806c7

[CJM]

Before you do anything, why dont you pull the 17mm nut on the bottom of the carb and check the jets. If it does have work done to it usually the person tends to up the jet size to compensate. It wont be a sure thing, but if the jet is somewhere around 175 or better either they jetted it WAY to rich (and you would tell if you rode it-it would bog) or theres a good chance they didnt lie to you.

In the end, only surefire way is to measure the bore.

[01boneless]

the valve cover gasket can be reused if you apply some rtv to it. ^^ cjm has a good point but it wouldent surprise me if it had a 440 and stock jets knowing people these days. id just take the head off and run the piston numbers or check the bore.

[CJM]

fwiw I never put rtv on the rocker cover gasket lol and I reused a few of them. just my opinion tho.

[caseywoods5]

alright guys i'll check the jets when i get a chance (probably tomorrow)... it isn't rich for sure, it sounds very lean (no bogging but pops like a mother)... but if it's a 440 they would have to up the jet size some right? it starts up easy when cold, it actually starts better when cold without using the choke, so if it's a 440 and lean it can't be too far off if it starts and runs good other then popping right?

[dxcody]

its probably not jetted too far off from the way it sounds. Just all depends though. Jetting is different on every quad. Literally every quad.

[caseywoods5]

well i pulled the plug off the bottom of the carb today and took out the main jet only to find that it had no number on it to tell what size, but i did find that the a/f screw was at 3.5 turns and if i put it to the stock 2-2.5 turns then it pops really bad just sitting still revving (didn't pop at all at 3.5 except when decel at riding) and it wouldn't idle at all. so i put it back at 3.5 and it ran happily ever after until i rode it then it popped on decel like before haha... any ideas on why the main jet had no number on it?