inexpensive 400EX mods & tune-up tips for trail riding
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1. install a K&N air filter, and trim intake/snorkel flange at the airbox
2. drill holes in end baffle of exhaust pipe, and remove spark arrestor
3. properly clean and re-jet the carb
4. change the sprockets from 15/38 to 16/36
5. run high octane gas, and use some carb cleaner once in a while
6. reverse the front wheels for better handling
7. change oil, oil filter, fuel filter, and spark plug
8. adjust i/e valves, chain, and clutch/throttle/choke/brake cables
9. water-proof all electrical connections with silicone
10.set tire pressure to 4psi fr / 3psi rear, and soften all preload shock settings
11.charge battery, check water levels, and clean the terminals
12.remove swingarm skidplate for better ground clearance in the mud and snow

 

DSAPP

Would you care to expand on number 1, 3, and 4?

1. How do you trip the intake flange and would holes in the airbox accomplish the same thing?

3. Where do you drill the holes in the baffle on the exhaust pipe? Remember, a picture speaks a thousand words.

4. What should the stock jetting on the carb be changed to? Should this be done on the main jet or the main and the pilot?

Thanks for any help.

 

Acually a 16 tooth CS sproket, in a drag race yes, in the real world, no. Too high of a gear ratio for the type of riding the 400ex is made for. Also, with the exhaust, messing with the S/A unit/endcap will yeild no power gains as the main restriction is deep inside the silencer. A sleeper is what I am going for, and with what I have so far, it should be a pretty good setup. My stuff should all be installed by next weekend, so I'll see what my 800 dollar investment got me.

 

250rampage
he never said messing around with the end cap. he is talkin about opening up the the end cap and making and extra hole for exhaust to pass though. this causes more torque and midrange.

 

Oh, I just wasn't sure what he had said, I just put that on there so it wasn't misunderstood. What you speak of with the exhaust baffle is what I did, only on a larger scale (I took out the 3rd plate in the silencer), and I also took off the headpipe, ground the lips off the inside with a die-grinder, and polished the whole headpipe up. The gearing up may be good for some people, but with where I ride, it isn't an option.

 

I have silencer diagrams and pics on my website



Other more serious sleeper mods include the cam of your choice, FCR carb, piston of your choice, etc... Pretty much you can do anything you want to the 400 if you leave the pipe stock (in appearance) and no one will suspect a thing (until you're smoking them).

Also, not really a mod but definitely worth mentioning - ADJUST THE THROTTLE! I still find an amazing number of people that don't know about this condition & haven't performed this yet.

On the snorkel - it's not the same as cutting holes in the lid, etc. There is a portion of snorkel that blocks a significant area of air filter. Trimming this should increase the flow potential of the filter somewhat.

If you plan on cutting holes in your airbox lid, do so behind the filter, so that when you splash mud/water up there, it won't drain directly on the filter itself - also if you open up the airbox lid, you need to do something to allow water to drain - simply remove the bottom plug or do something more elaborate.

 

Also, not really a mod but definitely worth mentioning - ADJUST THE THROTTLE! I still find an amazing number of people that don't know about this condition & haven't performed this yet

86atc250r, how can I tell if my 400 throttle is set correctly? This is my first quad, so I am a total n00b

Also was tinkering today, and noticed something..
When spinning the wheels, the chain brushes ever so slightly against a chain guide (?) behind the front chain gaurd (not that bad, not like you can feel it when you ride or anything, just noticed it when I had the back tires off the ground and spun em). Its a metal plate by the front sprocket behind the gaurd. I imagine it would eventually wear down, but I didnt like the idea of my metal chain brushing that metal plate (metal on metal = bad hehe). Anyways, I loosened the gaurd and rearranged the plate, it just touches by a hair now.. Thought Id pass it along....

 

jetting is "trial and error" 'till you get it right thru plug-tests

 

remember I said "BASIC" mods... that means relatively inexpensive and easy to do

drilling some holes, and changing the sprockets is pretty easy, even the main jet is easy to get too, and swapping an air filter is even easier!

Cams and Pistons, etc. ... now you're talking a whole-other world !

 

The easiest way to do a "quick check" is to pull the rubber boot back where the throttle cable exits the thumb throttle assembly... If the adjuster is screwed all the way in, it's not adjusted correctly and you are only getting approx 3/4 throttle.

If you need any more help, let us know.....