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all kinds of 300EX info!
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Posted by: honda300EXtreme

i know me and others have answered many of the same questions over a short period of time, so i figured if there is one reference chart with a majority of 300ex frequently asked questions, in theory this could save everyone some time, i will keep adding to the list feel free to add something useful!

ok, here we go remember this all 300ex info, some corresponds to the 250x some doesn't.

stock valve lash =.004
Stock jetting = 122 main , 120 main (high alttitude), 38 pilot, stock needle position - 3rd groove
Wheel offsets - front = 4/144 rear =4/110
Stock gearing = 13 / 38
stock spark plug # - DR8ES-L

stock carb 32mm keihin with accelerator pump.

Ignition: CD with electronic advance

Ground Clearance : 4.6 in. (stock)

Will 400ex a-arms work?
yes, you will need a-arms, tie rods, and 400ex length shocks (16.25), and a shock relocator bracket, 400ex spindles are not neccessary but are an improvement with this set-up,and yes stock brakelines will stretch far enough.

will a 400ex steering stem work?
yes, stops on bottom need cut off beacuse there 180* off, and the little washer about 3/4 will need removed, it is roughly 1'' longer

will a 400ex carb work?
yes, i recomend it for engines that have atleast the basic mods, such as pipe. filter, ect.. stock boots will stretch, all you need to do is rejet, and i recomend a 42 pilot jet

Hardweld rockers are only necessary for a hard weld cam -
EX. web cam, billet cams such as hot cams do not require hard weld rockers, they will actually cause damage to your cam

What is max. compression piston on 93 octane. - 11:1
any thing over is pushing and detonation could result.

engine idle speed = 1,400 +/- 100 rpm
stock pilot screw setting = 2 1/4 out from closed

engine compression with stock piston - 171 - 200 PSI

engine oil capacity -
oil change only - 1.6 quarts
oil and filter change - 1.7 quarts
totally engine dissambly - 2.11 quarts

*if you run a oil cooler about 2 quarts even on basic oil and filter change*

Suspension
Front: Independent double-wishbone with dual hydraulic shocks, 5-position spring-preload adjustability; 7.1 in. travel
Rear: Swingarm with single shock, 5-position spring-preload adjustability; 7.9 in. travel

Fuel Capacity- 2.2 gallons, with a .5-gallon reserve

chain free play - 1 3/4 in. at most

heres a gearing calculator to show how variables such as rev-limit, tire size and gearing affect speed
gearing calculator

here is the link from the tech section on how to rig your reverse set-up, used when you use a aftermarket clutch lever & perch or if you are just tired of spraining something when you try to engage reverse
reverse bypass

quad clicks when start botton is engaged -
its can usually be narrowed down to 2 things, assuming your battery has a proper charge, and it putting out correct voltage at (100% it should be reading about 13 volts)
now, its either your solenoid, or contact brushes in your starter

more info will be added by me constantly,, don't be shy feel free to add anything you think would be useful

Posted by: ridered92

quote:
Originally posted by honda300EXtreme

Will 400ex a-arms work?
yes, you will need a-arms, tie rods, and 400ex length shocks (16.25), 400ex spindles are not neccessary but are an improvement with this set-up,

[/B]

you will also need a shock relocator with the 400ex a arms and shocks

Posted by: honda300EXtreme

^ good call cody, i knew i was forgetting something

Posted by: ridered92

not a problem mike great thread

Posted by: 2muchquad

quote:
What is max. compression piston on 93 octane. - 11:1

This is debateable.engine set ups along with location are just a few of the variables to add to this.Did i mention cam as well?Valve overlap plays a huge factor in ACTUAL compression.Im at around 12 to 1 with my 385ex and i have never ran anything more than 93 oct.Thats almost $3.50 a gallon and that enough let alone paying for race gas.Of course the higher the compression the more strain it puts on the bottom end so i shoot for a happy medium

Posted by: honda300EXtreme

i agress 100% that there are too many variables with particular engine set-ups,

saying 11:1 is the highest you can go is a broad statement, but on the other hand is a good general rule of thumb.

im trying not to get technical in this thread,, its just used to answer a bunch of the basics to save me and your self some time,

Posted by: MY FYN 79

Maybe its just the car nut in me, but I find it easier to understand the difference in our gearing if we use a ratio rather than the sprocket sizes. Treating this the same as rear gears in a car, heres a list I made going from lowest gearing (numerically higher) to highest gearing (numerically lower). The ratio numbers dont really mean anything other than giving a good idea how drastic of a change we'll make.

12/38 - 3.17
12/37 - 3.08
12/36 - 3.00
13/38 - 2.92
13/37 - 2.84
13/36 - 2.76
14/38 - 2.71
14/37 - 2.64
13/34 - 2.62
14/36 - 2.57
14/35 - 2.50
14/34 - 2.43

Posted by: mudrat454

to the top for all to see!

Posted by: Uphill Rush 450

up!

theres alot of great info in here

Posted by: panther99

ttt

Posted by: SET THE STAGE

am i the only one that runs a 33t rear?

Posted by: atv70x

Great info., but I need more. How can I figure what sprockets to use at the TT national over the fourth? I heard it has a 1000' straight away. We have a 300ex with a TC motor and are running 14 in the front and 37 in the rear. This works great for mx and 1/4 mile oval. The tires are 18x10x8. Also, what is a good max RPM?

Posted by: honda300EXtreme

well it sounds like you have a good motor, so i would drop one more tooth in the rear go to a 36.

a 300ex with a well built motor can greatly benefit from a 1000 RPM increase, that is if you still running stock box with stock rev-limit

other than that, you could possibly go to 20'' rear tires but if your running stock width rear end that could hurt you racing TT cuse the 300 is known to be a tad tippy

Posted by: Uphill Rush 450

honda300EXtreme you seem to be good with the 300's

i have been pondering the thought of rebuilding my 250x for quite some time,

now im starting with a stock motor, what do you recomend doing, budget is really no concern at this point, i want to make this thing run strong, i was thinking 11:1 piston, and maybe port and polish,

what do you think about over sized valves and that sort of stuff and what about exhaust and cam?

thanks alot bro, this thread has helped me alot, this should be pinned at the top of the page!

Posted by: honda300EXtreme

ok..

i would first go to four stroke tech and get a 80mm piston kit, it includes sleeve, piston rings, circlips, and head gasket
this kit uses a 11:1 piston and the valve recesses are large enough to accomodate oversized valves,
next i would send my head out to a reputable builder and have them install +1mm valves, all 4 oversized valves will allow alot more airflow to your engine, and show a nice increase across the board, and also have them port and polish your head, for your riding style, then your gonna need HD valves springs because it sounds like you want an aggressive cam, also remember to have them replace your valve seals because it added insurance and there cheap.,

also look into a 400ex carb because the stock will hold you back once you start going this far into it

as far as exhaust, curtis sparks and hmf are both great pipes for the 300 and add great power, just remember to get a full system because 300ex headers are very restrictive,

as far as cams go,
personally i had a hot cam and wasn't impressed, so i would find something a bit more agrressive,

web cams are good, FST can make you a custom cam, curtis sparks sells them and there are many others, you will also need hardweld rockers

hope this helps

Posted by: Uphill Rush 450

thanks alot,

i appreciate all the help

if the wife gives me the okay i might just have to tear into it

thanks again

Posted by: honda300EXtreme

no problem

happy to help

Posted by: dabomb_350x

The Stock carb on a 300EX is as followed. '93 though '98 (49-states), Non emissions, is a 28mm Keihin '98(California) thought current, emissions, is a 32mm Keihin. All shock 400EX have a 38mm Keihin.

Spark Plug gag is .024-.028.

I have a sevice manual if any one need more info. I try to get it for them.

Posted by: honda300EXtreme

to the best of my knoledge the 300ex carb has always remained the same (32mm with acc. pump) in every state, in 1998 i believe they re-routed the crancase breather to the air-box to make it more "emissions friendly" i guess.

i know in certain parts of the country they jet them a bit lean for lower emissions.

again im not calling you a liar. i just have never heard this, and to be honest i dont think it is accurate,

Posted by: dabomb_350x

Carb model number on non emissions is QB02A and emissions is QB04A. 4 mm is not a very noticable difference unless you get a set of mics out and measure.

It list them different in the service manual and a article I have from that Mickey Dunlop in '96 that said you need to put a 32mm carb. on the bike in place of the 28mm.

I look in my owners manual to see it that spec is there or not.
And get back to you. I have both models.

Posted by: Uphill Rush 450

never heard of this either???

why hasnt this been stickied yet? this is the only post in this section that is actually helpful its like my on line service manual

Posted by: dabomb_350x

I was right and I was wrong, it is not a 28mm. In the service manual it says it has a 29mm ventri dia. carburetor.

And a link from on here.
http://www.exriders.com/vbb/showthr...p?postid=218084

Posted by: dabomb_350x

I think the difference, in the size of the carb, is to get the clean air to gas mixture, as close to being the same, as it was on pre-emissions add on. On the emissions bike, they are adding blow-by gas back into the air intake, which would cut into the clean air mixture, so they increased the carb size to offset this issue.

Posted by: 300EXC

jeeze,

this thread here answered every question i had

lol

thanks for posting this up

Posted by: honda300EXtreme

glad this helped

as long as it helped one person it makes this thread worth the time put into it

Posted by: sparks427

hey all would it be better to widen the front or rear of the 300 first cuz i'm gonna do somthin w/ the suspension but i got to thinkin bout it and dont knwo what to do first. thanx

Posted by: SET THE STAGE

front for sure. widening the rear will make it handle horribly

Posted by: sparks427

right on well then i think i'll find some a-arms then. how much wider are +2 400ex arms than 300s?

Posted by: SET THE STAGE

+2 400 arms on a 300 would be about +3.25 (so about an extra 6 1/2" added)

i run them on mine
http://www.uscconlinealbum.com/photos/photo01/9d/71/5a417563f589.jpg

you'll also need a relocator bracket and 400ex shocks. you can get the bracket from jb racing or diamond j's (i think that's what it's called)

Posted by: sparks427

ok for one dude thats bad ***. i'd like to set mine up like that and i foud a couple 400ex a-arms for a pretty good price. is ur rear widende?

Posted by: honda300EXtreme

yea, the 300ex's front end is to say the least a weak point,
the shocks are terrible, and the front end is too narrow for any real kind of aggressive riding (IMO)

+2 400ex a-arms with stock offset wheels should put you somewhere in the 47-48 inch range i do believe

i personally run +1 400ex a-arms and with stock offset wheels i measure in at 45''

Posted by: sparks427

awsome well i just bought repomans +2 400ex lonestars so they should be here in a week. i need 400ex shocks and a relocater bracket and brake lines now so i'll be doin all that here soon. thanx guys for all ur help.

Posted by: NV300ex

ok i have a question only cause im searchin n lookin for it.. maybe im overlookin it... wheres an online download for service manual on the 300ex?

honda300extreme, what brand are your foot pegs, im diggin them.

Posted by: dabomb_350x

In all my searching I was never able to come up with a manual for the 300EX, I ended up purchasing one off ebay. I did come up with a few other models, but they are no long available either do to copy write issues.

Posted by: NV300ex

dabomb---- looks like im going have to do the same exact thing myself...

Posted by: honda300EXtreme

my footpegs are stock, i did make some foot peg extensions but there not pictured..

as for the online manual, most of the sites got shut down,
your best bet would be one off of ebay