All kinds of 300EX info II

[honda300EXtreme]

Im glad to see the original thread has helped people out. But I was reading through it the other day and it has started to get a little cluttered so i figured i will make another one that is a little bit more organized. This one will contain the same info but it will be a bit easier to use as a reference.

i apologize to those who have posted info. i cant take credit for alot of the info in that thread so if something usefull was posted by another there name will be underlined at the top of the post. (gotta give credit where credit is due)

as always if you have something usefull to post or have any questions fire away

thanks to every body who has helped.

[honda300EXtreme]

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
(300ex CDI will not work on 250x)

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 cams. 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 hurting yourself when you try to engage revers 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

Common Rear end Swaps:
A 01 raptor rear shock will work but they are famous for blowing bladders on the 300ex. newer raptor shocks can be made to work. but because these shocks have a piggyback resivior the left tube that goes to the airbox will need to be cut out and the hole in the airbox will need to be sealed up.

a 450R swingarm will also work, how ever this set-up requires tabs to be welded or bolted to the frame to accept the linkage. You WILL have to use a 250R rear shock, linkage is up to you, the 250r or the 450r linkage will work, carrier and axle, and rear brakeline will also be needed. the swingarm is around 3 inches longer
the 350x rear end will also work
same as 250r
more info will be added by me constantly,, don't be shy feel free to add anything you think would be useful

QUAD BOGS WHEN IN WATER?
alot of times it is your carb vent tube. the one that hangs down behind the motor. the problem is this tube gets submerged, you can either trim the tube shorter, or put a T splittler on it and add a different length hose. other possibilites are an exposed wire.

[honda300EXtreme]

MY FYN 79

sprocket combinations broken down into gear ratios.

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

[honda300EXtreme]

2muchquad debating the opinion of 11:1 compression piston as the maximum on 93 octane


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

[honda300EXtreme]

If budget is not a concern and you are looking for serious gains here are some suggestions:

big bore. most common size being 330 cc's but there are people running as large as 390. 4 stroke tech has several options
as well as C&D racing (site sponsor) he did the head work and the machine work for my motor and i was very impressed.

next i would send my head out to a reputable builder and have them install larger valves +1 and +2 being the most common. 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 if you plan on running any type of agressive 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.

alot of people ask why do you need hard weld rockers. the answer is simple. If you buy any type of agressive cam the process in which it is created makes the surface much harder than the stock or billet cam. A stock core will be taken and they will build the surface up and machine it to there specifications. the new surface will be harder than your stock rockers. if ran this way for an extended period of time you will destroy your new cam and the rocker arms. hardweld rockers go through a similar process as the cam.

[honda300EXtreme]

dabomb_350x

The Stock carb on a 300EX is as followed. '93 though '98 (49-states), Non emissions, is a 29mm Keihin '98(California) through current, emissions, is a 32mm Keihin. All stock 400EX have a 38mm Keihin.

Spark Plug gap is .024-.028.

[honda300EXtreme]

SET THE STAGE

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



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 ran +1 400ex a-arms and with stock offset wheels i measured in at 45''

[honda300EXtreme]

heres some random info that was thrown around

torque for the clutch basket nut 81 ft. lbs. and the bolts that hold the clutch springs in should only be snug. the spring tension will hold them in.

a 400ex bumper will work however a few spacers will most likely be requied to fill some space

stock speed - 54-55 MPH

stock horse power 15-17


will 450r a-arms work on a 300ex?
QuadCobbler

The mounting tabs on a 450 frame are wider than a 300ex. You would have to cut the tabs off and move them about 1". 250r and 400ex arms both fit the 300. The is some one on here that had a frame moded to fit 450 arms.


common shock swaps (if your using a relocator bracket) 400ex, 450r, yfz 450 they are a little shorter (15.75) and need ground down, z400 as well as others

[honda300EXtreme]

Uphill Rush 450

he asked: my 250x has a brand new wiseco piston, and recently new valve seals, but it still smokes untill warm is this normal?

yes this is normal, the rate at which aftermarket pistons expand differs from that of the stock pistons,

different metal types : (cast & forged) are the main factors in this


sparks427
how much more power do ya get w/ a 330 big bore, a stage 3 web cam, port and polished head, oversized valves, an oil cooler, sparks x-4 pipe, and k&N filter w/ 400ex carb. not sure if the hardened rockers and the HD valve springs figure into that but if they do how much more does that add

with that set up, anywhere from 28- 31 HP is respectable,
(stock 400 range)
the engine builder plays a huge factor into this though

[honda300EXtreme]

chargercalvin asked
can i put a 450r or 250r hood on my 300ex? it has stock front plastics

yes either hood can be made to work. the fender style and year will determine how much modification will have to be made. it will not just bolt on.

he also asked

what is this thing??? it is loose. i can pull it right out with ease. should i put a little liquid gasket on it?


that is a crank case breather and a think layer of silicone would not hurt.