Makeing more power on my 300ex

[whitebros300ex]

ok guys i need some help. im trying to find the best may to get my quad faster. its a 03 300ex. so far i have a full white brothers e seires exhuast, k&n filter, stage 2 amr cdi, amr coil and a 14t front sprocket. Just that stuff got my 300 alot quicker but its still just not fast enough. i cant find anymore bolt on things so i was starting to think on the internals. 1 thing though i dont want to bore it. what should i do next?:confused:

[GPracer2500]

How about a cam and/or a higher compression piston?

[razor777]

porting and a cam

[John451]

Cam and 11:1 piston. I just have a cam and an exhaust and it beats my friends 04 soo bad. Idk how much porting really does for it. But id go cam and piston at same time, go with a hot cam so you dont have to get new rockers. You can get your cylinder honed so it will be the same bore but cleaner so the new rings from the 11:1 will ride smooth. It costs like $15 to get it honed. You can get 12.5:1's but you would have to get racing gas for anyting over 11:1 and thats a pain. Putting bigger tires on makes it go faster too but it cuts torque down. So does putting the bigger front sprocket on as you should kno.

[whitebros300ex]

ok so if i get a stage 1 hot cam and a 11:1 compresion piston with a port & polish job u guys think that would make it alot faster? also should i get a racing clutch to handle the power? thanks for the help

[John451]

If you're running stock sized rear tires it should be fine. But i guess you could. it would work better if u got one no matter what you have done. You'll need to rejet for the cam and piston btw. But if you do get a racing clutch let me know where and how much it is cuz i mite want one. Cuz i think i still have the stock 12 year old one...

[honda300EXtreme]

if you want to make any decent power out of a 300ex you will need to dig into the engine and your wallet

id start with a 11:1 piston,
get a cam, hotcam is a good drop in cam, but its definatly not an agressive cam,
id also get a 400ex carb

if budget alows id also get the head ported and polished, the ports in a 300ex are very restrictive,

[GPracer2500]

Don't forget about exploring an altogether different option: sell the 300EX before you sink more money into it trying to turn it into something it isn't and may never be.....and buy a used 400EX to replace it.

[whitebros300ex]

what about that 400ex carb? does that make a noticable power gain? and what size jets do i use? does it bolt right up?

[wilkin250r]

I think you've run out of all the easy options. I can tell you like the idea of that 400EX carb, but you're really not going to see much gain from that when the engine internals are still stock.

You're next mods are inside the engine.

We realize that not everybody can afford a complete motor package all at once, so you can do it in stages if you need to, but you'll end up paying just a little more because you have to buy new gaskets each time you get into the motor.

Your first mod should be a high-compression piston (anything over 11:1 and you'll have to run race gas), then a camshaft. Combine these two mods if possible, and you'll see major gains.

Porting is an excellent modification, but it's expensive, and I wouldn't do it without a piston and camshaft. If you have the budget to combine them all, you'll be screaming. Otherwise, porting is your last option internally.

[John451]

Oh, I found out about a new thing, it's called a 400ex and 450ex. Haha, after riding them, man its hard to go back to the 300, well the 450's just kinda like ehh for me without a pipe.

[honda300EXtreme]

Originally posted by whitebros300ex
what about that 400ex carb? does that make a noticable power gain? and what size jets do i use? does it bolt right up?

yes it will make a noticeable gain, more so if you make internal improvement to your motor, it "bolts right up" the stock boots will work but they are a tight fir to get on.

your jetting will depend upon the mods you do to your motor,
we can help you with that when the time comes

cam and piston would be your best bet to get quite a bit more power. Also is your air box lid removed and is your quad jetted correctly?

[whitebros300ex]

ok im thinking about getting the wiesco 11:1 compresion piston this weekend. what kinda other stuff will i need besides the topend gasket kit?

[John451]

Piston, rings, gasket, maybe wrist pin and bearing. You should defiantly get the cylinder honed or bored. Honing just cleans it and keeps same bore, but with boring, you have to get it bored then get the piston. If ur doing it yourself, make sure to keep from dropping the camchain down into the crankcase and once you get to the piston, put it at TDC aka pull the piston up out of the engine and wrap a rag around the connecting rod so it covers the hole down into the crankshaft because you dont wanna lose the wrist pin clip or anything down there.

[whitebros300ex]

update! i should be getting my 400ex carb somtime next week. what size jets do you guys think i should be running? dumb question. can i stick a 400ex aluminum air box on my quad?

[kawiefan]

check this out http://www.cycleworksracing.net/

[whitebros300ex]

ok i got my carb in yesterday. i put it in im running the same jets i was running in the 300 carb. but for some reason when i hit the gas it trys to die. it started up on the first try it runs good idle low mid but when i tyr to hit fulll throttle it tries to kill itself? whats going on?:confused:

[whitebros300ex]

ok i found out what was going on im running way to lean i pulled the plug and its has white on it. im running a 128 main and a 38 piolt i was thing about getting a 134 main. i think that would do it. sugestions?

[Hondamaster5505]

Supposedly porting does wonders on a 300ex.

I read somewhere that they use the same ports as the 250, so they are way restrictive.

Porting depends on the bike. On a stock 400ex, it barely does anything because the ports are already a decent size. Whereas on a 300ex, they use slightly undersize.

[whitebros300ex]

hey guys welll i got the carb in and got it running real nice. i had to go all the way up to a 170 main.:eek2: i bought like 10 jets to get it right but it pulls real nice. there was a big notcie in acceleration. A+++ to this mod.

[John451]

Originally posted by whitebros300ex
hey guys welll i got the carb in and got it running real nice. i had to go all the way up to a 170 main.:eek2: i bought like 10 jets to get it right but it pulls real nice. there was a big notcie in acceleration. A+++ to this mod.

So what did u need to swap to go to the 400 carb? did the airbox and intake boot fit?

[whitebros300ex]

all u need is the 400ex carb and jets. i need a bigger jet because i took out the choke plate. but for the intake boots i needed to heat it up to expand it. its a real tight squeeze but it fits.

[honda300EXtreme]

whitebros300ex did you seal any open holes after removing the choke, such as the one the choke plate arm goes through, are you running dyno jet or stock keihin jets? because a 170 keihin sounds way rich, i was only at a 148,, and id suggest running a 42 pilot if theres not already one in there, it will help alot in cold weather starts ;)

and just a tip once you stretch the intake boot over the carb, and get it clamped on there, in the future remove the boot from the air box end, rather than from the carb, it will save some time and a few choice words