Best boost for 300EX

[Israeli 300EX]

Hi all,

What for yours opinion will give the best boost for stock 300ex engine with the Max of about 300$ to 400$ for parts only.

Long life is important so CDI is not part in this game…
Exhaust is a different discussion also.

Normal use for ATV W/O racing
(Sportive trips and so)

Please put links of nice kits or mod and prices if you have so.

Thanks
Boaz - Israel

[465Stroker]

I have built many 300EX's and I can guaranty you that a 330cc kit will give you the biggest bang for your $$. You should be able to but one for around $300 which would include: piston, sleeve and gasket kit. Figure an additional $80 to have you cylinder bored & sleeve installed. The stock exhaust will hold it back a little but it will still make a huge improvment. Reliability should not be a problem if you keep your compression between 10:1 and 10.5:1 with the stock cam. Stock your motor is 282cc so that would be a 48cc bigger motor!:macho

[bwamos]

Absolute Best bang for the buck for under $500 on a stock 300ex is to get an Aftermarket Pipe, K&N Filter, and rejet.

Dyonojet Kit is a little overpriced but excelent if you're not good at doing your own carb jetting. I used one several years back before I really got into wrenching. Just follow the directions and you're set.

Reccomended Pipes:
HMF Slipon (best bang for the buck), w/ a White Bros Header pipe.
WhiteBros E-Series (middle of the line) w/ header pipe.
Curtis Sparks X-4 (more expensive and loud, but my favorite), full system

I reccomend replacing the header pipe because the stock header has a very small diameter and doesn't allow much flow.

Regarding Cash limitations.. I'd go HMF w/ WhiteBros header pipe. (looks and sounds good too)

With the pipe/filter/jets you will see a HUGE difference. Stock hondas are very "corked" due to people looking for any reason to sue someone.. lol.

The next step on the power scale is lots of engine mods.

Just go with the pipe/filter/jetting. You'll be pleasantly supprised. Any more you'll jsut want to buy a 400ex. ;)

[maxim]

a 400 ex carb would be hard to beat on a cost vs. power gain.:)

[bwamos]

Won't do any good w/o the pipe and filter. ;) You'd just loose bottom end torque because of the lower intake velocity.

[Israeli 300EX]

Thank for all answers till now!

I'm going to open the engine top end for cam chain and piston replacment.
The cam chain make's some noises and the piston still stock and old.

I'll do all the work so the price limit is just for the parts.
(W/O the cost of the cam chain and gasket kit).

I mean - what piston, with or w/o sleeve, with or w/o dynojet, etc.

Thanks again

[mutmut]

Hello,

I also have a 300ex I want to put an exhaust on. I know bwamos said HMF (FMF?) slip on...Which one?? also, if I get a header pipe do I also need a mid pipe?? Thanks!!

[bradley300]

there is FMF and HMF, most will agree the HFM is the better of the two;) HMF does not make a header for a 300ex, but you can use a white brothers e-series header (no mid pipe needed) you can more than likely get the HMF slip on and WB header from the same dealer such as thequadshop or C and D.

Israeli 300ex, if you want the most power possible. order a 350cc pistom kit from gthunder (www.gthunder.com) you will need a sleeve and it comes with it. for less money, just do a normal bore job a few thousandths over just to clean u the cylinder and use a good high compression piston (11:1 is good, but still shouldnt require race gas) the 350 kit will deffinatly run better than stock, but the best idea is to get gthunder to port it and use what ever cam they suggest along with it, as weel as a good exhaust and air filter

[frosti108]

maxim has a point. after all of the mods ive done to my 300ex, the most impressive was my last one. the carb.

it feels twice as fast now after only changing the carb from stock to a mikuni 38mm

[jgray]

Great post !! I have to replace my valve seals. Blowing some smoke !!! I wanted to see what I should also do while I am in there. I was just thinking a .020 or .040 over. Could someone break it down on what all should be down. I have read about boring out the exhaust ports, but no the intake ports ??? Is it worth just going to the 330 kit. I don't want to loose reliability and want to run pump gas. Maybe its not worth doing anything, but since i'll have it open, thought i should take care of business if needed !!!

Thanks
Jason

[bradley300]

if you get a 330 (or 350), it will be faster than the stock one, but IMO, its really not worth it unless you get a good port job, cam, carb and a exhaust. you can get an 11:1 comp. piston and be just fine with pump gas

[bwamos]

A couple short bullet points.

A 330 kit will require you to resleeve.

If you just want to bore out and hone the existing sleeve go with mid sized bore w/ 11:1 comp. (you'll rev a little faster too). No matter what you do you will have to hone out your sleeve to put in a new piston.

If you have to do headwork anyway.. of course get it ported and polished.

If you want more top end HP (what the 300 is lacking) get both the Intake and Exhaust valves oversized.


its really not worth it unless you get a good port job, cam, carb and a exhaust.agree (carb is optional depending on what your looking for though)

[jgray]

I am gonna rule out the 330 kit. If I just go to a mid-sized bore, port & polish & oversize the intake & exhaust valves. I should be good.??
When You say mid sized, What size?? .040" over ??
So parts needed will be:
Piston (w/rings & gaskets)
Oversized Valves (Intake & Exhaust)

Modifications & Labor needed:
Bore out Sleeve
Port & Polish
Bore out Valves.

Does this sound right. I will feel an noticable difference with this right. I am not expecting a miracle here. I love the low-end torque, but enjoy flying down the dirt roads !! Any other suggestions !!

thanks
Jason

[Israeli 300EX]

Can anyone say more about the oversize valvas?

Is an oversize valves works with stock cam and rocker?

Do I have to buy other items for oversize valve work?
(valve guide or valve seats for example)

and finale - where to buy or what is the price of the parts for head work?

Thanks again for all.
Boaz

[bradley300]

you would be better of with stock valves and a good cam IMO

[jgray]

So stay with stock valves. Am I ok with just replacing the seals, or do I need new valves? Is there anything else I should get for the smoking issue ?? Should I do anything else since I am in there??

Thanks
Jason

[bradley300]

if the valves arent bent, they dont need replacedi would still clean around the seats and any carbon in the head since your in there

[44oEX]

Originally posted by bwamos
Won't do any good w/o the pipe and filter. ;) You'd just loose bottom end torque because of the lower intake velocity.

actualy, my friend with his stock 300ex with 400ex carb could easily take a piped/filter/jetted 300ex. so it does work, and you don't lose any botton end.

the 400ex carb is by far the best mod for a 300

[bwamos]

Originally posted by 44oEX
actualy, my friend with his stock 300ex with 400ex carb could easily take a piped/filter/jetted 300ex. so it does work, and you don't lose any botton end.

the 400ex carb is by far the best mod for a 300

And he has 100% stock filter, and pipe.. as well as everything else but the carb???

Doesn't make any sense to me.. lol. Not sure how it can push any more air out of the tiny 3/4 head pipe coming out of the engine, lol. I mean that thing looks like a 90cc headpipe.. lol.

Not saying your wrong.. I dont know anyone who has put a 400ex carb on a bone stock 300ex. Just seems very strange.

[spudwackr]

Not trying to hi-jack this thread but the stock 300ex head pipe looks like crap. At least mine does. I can't believe it works as good as it does.

[44oEX]

Originally posted by bwamos
And he has 100% stock filter, and pipe.. as well as everything else but the carb???

Doesn't make any sense to me.. lol. Not sure how it can push any more air out of the tiny 3/4 head pipe coming out of the engine, lol. I mean that thing looks like a 90cc headpipe.. lol.

Not saying your wrong.. I dont know anyone who has put a 400ex carb on a bone stock 300ex. Just seems very strange.


yeah 100% stock, with cut fenders, holeshot tires and a little paint.

the first time they raced I was on the back, so with the extra weight the piped 300ex could hardly keep up. And without me on the quad, he ran away from the piped 300ex, gearing is the same and tire size is the same

oh and a couple days later we had to rebuild his 96 300ex cause there has not enough compression to start it lol ( not cause of the carb, just cause it's old ). So yeah the carb does work wonders for some reason.:D . And yeah the stock pipe sucks

[spudwackr]

Not trying to be a d-head. You are saying that a possible $60 dollar mod http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=4554788946&category=43981&sspagename=WDVW could save me 500 bucks?

[44oEX]

well maybe, it all depends on what your 500$ mod is?

[tater_kamik]

boost would be a yfz :p jk