300EX help 4-stoke nOOb.

[wrossi2006]

Hey guys this is not my first atv i had a 04 banshee with a few mods...

Anyways ive not had one since 2005 i was in a bad wreck ive been threw all kinda rehab stuff (in the race car) and now im slowly getting my nerves back and i took a trade in on a 300ex for my truck and some cash.

Mods are Full header & Pipe HMF K&N few other's like skid plates .

The K&N has the prefilter with stock lid and the guy said its setup for 93 octane and he says its jetted ..

I am 286lbs and my brother has a 300ex and we run side by side and i kill him and hes 211lbs ... now i put at least 9-10 easy on him everytime. But the pipe is changeing colors (not red) but theres a slight poping when im WOT and i let off... but if i slightly put my thumb on the throttle it wont pop at all ... only when its all the way off...

Should i be worried?

I have not pulled the plug due to i dont know how i should do it ... should i make a WOT pass then kill it slow down and check the plug like you would on a carbed - car?

[SET THE STAGE]

you're running lean on your pilot jet, most likely. mine did that. it was at like 38 or something, now it's at 40 and runs great.

also, check your needle clip, too. if the pilot doesn't help, maybe move your clip down a notch.

[01exrider 281]

mine does that too i will give that a try tomarrow.

[wrossi2006]

ok sounds good im not 100% with thease carbs anyone got a walk thru ?

whats this clip your talking about ?>

[SET THE STAGE]

do you know the basics of a small engine carb like these?

these carbs have a vertical cylinder with a slide in them. the slide is controlled by the throttle cable (when you press the gas, it goes up) inside the slide there's a needle with a clip on it for different settings. the needle blocks off the venturi. so if you move the clip down, it keeps the venturi from blocking off the venturi all the way so it allows a little more gas to come in when your thumb is off the throttle and the slide is closed.

the pilot jet is the jet that's used for no throttle use to 1/4 throttle use. so if it's running crummy when you're trying to start it too, i'd check that. it also contributes to backfiring on deceleration.

you know what i mean?

[wrossi2006]

ok i fixed it .. now my next step is i did a 50/50 mix with 93 and 112 you think it might be a taste to hot for this bike ?

I think this bike is on a stock bore and stroke.

[SET THE STAGE]

yeah, i wouldn't run that. in all honesty, it could be bad for it. not sure if you know how octanes work, but the higher it is makes it less prone to detonation. which is why you need high octane for high compression. if you have a high compression piston, the piston takes a little longer to get to its peak so the gas needs to detonate a little later than normal

i wouldn't run any higher than 93. i run 89.

[wrossi2006]

dang ... the problem is i think its been bored/w a new piston so im going to do a compression test what kinda PSI should i be looking for on a stock motor ?

By all means im no rookie to the race gas but i am to quads with it ...

anyone know what the stock compression is for a 300ex?

[bwamos]

As long as it is an 11:1 or lower aftermarket piston 91-93 octane runs fine. ;)

I'm no help with the PSI.. sorry.

Stock compression is 8.9:1

"most" 300ex affermarket pistons are 11:1

[wrossi2006]

well ... my problem isint the powers its that the bike tops out at 50-52 mph with the GPS and my brothers car rideing beside me .

i would like to go about 70ish or so since i ride a crap load on the street/highway here in north county... i know this bike wont go 70 so im going to go get a 700r and be done with it .

[SET THE STAGE]

no offense but i don't know if a 700 will even go 70ish. it's got the power, but unless you gear it super high, it's not going to. you'll need a super small back sprocket, super big front sprocket, and huge rear tires

[wrossi2006]

yah .. i was just looking at the top speed but it looks like im going to sell the 300ex and custom build a quad .. i just got my hands on a honda cbr900 motor/trans/harness everything its a 03 maybe ?
(its wrecked and i gave 300 bucks for it and it runs)