300ex Issue I Think

[Tyler01]

I got 3 questions.

1} Well where i live we just got about 6.5 inches of snow and i been riding four a while today. I'll be in like 4/5 gear pinned full throttle and all the sudden it will spit and spuder then shut off like its out of gas. I gotta let it sit there for a min it or two then she will start right up? Is it me or is something wrong.

2} And another question is i'll be riding in 4 or 5 gear pinned and it will bog down and have a knocking noise near the top end but its like it just can't do it. Im 130 pounds and im running 22inch ITP Holeshots on the back. so i don't see why it wouldn't pull me.

3} (This kinda goes with question 2) Well i was riding and it cut off under pressure. Well i go to start it up and it had a little knock but went away 5 seconds later. So am i over reacting or what.

I was running it pretty hard so idk if it was running hot or not. and btw all this happen in one day except question 2.

You opinion is needed thanks Brandon

[dman66]

What kinda mods to the engine do you have???? Air filter,air box,carb,piston,valves and rockers?????Sounds like water or junk in the gas tank possibly,or the tank fuel valve screen could be partially blocked,or the carb may have float problem,or carb jet problem,or spark plug going bad...... I could keep going on and on. So lets start with the above stuff I mentioned. Mine did the same thing, and turned out to be water and sludge in gas tank,which also led into a carb cleaning and rejetting. Check those things and post back...........

[Tyler01]

Its all stock except UNI filter. I went out side today and checked the oil and it was pretty low.It was past the low mark. So i believe that had a kinda big efect on it...But i cleaned the carb not to long ago. so idk

[TheLane]

Sounds like you need to jet your carb for you altitude. Different jets effect different throttle positions. sounds like its your main jet.

and most 4 stroke motors clank and clunk at super low rpms.



http://www.atvriders.com/articles/jetting.html

[Tyler01]

Well i mean it runs fine some days. It will run like a champ but other days it will just wanna die and not do anything. And i didn't know if it was supposed to knock or whatever like that. but when all the snow melts i will get out there and tinker with it. and see what i can dig up

[dman66]

My 250x,which is the same as a 300ex pretty much, engine wise is loud while runnig,but I don't have knocking coming from my engine. It does have a little bit of minor clanking coming from the right hand side of engine mid clutch cover, but I could not figure the sound out. People do say thats normal. Piston rod knock is hazardous!!!! and it's a different sound all together.The knock you hear, is it all the time running? Or is the sound there only when it's running wierd?

[TheLane]

weather also has a big impact on it, what type of oil are you running? and do you notice it start to act like crap when its really cold?

about half way down he talks about oil in cold weather
http://www.atvriders.com/articles/askmickey1.html

[Tyler01]

My motors is like yours...Its louder than my stock exhaust. The noise i hear comes from the top of the motor. Like i said i will be in 4 or 5 gear pinned and it just kinda bogs down and makes a loud knocking {something like that} noise. But i check the oil before i went riding and it was full but after i got done riding and check it the next day it was near empty. So i started it up today and it run fine so idk might just be a freak thing.

[TheLane]

hm weird, it sounds like it might be pistons...and you shouldnt be burning oil that fast....

[dman66]

Back in February of 2010, I installed new piston rings,valve seals,a fresh honning on cylinder.The engine ran with no blue smoke,and ran good.I let my 11 year old daughter ride the quad,but she did'nt lnow how to shift real well which means she stayed in 1st and 2nd gear alot.I believe this overheated the engine alot. Now I have blue smoke,and eat oil.Time for new rings and seals again - sucks - learned my lesson.The compression is good though @180 psi. Now I also ride in creeks alot, which allowed water to get into the engine once when I submerged her in a 5ft hole.Many oil changes on that one.This led into my engine bogging down and no power on engine. I cleaned the carb like 3 times with a rebuild,rejetted carb until it ran correctly and the plug looked good.I also removed the gas tank,and cleaned out some kinda sludge in the tanlk.Put in fresh fuel and gas stabilizer, and she runs pretty good now.I imagine when the weather gets warm again, I'll need to rejet a little again.Before the rejetting of carb, my engine would bog down on 4th and 5th gears also. Now with rejetting, the bogging has gone. My engine basically has stock guts other than a wiesco 12:1 piston,new DID cam chain,K&N air filter,and stock exuast. Sorry that I was rambling on and on.Sometimes this info is usefull to others.

[Tyler01]

I know it needs new value seats cuz it smokes when i rev on it but like i said i started it today and it sounded fine so idk. When i get it back out again ima see how it does and i'll get back at ya

[dman66]

OK, I just got back from riding. My engine is running normal, but I pid more attention to the engine noise - It actually sounds kinda like a push mower engine sound while running. I really never paid much attention to what the engine actually sounded like. While riding I did notice engine slightly knocking,but nothing major. I believe it's caused by downshifting/upshifting and the fuel loading up in the head during shifting.During idle, it just sounds kinda like a push mower - LOL.