I have a month old 300ex. Yesterday I was adjusting my throttle so it would open up fully. Well ever since then it has run very bad. Yesterday I rode it for the first time since adjusting it and it died on me going full speed. It was sputtering and backfiring and all that bad stuff. Then after that it ran fine for about 1 hr. Well 2 hrs later I rode it around the yard again. It died on me again. Sputtered and backfired again. Today I was going to ride it and I couldnt even start it. The plug fouled so I cleaned it and got it running. I start goign down the road and it does the same thing to me. Will adjusting the throttle do this? Someone help me please. My dealer told me as long as I didnt add or change something internal then my warranty wouldnt be voided with anythign external. Is the throttle counted as internal? Will my warranty be voided? Someone please help me. Thanks

mpm

00'300ex (broken)

 

If the plug is fouled...than your jets are wrong, you will need to change your jets. SOmone who knows more than me about it could tell you what size to run. But i am almost sure that it is just your jets. Not a big problem at all. Everytime you even THINK about doing someting to enhance motor performance you need to change the jets.

 

I'm assuming you haven't done any mod's to you 300EX...which could very well affect jetting...so on a stock machine I can't see how adjusting the throttle cable could cause your problem. But if it's fouling the plug, it sounds as though you're running too rich at wide-open throttle. On the other hand though, if you removed anything on or around the carb, it may be that you have an air leak and it's running too lean. Kinda hard to troubleshoot without knowing more, or actually seeing the machine. If the problem is only at wide-open though, I would try to re-adjust the cable again by removing the intake boot on the airbox side, and adjust the cable so that the slide in the carb is just at the top when the lever hits the stop in the throttle housing. Then reinstall the boot securely, check to make sure everything is connected to the carb, and then start it up to make sure the cable doesn't bind (or the motor rev up) when turning the handlebars from side-to-side. Lastly, I'm not trying to insult your intelligence, but make sure you're not running with the choke on. I had the same symptom once...started up my machine and rode kinda easy for 5-10 minutes to warm it up, but when I first nailed the throttle it sputtered and bogged out real bad...took me a few minutes to realize I still had the choke on.

 

Well mine is stock for right now. I have never heard of having to rejet my carb but who knows. I looked at my spark plug and it was black which could possibly mean it is running too rich. I am not for sure though. I will check to see if my throttle increases tomorrow morning. Thanks for your help.

mpm

00'300ex (stock and possibly broken)

 

If you only had it a month take it back to the dealer!! Ever heard of a warranty?

 

Well it quit doing it after I changed the plug. I guess it was that but I dont know why it would have fouled it.

mpm

 

You are probably loading up with too much fuel causing the bike to run very rich. My guess is your plug was black, not white. This means you are running rich. Adjust your cable back where it was and recheck your new plug after a ride. Don't take every peice of advise you get on this forum as the gospel. If your bike is running smooth and reliable, don't change anything.

Let me know if I was right. If I was wrong keep it to yourself please.

Greg

 

Ok, you're running rich! It wasnt running bad before cuz teh throttle wouldnt pen all the way up. When you adjusted this it allowed the throttle to open further therefore putting more fuel into the cylinder fouling the plug. You need to take out the main jet, look at the number and get 1 to 2 sizes smaller, probably just 1. Put the new one in and that should fix everything!

 

Alot of people don't understand that a motor is an air pump. It works on the principal of what goes in must come out effeciently. The problem is you are looking for a way to get more performance by getting more fuel into the carb. If you really want more performance, you have to improve the pump from input to output. You want to keep the fuel/air mixture basically the same. So if you add more fuel, you need more air to go into and out of the bike. The guy that said to change jets confuses me. The bike was fine before. You adjusted the cable in order to lift the slide more and get more fuel into the bike. Apparently you got more fuel, but you are not flowing more air. This fouls plugs as you have learned. He suggest changing your jet.

Why? To remedy the problem you have caused. return the bike to its original adjustments and you will be fine.

Greg

 

Well if this is so then why does it run fine now? My dad adjusted the cable more. I didnt have it all the way open and now ti runs fine after I changed the plug. It was running rich for those 2 days but only those 2 days. I have checked my new plug 2 times since then and it has been kinda black around the edges but a nice tan color on the prong.

mpm

00'300ex