i have a 99 300ex and it runs like crap. everytime it reaches high end it wants to cut out every time. i put a new cdi box on it and i got my valves adjusted. by the way my valves are ticking again. i was wondering the reason y it cuts out is A) timing chain B) valve springs making valves float C)rev limiter kicking in to early or D) time for a new machine?
Thanks dudes for ur time, advise will be greatly appreciated.

 

It cuts out because you have an extreme jetting problem. Thats prolly the reason the valves are off. If you've ran it to long with that filter and pipe then your top end is probably toast. Did you ever rejet it?

 

Arent you the fool who was running nothing but a header ? If so that could be your problem.

 

Well if I decided to take my silencer off and then it started running like crap I wouldn't be askin any question on why it not running right. It would be obvious to me to put the silencer back on.

 

the silencer is not my problem people. this thing has done it before i even thought of taking it off. the only reason y i took the silencer off is b/c i busted my clamp and wanted to hear wut it sounded like. im not a fool!

 

The rev limiter on the 300EX is built into the CDI on the 300EX.

Be sure that your jets aren't stopped up and that you don't have a restriction in the air intake ducts.[front of the frame]

Are you running lower gearing or smaller rear tires since the problem started? If so, you could very well be hitting the rev limiter.

As far as this back pressure thing is concerned. Unless your header is 6" long, you don't have any more backpressure with an aftermarket exhaust as you do running a header only. One of the magazines tested this a few years back on a 250X. If your header length is short, you possibly stand the chance of burning the exhaust valves.

If your valves are rattling and you just had them adjusted, then you could have a stretched timing chain or worn rocker arm. I have seen alot of 300EXs with severly worn rocker arms.

While a cause of your problem could be explained by a weak valve spring, it is very rare, and wouldn't be the first thing that I would look at.

Have you reved it high in neutral to see if it still misses?
Hope this helps.

KNOWSALOT

And no, you aren't a fool.

 

thnax dude. here how its went. i wore stock tires off and got vipers put on back. i put fmf pipe on and it ran fine. put kn power kit put in it and then thats when it started to cut out. yes it does cut out when reving in neutral. i dunno dude

 

Well, to quickly check the main jet question, before going back into the carb., put your STOCK air filter back on and see if it does it then.

If it runs better on top end with your stock filter, then you will have to go up on the main when you run the K&N filter.

If it STILL runs badly, it could STILL be the main jet, but could also be the position in which you have the needle set at.

If you run the machine EACH time you adjust or remove something [or add something], it makes it alot easier to pin point the exact cause of your problem. Test ride between each setting, jet size, swap, or whatever.

It takes alot of time to do this, but is quicker in the long run.

KNOWSALOT

 

Hey, KNowsaLot, i have a problem with my 400ex. Some history, last Febuary i was all stock and i went with a K@n air filter and a Pro Circuit t-4 slip on. I left the air box lid on and i only changed the main jet to a 155. It ran fine but not really a big noticable hp gain. Anyway i wanted to get my valves adjusted so i took it to a local mechanic. He did the valves and he redid my carb because he said i did it all wrong and he claims the jet i used was way too big. I didn't want to argue so i let him do it. When i went for a ride it backfired alittle and i noticed when it was held at a high rpm it would hiccup or hesitate a little bit, i never noticed that before. I went with a bigger jet and no difference,he put a 148 on which is the stock size anyway. I can ride ok, actually i have been on it since I had this work done and as long as shift just a little bit earlier than i feel i should i dont notice anything, only when i hold it wide open in 1st, 2nd, or 3rd, its not as noticable in 4th or 5th, probably because i run out of room where i ride. But still, i feel i have to shift too early to avpoid the hesitation, when i rev it in nuetral i dont notice anything. I tried taking the lid off and i used some dyno jets, 165, 170, and still no difference. Do you think the needle position needs to be changed or the pilot jet? 2 weeks ago i gave up and brought it to my local Honda dealer for a tune up, they did the valves, they did not mess with the carb. I told them it ran sluggish on top end, i runs ok but still a hesition on top end. AM i hitting the rev limiter, What does it feel like when the rev limiter kicks in? I did order a WHite Bros rev kit. Well, any help would be appreciated. Thanks.

 

danyeo -

Check out my post regarding your problem, the pertinent info is about 2/3 down the page; here's the link:
click here

Oh, and by the way, I'd switch to using factory main jets instead of dynojet mains. They're the same thing, only dynojet has their own sizing system. Why the different sizing system? So when you need to adjust your main jet, you'll have to go to them in order to keep the sizing straight in your head ~ very profitable for them!

hope this helps,
ogre