Can anyone give me a idea of what size main jet to put in my 00' 300ex.I've drilled 8-1 inch holes in the box lid,and will be putting on a supertrapp ear exhaust system w/headpipe on the bike.Should i start with 5 sizes bigger on the main or maybe more? I live in the flat lands of Arknsas so high altitude isn't a problem. I would appreciate some idea of where to start with the main since they cost around 10 bucks apiece. Also if i can find one i'll get the 350x throat pipe.

Also any reccomendations on where to send black box for hi-po make over.I read that some places re-do the box for better power especially when installing a cam. Ahhh the cam that is another question,but maybe i'll save that for later.
Thanks

 

I also have a 300ex and just modified the airbox and put on a supertrapp IDS exaust system. I'm also trying to figure out the jetting. I actualy got some really good advice from this guy topcat from the forum. he suggested starting at a 135. and work down from that. he also said to run it for a while then pull the plug and check it. if it's white your running too lean (Too small a jet) if it's black you're runnin to rich (jet too big)
he said you want the plug to be a "milk chocolate" color then you're good. but it's trial and error and if you're gonna error error on the rich side. because running to lean makes for higher engine temps and that's a bad thing. of course you also have to feel out the performance as you change jet sizes.

as far as the cdi box I sent mine to TC racing in PA their number is (814)-723-3514

(FYI..Feb. 2000 "ATV Sport" magazine modified a 300ex and showed results)

hope this helps! I've picked up a lot from these forums!

 

So howz the performance of your 300 ex so far (fondahonda) ? How much did the cdi box work cost? Did you notice a real improvement when you installed the pipe?
Seems to me that just by drilling holes in the airbox lid has made a difference in mine.It seems to pull the front end up alot better in second.I could live without the noise that it makes though.Maybe when i install the pipe it will drown out the sound.
I think my next big investment will be some WORKS shocks for the front.

Later
scott

 

I think you would be way too rich with 5 jets fatter. At the most I would start with 3 fatter with just a pipe and drilled airbox lid. You could start with 3 and test ride at 3/4 throttle for a good 1/2 mile. Shut it off without any idling or low end riding, pull the plug and read it. The electrode will possibly be a little dark rather than the chocolate brown you should have. If so, you probably had a little missing or cutting out when testing so drop down one size to two fatter & retest, pull the plug, etc. If the engine was pulling strong and smooth & the plug looks right you're all done & you still have an extra jet for that header pipe or a filter upgrade.
I'm only running three sizes fatter on my Warrior with a vented lid & a Pro Design filter kit so surely you won't need more.
also I have never paid more that $5 for a main jet, even from the Yamaha dealer

------------------
THE AZ HARD PACKER, calmiller@kachina.net

save the public land FOR you, not FROM you..join the Blue Ribbon Coalition online @ www.sharetrails.org

 

Oh, just in case you weren't aware, the main jet functions at 3/4 to full throttle, so that's why you test at that rpm

------------------
THE AZ HARD PACKER, calmiller@kachina.net

save the public land FOR you, not FROM you..join the Blue Ribbon Coalition online @ www.sharetrails.org

 

Thanks for he info AZ Hardpacker(what does that mean anyway)?. I went to honda today and yes their main jets are 10 bucks a piece.But i ordered a kit from keihin that has 5 diff. mains for 18 bucks.Sounded alot better to me.

scott

 

hey scotster 750,
The difference is like night and day.
It's just a whole lot more responsive off the line and the front end lifts up into second. Another thing I did was change the 22" rear tires to 20" shredder they handle much better, grab better, and by going with the smaller diameter tire it helps the gearing a bit.

My friend just picked up a 99 today. It's like brand new. and Its got a pipe and the carb is jetted, and when I rode his with no air box lid it was not as fast, I think it's got a lot to do with the cdi box. Off the line I felt it hit the rev limiter and the bike just kinda leveled out. big difference.I got that done from TC Racing for $85 They're in PA. you send your box to them and they reprogram it. There's an article in Feb 2000 ATV Sport Magazine where TC modifies a 300EX their number is
(814) 723-3514
definately check out the article!
I'm real happy with the mods.... for now.
that is till my friend gets as fast.
have fun! -wayne