Has anyone changed the jetting on the evo 300 4t. Mines runs fine at low-med rmps but will not rev out and is producing black exhaust. At high revs it cuts out then revs up then cuts out etc. but never smooths out. I installed a jetsie air screw but it does not change the high revs. The stock main is a 120.

Edited September 3, 200916 yr by Fpete

The Jitsie screw only affects the bottom it has nothing to do with the top. Have you moved your needle ? If not move the clip up one slot to lean it, you will find there is also a thick and thin plastic spacer on the needle that can be used to half step the needle also. Go down on the main one or two sizes. The bike could use more air flow but I want go into that.

The factory has a Ti pipe that works really well, adds a little more power all the way across the power and let's the bike breath. The stock pipe is really quiet but chocks the bike from reving up. The 2010 Evo uses a differant cdi I believe to help the mid and top power, I may be wrong and am sure some one else will chime in to help you also. Loved my 300 evo.

Sorry Pete I just seen the above 6000ft. What you need is the spring kit for the carb, it is a must have option. The kit consist of 4 or 5 springs, allowing you to tune the CV carb. The stock spring is to stiff not allowing the slide to raise properly, less atmosperic pressure. It makes a big differance !!!!!! Get a spring kit you will be happy.

I would have thought more would have chimed in ?

I would have thought more would have chimed in ?

There is only one Ok'ie that goes up to maximum altitude! On a Beta 4T!

Good job Ronnie!

What spring you running at 13000, I suspect about #3?

Copie, I think you better site down ! Ok- are you sitting ? I was on a two stroke ! and -O- i'll tell you the rest later cause it would cause you to have a heart attack. And your to much entertainment for that.

At 13500 feet it would be spring #5 ! As light as you can get.

Hi

FWIW on my rev4 250 4T .... they are sent from the factory with lean mid range to pass emissions testing and a large main jet to stop seizing our new bikes.

I reduced the size of my main jet from a #127.5 down to a #112.5 and moved the needle clip all the way down (to raise the needle). Boy did it make a big difference in the mid and high end, really helping to get it to rev out and bags of power.

I'd pick that the 300cc should have a #115 or #117.5 main jet at sea level to help it to rev properly. For altitude I'd be going down a size (ie a #117.5 would go down to a #115..... or even a #112.5 if it bogs down)

Ralphy

The key is he's above 6000 feet the slide can not over come the spring in a CV carb. There is less atmospheric pressure, so when you open the throttle the slide can't open correctly. It will come up part of the way and then no matter how much you turn the throttle it will not open but part way and make you think it's in the jetting- the jetting is only part of it and you can chase it all you want and it will never work correctly till you get the proper spring in the CV carb.

I have rode my beta 4-stroke at altitude with out the spring kit and was NOT happy (around 7000'-9500') so I know the spring set is a must ! And have rode at altitude with the spring kit it works ! Once you have the spring set you want have to move the jetting very much from stock. If I remember I was around 117-120 main, and down one or two on the pilot also it was a 300. I know stock at my elivation around 800' it needed jetted just a little so i'm with you on that one Ralphy. At 800 ft. I ran the second or third spring for a quicker reponce.

Thanks all!

I already changed to the lightest spring (4th, blue) and will try a smaller jet and let you all know how it goes

Pete.

Edited September 3, 200916 yr by Fpete

Blue spring, 115 main and the needle clip up one from stock. Works great!!!!