[AlexE]

I AM WORKING IN A CRF 450X YOSIMURA SYSTEM
WHERE CAN i TAKE A LOOK OF THIS MOD???
IS THIS A REV LIMITER???

i HATE THIS MUFFLER IT HAS VERY LITTLE BACKPRESSURE MAKING MY SETTING RICH PAST 9000 RPM´S I INSTALL A 158=9300PRMS REMOVE THE FILTER=10300 PRPM´S ONCE IT REACH THE LIMIT IT BACKFIRES AND THE ENGINE SPEED DROP DOWN TO 6300RPM'S.

CONSIDERING THE ENGINE STROKE I HOPE TO REACH 11300 BUT WITHOUT EXPLOSIONS.
PLEASE HELP FIGURE THIS OUT

[Asmith]

First off,

Why are you trying to over rev the engine?

It makes max HP at about 8000rpms and max torque at about 7200rpms.

The rev limiter kicks in at around 10000rpms. The pink wire will get another 500rpms but why? You are way past peak power at that point...

Have you thought about a gearing change if top speed is what you are after?

You are on your way to building an expensive grenade.

[AlexE]

yOU ARE RIGHT, I AM GOING TO TALK TO THE CLIENT AND EXPAIN THIS SITUATION. WHEN HE BROUGHT THE BIKE IT HAD THE MAIN IN 145 AND THE BIKE COULD NOT REACH THE 9000 RPMS NOW WITH THE 158 AND ALL THE CARB MODS THE GUY WANT TO KEEP THE THROTTLE ON UNTIL VALVE FLOAT. HE WANTS TO INCREASE SPROCKET SIZE TO HAVE SHORTER GEARING FOR THE TIGHT TRAILS THE RIDE AROUND HERE WHOSE AVERAGE SPEED IS 10MPH. STOCK GEARING CALLS FOR 1ST AND HALF WAY OF 2ND GEAR.
I ALWAYS TELL THESE GUYS TO BUY A REAL TRAIL BIKE.

[Asmith]

What altitude are you tuning for?

A 158 is mighty small for a 450X. Most of us run a 170 at sea level down to a 162 for above 9000'.

Have him drop the countershaft sprocket to a 12 and he'll be able to climb trees with it.

[AlexE]

ONE MORE THING THIS BIKE AN IRREGULAR IDLE IT MOVES FROM 1650 TO 1750 BACK ANF FORTH. COULD IT BE A LEAK OR IT TOO LEAN??

[Asmith]

Could be either.

Try opening the fuel screw up 1/8 to 1/4 turn and see if it stabilizes.

An air leak at the boot can be diagnosed with carb cleaner. Spray at carb boots and see if idle changes.

[AlexE]

Gee thanks for the tip!!!