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1/28/2025
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DeSoto, MO, USA
I've read and seen where you're supposed to leave the stock Yamaha read valve spacer out while installing the v-force 4X reedvalve system..and I've also seen people and heard that you're supposed to leave it in.. there's claims that in the official v-force instructions you're supposed to leave the stock spacer out but the kit that I got contained no such information either way! So what is the correct way.. leave the spacer out or leave it in with the new 4x system
2026 YZ250
Not much help but if the reeds clear without the spacer, then you can do either.
The spacer will increase the crankcase volume, which may give some gains to the bottom end. It's a tuning tool you can use to alter the engine characteristic a little. Do some digging and see what direction will best suit your riding.
On my RM250's, I've always left the spacer in with the V-Force.
Have you tried fitting it yet? Which ever option makes the V-Force sit in the same position as the stock reed cage, is probably the safest one to go with.
Sometimes, leaving the spacer out can allow the reeds to get too close to the inside of the cylinder and contact the cylinder intake tract walls, depending on what type of reed limiter they have. Leaving the spacer out might also shift the manifold and the carb front enough to cause the shock spring to rub the intake boot, especially if you have a heavier aftermarket spring.
I run mine without spacer
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