The compression release may be nice if you use a kick start all the time, but isn't necessary on the 250 and likely on the 300 either if using the electric start. The starter is significantly stronger than the compression it is up against.

Some KLX650 riders take them off their bikes. It definitely helps the 650 in general, you can hear how hard that starter works. But the 250 starter spins the engine so easy it just doesn't need the help of the compression release.

I've been running without the compression release now for over a year, no issues. When I disabled it there was discussion going here about it I think in the MCM thread. It was dead of winter, 8 degrees F out. My garage is unheated so it was near 8 degrees as well. I figured perfect test - results were the bike fired no problem, no noticeable slowing of the starter.

The release is there to ease the engine in starting to spin, so it is only working when the engine is spinning below probably around 600 rpm. After whatever that low rpm is, the shoes are pulled out of contact. All the compression release, manual or automatic, does is to get the piston past compression on the first spin to gather momentum to spin past with full compression after the initial kick or the first spin of the starter. Experience tells me it isn't needed with the electric start.

That small bore doesn't need the help when using electric start and knowing how to kick start a single with a manual compression release can allow kick starting without a compression release. With a kick starter one puts pressure on the kick start lever easing it just past TDC compression, then lets the lever up to the top to get a full kick, then gives a normal hefty kick for a big single. I've done it with my Yamaha SR500 and it is essentially exactly what a rider does with a manual compression release, get it past TDC compression to get maximum rotation to generate momentum before hitting compression again to start.

Flat track racers do a similar process when bump starting, but do it by rolling the bike backward in gear, until it hits compression - just after TDC. Same deal, allows gathering of momentum when the clutch is released, to hit compression and not slide the rear wheel. Remember this if you ever have to bump start your bike - in gear, pull back until hitting TDC, bump start.

Now you know more about compression releases than you really wanted to know.


As for the MCM, from the thread, it seems it has minimal effect on the 300/330/351 bore engines. I don't know if an actual consensus was reached, so the only way to see would be to try. Do the 300, see how it pulls, do the MCM and see if it does better. A side by side roll on with another bike would tell, though obviously dyno work would be the ultimate test.

 

Parts are here, though I won't have time to start the rebuild for a couple weeks.