On the compression release, I'm kind of wondering, is it really needed? As freely as the 250 spins, is the release really needed? I know some KLX650 riders pull the release off their bikes and still spin it over - if you ever heard the 650 turn over with the release you'd wonder how it could do it without!

I know when the spring came off the compression release in my 650 somehow it beat the snot out of the shim on that valve (shim over bucket) so I'm wondering will there be a similar issue with the 250. Is it mechanically safe to pull the spring off.

I know Marcelino said when they did just the cam timing without altering the release, the engine was near impossible to start when hot. Apparently enough thermal expansion to cause a large loss of compression.

 

Good job tackling the cam mod! It is well documented that the cam mod likes a bigger jet.
I really liked the cam mod, gives it a nice boost and feels more like a dirtbike.

 

After having worked on a few DOHC bikes without compression release, I'd say it's fine. The case I wanted to make was a CBR1000 I replaced a cam chain tensioner on. It was a shim-over bucket design. For the sake of comparison, it was essentially 4 250s. But because it was a 4 cylinder, you typically had a cylinder in the "combustion" stroke (minus combustion) so there was no release. But you also had cylinder(s) in compression, so I imagine the stresses were similar. That's my justification for not needing. I've seen lower compression thumpers also not have it but that was SOHC stuff.

I could be totally wrong, but after viewing the design of that compression release, I feel like it's not a big deal. One thing I did note though was that it 'flapped' around a lot when the engine was cut off. If you cut it off just right the ACR and starter clutch make this loud click noise. That'd be the only concerning thing, but is infrequent.

Thank you! I stepped up to a 124 here at almost 6000' feet and I think it still prefers the 120. I'm hoping I can go back to having my snorkel on... I just prefer a more stock setup when it comes to induction. I ride in dusty areas a lot.

 

Do you have a KDX snorkel? If you must run a snorkel that is the one you want. My cv carb seems more responsive with the snorkel than not.

 

And yet KDX owners routinely remove their snorkels..

 

Thing with a 4 is that one cylinder is also coming off compression, giving a bit of a push to offset the compression. I do know there were a few twins that ran compression releases. I will also tell you having owned a couple Yamaha SR500s you DON'T start one without the compression release unless you literally stand on the kick start until it slowly eases just past TDC compression
and that ain't a snap. Much quicker with the manual compression release, kick it up to TDC, then pull the trigger and quickly move it just a shade further and KICK! Only other options are to pull it backward up against TDC compression then either KICK or push and bump start (like a flat tracker). That experience and how slow the 650 turns over is why I won't take the KACR off the 650, but the 250...

I think you're right. I think the compression release was there from the kick start versions and not really needed on the electric start versions - considering the Honda NX250 from the 80s didn't have any compression release on that dual overhead cam thumper nor does the current CRF250L dual sport. I'm thinking I may just press the release out of the cam and leave it out.

 

You are right on the 4 cyl always having one coming off compression. My point was that the valvetrain won't know the difference and disabling the ACR would just make the 250 like any cylinder off the CBR1000 (albeit some massive differences haha) I couldn't really imagine kicking over more than a 250 without a compression release though. Just for comfort. The rod sees way greater stresses under operation but I figured it'd be a pain having to through your weight in possibly multiple times to start. Also, I'm jealous of your SR500s haha I've wanted a new SR400 since Yamaha announced them.

If it makes it any easier, I'd just leave the ACR in with the spring out. If you run in to trouble for whatever reason its easy enough to put back in. Though if you end up getting new cams or something, I wouldn't bother switching it to the new cams. That being said though, I do also believe it is fair to remove something that would otherwise be flopping around at the end of the can every time you killed it or started it.

 

I did some quick internet research and found that the old Honda NX250 had no compression release and the new CRF250L doesn't either. I'm thinking the compression release is a throwback to the KLX300, which might need it due to the kick start. I may try taking the release off completely.

 

It would free up some reciprocating weight also... The cams are half crank speed but still....

 

Good point. I may remove mine when I replace the crappy valve cover gasket. It is easy to remove with a long bolt fed through the cam (Kansasklx style). It just taps out no problem, with the cam off the bike of course.