Why do we have a manual compression release?

Here's a question that's been on my mind for some time. Why, if our bikes have an automatic compression release mechanism on the exhaust cam, do we need a manual compression release lever?

My understanding of the auto release on the cam is that at low enough rpm, a second, movable cam "lobe" prevents the right exhaust valve from closing completely. When spinning sufficiently fast, the "lobe" pivots away from the rocker and no longer prevents the valve from closing, thus full compression.

If at zero to low starting rpm the compression is released, why do we need that manual lever? Shouldn't that "lobe" engage the rocker when we are just slowly moving the kicker to TDC?

If you hadn't already guessed, I'm still trying to troubleshoot my TE250's hard starting. New intake valves, although needed, didn't help.

Is it hard starting with the kick only or with the kick and button?

Both, unfortunately. The only way I get it to fire is cracking the throttle a bit, which scares me to do because of the occasional kickback through the kicker. I DON'T need a snapped kicker shaft.

The reason I suspect something amiss with my decompression system is that long ago, when I got the bike, I needed to use the manual lever to get the engine just past TDC for kick starting. These days, there doesn't seem to be a discernable compression stroke with the kicker.

I thought the problem had been my worn intake valves. Just had them done, so I shouldn't be losing compression from them. Then I thought that maybe the rings on my Athena kit weren't seated well, or the break in was insufficient, and that I wasn't getting compression from that. However, when it's running, I don't get any smoke. Worn rings would smoke, right?

This weekend, I'm double checking valve clearances, maybe do a compression test (what's a good psi value?), and adjusting my float height (I get a little dribble from the overflow). I'm also looking really closely at the auto compression release--maybe even deactivating it somehow to see if I get my compression back. If I am in fact low on compression.

Anyone else have thoughts?

Did you happen to mess with jetting after the Athena was installed? Could the pilot be clogged or too small? Does the choke on/off make any difference?

Jetting is per the JD kit. Fuel screw is 1.5 turns out. I leaned the pilot, and the only thing I got was an increase in the popping on decel, so I went back to the JD setting.

When the bike is running, it runs hard. In fact, I have no complaints about power delivery or driveability anywhere in the rev range.

It's just that when starting, the starter spins the engine like crazy and I get the occasional cough/hiccup like it wants to start, but I have to crack the throttle open to actually get it to start. And cracking the throttle isn't always effective. I sometimes crank until the battery is flat.

Choke on, choke off, hot start open, hot start closed, it doesn't seem to make a difference in the starting. I get faster idling with the choke, and a lesser elevation of the idle speed with the hot start open. Both of those things seem normal.

Again, it runs so nice when running. I'm anxious to see if disabling the compression release changes anything. Is there any way to remove the compression release mechanism from the exhaust cam without damaging anything?

I'm just wondering if it's getting enough fuel through the idle circuit during starts. If you are sometimes more successful by opening the throttle a bit, sounds like the pilot may be clogged or too small (lean). Fuel screw may also need tweaked? I'm no expert, so take what I'm saying with a grain of salt.

Yeah, I've checked and cleaned the pilot thoroughly. I suppose I can still fiddle with the fuel screw. It's just such a pain to reach.

I tried the flex jet for the pilot, but the starter interfered with it, so I took it off.

It sure sounds like your pilot circuit is starving for fuel. Did you put air pressure to the pilot circuit passages? Do you need to screw the idle screw in quite aways to get it to idle? If you choke it and get more RPM when warm, it sounds lean.
I would make sure there is a good flow of air through the idle passages. If that doesn't help turn the mixture screw out about 3 turns or more. If that helps put in a bigger pilot jet and go back to 1-2 turns out.

I would think that opening the throttle also gives a healthy dose of air as well....and if it really is lean it should fire pretty quick with a few twists of the throttle as the accelerator pump gives a spray of fuel.....

as a rule 4 strokes dont like rich mixtures when hot starting.....

I would make sure your float level is OK and isnt dribbling....and if the bike runs reasonably well when hot...try the fuel screw leaner...try half turn at a time clockwise

as a test..try opening the throttle twice to wide open to wet the cylinders a bit.....and then try it....if its worse then your rich

just my two cents....

What pilot are you running? I ran a 38 pilot jet in my '07 TE250 and it seemed better starting and idling than with the 42 pilot.

Sounds familiar... Bike runs good with JD jetting, but starts hard. Sounds EXACTLY like the issues I was having with my last KTM 450 before I adjusted the valves and all those pesky starting problems disappeared. Just another thought.

my vote is decomp/decomp cable

SInce the starter is spinning the motor over so freely, this sounds more like a compression problem to me rather than a fuel problem. I had a DR-250 that I had slightly stripped the plug threads on. It was difficlut to get any socket on the plug way down in the head like it was. Anywhoooo, As soon as I tried to crank it, no compression. Took it to the dealer, Took them 15 minutes to figure out I had a little piece of thread from the plug hole stuck in the exhust valve. It was doing bsically the same thing as a stuck decomp would have done. In fact, they looked at the decomp first because they though it was stuck open.

I would say that you may be slightly loosing compression from teh decomp. In other words, I think you're on the right track. Knowing what I know, if this were my bike, that's where I would be looking this weekend. Your decomp cable may be slightly stuck, and not allowing the valve to close completely. As slight crack as small as a couple of thousandths would be enough, but it would still run. Unhook the cable, make sure it moves freely. Make sure the decomp swith activates freely and closes completely. If not, open here up and clean here out. You could have some slight carbon build-up keeping it cracked open, maybe even mud. Also, if it seems o.k., try to turn it over with the cable unhooked, this would tell you quickly if it's the cabel or not. The cable may also just be too tight, or pinched on something.

I think you're sniffing in the right direction. I think if you keep at it, you'll sniff out a problem with either the cable or the decomp. That's where I'd be spending my time. Not saying it couldn't be something else, but this just sounds all too familiar to me.