Author Topic: Decompression lever (Read 11943 times)

Phlakaton · **on:** October 16, 2012, 01:25:16 am

So what would cause mine to just not move after riding to work - coming out 8 hours later and - it just wont move. I had to turn the key on and off to get the kick start lever to move to a top-dead spot before I could get it started. 2008 ES Bullet 500 Iron.

Ice · **Reply #1 on:** October 16, 2012, 04:15:51 am

I'm not sure I am understanding which one is giving trouble, the de-comp lever, the kicker or the ammeter needle ?

Arizoni · **Reply #2 on:** October 16, 2012, 05:13:10 am

I'm just guessing but if it were mine the first thing I would do would be to lube the cable and the handle bar lever.
That might not help but at least I would know they were moving freely.

Next, I would remove the compression release valve and try to disassemble it to remove any dirt, old oil that had turned to carbon or anything else that could cause it to stick or bind up.

If I couldn't take it apart I would soak the valve in a good penetrating oil and then try to free up the movable parts.
If I succeeded, I would soak the valve in brake cleaning fluid to remove the penetrating oil and then reassemble it into the engine.

Phlakaton · **Reply #3 on:** October 17, 2012, 12:18:47 pm

Quote from: Arizoni on October 16, 2012, 05:13:10 am

I'm just guessing but if it were mine the first thing I would do would be to lube the cable and the handle bar lever.
That might not help but at least I would know they were moving freely.

Next, I would remove the compression release valve and try to disassemble it to remove any dirt, old oil that had turned to carbon or anything else that could cause it to stick or bind up.

If I couldn't take it apart I would soak the valve in a good penetrating oil and then try to free up the movable parts.
If I succeeded, I would soak the valve in brake cleaning fluid to remove the penetrating oil and then reassemble it into the engine.

Wack thing - this is the lever on the left handlbar - after I have the bike running for a time and I stop and turn her off... the decomp lever works again. Its seems to be when its cold and hasnt been running overnight or during the day at work. This just happened out of the blue (like you guys havent heard that one before - haha). Without looking in person -- where is the compression release valve?

Thanks for the advice everyone!

ace.cafe · **Reply #4 on:** October 17, 2012, 01:43:05 pm

Maybe it's carboned-up or something. Wouldn't hurt to clean it and lube it with ATF.

It's located on the cylinder head, on the opposite side of the head from the spark plug. It looks like it's in a spark plug hole on the head, except on the timing side and not the primary side.

You have to be VERY careful when disassembling it, because it can fall into the engine when the valve is completely disconnected from the body.
It might be a good idea to do this when it's stuck closed, and can't fall out into the engine.
In any case, do it with the engine on TDC, so if it does fall in, it might not go all the way in.

ERC · **Reply #5 on:** October 17, 2012, 01:43:27 pm

On the right side opposite the spark plug. Follow the cable down from the handlebar. ERC

AgentX · **Reply #6 on:** October 17, 2012, 02:14:38 pm

I'm still confused how turning the ignition on and off helped you get the piston to TDC...

ROVERMAN · **Reply #7 on:** October 17, 2012, 02:30:47 pm

Mine did the same thing, would not budge but the decomp worked when i pushed it with my thumb. The valve is on the right hand side of the cylinder head. I took the decomp lever apart and lubed everything, cable was free etc. The lever now operates but still needs a push on the valve to get going. Just a poor design i'm afraid. Unless ou want to retrofit an old style lever you will probably have to live with it, that's assuming that the valve is OK. You know what they say about assuming!
Robert & REnfield.

ace.cafe · **Reply #8 on:** October 17, 2012, 02:33:20 pm

Quote from: AgentX on October 17, 2012, 02:14:38 pm

I'm still confused how turning the ignition on and off helped you get the piston to TDC...

I"m confused about that too.

LarsBloodbeard · **Reply #9 on:** October 17, 2012, 06:38:27 pm

Quote from: ace.cafe on October 17, 2012, 01:43:05 pm

You have to be VERY careful when disassembling it, because it can fall into the engine when the valve is completely disconnected from the body.

As long as you don't take that cotter pin out, you're in no risk of this happening. You can take the spring off and then slide the cable out of that grove and pop it out of the body of the valve. Then simply unscrew the valve. I'll try to attach a pic later... maybe mine is different?

barenekd · **Reply #10 on:** October 17, 2012, 06:40:48 pm

He's using the ammeter to find TDC. When the ammeter centers, that is about TDC.
Bare

Phlakaton · **Reply #11 on:** October 17, 2012, 09:15:08 pm

Quote from: ace.cafe on October 17, 2012, 02:33:20 pm

I"m confused about that too.

I think I confused myself... I just figured what else can I do - turn the key on and off --- and when I did that I kept messing with the kick start arm with my foot. I guess I might have been pushing on the decomp lever off and on even though it wasnt technically moving at all - eventually I could get it top-dead and give it a small kick and start her up. Am I doing something horrible if I do get it started without the decomp lever working? Seems to run and do everything else fine. Man - I love these bikes... so crazy. I keep learning though.

Arizoni · **Reply #12 on:** October 17, 2012, 11:16:33 pm

Unless you moved your hand over and pushed on the handlebar lever, you didn't move anything on or off while you were messing with the key and kickstarter lever.

The decompression valve is there to let the compression out of the cylinder as the piston is rising on the compression stroke.
This allows the engine to rotate fairly easily so the rider can position the piston at the top of the compression stroke prior to starting the engine.
You know the piston is very close to the top (TDC or Top Dead Center) when the ammeter reading goes from minus (the battery is charging the coil) to zero (the points have opened, disconnecting the battery).

Having the piston at TDC before you start giving the kickstarter lever a stout kick makes starting easier because the crankshaft has 1 1/2 revolutions before the next compression stroke.
This allows the kickstarter to get the heavy flywheel (crankshaft) rotating at a good speed so when the next compression stroke starts the momentum of the flywheel (crankshaft) can help to compress the fuel/air mixture.

Starting the engine without using the decompression lever won't hurt anything. It will just make it a little more difficult to get the piston to TDC when your trying to start it.

Phlakaton · **Reply #13 on:** October 18, 2012, 02:32:15 am

I rode home tonight and when I shut her down - it was easy to move the lever. Pulled open the compression valve just fine. But once it sits for a while... no dice. I'll just take a look at the valve this weekend and see if the sucker is fouled up and lube everything good. Thanks again.

baird4444 · **Reply #14 on:** October 18, 2012, 03:37:38 am

I'd give it good squirt of PB Blaster and let it do it's thang overnite. also make sure the cable is lubed. the blaster will clean any buildup and allow it to seat; then burnoff next time you hve a good ride.
- Mike

LarsBloodbeard · **Reply #15 on:** October 18, 2012, 04:01:48 am

Here's a slideshow of how to detach the cable without risking dropping anything into the cyl (note: you might need to loosen your cable). I took it off the bike first just to make it easier to see what's going on. My valve is uncharacteristically clean, since I just rebuilt my engine. I also lapped the decompression valve along with the intake and exhaust valves, just to make sure everything seats nicely.

Hopefully this forum supports animated gifs...

Phlakaton · **Reply #16 on:** October 18, 2012, 12:27:32 pm

GIF anim worked great! That is really helpful man. Thank you!

LarsBloodbeard · **Reply #17 on:** October 18, 2012, 05:16:49 pm

Quote from: Phlakaton on October 18, 2012, 12:27:32 pm

GIF anim worked great! That is really helpful man. Thank you!

No problem. After unscrewing it from the head, just take the cotter pin off, pull that valve out and clean it up. If it's pretty gunked up, you might be able to squeeze a .22 bore brush into the body, or perhaps .17 (I've found gun cleaning rods to be pretty useful for my motorcycles)... I didn't bother with that though, just soaked it in chem-dip for a few days and all the gunk washed off.

barenekd · **Reply #18 on:** October 19, 2012, 07:28:24 pm

Those things look like what we put in 2-strokes in the '60s and '70s. They made for great engine braking. I think what put them out of style is that they sucked in as much dirt as they blew out air!
They worked like jake brakes on diesel trucks and they really slow you down without locking up the wheel.
Bare

LarsBloodbeard · **Reply #19 on:** October 19, 2012, 08:16:28 pm

I was thinking of plugging mine for that reason. I'm concerned about air leakage when I don't want it, both in and out. Gonna wait till I try out the engine rebuild though... I might need that lever for kickstarting now that I have decent compression. The electric start is crap on my bike.

tooseevee · **Reply #20 on:** October 19, 2012, 08:19:08 pm

Quote from: barenekd on October 19, 2012, 07:28:24 pm

Those things look like what we put in 2-strokes in the '60s and '70s. They made for great engine braking. I think what put them out of style is that they sucked in as much dirt as they blew out air!
They worked like jake brakes on diesel trucks and they really slow you down without locking up the wheel.
Bare

That's inneresting - please 'splain in a little more detail. I unnerstand how decompressors work, I unnerstand engine braking, I unnerstand engines. I just don't get how this works. How do you get compression braking with a decompressor?

I'm sure it will all be clear as mud if you just clue me in to what I'm missing.

LarsBloodbeard · **Reply #21 on:** October 19, 2012, 08:29:45 pm

Quote from: tooseevee on October 19, 2012, 08:19:08 pm

That's inneresting - please 'splain in a little more detail. I unnerstand how decompressors work, I unnerstand engine braking, I unnerstand engines. I just don't get how this works. How do you get compression braking with a decompressor?

I'm sure it will all be clear as mud if you just clue me in to what I'm missing.

I don't really know HOW they work for engine braking, but they do. I suppose it probably floods the cyl with too much air, plus not as much air coming through the carb = even less fuel. So basically no combustion, or very weak combustion. Perhaps someone with more knowledge can chime in...

I used to have one on my 3-wheeler and I'd pull it if I needed to slow down in a hurry. It was kind of a cool setup in that it was a lever that stayed open till the engine started to turn then it closed itself. So it gave you a bit of extra oomph when pull-starting.

barenekd · **Reply #22 on:** October 20, 2012, 12:34:50 am

It works because it make a pump out to the engine. If you don't have a decompressor, when the piston goes up on a two stroke, it compresses air in the cylinder. When it comes down the compressed air helps push the piston down, so nothing is really gained. The decompressor forces the piston to push the air out of the cylinder as the piston goes up forming a vacuum in the cylinder, but then has to suck it back in to fill the void as the piston goes down. All that heavy breathing is hard work!
But while it's sucking in that new air, it also sucks dirt!
Some guys did use air filters on them, but I think it lost efficiency.
Bare

Arizoni · **Reply #23 on:** October 20, 2012, 01:02:32 am

It's kinda like the "choofer" I have for my 4 wheel drive truck.

It is intended to be used as a tire pump that screws into one of the engines spark plug holes. A very handy thing to have after you've deflated your tires to drive over long distances of very sandy areas and want to re-inflate them for highway use.

Anyway, it has one way rubber flapper valves on it so when the engines piston is going down on the intake stroke, outside air rushes in thru the flappers.
No fuel/air mixture is sucked into the cylinder because there is a high vacuum in the intake manifold that is also trying to suck air into the cylinder when the intake valve is open.

Another valve between the choofer and the tire closes to keep the air from being sucked out of the tire.

When the piston is on the compression stroke, the air pressure closes the flapper valves and is pushed past the one way valve into the tire.

On a V-8, there are enough cylinders still operating that the engine idles quite nicely but that choofer makes one hell of a racket while its operating.

LarsBloodbeard · **Reply #24 on:** October 20, 2012, 01:59:06 am

Quote from: barenekd on October 20, 2012, 12:34:50 am

But while it's sucking in that new air, it also sucks dirt!

I don't think this is an issue with mine. If you look closely, you'll notice there are two seals. One is smaller, just above the threads. The other is after the vent holes. It vents into the head. I assume into the crankcase... Or maybe that's what that mystery hole was inside the exhaust port.

Ice · **Reply #25 on:** October 20, 2012, 02:53:40 am

Quote from: LarsBloodbeard on October 20, 2012, 01:59:06 am

maybe that's what that mystery hole was inside the exhaust port.

It is !

I have the head off mine right now. Lets see if I can take a decent pic or two.

LarsBloodbeard · **Reply #26 on:** October 20, 2012, 07:22:44 am

Cool! I was wondering what that odd hole was... I didn't give it much thought since it seemed to be there for one reason or another.