Tim's ATC500R Decompression Mechanism - FINAL UPDATE!!

[atctim]

Hi all - I don't really consider myself a "Mad Scientist" by comparison of some of the other members here - but here goes:

First off - my problem was my 500R is an 85 motor and pretty hard to kick over - much harder than my 12:1 compression 350X. So a long CR kick starter had to be used for turning the beast over. In turn, that long kick starter interfered with the rear fenders. I had to remove the rear fenders everytime I had to start this bike - and a stall in the middle of an MX race spells disaster when you have to do all that.

My way to overcome this problem is this: short Blaster kicker - decompression release mechanism. With the short kicker - it won't interfere with my rear fenders.

I found on ebay a spark plug hole decompression release mechanism designed for an early 80's dual spark plug head big bore 2-stroke dirt bike. It is designed to simply be threaded into one of the spark plug holes and is operated by a handle bar mounter short cable operated lever. Purchase price $40.00 USD.



My next issue was that a CR 500 head obviously only has one spark plug hole. I took my head to a local expert aluminum welder / machinist. He bored a hole in the head, then plugged it with a aluminum slug. The slug was then bored out to accept the release mechanisms 14mm thread. Machinist price $20.00 USD.





My next step was to retro fit a blaster kicker to the engine. Lots of grinding and trial and error was involved. I used a 1997 CR250 knuckle for this. The knuckle I used had a smaller starter hole for the kicker than the blaster kicker. I simply hogged out the knuckle to accept the kicker. A little more grinding on the length of the kicker that goes into the knuckle for fitment. *NOTE - the blaster kicker is approx. 3 inches shorter then the stock CR kicker.

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I will follow up with installation fitment - and review of how it works once installed in the bike. back to work.......................................

[Louis Mielke]

Looking good Tim. Keep us updated. This would be a lot simpler that the decompress in the side of the cylinder.

[atctim]

Well - I wedged the engine in and slapped the kicker on - and it is indeed very easy to kick over with the decompression release engaged.

[BigGreenMachine]

Cool! A fourtstroke clutch lever with the attached hotstart lever would get rid of that big clumbsy lever from your bars. Just use the hotstart lever as your decomp lever.

Looks great Tim. Does it kick like a 250R now?

[200x Basket]

Looking good Tim. Keep us updated. This would be a lot simpler that the decompress in the side of the cylinder.

true but I would be worried about the squish and detonation.
I love the 500r's, we all come up with a different way to get around the problems!!!!

good job!!

[Louis Mielke]

Lou waits patiently for a fire & ride report.

[Kintore]

Very nice good buddy, still cant beleive how much it cost you, 20 bucks!

I cant wait to ride it again!!

[RedRider_AK]

I remember reading an article somewhere about how those decompression levers were the hot way to go into a corner without brakes on old MX bikes from the early 80's...

I wonder how much compression that mechanism can take before it starts to leak, though?

[atctim]

Cool! A fourtstroke clutch lever with the attached hotstart lever would get rid of that big clumbsy lever from your bars. Just use the hotstart lever as your decomp lever.

Looks great Tim. Does it kick like a 250R now?

Yeah - the lever is kinda big - but not as big as it looks in the picture. It kicks over like a 250cc now - maybe even easier because it kicks like a 250 with a stubby little kicker.

Lou waits patiently for a fire & ride report.

Tim does too - ran out of time on Saturday - will work on it more this evening.

[Louis Mielke]

Cool! A fourtstroke clutch lever with the attached hotstart lever would get rid of that big clumbsy lever from your bars. Just use the hotstart lever as your decomp lever.

Looks great Tim. Does it kick like a 250R now?

If the spring on that valve is anything like mine it feels more like a weak clutch pull that a 4 stroke hot start pull.

[KASEY]

i only have one thing to say about this,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

when you KICK a sleeping one eyed bull most of the time you will be in his blind side,,,,, there will be a day when he fools you and sleeps on the other side ,, that will be the day you pay .....


i have a very long kicker and i kick it like i mean it EVERY time i start it .... everytime .. if you have ever been on the recieving end of a cr500 kickback you know where i am coming from,,,BE CAREFUL ......................

so i feel with your half hearted blaster kicks ,,, one time when that compression release closes at the wrong time something is going to break,, EI: FEET ,LEG, TOES, HEAD ,

[Louis Mielke]

Kasey I bow to you're experience I really do, but I've got tell you though I've started mine with the decompress at least a million times now without fail.

I'm sure its got to do with design, but the way my decompress is you choose when it closes. Engage, fire, disengage after its running. Makes farting noises until you close it and I'm sure it wouldn't be healthy to hold it open an extended period of time but I'm just not sure how there's a chance for kick back.

Once again it might depend on design.

[atctim]

Also - I would like to add - I can kick it every bit as hard - if not hard with the blaster kicker. Think about this - with the long throw kicker - you have to kick it faster - ie - same kick speed with shorter kicker means faster crank spin (think about a big sprocket vs a small sprocket and the effect of the axle spin speed)

I am having some reed issues at the moment. ride (start) report to come ASAP.

Lou - I see that it is indeed the identical compression release we are using.

Kasey - I too respect your opinion on this - and do know EXACTLY what you are saying about kicking back - but as Lou said - you control it with a lever. It can not go closed until you let go of the lever.

[Louis Mielke]

Tim make sure you post up some pics with the fenders on. I wanna see how much you had to cut your fender on the stock ATC setup.

[Jason Hall]

Wow you guys talking about kick backs makes my knee cap hurt lol. I had my 310 kick back and slamm my knee Into the thumb throttle, that friggin hurts badd. Not only my knee but also the bottom of my foot, and thats not a 500

Looks like It should work out good for ya Tim. I would hold It open until you hear the engine run,and not just flip the lever loose thinking ahh It'll start