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.

http://www.venustel.com/~tkeister/decomp1.jpg

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.

http://www.venustel.com/~tkeister/decomp2.jpg

http://www.venustel.com/~tkeister/decomp3.jpg

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.

[img]http://www.venustel.com/~tkeister/decomp4.jpg

http://www.venustel.com/~tkeister/decomp5.jpg


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!!!!:D

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 ,:D :D :D :D :D :D

[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.

http://i106.photobucket.com/albums/m254/louis_mielke/500/decompress.jpg

[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 :Bounce :lol:

[Louis Mielke]

Jason it's not like a 4 stroke decompress. Its doesn't "catch" you're literally holding it open with the lever, it snaps closed immediately when you let off.

[BigGreenMachine]

Very cool! Some info I did not know before.

Do you think it is possible to hold it open with the hotstart lever?

[Louis Mielke]

Its possible but honestly I WAS using the stock 450r decompress lever and it was VERY uncomfortable.

[BigGreenMachine]

Thanks Louis! Going through with this on my own 500 the summer. The g/f has to be able to kick it over. lol

[Louis Mielke]

I hope your kidding, that or your g/f is a freakin football player.

Yah know I hadn't really thought about it but sorry for littering up your thread Tim.

[BigGreenMachine]

Goldfinger I think makes a lefthand operated throttle for snowmobile hillclimbing and sidehilling. It lets the rider hang off the left side of the sled and still control the throttle. With that system you pull the lever in like a clutch but its smaller then a clutch lever.

Just something to look at if your like me and do not like the idea of that big lever on your bars.

[KASEY]

hey i always say theres got to be a better way,,,,, i like the way yours is mounted louis.. i had one on an old suzuki i had 50 some years ago,,, maybe your on to something,,,,,,,,,, my daughter rode my 500 last season,,, it was funny :lol: :lol: :lol: :lol: :lol:

[cr480r]

i would just run a fywheel weight and a cylinder with the decompression scallops above the exhaust... blaster kicker should work just fine while wearin boots...

[atctim]

Lou - Don't worry - you aren't littering it up too bad yet :)

BGM - while troubleshooting my starting problem yesterday - I had the wife kicking it over for me while I was checking for spark. With the blaster kicker - it kicks like a stock 250R - really pretty effortlessly. And I think it could pretty easily be held open with a hot start lever - it really don't have much tension on it - or maybe it really does and the perch and lever are designed to make it feel that way.


Anyway - I have a few things I am working on right now with it - it has always started hard when cold . I am getting some new reeds as the old ones were shot really bad and frayed - that is trouble A. Trouble B is that the carb needs gone over. it was dirty when I got it - and I half heartedly cleaned it out in the fall. It needs a thorough going over. ultrasonic the carb and jets. Then we'll see how she fires up. more to come as it progresses....................................

[Billy Golightly]

Tim, what carb are you running on there, PJ or PWK?

[atctim]

Tim, what carb are you running on there, PJ or PWK?

To be honest - I don't even know. What is the difference? I am thinking it is a Keihen - maybe.......

[Louis Mielke]

PWK is a D slide I think, the PJ is a round slide? Also whats you're pilot jet at? Mines at 55. I think it could stand to go down one more as it still has a lot of goop at the pipe. I can't wait to get home and get mypart back. I know my 500 needs to go richer. I think I've got the main too lean still and thats why it gets hot still.

[cr480r]

PWK is a D slide I think, the PJ is a round slide?

The PWK is the D slide... The PJ is the flatslide that most hondas use stock(it has the choke plunger idle circuit)... The old round slides are PE's

[atctim]

My Carb is a Keihin. It has a 160 main and a 55 pilot. What can you guys tell me about these Keihin carbs? Aren;t they what come stock on most Hondas? Must be a stock CR500 carb.

[Louis Mielke]

Sounds like the stock carb. Check to see what shape the slide is. Also, I'm pretty sure 55 is the correct stock pilot. Pretty sure the stock main is a 170 but thats meant for an open air box. Does yours even run an air box Tim?

[atctim]

The slide is in pretty good shape - not worn too much. There is no airbox - just the rubber boot back to a sideways mounted filter. Should I try a different main?

[Louis Mielke]

I meant the literal shape, is it round, flat with curved sides, or is it shaped like a D. The main is up to you, depends on how your plug looked that kinda thing. I really wouldn't suspect the main for starting problems but I'm far from a jetting guru. Billy would have better jetting advice than me.

[cr480r]

The easiest way to tell the differences if you are not familiar with keihins is by the idle adjustment... the PWK have a idle screw, and the PJ's adjust idle speed with the choke

[Louis Mielke]

I have a 39mm PWK. 55 pilot, 172 main. I think I really need a 175. blah. Man I wish I was at home.

[Jason Hall]

Tim has a PJ carb on his 500. It Idles perfect with no trouble when Its running. I was going to adjust on It at the last Indoor race, but It needed nothing. I think he just needs to figure out what technique the engine wants to make it start.

[atctim]

Yeah - plug looks great after plug chop - it is a starting issue - and I think I do need to learn the technique, but I also believe that the reeds are playing a big part in that. They were really shot. I will know as soon as I get them in.

Thanks for the comments and info guys.

So when you guys are talking about PJ and PWK carbs - those are Keihin models then. I always thought PWK was a carb name brand. Show how little I know.

[Louis Mielke]

Tim have you tried adjusting the decompress so maybe it doesn't hold the vavle open so far? Maybe you're loosing a little too much compression? I would think you could adjust the cable so it just cracks the valve open when you're on the lever. I would think with cable adjustment you could adjust the speed of the compression being bled out.

I know it took me some fiddling until I found out how it worked best.

Jason what do you think of this idea? I know you're really experienced here too.

PWK, PJ, PE are all types of Keihin carbs Tim.

[atctim]

didn't think of that Lou - I will try that.

But not until I get it all back together again. Will be at least a week. waiting on reeds - need to modify my brake lever now, kicker hits it - I have to get the shifter fixed too.

Will let you all know when I know.

[Louis Mielke]

Will you have it for these weekend do you think?

[Jason Hall]

I think If the reeds are hanging open and the compression release Is opening to much, It's possable he Is bleeding off to much compression. Did you try flipping the reed pedals Tim, or are they just totally hit?

[atctim]

Jason - the reeds are Tostidoed! no good on the flip.

Lou - I'll be running the 86R this weekend - no way the 500 will be ready.

[Billy Golightly]

I was just curious on the carb, I ran the PJ on mine for 2 years in a row at TF, and once it was dialed in it ran very well. The 39 or 41mm Taperbore PWK carbs are even better, there a little bit more forgiving on the jetting and when you do get it to sweet spot good christ does whatever its hooked to run good :)

My 500, for the most part had a trick to it, I think all of them do when their dialed right. I always when I kick it, use the tip of my boot, out right behind my toes, and I "flick" the kick starter, which allows the motor to turn quicker and I always do it as the motor is coming UP on TDC, where the compression is building. I'd try it 3-4 times with the choke on if it was cold, and if that didn't work I turned the choke off and held it wide open, and normally within 5-6 "flicks" of the kicker it would start and scare the bejesus out of ya when it did.

[FPMXer]

This should help with kicking over the hundy motor.

http://media.putfile.com/Crankin-up

[Louis Mielke]

Thanks for the vid but you're missing one small detail. We're using a shorty yamaha blaster kicker to clear the fenders better on our bikes.

[atctim]

Your bike is an 1989 - my engine is a 1985 <no scallops

Big difference in kicking them over. People that don't have these conversions and older style engines must have it pretty easy!:rolleyes:

As Lou stated - I did not put this compression release in to make it easier to kick over - I could kick it over just fine. Also - in your video - you say "gas on, no choke" - does that apply to me? It looks nice and sunny in that video - leaves are on trees........it is 5 degrees Fahrenheit here.

[Louis Mielke]

Yeah but we got more powa!!!!! YOWZAAA!

[hondahaulic]

If your still trying to decide on a lever to use you could use the same kind of clutch lever that 400ex's come with and a few other atv's. The lever is designed to operate the clutch and if you push a small pin down it operates the parking brake cable at the same time. Then, just hook the compression release cable up where the parking brake cable goes.

[Louis Mielke]

That's how mine is. Used an old 250r one though. I already suggested the idea to Tim, I think he wants to do it differently though. :P

[3leggeddog]

o man,so the 5 hundy is gettin some good improvements it looks like.sweet deal.how about some current pics of the old girl?

[3leggeddog]

o,and that knuckle you used is from a 97 cr250 kicker

[atctim]

B - thanks for the info on the knuckle - I will edit my 1st post.

As soon as I finish her up (within a week) I will have a grand unveiling. I actually don't have any good pics of her - but you saw the "color" scheme at the indoor race. I may be the first to go all that color as far as I know.

[Louis Mielke]

Did you get the reeds Tim? Hows it starting now?

[atctim]

Did you get the reeds Tim? Hows it starting now?

Well - like most of us know - with many problems solved - another is created. I did install my new reeds -still can;t get her to fire up. I am getting good consistent spark that is blue - however it is weak. I have ordered a new Coil and it should be here any day.

Upon troubleshooting - my coil resistance was way weak (OEM calls for 14 - 23K Ohms resistance) I was getting 9.4.

I do believe this contributed to the hard cold starts. once warm - the weak spark was ok - and once running - you could never tell it was weak. But those cold starts are a problem. Pull start it with another machine and it is OK too!

Will update soon! I can't wait!

Once I get her to start good - I only have left to put a stock swinger on her - then she will be done and race ready.

[BigGreenMachine]

Hehe, stock swinger! Fun!

Thanks for the update Tim.

[85 250sx]

like hondaholic said about the levers that do more than one function. you could use a 250sx hand brake for the rear tires they have the two hook ups one for the brakes and another for the mechanism that lets you put it in reveres.

[200x Basket]

tim

Do you know the cr500 starting ritual? there is definitely a trick to it and that short kicker is not helping you any.

tip the bike onto the left side until gas comes out the vent. now with the kill swith off and the throttle wide open, kick it over slowly about 3 times. now slowly kick the kicker over until the piston is at the top. it willbe hard and then get easy. now let the kicker all the way to the top and kick the snot out of it.

you really need to be able to get a FULL stroke when you kick. if the brake is in the way pull it off and give it a shot.

you may also up the pilot jet a size or two, you should be between a 52 and 55.

[Louis Mielke]

Trust me, with the decompress the "starting drill" is not necessary at all.

[200x Basket]

Trust me, with the decompress the "starting drill" is not unnecessary at all.

so what are you trying to say?

that he does or does not need the starting drill?

it seems to me like the lower compression may make it HARDER to start when cold.

[Louis Mielke]

Typo, I fixed it.

On a normal temp day my 500 will start in 1 kick with the decompress. On a COLD day in winter it takes a few more but its still starts easily. I don't rock the bike, tip it over or set the piston at the "sweetspot" I get on, hold the decompress and kick it like my 250.

55 pilot, 172 main. i actually think it could stand a 52pilot and a 175 main but I haven't had a chance to do anything more lately because of work.

[200x Basket]

gotcha :)

I am running a 52 pilot and a 165 main. I think the OEM 250r airbox is holding me bag. I plan to pull the lid and so some plug chops this weekend.

Normally i do not have to tip it, but i do kick it over 3 times with the kill swith off and then kick the snot out of it. :)

[Louis Mielke]

Yeah, mines a VERY open air box, 39mm carb, and obviously the CR pipe. I know your pipe is made of CR pipes. How much did you have to modify your pipe?

[200x Basket]

barely. I cut a 1/4" to zero wedge out of it. otherwise i jsut cut and twisted it.

[JohnR.]

I am running a 52 pilot and a 165 main. I think the OEM 250r airbox is holding me bag.

Removing the stock air lid on my 250R made quite a difference. Actually I should say installing it did. I had it very well dialed in when I built it the first time (13 years ago) with a PTR pipe, DG Silencer, Duncan Pyramid reed cage, 39mm PWK, a bit of compression, and some mild porting. It pulled hard and ran smooth. We went riding in Southern NJ and it was kind of wet so I put the airbox lid on. At the top of every gear the thing would break up like there was no tomorrow, I pulled the lid back off and it was fine again.

I'm surprised that you don't need a bigger main with the 500 (assuming its a 39mm PWK carb). My FTZ 250 liked a 190-195 when ice racing (20* temps) and the 330 kit I have on it now likes something in the same range but with a 39 PWK bored to a 40.5mm.

Try going up on the main, it will probably like it. Nice build and good luck!

John

[200x Basket]

158 is stock on the 500 and mine is all stock except the pipe.

[JohnR.]

WOW! I'm surprised that's all the jet it needs. Whatever works. :D

John

[atctim]

fellas - believe me when I tell you - I am no stranger to start up procedures. I understand each machine starts a little differently- I have nearly one of each - but lets wait until I get everything dialed in and tuned correctly before we start thinking it is just start up procedures. With as weak of spark as I have - what could you expect? I'll update starting status once I get the new coil - hopefully today or tomorrow it will come in the mail.

[200x Basket]

the pick up/ignition coil is also known for getting weak and making it hard to start. you can replace just the coild pretty cheap if you are not acred to put it in yourself.

[Louis Mielke]

As far as the manual I read said that stock jetting on an 87 is 55 pilot and 170 main.

[200x Basket]

HMM, my manual is a 85/86 LOL.. thanks!!

[atctim]

Yup - that is what I am replacing - the coil only at this point. Ebay has "better performance than stock ones" for $80 - more expensive that what I thought - but hey - I need it.

[atctim]

OK guys - new coil tested double the ohms resistance of my old one. Put it on and viola - she came to life. I actually need to adjust my decompression mechinism now. It is opening up too much. I can start it with the little kicker without it though. Once I get it dialed in - starting it should be a snap. Now with getting all of this other stuff fixed - I have a head gasket leak!!! DANG IT!!! it warped when welding in the threaded plug - looked like the welder ground it - but it is way bad - coolant leaks right out when not running.

So - more updates to come - but just so you all know - it starts easily now - hard start problem fixed with coil - need to adjust the mechanism - will follow up soon with another update!

[evand]

man that sucks about the head, but its a excuse to deck it and rlly make u need that decomp. set up lol:beer :beer

[200x Basket]

great news on the starting!!

[atctim]

Final report - Ronnie resurfaced and redomed my head - no more leaking head. He did awesome work - thanks Ronnie! With the new coil - and the decompression lever - this 500 starts up really easily. as easy as a 250. I now need to work on the foot brake pedal as there is a slight clearance issue with the kicker and it.


Other than the kicker / brake - everything is 100&#37;

[300rman]

Typo, I fixed it.

On a normal temp day my 500 will start in 1 kick with the decompress. On a COLD day in winter it takes a few more but its still starts easily. I don't rock the bike, tip it over or set the piston at the "sweetspot" I get on, hold the decompress and kick it like my 250.

55 pilot, 172 main. i actually think it could stand a 52pilot and a 175 main but I haven't had a chance to do anything more lately because of work.

jesus! my 300r is running a 175 main!
the carb came from a cr500, and i havent touched the jetting one bit! runs great, starts right up!