Tim's ATC500R Decompression Mechanism - FINAL UPDATE!!

**Louis Mielke** · 03-05-2008, 10:04 PM

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** · 03-05-2008, 10:12 PM

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

**JohnR.** · 03-05-2008, 11:26 PM

Originally Posted by 200x Basket

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** · 03-05-2008, 11:31 PM

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

**JohnR.** · 03-05-2008, 11:35 PM

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

John

**atctim** · 03-06-2008, 09:30 AM

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** · 03-06-2008, 10:11 AM

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** · 03-06-2008, 10:32 AM

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

**200x Basket** · 03-06-2008, 11:13 AM

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

**atctim** · 03-06-2008, 12:57 PM

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** · 03-09-2008, 08:32 PM

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** · 03-09-2008, 09:32 PM

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

**200x Basket** · 03-10-2008, 03:09 AM

great news on the starting!!

**atctim** · 03-24-2008, 08:27 AM

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%

**300rman** · 03-24-2008, 11:03 PM

Originally Posted by 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.

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!

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