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big 2-stroke decompression valve

21K views 17 replies 11 participants last post by  exit90a 
#1 ·
I have a CR480.....for an old bike, I just love the thing. It has a boat-load of torque, a really fun carnival ride.
I have a routine for starting the thing, but the first time I thought I tore a hole in the bottom of my work boot, I knew I was in for a work out. I bought a pair of Sidi boots to make it painless, but kicking the big beast was still a chore.

I was across town and stalled the bike one day (tall street gearing...stupid mistake) and I thought it would never refire. That was it, I wasn't putting up w/it any more.

My CR500 is almost complete....a new top end, so I knew it would be the same issues with that one as well, but on a larger scale. So, the 480 was to be the test vehicle.
I located a vendor for the self-cancelling (stainless steel) valves, pulled the head, drilled/tapped the hole and screwed the valve in place.

I can't believe the difference.
Snap the valve down and kick away.
Before I'd have to bring it up to TDC and jump on the kicker. Now it's like kicking a strong 125. Cold, hot, or flooded, it doesn't matter. It'll bust off with 3/4/5 kicks every time....I could start it w/tennis shoes (not that I would).

I was out running a few errands and had to make several stops. It's a pleasure to know it'll start easily every time...instead of the fear of it possibly leaving me stranded.

I'm a firm believer now in decomp's.
 
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#3 ·
I always slow kicked mine, then up to TDC and ard really hard stab on the kicker. It gets tiring after may tries.

Slow kick now? Nope.
Snap the valve and start stabbing the kicker....instant happiness.
 
#6 ·
rode a friends cr500 with this valve on it. It literally kicks over easier than my RM250 and my Crf450!
 
#10 ·
I could kick it over in slippers seriously, but my bike was tuned properly and would start first kick every time. He'll it started first kick after I built the motor. It was easy as he'll to start without the decomp as well. The best thing about the decomp is that you can start it sitting on the seat. So at long traffic lights I would shut the bike off, set the decomp and get the piston just before tdc and wait.
 
#7 ·
I never had a problem starting my 1990 CR500. As long as you follow the right "routine" it was a 2-3 kick job at most. Also, it was a great deterrent for potential jobbers that wanted to ride it: "If you can start it, you can ride it." Never had anyone that couldn't handle it, ride it.
 
#14 ·
The best way to start a big bore is.. Turn fuel on. No fuel should be left in the carb the fuel will slowly evaporate and leave just the premix oil. Anyway once the fuel is on for a few sec slow kick threw a few times. Get the piston a c- hair past tdc. Bring the kicker back to the top and kick all the way threw. Having the carb set up properly is key!! Also a good set of reeds and a clean filter. Also when you kick make sure the throttle is open about 1/8. This allows air to get sucked in with the fuel. The throttle being slightly open is very important.
 
#15 ·
And a big f-'ing leg don't hurt either.....
 
#17 ·
Mine starts 2nd 3rd kick every time using above method. Unless of course she is on the rag. That's only on really hot steamy days or at the start of a recent "dead engine start" race I went to. Lot of fun blowing by all those guys on there 250f woods weapons in the open sections though.

The little blue knob looks like the $hit but I really don't want to go messing with a good thing though. You know, " If it aint broke, don't fix it".
 
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