sc500 did kick back.
so did i.

bitch

Blimey, sorry to hear that. Must've been a hell of a kickback. Hope you mend ok & soon.
My first & only thought if its an original systen is the flywheel key has broke & flywheel moved.
If its some fancy aftermarket system with No key then i still think its moved.
All a guess of course but it just shouldn't kick back as retard off to near TDC for starting originaly.
Had that on my YZ490 & they don't have a decomp so broke the kick gear teeth off. That was a very hard kickback. Luckily i had my MX boot on to kick with. still hurt enough.
Bike came from California already broken unbeknown to me untill i kicked it.

The first week that I had my DT400B, it kicked back. I tore a ligament fractured a bone in my foot. The doctor's bill with an x-ray ended up costing more than I paid for the bike. Took a nice chunk out of my leather work boots too. Thank goodness I had a steel shanked boot on or it would have been much worse. Still ended up on crutches and in a boot for a couple of months and couldn't ride it. I took the time off to clean the decomp valve and double check the timing - spinning it over with a drill since I couldn't kick it. I still wear the boots every day and the missing chunk of leather and rubber is a good reminder to never kick it over with sneakers, even if I am just riding it down the driveway.

I've read that if the ignition trigger is starting to go bad, you lose the timing curve at kick-over speed. It's possible that it's going bad on your bike and it reverted to the normal ignition curve. It also might be wise to check the decompression valve for caked on carbon if you decide to keep the bike. Regardless, these things can be a bear to kick over even on the best of days. My DT3 never bit back, but was still loads of fun. I wouldn't hesitate to trade my 400 for a 250 if I were in your shoes. Hopefully you heal up quickly and can get back to work soon.

Good info there above.

Sorry to hear your demise. I kicked over my 73 rt360 in tennis shoes, never again without full fledge war boots, LOL.

In any event, my decompression mechanism was missing thus I am fixing/adding the decompression mechanism back to mine (these are the Manual lever activated ones. I

I just looked and the 400s also have a similar decompression mechanism, however the cable is routed and it is automatically engaged by the Kickstarter.

Thus it leaves me wondering if yours is disconnected, cable broken, or decompression valve stuck.. I would think if yours is in place and functional, it should not be kicking ack so severely.

Hope you heal quickly

I (as someone who isn´t nearly as experienced as many here) had similar issues, though I was lucky it just tore a hole in my boot and sock and not my foot. In my case my ignition trigger was bad as TheBeardedOne said here already additionally I played with my timing (learned the painful way not to do that again) too much.

Now a year later I looked more into my decompression valve. After getting some kickstart experience on other bikes ( I am a tad bit younger than many here I´d say so I was only used to e-start) I felt like the DT was really hard to kick for supposedly having auto decomp. I realised mine actually never worked at all.

I found out my link to the decompressioncable ( www.cmsnl.com/yamaha-dt400-1976-usa_mode.../partslist/B-10.html , #28 here) was worn down heavily on on one side. So I welded one material and got it down to its original shape. Now I have a way easier kick than ever before.

I´d maybe suggest removing the sparkplug and get someone to turn over the engine by hand and whilst that look at the decompression valve in front to see if your cable might need some adjusting for it to work properly or if there is something broken inside the engine.

Good Luck to your healing though!

Those adjustable, stators with slots on the 74’ and up can be problematic. I experienced the same thing on a 1974 DT 250. And I believe that CDI electronic ignitions are even worse. One of my colleagues who lived at the top of a hill and he used to jump on the bike and pop it in gear and run it down the hill and never had to kickstart a bike ever again. Unfortunately, it cost about $4 million for that property.

Think of all these old bikes they coulda bought! Out in the country on a hill…
Sneezles61

I have an 1972 rt2 360 yamaha,  rebuilt engine  & fitted with a VAPE ignition system with flywheel, previously called power dynamo i think,  meticulously set to 2.9mm Btdc and thankfully never had a  kickback ( touch wood ) as my tib and fib has plates screws and pins from an accident 30 years ago.

Ive never had any of my many 360s,400s kickback with a properly working ignition and properly adjusted decompressor, fwiw