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DT400 ANKLE-BREAKER

22 May 2020 18:42
Bbd83
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DT400 ANKLE-BREAKER #1
So I picked up a couple more bikes...I have an AT1 and found another 70' listed for 200 bucks, froze, missing throttle assembly and a few other things, already got it free'd up and in process. Now comes the fun one...one of my holy grail bikes is a DT400 and I got one with the AT1. Just got it yesterday, owner said 78' and then 77', I haven't nailed down the vin yet but will. Upon buying it he wouldn't kick it himself as he said he had a leg injury and it's hard to kick. I'm guessing this bike severely hurt his ankle because it kicks back like you wouldn't believe. It did fire and ran for a bit then died so I bought it and brought it home. After unloading, some fresh gas etc. I had to try again...terrifying. I did read up on this and I know it's an issue and expected the 400 beast to be a hard kicker, maybe never a 1 kick bike but I am literally afraid to kick it. I inspected the decomp valve and I'm not sure the cable is opening anything. It's dirty but not completely gunked up. I took the valve completely out and kicked it...kicked back like pissed off mustang immediately and popped. I put it away. Shouldn't it have been really easy to kick with that taken out with 0 kickback? I understand that to inspect the other side I'll have to pull the cover/kicker arm which I may end up doing. I just got bogged down with alot of other reading and wanted you guys to help me in the right direction. I've had amazing luck with this forum and now own 6 vintage Yammy enduros...and that's just the Yamahas. So...how do I conquer this kicker situation so I can enjoy one of my dream bikes?? What am I looking for? I've also thought timing but it's cdi, shouldn't get that off right? It did run a couple times but not long/well enough for me to spin it. Hadn't touched carb yet and it pisses out the drain with the cock on, needs a clean and float height set. Why am I not seeing electric start conversions all over on these type big bore bikes haha. Here's some pics...

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22 May 2020 19:25
Makotosun
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DT400 ANKLE-BREAKER #2
Looks like 1976. That was the last year of the twin shock DT400.

Sounds like either timing is way off, or the CDI box is malfunctioning. DEET on the site could test for you. If it’s the box, you need a new used one (iffy and expensive ), if the Stator and trigger could are good, this aftermarket box will work:

cdibox.com/product/fireplug-cdi-1975-76-...a-dt400-motorcycles/

There are a couple aftermarket full systems at around $4-500, or convert to a DT250 points setup.

Great bikes, but the ignition are a known weakness. Your symptoms make me lean towards a bad CDI box, but I’d have DEET test before dropping coin.

Welcome! To the site!


Mako

IF it isn't one thing, it's another.
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22 May 2020 19:35
TerryM
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DT400 ANKLE-BREAKER #3
Bike is either a 1975 400B or 1976 400C. Post the VIN and we can tell for sure.

The kickstart decompression valve only reduces compression slightly. The aftermarket cable-operated job that fits in the second spark plug hole (on bikes so equipped, and the DT400B and C weren't) releases virtually all compression and will kill the motor, not help you start it.

It's not really the high compression and high volume that causes kickback, it's timing. I'm certainly no expert, but I know that if the timing is correct, you seldom get that ankle-busting kickback. Check the timing.

When I was a new rider back in the late 1970s, my neighbor had an RT2. He sent the jug off to be bored, and it got 'lost' somewhere. He found that he could put a DT400 jug (and piston) on it and it would run. The RT2 compression release didn't fit the DT400 jug, so he had no compression release available. The exhaust pipe also did not fit - we cut the pipe and strapped it back together with soup cans and hose clamps. To start it, you needed to be wearing solid shoes and kick it firmly and cleanly all then way through to the bottom no matter what. I started it and rode it a number of times, and I was a very green new rider with my Honda 100, then my Yamaha CT green machine. Never my favorite ride, but it was a thrill!
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22 May 2020 20:29
FrankC
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DT400 ANKLE-BREAKER #4
Try running a small drill bit or nail through the small hole through hole to cylinder. May be completely stopped up with carbon. Make sure piston is not at the top.
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22 May 2020 20:58
Bbd83
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DT400 ANKLE-BREAKER #5
It's a 1976 DT400C. Finally grabbed the vin and looked it up in the tech library. Was too busy trying to lose a limb until tonight. :S I'm not gonna lie I'm bummed with the thought of putting a big chunk of change into it but I got the bike for 500 with an AT1 for 200 so I have some room to play and again this is a holy grail bike for me since falling for these vintage Yamahas. I looked through the decomp valve hole and as best as I can see there's a small hole there that I can see through and could see piston so I don't think it's completely stopped up. Should I worry too much about poking that through getting gunk back into the jug? Pull the head and all that? Even if that's completely clear this kickback is something else I mean literally scary. After hearing it run I wanted nothing more than to take it around the block and I was too afraid to keep going. Bottom of my foot is a big bruise. The seller showed me a picture of the "ankle injury that prevents him from kicking the bike anymore", didn't admit it but I'd bet that 200 dollar AT1 he got that from this bike. I now remember the look on his face when I was kicking away before purchase. Here's the part where I hang my head in shame and say I know nothing about setting the timing. I've of course read up on it in my travels but always get confused and the manual talks about a dial gauge that I don't get. It's TIME TO LEARN for sure so I'm gonna need the idiots guide or some help. I pulled the cover tonight and the flywheel is white-ish making any marks unreadable. I'm hoping I can learn timing, clean up the decomp stuff, put back together, re-do carb and ride this thing cuz' I'm in love but apparently it's gonna make me work for it! I'll say it again this forum and it's members is part of the reason I've fallen hard for these bikes...appreciate all the help!

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22 May 2020 21:07
MarkT
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DT400 ANKLE-BREAKER #6
The compression release will NOT stop kick back if the timing is off. All it does is make it slightly easier to kick through.

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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23 May 2020 00:32
apex
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DT400 ANKLE-BREAKER #7
Definitely could have a CDI timing issue. But, and I saw this mentioned earlier, you must kick through all the way. If you do not commit to a full throw kick, you will encounter kick back even with a properly timed and setup DT400. Kicking it through is not for the faint of heart, but anyone can, and you do have to commit your leg and drive through the kick stroke unending until the bottom. It is a true technique that is doable, but takes time to master.
The technique is a full stroke, unending kick, after letting the initial push in the kickstart "top out." Let the kick lever return to the top after a small movement of the kick starter (top it out). Then, you must drive your leg through the entire kick start stroke. Even if you must jump your body up to weight your leg for the kick. Until you have the technique mastered, wear a boot with solid sole so you can "in your mind" know your foot will not be hurt if it kicks back. By kicking a "full stroke" to the bottom of the kick starter's travel you get the piston into the 2nd combustion cycle which is imperative to a big bore 2 stroke starting.
I can start my '72 360 in flip flops, only because I learned the technique of a full stroke kickstart on previous bikes.

Allrighty Then
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23 May 2020 09:44
Bbd83
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DT400 ANKLE-BREAKER #8
I guess my bruise may have healed enough to try this full commit kick through but I just feel like it just plain won't let me due to the kickback. I think a 185 dollar investment in that cdi recommendation may be a solid choice even if it doesn't 'need' it but how can I go about checking my timing? Doesn't it need to be running and I don't think the flywheel has ever been off or messed with.

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23 May 2020 12:41 23 May 2020 12:42 by Makotosun.
Makotosun
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DT400 ANKLE-BREAKER #9

Bbd83 wrote: I guess my bruise may have healed enough to try this full commit kick through but I just feel like it just plain won't let me due to the kickback. I think a 185 dollar investment in that cdi recommendation may be a solid choice even if it doesn't 'need' it but how can I go about checking my timing? Doesn't it need to be running and I don't think the flywheel has ever been off or messed with.


First go to the tech section and download the service manual.

Link is: yamaha-enduros.com/index.php/workshop/se...ctory-service-manual

THEN, go to the ignition section in the book, and it will detail out how to check the timing. I believe it also has some resistance tests you can do to check on the functionality of the parts and pieces. The timing is pretty easy on that bike. If the timing appears to be correct, then I suspect your culprit is the CDI box as you had it running, but are getting a severe kickback. You could send just your CDI box to DEET who could verify its condition.

IF it isn't one thing, it's another.
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23 May 2020 13:45
Bbd83
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DT400 ANKLE-BREAKER #10
Can I get a dial gauge indicator locally, special order, or make my own with an old plug?? Which is best?

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