Help!

[firecracker22]

Ok I have a DT 400 of indeterminate age (it's yellow with a monoshock so I'm told that means it's a 1978) and it puked on Saturday.

I inherited it from my little brother, so I have no idea as to its history or its care and feeding. I've been using the same gas and oil as I do for my KTM only mixed at 32:1 as I've been told.

It seemed to run strong, though it is very down on power. I am guessing that is just from being long overdue for a top end. It starts very easily, idles, and runs fine (no coughing, backfiring, stuttering, blubbering, etc). Until Saturday that is. I wasn't riding it but when I couldn't hear it behind me for a little while I turned around and poor Keith was kicking and kicking. A new plug didn't help at all, and the plug that came out was a little dark but otherwise looked good--cleaner in fact than the plugs I take out of my KTM.

Couldn't kick it or compression start it at all, had to tow it home (now THAT was an interesting procedure!).

What do I do? Where do I start? I did pull the cap off and kick it, didn't see a spark. Or do I need to leave the plug in the cap in order for the spark to be visible? I am not sure if it is a gas or electrical problem. Does this bike have points? Where are they? I followed the plug wire but it seemed to go into some kind of black thing, but I wasn't sure when they came out with CDI. It does pee gas which indicates a float problem but I have been chicken to tear the carb apart so far. However this problem came on so suddenly I am not sure it is carb related.

This is a spare bike I am taking care of for my little bro, and all I want to do is keep it running. It needs new brakes, seat and cover, and a few other things so I dont' want to spend a whole lot of $ on it, but it was such a stout bike that it has been great for Keith to ride since he is uncomfortable on my bike. (He's just starting--maybe the DT isn't the best beginner bike but it's all I have).

Any input will be greatly appreciated! Thanks guys!

 

[VintageDirt]

You would need to have a sparkplug inserted in the cap to see a spark. Also the plug will need to be held against the cylinder for grounding. Make sure you don't hold the metal part of the plug when you kick the engine over. Unless you're into that sort of thing.

The points are underneath the flywheel, which is under the left side engine cover (if I remember correctly and if I know my left from my right but it's definitely on the side opposite the dipstick, I think). If you try to install new points you will need a flywheel puller for sure. I don't remember if the DT400 has marks for timing or if you need a dial indicator (I can check my library when I get home tonight :confused: ).

If it was me, I'd try a new spark plug before I did anything.

 

[firecracker22]

I'm glad you replied Wes. I was hoping for your expertise.

So you are sure it has points not CDI? (sorry for the dumb questions, I don't know anything). Keith does have a Clymer's manual for it but I haven't had time to get it and read it yet.

 

[VintageDirt]

Can't be to sure about anything that I have ratteling around in my head. But, half the time I'm almost 90% certain that it has points. Clymer will tell the tale though.

 

[Zoomer]

All the 400 DT's had CDI ignition (75-78) One of the first things I would do if there is no spark, is to trace down the kill (on-of) switch on the handle bar and disconnect it.
When you have the plug out for checking spark, if there is spark, dump a tablespoon full of gas in the plug hole, reinstall the plug and give it a kick, if it trys to fire, you probably have a fuel problem.
:thumb:

 

[VintageDirt]

:o Why is the "Law of Averages" always against me? :confused:

 

[Zoomer]

Wes, I cheated :uh:
Go to Yamaha-motors.com (parts) and you can bring up all there bikes from present back to the 60's.
You are the MAICO man :worship:

 

[VintageDirt]

Zoomer,

I went to that site too. But even though the heading in the 1978 DT400E folder was "C.D.I. Magneto DT400E", I didn't believe it because my brain took me back in time to my 1969 AT1. And then I didn't have my right glasses on to really study the parts drawing. But in the description, it listed "contact breaker ass'y", so I just went with that. Now that I look at it with my good glasses, on my big monitor at work, I can see that the description does not correspond to the drawing.

Me, the Maico man? That's a good one.

 

[DougRoost]

Something else I recall from my old DT100 that I'm pretty sure is true on all the DT's. You didn't pre-mix your gas and oil. There was an oil tank under the seat and it fed an oil injection pump to mix the gas and oil depending on engine need. All you had to do was keep an eye on the sight glass on the oil tank to ensure you had enough oil.

Looking at http://parts.yamaha-motor.com confirms this bike still had an oil tank and pump.

 

[Zoomer]

Most of them had oil injection, (I have a 100 and a 125) but you have to watch it, lots of people would disconnect the oil pump and mix gas and oil on older bikes if they had any problems at all with the injection system.

 

[TheJunkMan]

most of the problems were the cable operating the pump broke so people disconected it.

 

[2stroke]

Well, believe me, if the carb is leaking gas from the overflow constantly its possible you got some dirt in the inlet valve and the carb is flooding. A badly flooded carb will shut you down like a switch. Wont start for **** either. Ive had it happen on my '72 Kaw 350.
Also, remeber this, if its been sitting a while the floats may be full of gas, and they lose their ability to shut off the fuel flow. Ive had that happen too, and it causes constant flooding. WIth your DT I think it had composite floats (plastic) so that may not be a problem.

As for spark, unscrew the plug and hook it to the boot, and lay the bottom of the plug on the cylinder head and kick it over.

Just remeber the basics, as they say- Fuel, Compression, and spark at the right time.

FUEL:
Heres a crude carb function test:
Try a new plug, and of your getting a nice fat spark, try dribbling a little gas down the spark plug hole directly into the cylinder, maybe 1/4 cup, then replace the plug and see if it will fire up. If it fires breifly and dies, then you got a carb problem because what its doing at this point is burning off what you dumped in, and if it dies very shortly, that means the carb is not suppling gas to the engine.

Carbs are not that bad, Ive done somewhere around 30 of them.

FIRE:
DO the plug test mentioned above

COMpression, well it would run, just crappy if that was all, unless the rings just cracked right apart...

Let me know what you find!
The DTs are my second favorite old bike besides the Bighorn!
A buddy of mine had a '76 DT years ago, and I spent alot of time riding it. Awesome tractor like torque!

 

[firecracker22]

Okay, thanks for the ideas. I will start messing with it after a couple of more weeks when I am a little more mobile (knee surgery tomorrow).

I do not think it has the tank anymore or it may just be disconnected because my stepdad (who has a similar bike himself, in better repair) said to mix the oil.

Also, the kill button has been disconnected at some point. The wire was cut (not broken) right at the throttle housing (it is kind of all one part right there). We were just dumping the clutch with the brakes held on to kill the engine. Kinda redneck-y but it's one of the more minor things that is wrong with the bike.

 

[jmics19067]

If your carb is overflowing and flooding out the engine<gasfouling the plug> is a strong possibility ,adding extra gas into the spark plug hole probably won't work.


You could try, take out the plug see if it is wet and smells like gas, check for spark, if no check for spark with a new plug if spark, remove plug from boot,put bike in gear and push it around the driveway with fuel off,throttle wide open, put in new plug keep throttle wide open and kick. If you get 1 real loud pop<you just fouled the plug again> or it tries to run look for the needle and seat /float problems and/ or bad reeds.

 

[DougRoost]

FC, what did you find?

 

[jboomer]

She's still recovering from her surgery. She's got a post floatin around here detailing THAT!

 

[firecracker22]

Thanks Jboomer. I might get to it this weekend, possibly next weekend, but more likely the following weekend. I will have to drag it to a friend's shop where I can sit on a rollaround stool instead of crouch or kneel on the floor. I will save this thread and post when I do have a better idea of whats' going on.

 

[TooTall]

I bought a new DT400 in 1975 and it was yellow. I don't think the '78's were yellow. Shouldn't make any real difference regarding the problems you're having though. Good luck!

TT

 

[TooTall]

Something else just occurred to me.......as I recall, the 400's used an automatic compression release. Perhaps yours is stuck open which could reduce avaiable compression below what is require to get her started. Just a thought.

TT