Somehow I get roped into fixing everthing.....

My son's friend has a 77 DT 100 Enduro. He "put it away" last fall and this spring it wont start.

First thing is, the battery is missing. Will this thing run without a battery installed? Is there a way to "re-wire" this thing to run without the battery?

I checked the spark and I'm getting spark. Even without the battery. Seems odd. (but it is a 1977??)

It has compression but not a lot....

It seem to be getting fuel. Wet Plug, Tried starting fluid.


I figure it has to have a battery or be rigged to run without one.

Any thoughts?

Bill

It should have spark, even without the battery. I think the battery was just to run the headlights and such. The quality of the spark is important too. It should be a bright, blue spark. A weak spark will cause problems if everything else is fine. You didn't mention if you replaced the gas in the tank and carb. If not, you must drain everything and use fresh gas. The carb on a DT 100 should be easy to remove and check out. Pull the bowl and clean out the jets and float valve. Buy a can of brake cleaner at an auto parts store (about 4 bucks). Use gloves and eye protection, and blast that stuff through every jet, channel and orifice you can find. Put 'er back together and then make sure the air cleaner is clean and has no obstructions. As long as you have spark, fuel, and air, it should go bang.

Not sure about the compression, but I wouldn't think a 100 should have much anyway. Oh yeah... If I remember right, I think 70's DT's had a reed valve. I'd make sure that is not froze up too.

Good luck!

Thanks Kerchak,

I replaced the fuel in the tank but have not cleaned out the carb.That will be next.

I thought that with a squirt of starting fluid it should, at least, try to fire if "electricaly" all was well. I'm not even getting a hint that its trying to fire.

The compression seems a bit low. It will push my thumb out but only if I dont push back real hard.

With spark, fuel (sarting fluid) and compression, I thought it should at least give a hint of running. Thats why I was thinking it was an electrical type problem. Like something was not hooked up (battery) but still allows it to spark.

I'll pull the carb next. I'm sure it is in need of a cleaning.

I tried the starting fluid bit when I was trying to get my XL600 running. I could get it to pop a couple times, but my issues ended up being a bad stator (which gave me very weak to no spark), and clogged carbs (this bike has two). Even with a 100 though, I would think that there should be enough compression to completely remove your finger from the hole. That air has to go somewhere, so if your finger stays there, my guess would be it's blowing by the rings (assuming the head gasket is in good shape).

Hey! Didnt think I should start a new thread.

So... Same bike, different problem. Bike was sitting for a year when I bought it, cleaned carb to best of my ability, put (what I think is fresh) gas and it started! (albeit I had to manually bypass the ignition as the key slot is busted) Thing is, it idled for 5 seconds, then cut out. So I started it up again. Same thing. Started messing around with the air/fuel mixture screw, seemed to change idling time and RPMs depending on position.

More information:
Had original spark plug, which I think has a good spark or it probably wouldn't run right? I replaced that with a spare to be sure but changing the spark plug didnt help.
It seems to be like an idle speed problem, but I dont think/ am not even sure the bike has an engine idle adjustment.
The oil is about as old as the bike has been sitting (I will change it, but could that be my main problem?)
Didnt replace any of the carb parts when I cleaned it, but everything seemed to be in okay condition.
There is a small (very small) split in the bottom end of the muffler (just after it connect to the cylinder) When it runs a bit of smoke leaks from there

So the question is: What could be causing this? Could something in my carb still be clogged or just damaged and is not allowing it to run continuesly? Are both my spark plugs bad?


So you know, the bike has a magneto, so it doesnt even need a battery to run all of its electronics.

Sounds like a carb issue to me.  You have good compression and spark, so likely a fuel issue.  Unscrew the brass jets out of the bottom of the carb and check to make sure all the little holes in them are cleaned out.  Blow through all the ports in the carb with carb cleaner and compressed air - use safety glasses!

Check the intake and exhaust for obstructions like mouse nests.  Reassemble and try again.

you could also check the float level, and make sure that the fuel petcock is clear and flowing well.

gsa102, on 19 July 2012 - 09:02 AM, said:

Thanks. I cleaned the carb (twice) but chances are something is wrong still. I ordered a carb rebuild kit and am awaiting it.
I saw on another post that if the exhuast is a problem to just remove it and try and run it (briefly) The problem remained.
I tried completely removing the air filter so the carb was sucking in pure air, and it seemed to run... different, maybe even slightly better. But still wouldnt run for long.

I cant seem to unscrew the jets, probably because ive been prying them too lightly for fear of damaging them. How can I tell which ones can be unscrewed? An what should I use to unscrew them and make sure they remain undamaged?

mxxx rrrider, on 19 July 2012 - 11:13 AM, said:

How can I check the float level? and would I have to open the petcock to clear it?

One thing I have noticed though, is that the fuel cock has three positions, one closed, one open, and one that seems like its restricting it but still letting it flow. However, even when in the closed position gas still dribbles out, kind like a leaky faucet, Im guessing that means something is wrong.

Thanks for the advice!

Edited by NoPetRides, 19 July 2012 - 06:48 PM.

The jets should be snug. Provided you're using the right sized screwdriver you shouldn't booger them up getting them out. Go ahead and put some back into it to snap 'em loose.

Floats are easy. But first you should check the float valve. Look between the floats and you should see a small tang touching a plunger that goes into the carb body. The plunger goes into the float valve, which has a point on the opposite end that resembles a sharpened pencil. There will be a rubber seal just shy of the pencil "point". If the seal is anything but symmetrical with the shape of the "pencil point", it needs to be replaced. (The whole valve).

To get to the float valve, remove the small pin positioned between the floats and the floats will slip right off. The float valve just sits inside its little channel, so be careful it doesn't fall out while you're not looking. It may have a little wire connector connecting the two. If the valve is good, put the floats and the float valve back together.

The adjustment of the floats is a simple matter of bending that little tang up or down until the floats are set at the proper level. There is a specific height the floats should be at, but I learned from a Honda tech a much easier method than farting around with a float gauge, which you probably don't have.

With the float bowl off, and the floats properly attached, turn the carb in the horizontal position (sideways). Look at the aforementioned little tang to see where it hits the plunger on the float valve. What you want is the tang to just be touching the plunger as the carb is resting in the horizontal position. If not, bend the little tang whatever way it needs to go to get the above described level.

Floats that are set too high will shut off the gas flow to the carb and the bike won't run. Too low and the float valve won't shut off and gas will pee all over your bike.

Hope this helps!

Oh yeah. Regarding the fuel petcock, it should simply unscrew from the bottom of the tank. There should be two posts (one for the "ON" position, and a shorter one for "RESERVE"). They should have screens on them, which will probably be clogged with crud. De-crud the posts and re-assemble. If the gasket is shot, go to ACE Hardware and overpay them for a new one. Just make sure it is okay for use in a petrol environment.