75 DT125 - No Start?

[corder13]

I just picked up a dirt bike a week ago, and I've gotten to ride it once: the day it was brought to my house. It's a 75 Yamaha DT125 (according to him). He got it started when he brought it here, although it took him a few minutes. After he left, I kicked it over one time (it was still warmed up) and it fired right up. I tried to start it the next day and I haven't been able to get it started again. He did say something about a "sweet spot" on the throttle, but I haven't been able to get it to do anything no matter where I twist the throttle.

I did take off the carb today after kicking it over about 20 times or so. I noticed when I took the fuel bowl off, you could see the dampness of where the fuel level was, which was almost none. When I saw that, I checked the floats, but they moved freely, so I would imagine the floats are fine. This is my first dirtbike, so any help anyone could give would be much appreciated. Thanks.

Rick

 

[2stroke]

Hmmmmm.....
Are you using the choke? would be a rod that you pull up on the carb....may or may not still have a knob on it....you know, pull it up to start a cold engine, and push it back down after its warmed up.

Heres another idea...."pop start"....that is, turn the gas on, make sure the kill switch is set to run, put the bike in neutral....run with the bike and then jump on, and whack the shifter down into first....the engine will start turning over, and you can play with the throttle.....or get someone to push you...the idea is you have to get some speed going and throw your weight down into the seat as you pop it into gear so the rear wheel wont just skid.

Works especially good rolling down a hill, with the obvious drawback that you have to push it back up if it doesnt fire!


Then theres the old take the plug out and dump some gas into the clyinder (a LITTLE...like 2 tablespoons) and see if it will fire up......

 

[corder13]

I've tried the choke, which didn't work. I also tried pop-starting it a couple of times, but it didn't do anything, either. I was told by a friend at work yesterday that since the fuel bowl was almost completely empty that it was starving for fuel (which crossed my mind anyway). The petcock is also leaking. Could that cause it not to get any fuel to the carb (or not get enough)?

Rick

 

[Masterphil]

You need 3 things to start an engine: spark, fuel, air.
Pull the plug and set it against the head of the motor, kick it over and check for spark. Yellow is ok, blue is better. If you don't have spark air and fuel don't matter. If you have spark, check the needle valve that the floats push up on. Make sure it isin't leaking.

 

[VintageDirt]

You know what I think, I think that the Yamaha DT125 was formerly called an AT125. The biggest difference between the DT line and the AT was that the AT came with electric start and that also meant that it was the only DT(AT or whateverT) that had a 12 volt ignition. Unlike the 6 volt ignitions that came on the DT175 and DT250, it was a "battery" ignition and that meant that the battery had to be installed and charged (at least not dead as a stump) in order for the bike to start. But then I'm not too sure what happened to Yamaha DT/ATs after 1970. Eventually they got rid of the points and went to CDI but I'm not sure when that happened. Does your bike have a 12 V battery and a points ignition? A little black button on the right handlebar?

Don't mind me I'm living in the past, again.

 

[corder13]

It originally had the button, but the box that it's in has been gutted. It still has the battery and voltage regulator on it, though. So now it's only a kick-start, but he said the battery was only a week old when I got it, which makes it about 2-1/2 weeks old now.

Rick

 

[Succubus]

Check the spark, but from what you describe it sounds like the carb isn't getting gas. When you pulled the bowl on the carb it should have been full of fuel and not just damp if the petcock was open. As mentioned earlier, make sure the needle valve in the carb moves freely and lets fuel in. Also pull the fuel line off the petcock and make sure fuel flows freely through the petcock when you open it. Finally, reattach the fuel line to the petcock, pull the other end off the carb and make sure the fuel line isn't clogged. Open the petcock and look for a solid stream of gas. If it has the original carb the choke is a lever at the front of the carb. Push it down and the carb is engaged. Pull it up when the engine starts up.

If you getting good fuel stream to the carb, write again and I'll suggest some things you can check with compression and spark. It shouldn't be timing because I'm pretty sure you bike has a CDI instead of points. Look for a black box bolted to the frame under the seat near the battery.

Good luck.

Patrick