DT250 starting problems.

[MotorbikeBruno]

Well gents, I finally got a moment to get to a 1979 DT250F that I got a while back. The problem is that I can't seem to get it to run well. I've been lurking on Yamaha Enduro forum too, I got all the wiring sorted out, but I thought I would see if anyone on here has any knowledge of these bikes. This particular carb has 3 adjustable points, seems like a fuel/air mixture screw towards the air box, Idle adjust in the center, and then I'm hearing conflicting info on the rear one (near the reed cage) as it could be another mixture screw or the oil adjusting screw because it's oil injection? Symptoms are that it fires up for a little bit, then coughs hard and dies. I pulled the plug out and its soaking wet. If I spray it down with carb cleaner it looks brand new again, I let it dry and when I put it back in, it seems to start easier, but "fouls" very quickly. I double checked spark and when you kick it over, there's great spark. Battery is new too. 6V of course. Headlight is disconnected (so it doesn't draw any extra juice) and I do have a tach, I do NOT have a speedometer though. Here's a couple of pics. I'm going to attempt a video maybe tomorrow sometime. If anyone has any idea on where those screws should be at on the carb, that would help a bunch. Too much conflicting advice out there!

 

[crazypj]

Re: DT250 (MX) starting problems.

Left screw is fuel mixture, center is idle adjust and right screw is air only
Headlight is direct so no need to disconnect it, should only work when engine is running (side/parking light should come on with battery)
Bike should be old enough to have a switch on right bar?
Sounds like float level may be 'off'?
I removed the restrictors from air intake, they will pull out
I've had both the 250 and 400 at same time, don't have service manual here though but pretty sure I have one in Britain
Check the silencer isn't clogged with oil/carbon, it will make bike appear to be running real rich (only 1 bolt to remove it, there should be a rubber with sealing springs connecting it to pipe

 

[MotorbikeBruno]

Ok I'll pull the silencer, I did that before and I do remember it running better, someone on the enduro forum suggested using some torches at both ends to "burn" out whatever may be in there. I'm thinking it might be time to pull it apart and see how much sludge is in there.

I'll disconnect the rear tail light as it seems the battery is dying rather quickly. I suppose after 40 kicks it's about done eh?

I'll pull the carb and re-check float level. And get rid of restrictors from air intake as well.

Thanks for the reply PJ! Yesterday I cleaned out the reeds as they were very dirty with little pieces of leaves and such. I pulled them apart, cleaned off the surfaces and made sure they all laid flat without any light being able to be seen through them. This is correct right?

 

[djelliott]

Ha! Awesome. I love when I come across a thread that is dealing with the same problem I'm having. 73 DT250 keeps fowling plugs and acting like it's running rich. I'm going to use these suggestions and see how it helps. Thanks guys.

 

[MotorbikeBruno]

We're all in this together right

PJ just seems to be the guy that always bails me out of trouble! Thanks for that PJ, seriously, you rock man.

 

[djelliott]

PJ just seems to be the guy that always bails me out of trouble! Thanks for that PJ, seriously, you rock man.

I think 99.9% of the active members on this forum could make that statement.

 

[crazypj]

If you live out in the sticks an no one is going to complain, using oxy/acetelene on one end only until it's glowing red then turn off the DA feeding pipe neat oxy.
It will burn EVERYTHING out of silencer and pipe (but you wouldn't believe how much dirty brown smoke you get)
You can watch the burning 'ring' as it moves along inside of pipe
Probably illegal to do it just about everywhere nowadays ;D
I stopped doing it when the police and fire brigade turned up 8)

 

[MotorbikeBruno]

Haha, noted. I'm not that far out

I think I'll take a look at the construction of it and see if I can "pull it apart"

didn't get a chance to look at it today, hopefully in the morning tomorrow! Thanks for the EPA lesson PJ!

 

[djelliott]

OK, I burned the gunk out but while looking at a few other things I realized the PO had been messing with the reeds and installed one flipped over so it wasn't closing all the way. Flipped it back and everything seems fine now.

 

[MotorbikeBruno]

Lucky! I'm waiting on a flywheel puller that should be here today! I can't really seem to find anything else wrong with her, so it's time to look into timing. Every once and a while it will give a quick harsh kick back on the kicker lever (the kind that will break your knee if you were locked)...and since I had knee surgery a 3 years ago, I'd rather not do it again....