DT 250 Questions

[2smokewilleh]

Hey guys,

Few months back I picked up a (I think 75ish) Yamaha DT250, pretty rough, but only $200.

Looks like it has had the crap butchered out of it. No electrics left, no injector oil tank, but, it had compression and was otherwise mostly complete. Someone had put on a plastic gas tank.

Cleaned it up a bit, made up some pre-mix (About 35:1). Didn't have any spark. Pulled off the flywheel and found some mud stuck between the points. They're pretty pitted/worn, I will replace them, but in the mean time, cleaned them up, pulled the plug and grounded it, and ended up with ok spark.

ANyways, long story short got it running, it will rev up and will get through the gears ok, gear box feels strong, but it keeps fouling up the plugs and, it will only run with the choke on (Even when hot). If i take the choke off, it dies in a few seconds.... it otherwise runs pretty well when the choke is on, but smokes pretty heavily. (Doesnt seem to be leaking through the crankcase seal).

Otherwise, bike is pretty solid. the front fork dust boots are missing and the fork oil seals need replacing. Fortunately you can still get those parts at the local yamaha dealer!

So I have a feq questions:

1) For pre-mix, what Gas/Oil ratio to use? I highly doubt that i would ever get the oil injection system functioning properly, so pre-mix it will be...

2) What is the correct spark plug to use for this bike, and correct gap?

3) Carbs are my weakness - What can be done about it only wanting to run while the choke is on?

4) How much fork oil does it take? (before i drop out the forks and change the seals).

Any help is appreciated!

Thanks much,

[DTGordo]

Hi 2smokewilleh,

Almost a novice here but.....

On the pre-mix, I've been running 20-1. Sure that's heavy on the oil but on what I've read, it makes sense to go to the mix that has the maximum amount of oil when it's under load and high revs. A bit of smoke is better than having to replace the piston and grind out the barrell (and I'm right out at it's limit anyways). I am not totally convinced yet that the autolube pump works on mine so am still running the pre-mix plus the autolube. I am sure that it will run better just with the oil pump but want to be sure.

On the carby, I'd start by pulling it apart and cleaning it out. Sounds like some dirty/blocked jets maybe. That's probably the easiest place to start and the carby is pretty simple.

On the other stuff, you'd need to confirm which model and look it up. A manual will have all of that info and also about how to do the carby.

If the engine number is 450 something it's a '74 and I can look the stuff up.

DTGordo

[terps19]

Hey DTGordo

I just picked up a 74 DT250 in very decent condition at an action for $300 and I have a few questions for you. I hope you dont mind. Its an AZ bike so it is kinda faded on the top of the gas tank but otherwise it is a solid bike IMO- just the fork seals, clean out and replace gaskets on the carb, tires and basic oil changes are all it needs.

A key did not come with the bike (but it still starts just no elec when kicked) so I am looking for an ignition with a key (I want to register it and I think the DMV wont be happy about it not having a key). The NOS one is $170 or some crazy amount and I was wondering if you knew of a conversion chart of parts to see what other years' ignition would fit the 74 that I just got. Looking to spend NOT $170 haha.

Second, and most important, how do you like the bike overall? Basically I am using it to ride back and forth to work about 10 miles round trip, and on the fire trails here in Arizona (no sand). I just need something that will get me around on the trails (must climb some hills) and wondering if I made a good choice with the dt250. Not looking to do anything extreme. This is my first dirt bike but 6th bike overall.

I can post some pics in a few days. Thanks for the help!

[DTGordo]

Hi Terps,

Yeah I saw your post a couple of days ago and was going to msg you anyway as there's not too many 250a's around as far as I can tell. Happy to help and you might help me as well. I got my bike almost by accident on Ebay for $250. I was just looking for any items near home and saw the bike flash up. I went out and had a look and it was rough, wouldn't start blah blah. I had no idea and thought it would be fun to fix up and chucked a bid in. I'm pretty happy with it. Anyways, enough about me.......

No idea about part compatability. I reckon that's a dicey area. On the other side of things, you could go a year or two either side and up and down the engine sizes and lots of bits would fit. You got a wrecker near you? I'm lucky that one is not too far away and have been getting a few bits here and there. Main thing is to see it to make sure it matches/fits. I'd be surprised if you get failed on not needing a key. Does it have an ignition switch on it? If it does and it looks ok you could probably take it to a locksmith to get a key cut. That key will then fit the gas tank and steering lock which are useful too. The thing comes off pretty easy and then the actual switch can be pulled apart too if you need to clean it (or make a key for it).

Now the bike - I've only had trail bikes and four stroke ones at that. She's a basic ride and compared to current bikes has shite suspension, shite brakes and is doing it's fair share to make the environment shite. But I LOVE IT!! It's such a simple machine to work on, fix and tune. The 250 has reasonable power for the mix of on and off road. We've got hills around us and I've put on 13/49 chainrings. Really low but it will still do 100km/hr. I ride to work although it's getting a bit cold now and get up into the mountains near Canberra when I can. Hopefully up there on Friday. The bike has been reliable and fun so good luck with it and keep in touch.....

Gordo

Hey DTGordo

I just picked up a 74 DT250 in very decent condition at an action for $300 and I have a few questions for you. I hope you dont mind. Its an AZ bike so it is kinda faded on the top of the gas tank but otherwise it is a solid bike IMO- just the fork seals, clean out and replace gaskets on the carb, tires and basic oil changes are all it needs.

A key did not come with the bike (but it still starts just no elec when kicked) so I am looking for an ignition with a key (I want to register it and I think the DMV wont be happy about it not having a key). The NOS one is $170 or some crazy amount and I was wondering if you knew of a conversion chart of parts to see what other years' ignition would fit the 74 that I just got. Looking to spend NOT $170 haha.

Second, and most important, how do you like the bike overall? Basically I am using it to ride back and forth to work about 10 miles round trip, and on the fire trails here in Arizona (no sand). I just need something that will get me around on the trails (must climb some hills) and wondering if I made a good choice with the dt250. Not looking to do anything extreme. This is my first dirt bike but 6th bike overall.

I can post some pics in a few days. Thanks for the help!

[terps19]

Hi Terps,

Yeah I saw your post a couple of days ago and was going to msg you anyway as there's not too many 250a's around as far as I can tell. Happy to help and you might help me as well. I got my bike almost by accident on Ebay for $250. I was just looking for any items near home and saw the bike flash up. I went out and had a look and it was rough, wouldn't start blah blah. I had no idea and thought it would be fun to fix up and chucked a bid in. I'm pretty happy with it. Anyways, enough about me.......

No idea about part compatability. I reckon that's a dicey area. On the other side of things, you could go a year or two either side and up and down the engine sizes and lots of bits would fit. You got a wrecker near you? I'm lucky that one is not too far away and have been getting a few bits here and there. Main thing is to see it to make sure it matches/fits. I'd be surprised if you get failed on not needing a key. Does it have an ignition switch on it? If it does and it looks ok you could probably take it to a locksmith to get a key cut. That key will then fit the gas tank and steering lock which are useful too. The thing comes off pretty easy and then the actual switch can be pulled apart too if you need to clean it (or make a key for it).

Now the bike - I've only had trail bikes and four stroke ones at that. She's a basic ride and compared to current bikes has shite suspension, shite brakes and is doing it's fair share to make the environment shite. But I LOVE IT!! It's such a simple machine to work on, fix and tune. The 250 has reasonable power for the mix of on and off road. We've got hills around us and I've put on 13/49 chainrings. Really low but it will still do 100km/hr. I ride to work although it's getting a bit cold now and get up into the mountains near Canberra when I can. Hopefully up there on Friday. The bike has been reliable and fun so good luck with it and keep in touch.....

Gordo

Sweet man!! Thanks for the reply. I think I will just take the ignition switch off the bike and get a key made. New switches for the bike runs anywhere from $25 (for the chinese knock off parts that I dont trust) to $150 for the actual NOS piece.

I figured the suspension, brakes, and such dont come close to a more modern bike- I have a 73 BMW- so I am used to the bike I am riding not being modern. I just love older bikes I dont know why probably because they are easier to work on.

There are two bikes being parted out on ebay right now as we speak for the 250A so if you need some parts you can check there- however it seems like the sellers are trying to make the most money they can.

All and all the bike is pretty decent- only really needing a key and new tires to get back on the road. Cosmetics are fair but I am not in it for the looks of a bike. I plan on beating the you know what you of it. Thanks again for the info!!!

[tdemasters]

Hey everyone,

I am new to the form and hoping for a little help. I have a 1974 Yamaha DT 250. This is my first bike rebuild and I am having trouble figuring out where the tubes off of the Carb. need to run to. As far as I can tell there are 4 openings, from reading other forms I have found that (aside from the gas inlet), 1 is a vent, 1 is an overflow, and 1 has to do with the oil mixture system. I don't know which is which. Sorry if this is a dumb question just looking for a picture of the carb fully set up and a little explanation as to what each thing is.

Thanks in advance!

[DTGordo]

The small one right next to the fuel inlet is an overflow as well as the small one on the bottom. I've run most of the tubes down on the right on the front end of teh swingarm where there's a little holder thing.

Gordo

[Airhead]

Hey everyone,

I am new to the form and hoping for a little help. I have a 1974 Yamaha DT 250. This is my first bike rebuild and I am having trouble figuring out where the tubes off of the Carb. need to run to. As far as I can tell there are 4 openings, from reading other forms I have found that (aside from the gas inlet), 1 is a vent, 1 is an overflow, and 1 has to do with the oil mixture system. I don't know which is which. Sorry if this is a dumb question just looking for a picture of the carb fully set up and a little explanation as to what each thing is.

Thanks in advance!

This is my DT175 carb, your carb is similar maybe

[Richie_31]

Hi oldgitonabike! What a beautiful shiny Mikuni VM26ss carb! I have this on my DT 100 and DT 125. Im just wondering what is the standard air screw turns for this carb. Is it the same for both DTs?

[Airhead]

mines 1 1/2 turns and from experience its pretty normal

[dpehrson]

Here is my experience with the same issue. Make sure it is seating in the correct seat and not just going snug...

I had a similar problem with a 78 dt125 that I pulled from a scrap yard for $40. The engine would not idle after warm-up without the choke on. The problem... Apparantly someone before me placed a dab of thread locker on the air screw threads...

I cleaned the carb about three times due to this problem, After a very careful and timely examination, I discovered that the airscrew was going very snug, which I had previously thought was seated, way to soon. I observed that the needle portion of the airscrew was not observed as even entering the air port orifice on the intake side of the carb. I examined the air screw threads of the carb and noticed debris gumming up the threads. I then continued to force thread past the thread locker and adventually to the real metal seat. At 01:00AM, I assembled and installed the carb and started her up. I warmed it up with the choke on and then pushed the choke in to discover that it purred like a kitten. One final adjustment to the air screw of 1/4 turn in and it idles clean without the choke and accelerates without hesitation. Who would have guessed...

[gght]

hi 1982 dt250 fires up for about to seconds, cuts out tries to start sometimes back fires,plug wet, good spark, any ideas please