DR250 at altitude

[brad13ryan]

Hey Everybody.

My girlfriend and I just road from Argentina to San Pedro de Atacama in Chile and her DR250 was running so bad by the end of the pass that I actually had to push it up some of the hills. The thing is it ran fine up to 4100 meters and then it started to miss and sputter. By the end I could hardly keep it running and only in the lower gears and high RPMs. We removed the air filter but it only helped a small amount. Now that we are lower 2500 meters it is runing fine. We intend to go to Bolivia and I want to make the proper adjustments to avoid this problem again. I am thinking about a different jet if I can find one and I don´t know how to adjust the air screw because it is seeled which I am thinking about breaking the seel. Any advice would be great.

Brad

[Nigel Marx]

Hi Brad. Doesn't sound like much fun. The air screw adjusts the amount of air bleeding into the riser for the main jet, turning the fuel going up toward the carb throat into a foam. This makes it vaporise more effectively and mix better. Letting more air in will lean the mix up a little, but it's not as good as putting in a smaller main jet. If you can break the seal, turn the air screw carefully inwards COUNTING HOW MANY TURNS until it's gently seated. It's usually something like 1.5 turns. You need to know so you can re-set it. Then back it out to where is was and then try another half turn further out. I would guess that any more than 1 complete turn out from normal would be the most that will still let the motor run OK.

Have you been into a carb before? If not I'm sure there are lots of pictorial guides on the net. It's easy to replace a main jet. They are usually either the sort that are buried inside the riser and you need a correctly sized, well fitting screw-driver to get them out, or are the more external hex-headed sort that you need a 6mm (about) spanner to undo. There will be a number on it, something like 122.5 or 140 etc (the numbers on most carbs go up in 2.5 increments). Find what number is on your mainjet and buy the next two sizes down. IT"S A BAD THING TO USE TOO SMALL A MAIN JET FOR THE CONDITIONS! You can over-heat and seize the engine running too lean for too long. Fuel going into the motor and vaporising has a big impact on the internal cooling, especially to the piston. Try one size smaller before deciding on going two sizes smaller. It's a bit hit and miss, but that's how it is with carbs. Be very sure to replace the original main jet as soon as you get to lower altitudes. If you know that you are going to head up again and don't want to keep replacing the main jet all the time, it's OK to run with a smaller main for a while as long as you keep the throttle at less than 60%. The restriction of the main jet size on fueling doesn't come into play until you are getting close to wide open.

Hope this helps.

Kind regards

Nigel in NZ

[Frank Warner]

Yes - remove the plug that covers the air screw. If it is like the 650 then instructions exist on how to remove it on the web. It only changes things at low throttle settings ..

You will need to get teh smaller main jets - 1 one size smaller 1 two sizes smaller .. the standard size will be in a manula somewhere .. or in the parts list. Jets should be about $10 each..

[brad13ryan]

Hey Guys

thanks for the advise. I did take the carb out and found it was full of crap so I gave it a good cleaning and then proptly broke the little plastic piece on the side. Which I found a replacement for in Calama which they charged me 45 dollars for. So today I put it all back together and adjusted the air screw but could only make it to 3600 meters no matter how I turned it. The only jet I could find in Calama was a 108 and I am running a 115 so I was not sure if is was to small. So I ran a wire in the jet and made it to 4200 meters but it does not have any power at 4200 so I think I will return to Calama and look for more jets. The question I have is what size would be two steps down from 115.

Thanks Brad

[Dessertstrom]

I don't know if your carb has a throttle needle with notches on.
I used to be at 9,000 ft at my last base and the bikes we had all ran rough until we dropped the needles down to the last notch which had the effect of weekening the mixture. We also did this on our motocrossers for raceing but you have to do it all again when you come down to sea level.
Ducati 600 monsters,CR 250,RM 250,CR500 etc.
Cheers
Ian

[brad13ryan]

I was just trying to figure out if dropping the needle down would help. Right now it is on the thrid notch and it seems to me if I put it on the 1st notch it would push the needle into the jet farther and restrict flow. Is this correct?

Thanks Brad

[Dessertstrom]

Yes.
There should be four or five notches, we put the little circlip in the top notch which lets the needle drop lower into the jet. This made our bikes run better but not perfect.
We lived at 7,000 ft and rode up to 9,000 ft and down to sea level which didn't effect the bikes too much but when we raced at sea level we reset the needles.
Good Luck with yours.
Ian

[brad13ryan]

Well we finally managed to get the bike to the Titio Gysers at 4,300m with a 110 jet and a wire. We also moved it up two notches.
Thank you!
We{ve been also having problems with the bike not starting in the morning, but maybe the battery is just dead....guess we{ll see if we can get a new one in Bolivia.
thanks again..

[Nigel Marx]

If the air screw is out a little too far, that will make it difficult to start. If you have turned it out, try putting it back in a bit until the motor is warm.

Regards

Nigel in NZ