A forum for owners of Yamaha TTR250 trail and enduro bikes!

macker · Member

Higher altitude Carb settings

ttboof · Super Guru

I ride on the coast but head up the ranges occasionally

I find the bike drops power from about 1500 Metres to the point It struggles to pull top gear so I stick to 5th and rev it more the guys with fuel injected bikes don't notice the difference as it adjusts to suit

Adjusting the pilot screw will only help with the first third of the throttle opening above that its the main jet .

I'm sure someone on here rides at altitude and may have an answer

macker · Member

Thanks TTboof, not much response on this so will make a plan on the ride.

The last part of the ride ascends 1000 meters in a relatively short distance(+/-20 km) so the gain in altitude happens quickly.....holding thumbs it has the power to get to the top without issue.

ttboof · Super Guru

The highest road here is on 1600 Meters

The ttr still goes ok just a bit down on power drop a gear and rev it lol

I have tried cracking the choke open a bit but not any noticeable improvement

-- Edited by ttboof on Sunday 18th of April 2021 05:33:52 AM

mossproof · Super Guru

I don't think there's an easy answer/solution to rapid changes in altitude.

As you rise, the air gets "thinner" and the mixture gets richer, (too much fuel for the oxygen available) so pulling out the choke will make it worse. Pulling the airbox lid off can make a difference, but is not ideal if you're on dusty trails.

As ttboof says, adjusting the pilot screw (fuel screw) only makes an appreciable difference at small throttle openings, but it might do something - worth a try. Remember to count the turns so you can return it to normal later. Screw in (clockwise) for leaner. Put a dot of white paint on one of the lugs of the screw so you can see it's position more easily.

dlee22 · Senior Member

With the airbox cover off I managed to get close to 5000m, didn't run perfectly by any means but like Simon said, it is a quick short term solution if you ever need it.

ttboof · Super Guru

dlee22 wrote:
With the airbox cover off I managed to get close to 5000m, didn't run perfectly by any means but like Simon said, it is a quick short term solution if you ever need it.

Thanks for letting us it know I have opened the air box lid and have a couple of side holes in the air box that might help it a bit as well but 1600 Meters is as high as we get here

-- Edited by ttboof on Tuesday 20th of April 2021 12:11:07 PM

macker · Member

Thanks for the useful info ttboof, mossproof and Daniel, very helpful. I will let you guys know how things go.

Just to be sure.... when you say remove airbox lid you are talking about the lid on the left hand side of the bike behind the sidecover.

-- Edited by macker on Wednesday 21st of April 2021 05:29:45 AM

mossproof · Super Guru

Yes

macker · Member

Some feedback from the ride.

The bike performed with no issues up to about 2900 meters, other than losing a bit of power.
From around 2900 the bike started spluttering when opening the throttle just before half full.

The highest point was 3240 meters so I decided not to make any adjustment and took my time and enjoyed the scenery.

comeragh · Senior Member

That very interesting.You must have very high hills in your part of the world.Thats over 3km up.Would never get above 1000m where I live.Always loose a bit of power at altitude due to thinner air.

ttboof · Super Guru

Thanks for letting us know how it went

That's higher than anywhere here great info

macker · Member

I rode up Sani Pass into the Kingdom of Lesotho, Southern Africa.

https://www.mountainpassessouthafrica.co.za/find-a-pass/kwazulu-natal/item/410-sani-pass.html

elvis · Member

I've had the same issue, last couple of years i've gone on a 3 day ride in the victorian high country (Jindabyne - Omeo - Dargo and back) (Australia). the altitude / elevation gets up to about 2,000m. In the higher areas, particularly, on the serious hill climbs, the power drops right down and engine misses alot.

Just a thought, would a lower octane fuel help? to balance out the lower oxygen levels in the air?

Going on this ride again next weekend..!!