Altitude and the 4 stroke

Discussion in '4-Stroke Engines' started by Scottm, Jun 22, 2008.

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  1. Scottm

    Scottm Guest

    Only 10 day left till the kids the Titan and I head off to Lake City Colorado. My parents and the kids will be staying around 9,000 feet but I will be camping around 10,500 and plan on using my bike to get from the camp to the condo and just farting around up in the mountains on well maintained county roads.

    Does anyone have any warnings or advice for performance issuses dealing with the altitude difference from Fort Worth to 11,000 feet.
    I know I'm comparing apples to oranges, but I notice no difference when my car is up there but I don't know about the bike.


  2. stude13

    stude13 Active Member

    the car has a comp. look in members list and pm in colo.
  3. pedalpower

    pedalpower Member

    rocky mountain high

    don't know squat about the titan but go easy on the brewskis the first couple of nights,ha. less oxygen obviously, so will run rich and a litle less power after you adjust? just guessing-internal combustion basics? small engine, probably not much noticable difference-maybe run hotter?

    post no. 2 just my .02 from a Coloradoan. Where is Lake City?
  4. jimraysr

    jimraysr Member

    You don't say which model you have. I see they have both 2 and 4 cycles engines. You situation will depend on the type of carb. you have. Many 2 cycle have a cylinder with a metering rod attached. I have had to drop the rod down a notch or two in high altitude when I rode Yamaha 2 cycle trail bikes in the 60s. If the carb has a butterfly thottle, then you have a main jet and go smaller for high altitude. If you had a Honda you could go to a dealer and get a high altitude jet. It generally is in the bottom of the center tube inside the float bowl. They are threaded into it from the bottom. It is exposed when the bottom bowl retainer bolt is removed along with the bowl. If it is a China Honda knockoff the parts of the carb. might be interchangeable wt. Honda parts? If you have a fuel pump carb. then I think you are on your own. Honda uses a separate lift pump.
  5. fetor56

    fetor56 Guest

    Duane seems to be the expert in this Scott....i think u loose 1 Horsepower per 1000 feet in altitude but please don't take that as gospel,i know the figure's surprising though.
    Tell Dax your plans & i'm sure he would be happy to offer advice,he lives pretty high-up doesn't on this subject would be invaluable.
  6. Scottm

    Scottm Guest

    Thanks for the input. Duane and Large live in /around Denver, which is the "Mile High" city, so that will be about half of where I'll be.
    Jimray, I have the Titan 4 stroke/ Honda clone.

    Well this should be a fun experiment. I'm not out for speed, since I'll be on dirt roads and won't need the motor on the downhill streches.

    Lake City is in the Southwest corner. North of Durango and south of Gunnison. Only one paved Hwy in and out. There are some old mining roads that pass over 13,000 feet. It's a 4 hour 25 mile drive over the pass to Silverton.
    2 years ago I climbed a 14,000 foot mountain in the dark so we could watch the full moon rise over America, then the moon light lit our path back down.
  7. jimraysr

    jimraysr Member

    So is the tank on top and gravity fuel flow or down and has a diaphragm carb. to pump the fuel up? Wouldn't know what to do on a diaphragm carb. as most of them I have seen have the jets pushed into the body and not replaceable. Again if gravidty feed, a Honda dealer might recognize the carb as a knockoff and be able to supply a jet. I have a 11 HP Honda engine on the pressure washer and replaced the carb. before I learned to drain it each time after use do to the junk in the "modern" gas which gunked it up and I took it apart so many times, just bought a new one. Anyway Sams CLub had a pressure washer wt. a knock off 13 HP engine on it and I could not tell the difference in the engines and their parts including the carb. I believe you could interchange most parts. One note is even though China might copy the design, they may not use the same thread pitch or size? Hope if you have a power problem this helps. Desperate to get my trail bike running right at only 8000 feet I filled a jet wt. solder and drilled it with a smaller mini drill while camped in the boonies. Doubt most people camp wt. all the gear we did, but it saved the trip for me (my buddy rode a Honda and had a smaller jet wt. him) I bought a new jet from Yamaha when I returned to Tucson. Jim
    Last edited: Jun 23, 2008
  8. HoughMade

    HoughMade Guest

    Wow! At 3,000 feet, you'd be almost a horsepower in the hole! :smile:
  9. Scottm

    Scottm Guest

    LOL, I was sure I would get precise technical instructions from you HoughMade. I was actually looking forward to see what you had to say.:lol:
  10. Skyliner70cc

    Skyliner70cc Active Member

    Expect 3% decrease in HP for every 1000 foot gain in density altitude. This is best case assuming your mixture is appropriate for the altitude meaning adjusted or rejetted. It can be worse if carb mixture is too rich.

    I'm living back at sea level after living in Colorado for 5 years. I cannot believe how fast my na sports car is (na is normally aspirated).
  11. Scott. When I climb big hills I give it just a bit of gas and I pedal along. You're lighter than me by a whole lot and you're running on 24 inch rims so power should not be an issue with you at all. But expect less power of course.
    Man. I need to get off this hill and see how my Titan goes. It's plenty for me as it is. But as Duane mentioned,the power is amazing at sea level.
  12. Scottm

    Scottm Guest

    Duane says he ran his bike at 9,000 and it worked fine.
    Thanks Skyliner for the info.
    Yeah, Large, I don't think my 140 lbs will bother it too much. Most of the roads are smooth dirt roads well maintained by the county and I won't go fast so i don't slip and slide all over. The main road travels along the valley floor, so I'll avoid any steep inclines. I just didn't want to haul my bike up there only to not have it work.

    It will be interesting to compare the power from DFW to a higher elevation.
  13. Scottm

    Scottm Guest

    Running great

    Well the kids and the Titan rode well for 2 days and 800 miles, so adjustments had to be made.
    Once I got here, I had to adjust the idle pretty high to get the bike started and to keep it running. The Titan has been flawless on the steep dirt roads. I do have to pedal assist from time to time, but other than that I'm having a blast. My speedo isn't working and there's no wally world or bike shop for 100 miles.

    There is a fine dust on everything and when I get passed by a truck or ATV I get a good lungfull of dust.

    I have to stop the bike at the top of big down hills so I can kill the motor and coast down.

    My family says they can't hear the bike when I'm not close. I have been able to sneak up on some deer.

    Attached Files:

  14. I've been up there before when I shuttled for the airport. It was a Durango run.
    Laws stated that I needed to stay the night once I got there for I was running too many hours so to save money I pulled to the side of the road and slept there.
    That area of Colorado is beyond amazing.
  15. Skyliner70cc

    Skyliner70cc Active Member

    A tip for extra power at high altitudes only: Buy a quart of 20% model car fuel from a hobby fuel-quart is smallest size it is sold it. Add 5 oz to each gallon of premixed gas. Shake well and add to your fuel tank. Works great for sea level bikes not rejetted for high altitude operation. Do not use this below 5,000 feet in altitude or you will fry your engine.

    With 5oz of 20% fuel per you are adding the following to each gallon of gas
    a. 1 oz of nitromethane
    b. .7 oz of 2 stroke oil (usually a castor/synthetic blend)
    c. 3.3 oz of methanol

    Not a whole lot but just enough to lean out the mixture and restore some of the lost power at altitude. This is what I added to operate at 7,000 operation. If you are going higher, you can add accordingly.

    The small amount of oil in the fuel won't hurt a bit so don't even worry about it fouling the plug, it won't.

    I miss Colorado......AR is ok and we canoed for 5 hours this afternoon in the Ozarks but I miss the Rockies!
  16. jimraysr

    jimraysr Member

    Speaking of the dust, what does your air cleaner look like. Might be well to check? Jim
  17. Scottm

    Scottm Guest

    Okay, I've made it back alive to Texas. I got about 40 miles of riding in. I stayed close to the camp grounds, since there is no cell phone service up there and no one to call for a rescue ride. I did hit a big rock sticking out of the road and that may have cause my torque strap to snap.
    The bike ran great, but I had to have the idle set pretty high. The air cleaner and filter were fine.
    One thing I did learn about the altitude and tires though, air pressure is a lot different. I used my same air pump that I use here in Texas. By the time the gauge got to 20psi, the tube I was inflating exploded. The 6 pack of Bud Light bottles in the ice chest all popped their caps when I went over the 13,000 foot pass, except for the bottle that exploded.
    Large, it was frustrating to be in the same state and so far away. I would have loved to come meet you and Duane and gone riding on your trails.
  18. HoughMade

    HoughMade Guest

    That right- the manual for my Honda states that you can expect a 3.5% drop in power for every 1000 feet in altitude.
  19. Skyliner70cc

    Skyliner70cc Active Member

    That 3-4% really adds up in aviation. I remember OH-58 pilots in Colorado who didn't have enough power to do a 3 foot hover and would hover above the ground at a 6 inch-1 foot hover and do left pedal turns only because a right pedal turn would have caused an overtorque, overspeed, or overtorque of the engine. So how did they fly their little choppers if they were hovering at almost 100% available power in the hot thin air? Easy, a heli is more efficient in forward flight than in a effective translational lift (ETL)..its a neat feeling when a heli goes through ETL-you get a neat little shutter and the climb airspeed increases dramatically. In old aircraft with no pitch stabilization you get a nose up pitch at ETL too.

    Due to the 3-4% rule, lots of heli's don't have enough horsepower available to hover out of ground effect. This means that they can only hold a hover within a vertical distance about the lengh of a rotor blade and can't stop in a high hover in flight or do manuevers that require OGE (out of ground effect) power such as pinnacle landings, etc..

    This concludes your helicopter lesson for the day. Sorry, can't you tell I miss it.
    Last edited: Jul 15, 2008