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riding to high altitude

Old 05-04-2013, 11:22 AM
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riding to high altitude

I haven't seen anything here about carburetor function going from seal level to altitude, 7k to 10k feet, during touring. The vacuum slides deal with altitude well on other bikes but I've never taken the VTR over 600ft above sea level. So I guess my query is, can I expect any issues when going over high mountain passes on the VTR set up more or less stock?
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Old 05-04-2013, 11:27 AM
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Search for Denver based bikes, IIRC they need jetting changes for the altitude.
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Old 05-04-2013, 12:00 PM
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I live at 1380 ft. I have had the bike to denver 6 or 8 times and have never had any issues with it. It will be rich but not enough to cause driveability problems. If you lived there, yes, you would want to rejet. But for a visit, it should not need anything.
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Old 05-04-2013, 06:51 PM
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Originally Posted by Stixx View Post
I live at 1380 ft. I have had the bike to denver 6 or 8 times and have never had any issues with it. It will be rich but not enough to cause driveability problems. If you lived there, yes, you would want to rejet. But for a visit, it should not need anything.
Denver is exactly where I'm headed. Good to know the VTR won't suffocate going over Eisenhower pass or Rabbit Ears pass. I have no intention of going through Wyoming!
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Old 05-04-2013, 08:08 PM
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The 2001 S-hawk gets ridden from Myrtle Beach SC.(sea level) to The Mountains of North Carolina and as high as 6,685 ele. Mt. Mitchell, with no problem with missing... Yet I will suggest - It is not a commun need to use 91 octane in a S-hawk.. Yet when you ride from regular ele. levels to higher ele. Use the higher octane to raise the Pre-detonation of the fuel -to keep the miss to a minnium..
I did have issues -when i rode a 1993 CBR900rr / that i owned/- when i rode from Santa Monica to the top of Pikes Peak.. Yet most do have issues at 14,115 ele..
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Old 05-07-2013, 10:54 AM
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I recently tried the higher octane fuel, 91, for a ride to 7k. The bike has real issues with that. It coughed and stuttered leading me to think I'm running too rich. Also, when timing the bike using a manometer, the vacuum seems shallow. I make this assessment from other bikes I've tuned using the same tool. The VTR seems like the vacuum is weaker, could be due to the lower compression? Maybe I have a leak in the vacuum system. This miss/cough/stutter is driving me nuts. Mostly in the 3 to 4k rpm range 1st, 2nd, 3dr gear. Mostly 1st and 2nd. Happens after heavy throttle use followed by deceleration.
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Old 05-07-2013, 12:24 PM
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Originally Posted by twist View Post
I recently tried the higher octane fuel, 91, for a ride to 7k. The bike has real issues with that. It coughed and stuttered leading me to think I'm running too rich. Also, when timing the bike using a manometer, the vacuum seems shallow. I make this assessment from other bikes I've tuned using the same tool. The VTR seems like the vacuum is weaker, could be due to the lower compression? Maybe I have a leak in the vacuum system. This miss/cough/stutter is driving me nuts. Mostly in the 3 to 4k rpm range 1st, 2nd, 3dr gear. Mostly 1st and 2nd. Happens after heavy throttle use followed by deceleration.
Have you relocated the carb breather hoses? If not, do a search, and get it done...
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Old 05-07-2013, 02:04 PM
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Originally Posted by twist View Post
I recently tried the higher octane fuel, 91, for a ride to 7k. The bike has real issues with that.
Higher elevation requires less octane than lower elevation to run in similar motors... unless you were testing something with it that I don't understand?
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Old 05-07-2013, 04:10 PM
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Originally Posted by 7moore7 View Post
Higher elevation requires less octane than lower elevation to run in similar motors... unless you were testing something with it that I don't understand?
The 2001 S-hawk gets ridden from Myrtle Beach SC.(sea level) to The Mountains of North Carolina and as high as 6,685 ele. Mt. Mitchell, with no problem with missing... Yet I will suggest - It is not a commun need to use 91 octane in a S-hawk.. Yet when you ride from regular ele. levels to higher ele. Use the higher octane to raise the Pre-detonation of the fuel -to keep the miss to a minnium..
I did have issues -when i rode a 1993 CBR900rr / that i owned/- when i rode from Santa Monica to the top of Pikes Peak.. Yet most do have issues at 14,115 ele..

1971allchaos

I was trying 1971allchaos' idea out. Shouldn't the VTR run the same on higher octane? I may be wrong, but, it seemed to run worse.
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Old 05-07-2013, 04:43 PM
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Originally Posted by twist View Post
1971allchaos
I was trying 1971allchaos' idea out. Shouldn't the VTR run the same on higher octane? I may be wrong, but, it seemed to run worse.
Twisted, I set the jetting/carbs up on the 2001- to run 91 octane. No (your right) the Superhawks / and the RC-51 are low compression engines, and (HONDA) recommend 87 octane. Yet as stated I set mine to run the 91 octane simply because it is cleaner fuel.

And YES, if you just go and put 91 octane in a BONE/stock S-Hawk, it will perform like a PILE... you are not going to get any benefits, except wasting the extra change at the pump.
It "SORTA" changes the timing...

Last edited by 1971allchaos; 05-07-2013 at 04:46 PM.
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Old 05-07-2013, 05:01 PM
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Originally Posted by twist View Post
Yet when you ride from regular ele. levels to higher ele. Use the higher octane to raise the Pre-detonation of the fuel -to keep the miss to a minnium..
I thought pre-detonation was less of an issue at altitude due to less dense air. As in, the higher octane prevents pre-detonation, but pre-donation occurs when the compression reaches a certain pressure that causes the a/f mixture to combustion without spark. You get less pressure with less dense air.

Hence, in Phoenix, the standard unleaded is 87, but in high elevation areas (like when I lived in Colorado) you can easily find 85.
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Old 05-08-2013, 05:26 PM
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I have finally just bought the damn tool to adjust the air mixture screw. The issue presents itself at 3000 to 4000 rpm. For example, running in traffic in 2nd gear causes the stutter to come out. Running hard in 3rd or 2nd gear in the twisties causes it too. I believe I was told that this is the transition from pilot to main jet. I also know the bike is running rich.
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Old 05-09-2013, 07:50 AM
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Originally Posted by 1971allchaos View Post
Twisted, I set the jetting/carbs up on the 2001- to run 91 octane. No (your right) the Superhawks / and the RC-51 are low compression engines, and (HONDA) recommend 87 octane. Yet as stated I set mine to run the 91 octane simply because it is cleaner fuel.

And YES, if you just go and put 91 octane in a BONE/stock S-Hawk, it will perform like a PILE... you are not going to get any benefits, except wasting the extra change at the pump.
It "SORTA" changes the timing...
Just to clarify... This applies to all altitudes... Run 91 in an carbed engine set up for 87 and it only wastes money... No measureable gain what-so-ever, altough the engine probably won't miss and misbehave on "normal" altitude...

The basic reason for 87/85 on altitude is that it "sort of" matches how the carbs are set up for the 87... Or close enough at least...
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Old 05-09-2013, 08:07 AM
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Just to clarify... This applies to all altitudes... Run 91 in an carbed engine
set up for 87 and it only wastes money... No measureable gain what-so-ever,
altough the engine probably won't miss and misbehave on "normal" altitude...
Ya learn somthing new every day. I have been running 91 ever since I bought my Hawk, (2009), and although the only performance mods have been stacks, silencers and a flo-commander, I always thought I was running the better octane for performance for our bikes. I guess I will have to try 87 and save the chance for more mods? Interesting.

And just BTW, I was kind of surprised no one mentioned a flo-commander and remote adjustment for quick altitude change adjustments on the fly? Wouldn't that be one way to subdue drastic altitude changes?
Cheers.... This is a great site.
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Old 05-09-2013, 08:23 AM
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Yeah, a Flo-Commander does indeed give you adjustability of about one main jet size either way... (Promotion material says 1-2, but that's probably pushing it)

And that should be enough to account for high altitudes, at least enough to stave off misfires...
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Old 05-09-2013, 08:48 AM
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Originally Posted by Upland111 View Post
I always thought I was running the better octane for performance for our bikes. I guess I will have to try 87 and save the chance for more mods? Interesting.
Higher octane is used in certain motors because of the higher compression in those motors... it is actually less sensitive to combustion so that it doesn't pre-detonate due to heat and compression. Vehicles without enough compression won't know the difference. The oil industry doesn't really make huge efforts to correct people who think it will give better mileage or performance in standard cars because, hey, if they want to spend extra money on gas, why stop them? I always give it a try to see if I notice a difference, but usually that's only once

Have you noticed gas companies never make claims of your car running better based on octane rating? It's always the additives for cleaning the fuel system "sludge" and whatnot.
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Old 05-09-2013, 11:05 AM
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Originally Posted by 7moore7 View Post
Higher octane is used in certain motors because of the higher compression in those motors... it is actually less sensitive to combustion so that it doesn't pre-detonate due to heat and compression. Vehicles without enough compression won't know the difference. The oil industry doesn't really make huge efforts to correct people who think it will give better mileage or performance in standard cars because, hey, if they want to spend extra money on gas, why stop them? I always give it a try to see if I notice a difference, but usually that's only once

Have you noticed gas companies never make claims of your car running better based on octane rating? It's always the additives for cleaning the fuel system "sludge" and whatnot.
I wanted to try the altitude idea mentioned prior. Octane rarely solves problems, I know. One thing I have noticed, when I balance the carburetors, using a manometer, the vacuum seems weak, (compared to my old BMW with higher compression). On the higher compression, the fluid RACES to the top when not balanced, with the VTR, it moves slow enough that I don't have to be really quick to adjust so the fluid won't get into the carbs. Is this normal?
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Old 05-09-2013, 11:30 AM
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If I remember correctly I average around 20-21" Hg when doing mine.
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Old 05-15-2013, 10:51 AM
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OK, I broke down and bought the motion pro tool to adjust the fuel mixture screw. The front carb got turned in all the way and backed out 2 turns, the rear carb turned in all the way and backed out 2 1/4 turns.

That annoying hiccup/cough at 3k to 4k rpm is nearly gone. Bike starts easier, seems to warm quicker and the hiccup seems to be isolated to 1st gear at 3k rpm but barely. I didn't notice any big change in throttle response, the bike still runs like a scalded cat. My next move is to check the carb balance and see where that is.
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