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Old 07-03-2013, 11:06 AM   #78271
Foot dragger
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Originally Posted by Rusty Rocket View Post
Foot: have you adjusted the mixture screw?

I will probably be able to answer this carb question in a day or so. I'm picking up a totally stock (carb with the mix scew untouched,stock airbox w/ snorkel intact and stock exhaust) 2009 in a couple hours. I will compare it side by side with my cut airbox,K&N filtered, DJ kitted, drilled slide carb'd, stock piped 1996. I will decide at that time whether to go after the carb on my new (new to me) DR.

Totally seat of the pants, but I can wheely in 3 gears with the throttle alone 14/42 spkts. I'll let you know.


BTW: I live at approx 200 ft above sea level.
I havent taken the plug out over the fuel screw,seems ok so I dont mess with it.
The plug color on mine is tan not white so they must have jetted it better at the factory.
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Old 07-03-2013, 11:08 AM   #78272
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Originally Posted by motolab View Post
You have neglected one key factor, and that is that in a CV carb it is the throttle blade rather than the slide that ultimately limits the air flow for a given throttle opening
And that somehow changes the air fuel ratio as it goes up in elevation? Please explain how that works.
To compensate the mixture for lower air density you would have to have some additinal air get past the slide without picking up additional fuel.

The idea of "for a given throttle opening" is useful for tuning but a much better way to think about what is happening during actual riding would be to say "for a given horsepower requirement" or "to maintain a given speed". If you rethink the idea using that frame of reference you will see that the idea that CV carbs compensate for altitude in some beneficial way is false.
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procycle screwed with this post 07-03-2013 at 11:34 AM
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Old 07-03-2013, 11:10 AM   #78273
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Originally Posted by Foot dragger View Post
The plug color on mine is tan not white so they must have jetted it better at the factory.
Maybe it's worn just enough to work properly
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Old 07-03-2013, 11:12 AM   #78274
Foot dragger
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Originally Posted by Kommando View Post
Ride interstate at altitude, 2up, and you may want for some more power. This can be achieved inexpensively by opening up the flow of air and appropriately adding fuel.
Interstate at altitude 2-up on a DR.........Why would you do such a thing?
Im already sitting in the passenger area on mine going down the hiway and Im just 6' tall.
Cant be real comfortable with 2.

But Yeah Id always enjoy more power,Im just not willing to spend the money and time to fool with the thing,and it pulls my 180lbs around pretty dang well hiway or dirt.
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Old 07-03-2013, 11:15 AM   #78275
Foot dragger
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Maybe it's worn just enough to work properly
I try not to think about it,if I want to ride something faster I drag out the 1250 Bandit or 530 EXCR.
The DR is always ready to go and always gets me home,had some great trips on it.
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Old 07-03-2013, 11:21 AM   #78276
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Originally Posted by DAKEZ View Post


You do know that motorcycle riding is supposed to be FUN!!! (right?)

To hell with MPG! FPG is what you should be looking for.

F = Fun.
Unless of course you actually plan to adventure ride past Starbucks.....



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Old 07-03-2013, 11:33 AM   #78277
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Originally Posted by procycle View Post
The idea of "for a given throttle opening" is useful for tuning but a much better way to think about what is happening during actual riding would be to say "for a given horsepower requirement" or "to maintain a given speed". If you rethink the idea using that frame of reference you will see that the idea that CV carbs compensate for altitude in some beneficial way is false.
If the slide is open a certain amount for a given combination of throttle angle, rpm and altitude, the slide will be open less for the same combination of throttle angle and rpm at a higher altitude. If the rider now opens the throttle, i.e. there is a new combination of throttle angle and rpm at the higher altitude, the slide height would now be greater if he were to be able to instantaneously return to the lower altitude. If I understand correctly, you say this doesn't matter because the slide and needle rise and fall simultaneously. However it is the throttle angle the ultimately controls air flow, and not the slide. Therefore the needle will be lower in the emulsion tube for a given combination of throttle angle and rpm as the air density decreases.

Regards,

Derek
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Old 07-03-2013, 11:37 AM   #78278
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Originally Posted by procycle View Post
To compensate the mixture for lower air density you would have to have some additinal air get past the slide without picking up additional fuel.
It's the other way around, less fuel will be picked up for a given intersection of throttle angle and rpm.

Regards,

Derek
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Old 07-03-2013, 11:59 AM   #78279
Rusty Rocket
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Originally Posted by Foot dragger View Post
I havent taken the plug out over the fuel screw,seems ok so I dont mess with it.
The plug color on mine is tan not white so they must have jetted it better at the factory.

I received my '96 already modded so I have no idea how a stock one runs. I'm defiantly giving stock a chance before any carb/airbox mods.
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Old 07-03-2013, 12:01 PM   #78280
Mongle
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Originally Posted by Foot dragger View Post
How can one stock bike be so different from another? CA bike has different jets? Mine will wheelie in 1st and 2nd with stock carb and jets,I put a 14 countershaft sprocket on it and it goes fine. I live at 100' elevation and have ridden it to at least 11,000' with no problems at all.

Yet yours has a real narrow window where it will run right.
Odder then odd. I have never even adjusted the fuel screw on mine.
I later on did a carb kit and such since I mostly ride from 800- 5500ft. One reason my bike may be so different is that when I went to do the carb kit I found the idle mixture screw was all the way in! The guy on the assembly line must have been napping when my bike went across. I bought the bike new and had to take the plug out so I know there wasn't anyone messing with it before hand.

When I did all those elevations I had my 220lbs and another 70 lbs of gear so I was really working the bike hard...made it more noticeable.

Edit: on the plug color deal...I have found with newer-cleaner gasoline plug color is harder to determine fuel mixture. Having the dyno we pull plugs and look at them more for laughs than anything. With today's gasoline you can have a fuel mixture anywhere between 12:1 and 14:1 and it all looks the same. Also, plug color only matters where you shut the engine off. If you let the bike idle and then check plug color you are only seeing idle mixture.
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Old 07-03-2013, 12:01 PM   #78281
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Quote:
Originally Posted by motolab View Post
If the slide is open a certain amount for a given combination of throttle angle, rpm and altitude, the slide will be open less for the same combination of throttle angle and rpm at a higher altitude. If the rider now opens the throttle, i.e. there is a new combination of throttle angle and rpm at the higher altitude, the slide height would now be greater if he were to be able to instantaneously return to the lower altitude. If I understand correctly, you say this doesn't matter because the slide and needle rise and fall simultaneously. However it is the throttle angle the ultimately controls air flow, and not the slide. Therefore the needle will be lower in the emulsion tube for a given combination of throttle angle and rpm as the air density decreases.

Regards,

Derek
This is what I have read about the CV carb,it was built to compensate for altitude and seems to do so.

A normal carb is a carb,pull cable the slide goes up.
Bigger thumpers are able to change altitude easier with out re-jetting then the little pea shooters though.
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Old 07-03-2013, 12:08 PM   #78282
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Originally Posted by motolab View Post
It's the other way around, less fuel will be picked up for a given intersection of throttle angle and rpm.k
If the velocity is constant how does it pick up less fuel?
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Old 07-03-2013, 12:11 PM   #78283
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Ideally, you want a copy on your hard drive that you can study in the comfort and privacy of your own home, and a hard copy you can have on your lap as you stare at your engine trying to remember the right way to reinstall that part. If you do any amount of wrenching, it will happen.
And don't overlook Youtube as a source of information. Watch enough of them and you learn to separate the good information from the BSers.


Rather than Youtube, someone should take this thread; print, bind and sell it on ebay.

An instant hit!
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Old 07-03-2013, 12:13 PM   #78284
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Originally Posted by motolab View Post
It's the other way around, less fuel will be picked up for a given intersection of throttle angle and rpm.

Regards,

Derek
Actually, the fuel isn't picked up. It is pushed up by the higher pressure in the float bowl.



I also remember that it isn't a choke. Let's be correct in our terminology.
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Old 07-03-2013, 12:18 PM   #78285
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Originally Posted by motolab View Post
...it is the throttle angle the ultimately controls air flow, and not the slide.
The throttle cannot let in more air than can get under the slide. Therefore, the slide is really what limits airflow.

The throttle determines the demand for airflow but the slide will determine how much air actually goes through the carb.
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www.procycle.us - Everything for your DR650 and lots of other great stuff!
DR900 Big Bore Stroker buildup
TurboDiesel Corvette - go to the end to start at the beginning
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