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$15 WR reserve petcock and fuel capacity specs on a '02-'08 YZ results

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Just did a '03 WR reserve petcock on a stock '02 YZ250. ('02-'08 stock 2.11 gallon tank)

I tested the before and after volume with both petcocks and in various lean over angles.

A few interesting things came out of this.

First, the stock petcock/fuel capacity has some caveats.

With the bike level, the tank drained exactly 2.0 gallons.

With a +-20 degree angle, an extra 14 oz. or .11 gallons came out.

That seems to be where Yamaha came up with 2.11 gallons......the bike leaning back and forth 20 degrees. Now it gets interesting.

If you go to 40 degrees, you get another 13 oz. out or .1 gallons.

If you go to 60 degrees, you get another 12 oz. or another .1 gallons. Beyond 60 degrees does nothing.

So the bike, if you lean it over, has 2.3 gallons useable.

Could be useful to know if you run out while on a trail etc., you could get another .3 gallons by leaning it over.

One catch though. The tank on the petcock side only holds .15 gallons,

so you have to lean it over twice to get the whole amount ie.

run out of gas, lean it over, burn .15 gallon, run out of gas, lean it over, burn .15 gallon gas....clear as mud?

So this means that the tank on the right side below the frame holds .3 gallons.

Now, how about the reserve petcock? Remember that the tank on the petcock side holds .15 gallons

and that there is an extra .1, .2 and .3 gallons at 20, 40 and 60 degrees of lean.

The on function on the reserve petcock shuts off flow at exactly 1.85 gallons.

That may not sound like much of a difference, but you don't get the "lean over" benefit in "on" because

the "on" petcock tube is right where the frame separates the tank.

So by using "on", you effectively get a 1.85 gallon range with .45 gallon reserve. Not bad.

Enough to get you another 10mi.+ to get to gas.

Which petcocks work?

'99-'06 WR400/426/450 and '01-'06 WR250, $15 at the TT OEM store.

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thanks for the specifics on this mod. It was one of the first things i did to my bike but was never sure how much range I am getting after switching to reserve.

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HaHa someone else who's as anal as I when it comes to stretching out a tank of gas. All I will say is you better put this theory to test near the truck! I too thought that I could use the gas trapped on the right side of the tank as a reserve of sorts should the need ever arise. Instead of measuring it and calculating the distance I intentionaly ran it out, figured I'd tip it over get the trapped gas to the petcock and ride it till it died again thereby knowing exactly how far I could go on this makeshift reserve. To my suprise when I tipped it over there was no fuel to be had, she was in fact bone dry. Luckily this experiment took place at the track and push back to the truck was short. :thumbsup:

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Nice write up! Would offer gas, but I am not able to.

That is going to suck riding at a 60 degree angle, but its better than pushing.

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HaHa someone else who's as anal as I when it comes to stretching out a tank of gas. All I will say is you better put this theory to test near the truck! I too thought that I could use the gas trapped on the right side of the tank as a reserve of sorts should the need ever arise. Instead of measuring it and calculating the distance I intentionaly ran it out, figured I'd tip it over get the trapped gas to the petcock and ride it till it died again thereby knowing exactly how far I could go on this makeshift reserve. To my suprise when I tipped it over there was no fuel to be had, she was in fact bone dry. Luckily this experiment took place at the track and push back to the truck was short. :thumbsup:
Nice write up! Would offer gas, but I am not able to.

That is going to suck riding at a 60 degree angle, but its better than pushing.

True, I'd like a video of some guy trying to ride with it tipped over.....LOL

Joking aside, you just need to fill the .15 gallon on the petcock side and then it's trapped there if you ride straight and smooth.

hallsy, I know what prob. happened with you, it makes sense, and is another reason for the reserve petcock.

A little more discussion about what I was talking about.

I tested the .3 gallon on the right volume twice and got the exact same volume twice, but this was in the garage with the bike not being thrown around.

When you're riding aggressively ie. track, hard accel/decel etc., the .3 gallon on the right side sloshes around and finds it's way over to the left .15 gallon space.

It is possible though if you're out riding off road and getting low, that you'll have some fuel left on the right side.

What the reserve petcock does is, while in the "on" position, never accesses that .15 gallon capacity on the left side.

So no amount of sloshing/aggressiveness will dip into the .15 gallon left side. Then you also may have some left in the right side.

When you go to reserve you have at least .15 gallon and up to .45 gallon with the right side if you've been riding easy without aggressive maneuvers.

Like you said though, if you're riding on a track etc. (hard) you're prob. only going to have the left side .15 gallons with the reserve position.

That's still about 5 miles if you're easy on the throttle to get where you need to go.

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carver, What I'm saying to you is only count on the .15 gallons that is held in reserve being there when you need it. I don't think you could trail ride 60 miles slow enough or smooth enough to prevent the gas on the right from migrating to the left. I get 65 miles out of this stock tank, thats according to the trail tech which has been checked against several car odometers, other bike odometers, and a GPS. Many here doubt that kind of mileage is possible but from your calculations I'd say your gettig a similar distance. At my current mileage I could go another 4.6 miles on the .15 gallon reserve but those who say they get 40 miles out of a stock tank will only go 2.8. So my question is, do you see a way to extend the on position pick-up tube thereby creating a little larger reserve? If we could increase the amount held in reserve to say .3 or.35 gallons then we would have a range of @ 10 miles to work with. I think this would make a good mod even better. :thumbsup:

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I did add the reserve petcock to my Clarke tank. That one appears it will hold a decent amount in reserve.

Hallsy, you answered a question I was going to ask..thank you.

The question would have been...why are the tubes on the run position on the reserve petcock so dammed long. The answer is probably so the sloshing around of the fuel does nto deplete the reserve before you need it.

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hallsy, agreed, you can really only be sure of the .15 gallon part,

and it's good to know from your experiences how easily the .3 gallon on the right comes over.

I think that's another reason why YZ's get such good mileage, they're really 2.3 gallon tanks........LOL

Yes, it would be a cool mod to extend it to .35 gallons for a 10 mile reserve.

It would be pretty easy to detach the plastic "cap-screen" at the top of the on tube

and just extend the solid plastic part with plastic/rubber tube and re-attach.

Or you could braze on a brass extension, either way.

Roland that's right, the .15 gallon part of the tank on the left is so narrow and tall, it has to be long to avoid that fuel.

My guess is that once above that point, small changes in height gain large amounts of fuel because you're starting to access the whole tank.

It may be a very small height change.

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I also added a training wheel to the reserve side of my bike. When I hit reserve, I simply lean until the training wheel touches and drive back to camp.

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I also added a training wheel to the reserve side of my bike. When I hit reserve, I simply lean until the training wheel touches and drive back to camp.

:ride:

I actually thought about cheaping out on a PMB kickstand and getting a triangle stand and just packing it in my camelbak.:thumbsup:

I am sure on my next crash the stand would've turned itself around and then spiked itself into my back.

So, where do you haul this 60^ training wheel without getting impaled on it?

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