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Old 08-12-2013, 11:14 PM   #1
erics72
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Default Fuel consumption question

My apologies, as this will be a little winded. I'm a little perplexed on my fuel consumption. Not very consistent. I know depending on how you ride, and where you ride affects how much fuel you will use up. But mine is way off the mark. To my understanding the 2002 Vulcan EN500 has a 4Gal tank (15L). And from some posts I've read (here and others online), most say they averaged about 50mpg on a full tank. Let's say 200 miles (321 km) per tank on an optimal scenario. I bought my bike used. The previous owner said he never did any mods on the bike. So the tank is the original. I can fill my tank for $10 CDN. According to the pump meter, that's only about 8L. Not 15L. Mind you, the fuel doesn't reach all the way to the tank opening, just below it. I'm sure I can squeeze another litre or two in there and it would be totally full.

So let's say my tank is only half of the what the specs say. At 2 gallons (7.5L). Working the numbers above, I should still get about 150 km on a full tank (optimal). This held true my first time I took it riding. I filled the tank, and rode for the day (no highway). By the time I was done riding, I had put about 115 km. I rode for another two days city riding (work, meeting up with friends, errands, etc..) before it felt like I needed to get more gas. Putting the odometer at about 130-135 km, with some fuel left in the tank. Again, I filled up on about $10. By the next time I filled up, I clocked about 135 km. I used this is as my benchmark for how much I can go before I had to fill up, minus 10km, just to give some buffer.

Now when I got the bike, I was told to keep the petcock the way it is. It was set to PRIME. I asked him why, he just said that's how he's always had it. He wasn't sure if RES and ON were mixed up. Petcock is standard RES at the top, PRI at level, and ON at the bottom. So I decided to do a test. Knowing that the reserve will get me about 25km before I completely run out, I decided to turn the petcock to ON (as it should be). I rode for a while. Then my bike started to sputter, I pulled over and checked my trip meter, and as I figured I had gone about 25km before my bike was starving for fuel. Turned it back to PRIME, and bike started with no issues. Rode another couple of days before filling up. So by that, I figured the original owner was right. The petcock was mixed up. So ON is RES, and PRI is ON. Not sure what RES is though.

Using, the 125km bench, I never ran out of gas. Till one night, on the way home from a friend's house, I had about 115km on the trip meter, and I ran out of gas. So I started using 115km as a marker for filling up. Then 3 weeks later, I ran out of gas again at the 110km mark. I took this opportunity to test the ON and RES settings on the petcock. Neither one would give me reserve fuel. I checked my tank and it was pretty much bone dry. So now, I use 110km as my indicator to fill up.

With all that said, my question is, why the sudden change of fuel consumption. I don't do highway riding, I'm rarely heavy on the throttle, I take the same routes when I ride, and relatively ride the same amount every week. How do I go from filling up at 135km, to 110km or less? I don't notice or smell any leaks. Bike seems to run fine. I've even used Seafoam. And wondering how I can get my mileage back to about 150km per tank. And if anyone can shed some light on why my tank fills up at 7-8L (2 gallons), instead of the 4 gallons, that would be very helpful. It looks like the same tank on all the 2002 Vulcan EN500 pics I've seen. Thanks.
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Old 08-13-2013, 12:16 AM   #2
DustyRags
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I'm not sure why your fuel consumption is changing, but I've got some possible leads for you.

First, though, some details for ya!

1- your tank is going to be rated as maximum fill point by the manufacturer- that means the total volume. But part of that volume is above the filler hole, so that's right out. And of course you aren't going to fill it up all the way to the filler anyhow... and you probably have some space below the petcock in the bottom where all the tank sludge gathers... so not a full tank, ever.

2- petcocks! These bikes have a three-position vacuum petcock. One way is run, the other reserve, and prime in between. It's set up this way so that when you're running along and it sputters you can just flip it completely around and don't have to worry about which way to go (if it's in the middle) or fumble around finding the middle position (if you're going to the middle) or anything.

It's a vacuum operated cock, which means that you've got a vacuum tube running from your carbs to your cock (hush!) which opens the cock when there's a vacuum on the other end of the tube (yes, the cock won't work unless there's something sucking on it... everyone get the jokes worked out). No suction- no fuel. This way, when the bike stops, the fuel supply is automatically turned off.

Jutting up inside the tank is the standpipe, which has a hole at the top and a hole at the base. On "run", it's taking fuel from the top of the standpipe, and when the fuel level drops down below that, it sputters and dies... you flip it over, it starts taking fuel from the base (an inch or so lower down) and boom! You've got another half gallon or gallon or whatever it is.

That's RUN and RES. PRI (prime) is the same as RUN, but it's designed to prime the carbs if they're empty. If you've just installed clean carbs, or if you've drained them for the winter or to get water out or whatever, you'll need to prime those babies 'cause the bike won't start without fuel, and the vacuum petcock won't turn on 'till it's running. So you turn it to prime, which opens the cock without suction (yes, that can happen!), and your carbs fill up 'till the floats rise, the needle valve shuts off, and the fuel supply cuts out. Now you're primed, you set it to RUN, thumb that starter and rumble on out.

So, why not just run it on PRI all the time? Eh, no reason really, but if you forget to turn the fuel off (turn to RUN, since these bikes don't have OFF), and your floats stick, or the needle valve has an issue, or you gotta leaky carb, and now you've got gas trickling all over your crank case. Not a good scene.

So now the question becomes "Why isn't my bike running on RUN or RES?" Well, all three use the same fuel lines, so it ain't that... all three let fuel run through at about the same rate, so it ain't that either... RUN and PRI use the same source (top of the stand pipe), so it ain't THAT... it's gotta be your vacuum valve. I'll bet you dollars to donuts your vacuum hose is leaky or just plain disconnected.

Now, fuel consumption! How's your power? Are you running lean or rich? Did your idle screw get bumped and you've got a fast idle? All those things could affect your fuel rating, and course you might be putting different amounts of fuel in there- are you tracking by tank or by how much you're putting in per fill up?
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Old 08-13-2013, 10:35 AM   #3
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Thanks Dusty. Very informative.

Just to clarify, RUN/ON works. I get fuel. But as I mentioned, when I had it on RUN, I only got about 25km on it. At which point, I switched to RES, but that still wasn't giving me any fuel. But when I switched to PRI, I got fuel. Lasted me another two or three days. So your saying if I wasn't getting a vacuum on RUN, it wouldn't work at all? Especially not for 25km. Would a vacuum issue explain why I've gone from 135km per tank to 115km?

Power is good. Not running lean or rich. Not exactly sure how optimal my bike is running. But I've already adjusted the idle to run pretty even, and idle sounds good. A little note, on occasion, when I'm downshifting I've revved the throttle but it would lag (no power). I'd have to rev again for it to kick in. Not sure if that means anything.

I'm also tracking by full tank (or as full as it can get). So whenever I fill up, I reset the trip. When I ran out of gas the first time, my brother brought me a full 2L can of fuel. Got me to a gas station about 2km away, and when I filled up, I checked the meter and it said 7L. So I estimated with the 2L (from empty), the 2km ride, and 7L fill, that the tank is only about 8L (or 2 gallons).

I'm going to test out putting the petcock on RUN again. I currently have 65km on the trip. I'll see if the fuel cops out by 90km, and putting it back to PRI will give me another 10-15km before I have to fill up again. I was told that leaving the petcock on PRI all the time was ok, since it was a vacuum, it will close off anyway. I didn't realize that if I left it on PRI, that fuel will continue to feed. I will take your advice. If I have to run the bike on PRI, I will switch to RUN whenever I shutdown.

Curious, if by leaving it on PRI this whole time, what are some things I need to look out for if what you mentioned is happening? ie. "...your floats stick, or the needle valve has an issue, or you gotta leaky carb, and now you've got gas trickling all over your crank case."
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Old 08-13-2013, 11:43 AM   #4
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No, in theory leaving the gas on is OK- it just means that now the only thing that's preventing the gas from running entirely out of your tank is the float needle valve in your carbs. As the carb bowl fills with gas, the float rises and pushes up on the needle until the needle plugs the fuel line leading into the carb. As long as that mechanism works, you've got nothing to worry about. If you float sticks and doesn't rise, it'll just keep filling and filling and overflow. Similarly, if the needle doesn't plug it (worn needle, bit of dirt, etc). If the bowl leaks, then it'll never fill (or stay full), and again, it doesn't shut off.

The thing with these things is that a slowly leaking needle valve isn't an issue while it's running, and so it's usually not worth taking the carbs apart to fix that, but while it's sitting still it's a much bigger deal.

I'm still not sure what's causing the change in fuel consumption. It might be a petcock issue, but I rather doubt it unless it's leaking fuel or something. Frankly, 20 km difference over a tank is well within tolerance difference for riding styles. I've gotten anywhere from 100 to 170 miles per tank, depending on how full I filled it, how close to true empty I want, how much revving there was, etc.
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Old 08-13-2013, 12:12 PM   #5
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Just remember that the pointing end of the fuel cock is the end opposite the handle. It does have a little arrow. I made that mistake the first time I ran out of gas. My 2009 gets 119 miles (198K) to the top half of the tank.The reserve gets me to the gas station to fill the tank with 2.1 gallons.
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Old 08-13-2013, 12:16 PM   #6
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Wow. I never realized the difference can be as much as 70 km. Always thought tolerance was anywhere from 10 to 25 km at the most. Good to know.

I'm banking on that I've never experienced leaks, or flooded carb issues, that my needle is working fine. But with these new found knowledge, if I decide to run on PRI, I'll make sure to switch to RUN/ON when the bike is shut off to prevent any would be flooding. I just have to test out riding with petcock in ON position, to see how much I can actually get from it before switching to PRI or RES.

If I get much less km's in the RUN position, than in PRI, would this be a vacuum concern? Or is it because in PRI, I'm actually using up ALL the fuel, including what would be in RES? Since PRI bypasses the ON tube in the tank.
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Old 08-13-2013, 12:25 PM   #7
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Quote:
Originally Posted by OldNewRider View Post
Just remember that the pointing end of the fuel cock is the end opposite the handle. It does have a little arrow. I made that mistake the first time I ran out of gas. My 2009 gets 119 miles (198K) to the top half of the tank.The reserve gets me to the gas station to fill the tank with 2.1 gallons.
Thanks. I made sure I had that confirmed when I got my bike. I had made that oversight on my very first bike. Drove me crazy till my mechanic friend pointed it out. Noob mistake. But after 20 years of riding, I still find tips here and there quite useful. I've never had any major issues with any of the bikes I've owned. So I know basic maintenance. ie. tune-up, brake fluid change and bleed, brake replacement, cable adjustments, etc... But I still haven't taken apart an engine and put it back. Knock on wood, I will never have to (on my own bike). But maybe I should learn, just so I have knowledge of how to.
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Old 08-13-2013, 01:00 PM   #8
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The first thing I did on my first bike was an oil change... that turned into a two-month top-end rebuild. Best lesson ever. Nothing scares me anymore
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Old 08-13-2013, 06:27 PM   #9
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Dang! Talk about jumping head first in the shark tank. lol Other than oil change, I think the biggest thing I've had to do on my first bike was change clutch cable, change and space the spark plugs, and bleed the brake line. I do miss a garage though. Moving into a condo, and trying to work on your bike isn't the most ideal situation.
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Old 08-13-2013, 06:32 PM   #10
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So I rode home from work with the petcock in the ON position. I did notice a minor difference with the revving. It kind of felt like when you are on a higher gear but not going fast enough and your throttling to catch up. That's exaggerated, but the closest thing I can use to describe the feeling. Another would be less power, but I was booting pretty good. And didn't feel like I was losing power. So I don't know if that's a good description either. Riding this summer with the petcock on PRI, I've gotten used to the feel of higher revving switching between gears. I also, switched between PRI and ON between every other stop. That's how I noticed the slight decrease in rpms when gearing up in the ON position.

Does having the bike on PRI suppose to do that (higher rpms)? Or is there an issue with the vacuum with my bike running in the ON position? Or possibly, if my bike is suppose to run higher in PRI, I adjusted the idle based on having it in that position. And now I have to readjust the idle to compensate in the ON position? Hoping it's a simple as that. Any tips is greatly appreciated.
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