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Hi all,

Just diminished my first tank of gas. I have the Clarke tank which I believe holds 2.8 gallons of gas. Now I didn't top it off, I only filled it until the pump automatically shut off, so I'm not sure how much of the tank that left empty. But let's say for arguments sake I only had 2.3 gallons of gas in the tank.

I reset the trip odometer to zero, then I rode the bike sporadically, maybe once every 4-5 days. And then yesterday I ran out of gas and had to switch to reserve in order to get me to the gas station. But my trip odometer was only at 71 miles! I don't know how much gas is left at the point where you need to switch to reserve, but if it's half a gallon, then that means I burned 1.8 gallons in 71 miles for a total of 39 miles to the gallon.

Does that seem low or is that normal under these conditions:

1. I weigh 205 lbs
2. 90% of those miles was on dirt roads and trails, mostly in 2nd and 3rd gear
3. I let the bike warm up for 3-5 minutes before riding.

I'm trying to determine if I have a leak or am losing fuel due to evaporation, or if this is normal for guy my weight.


on my 2nd fill-up I made sure to top off the tank completely, so now that I know it has 2.8 gallons maybe I'll get a more accurate measurement this time around.
 

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Hi all,

Just diminished my first tank of gas. I have the Clarke tank which I believe holds 2.8 gallons of gas. Now I didn't top it off, I only filled it until the pump automatically shut off, so I'm not sure how much of the tank that left empty. But let's say for arguments sake I only had 2.3 gallons of gas in the tank.

I reset the trip odometer to zero, then I rode the bike sporadically, maybe once every 4-5 days. And then yesterday I ran out of gas and had to switch to reserve in order to get me to the gas station. But my trip odometer was only at 71 miles! I don't know how much gas is left at the point where you need to switch to reserve, but if it's half a gallon, then that means I burned 1.8 gallons in 71 miles for a total of 39 miles to the gallon.

Does that seem low or is that normal under these conditions:

1. I weigh 205 lbs
2. 90% of those miles was on dirt roads and trails, mostly in 2nd and 3rd gear
3. I let the bike warm up for 3-5 minutes before riding.

I'm trying to determine if I have a leak or am losing fuel due to evaporation, or if this is normal for guy my weight.


on my 2nd fill-up I made sure to top off the tank completely, so now that I know it has 2.8 gallons maybe I'll get a more accurate measurement this time around.
You really need to refill and make sure of how full it is.
Having that nozzle down in there can really throw off what u think you have in there.

Is the carb stock ?
I deleted all the rest of the questions i had until you answer that one up there with more accurate MPG figures.
Fill it up to a known level you can remember and fill it up that much next time. Like an inch from bottom of the filler.
Both times.

No that's not normal for your weight.
I am going by another rider i know that weighs a tad over you.
he gets +60 mpg highway on a travel loaded bike.

If you had leak, you would know it.
Evaporation no.
 

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Is this bike new? If so, it will use much more gas until it is broken in...
 

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Anyone north of that weight riding one of these things on the road. Especially up around 60 mph is probably holding it wide open most of the time. That being said, at 250lbs with the stock tank, I seem to get 70 to 90 miles when mine hits reserve on the road. If your riding lots of trails all bets are off. It very much depends on gearing and how hard your pushing it, and in what gear. That being said, and you having the plastic tank i'd think you should get over 100 miles before hitting reserve, I'd keep a close eye on the tank to petcock connection, and carb overflow tube. These petcocks recommend them to be shut off between rides, and a speck of dust can be caught in the float needle causing it to slowly over-fill the float bowl. Gas evaporates so fast it might not be leaving any drip stains.
 

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With a stock thank we get about 95 miles and are close to hitting reserve. That's mostly at 50 mph or so along with some dirt road 25 mph areas. If we used 1.5 gallons @ 95 miles that's 63 mpg. 200 pound rider 45 tooth rear sprocket.

As mentioned, retest with a measured amount of fuel. If it's that far off read the plug. You may need to look for all the causes of a rich condition. If the bike starts easy and basically runs good you shouldn't have a compression/mechanical problem.
 

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Since installing my Clarke tank I know my mileage has gone way down. I strongly suspect it is evaporation related. I do not have a fancy little cap at the end of my gas cap breather tube.......


Tom
 

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Discussion Starter #8 (Edited)
Since installing my Clarke tank I know my mileage has gone way down. I strongly suspect it is evaporation related. I do not have a fancy little cap at the end of my gas cap breather tube.......


Tom
You bring up a good point. I do have an aftermarket cap that the prior owner installed and it has a tube sticking up out of it with some kind of cap on it. I don't really understand how the breathing tube works. Is it literally just an open tube to the outside air? If so, it would seem that evaporation would definitely happen. Or does it have some kind of one-way valve that let's pressure escape when it builds up, but stays closed the rest of the time? The last dirt bike I owned was from the 70s and I don't recall it having a breathing tube at all so I really don't get how they work or why they're even needed.


edit: Just decided to google it and found a good explanation on breather hoses here: https://www.bikesmedia.in/reviews/utility-of-motorcycle-breather-hose-explained.html


I will ride out the current tank and report back with my gas mileage. I'm confident that there's 2.8 gallons in there now because I topped it off. It might take me a week or two to get that much riding in though. I really don't have time during the week and it's supposed to rain this weekend so I may not ride then either.
 

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While you are at it check your spark plug. If it is black and wet then you are running way too rich and sending a lot of unburnt fuel out the pipe. You would know if it is leaking gas by parking it in the garage on top of a piece of cardboard box. Both the Clarke and the stock tanks are vented tanks so I think that rules out the loss from evaporation theory. With the stock tank and starting full to the top I always hit reserve between 70-90 miles depending on the riding I was doing. The reserve gave me around 20 miles to get fuel.

GaryL
 

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Gas mileage riding around trails in mostly 2nd and 3rd gear will not be the same as riding on the road in 5th gear, even at 60 mph.
Go for a road ride with a full tank, if you don't go far enough to use up the whole tank, fill it up again to the same level and figure out your mileage from what you used and how far you went.
I bet it would be more in line with everyone else.

For those of you with a Clarke tank - can you smell gas through the plastic? Dryden-Tdub thinks he is evaporating gas through the tank. That would not be good.
 

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As a new data point, I just checked my mileage on the new 2018 after break-in. It's in line with the 2010, about 75 mpg in mostly 3rd, 4th, and fifth, with 10 miles of WOT on the highway, and 60 miles of dirt at ~ 6,000 feet.
 
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