Maxim-X specifications show the fuel tank capacity as being 13L (2.86 Imp. gal., 3.43 U.S. gal.), of which 3L (0.66 Imp. gal., 0.79 U.S. gal.) is left for reserve. In theory, that may be correct but empirically those capacities appear to be a lot less. It's not likely that you'll reach the theorectical distances specified in various resources.

For over two years now, I've kept very close track of the fuel consumption of my own 750 Maxim-X. Having filled the tank more than 200 times, I have a pretty good idea how much fuel it takes and how far I'll be able to drive. In over 200+ fills, I've arrived at the following average figures:

I usually drive quite a bit past the point of switching to reserve (determined by loss of fuel supply NOT by the fuel indicator light) but on those ocassions where I filled up within 10km after reaching reserve, these were the fill amounts:

If it wasn't clear, these numbers represent the fuel volume I used up to the point where reserve was reached which is essentially the main fuel capacity. Maxim-X specifications show the main fuel capacity theoretically to be 10L (2.20 Imp. gal., 2.64 U.S. gal.), but from my own experience, it's obvious that the main fuel capacity is a little closer to 8.5L (1.87 Imp. gal., 2.25 U.S. gal.).

To me it seems that rather than a 10L/3L split for main/reserve capacity, the Maxim-X is closer to an 8½L/3L split. The discrepancy of 1½L (0.33 Imp. gal., 0.40 U.S. gal.) main capacity is probably best described using a picture from instructions in the Owner's Manual.

Yamaha likely counts the tank volume above the maximum fill level as part of the main capacity, although drivers are instructed not to fill to full capacity as shown in the picture. Consequently, drivers who are under the impression that they'll achieve 185-193km (115-120miles) before having to switch to reserve are in for a surprise when on their best day, they only achieve 161-171km (100-106miles), about 12% less than spec.

To complicate the gas mileage situation just a little more, it appears that the relative MAIN/RESERVE fuel volumes may be a little flexible. I've never actually disected a Maxim-X gas tank to see how the two volumes are kept separate (I'm told it's two pipes at different levels) but judging by the relatively large fluctuations I've seen in distances on MAIN capacity and distances on RESERVE capacity, I suspect that the RESERVE input might not be entirely isolated from the MAIN input... at least not to the degree expected. I'm only speculating here but it seems that fuel can splash from MAIN to RESERVE given enough bumps and turns. I see evidence of this repeatedly because the further I'm able to travel on MAIN, the shorter the distance I can travel on RESERVE and vice versa. Naturally, this makes it difficult to guess just how much further you can drive on what's left. That's why I usually diregard my RESERVE indicator light (which stopped working a while ago anyways) but always keep a close eye on the odometer during long cruises. Over time, I've come to realize that I start to get nervous when I'm "out in the sticks" and my odometer reaches about 180km (112miles). This, of course, is based on a fill to the lower edge of the filler neck. Not long after 180km, the Maxim-X will be sucking wind so I usually don't let it get that far before refueling. If I do reach 180km, refueling becomes my first priority - even if it means putting in gas that the Maxim-X doesn't particularly like.

It's also worth noting that while the Maxim-X may still have fuel in the tank (which you can clearly hear sloshing around), that fuel doesn't always keep the bike running near the end. Other Maxim-X owners might also have noticed that when running on fumes the bike coughs and sputters but does continue to run, albeit poorly. I'm not entirely sure why this happens but I do have a theory: Because the Maxim-X feeds fuel by gravity alone, the more fuel you have in the tank the more head pressure in the system to force fuel through the petcock, the fuel lines, the fuel filter and various carburetor restrictions. I suspect that as the fuel level and corresponding fuel pressure drops, it may take fuel just a little longer to accumulate in the float bowls... possibly just a little longer than the X is willing to wait for the fuel it wants to swallow. Remember, that's just a theory. In reality it may be something completely different but the fact remains - the Maxim-X usually begins to experience fuel starvation well before the gas tank is completely empty. I've tried to estimate at what point I first notice fuel starvation but it's difficult to quantify. On one occasion, however, I had the misfortune of running out of gas in the middle of a congested highway, far from any exits. I patted myself on the back for having had an emergency 250mL bottle of gasoline with me that day, but the congratulations were premature. Having added 250mL of fuel to a tank that had just run dry at high speed didn't solve a thing. That quarter litre of fuel wasn't enough to get even a single cough out of the engine despite priming and despite endless cranking. It just seems as if the Maxim-X needs a certain minimum amount of fuel in the tank to provide sufficient fuel pressure to move the fuel through the system efficiently.

Apart from the capacities themselves, the rest is very subjective. Maxim-X gas mileage is obviously effected by a lot of variables:

	#1-Ethanol I've come to learn that gasoline with ethanol isn't favourable for the Maxim-X; it can cause a rough idle, reduce performance and reduce gas mileage. When you consider that ethanol generates only about 60% of the power of gasoline¹, and you combine that with the fact that ethanol-based gasoline contains up to 13% ethanol, it follows that using ethanol-based gasoline inherently results in an immediate loss of up to 8% of your potential power. After several calls to major oil companies I learned that in Canada in 2006, only Esso and Shell provided ethanol-free gasoline. That changed sometime in early 2007 when Esso also began combining ethanol with all of their grades of fuel. Now (late 2007), only Shell still provides fuel without ethanol. Their standard grade 87 octane fuel contains as much ethanol as you'll find at most gas stations. But their mid-grade 89 octane fuel conatins only up to 5% ethanol and their premium grade 91 octane "V-Power" brand contains no ethanol. Coincidentally, my best gas mileage and performance results have often been after fills with ethanol-free fuel. ¹ 1 gallon of ethanol ~ 77000 BTUs, 1 gallon of gasoline ~ 125000 BTUs
	#2-Octane Low octane gasoline also seems to reduce performance and gas mileage, but excessively high octane has the same effect. Octane wouldn't normally matter that much but because the XJ700X has 11.20:1 compression and the XJ750X has slightly higher compression, that changes things quite a bit. Over time, I've discovered that Maxim-X performance and fuel economy are best with 89-91 octane fuel. Personally, I choose 89 octane in cooler weather and 91octane in hot, mid-summer weather.
	#3-Weather Weather also seems to effect Maxim-X gas mileage in a noticeable way. Moisture and high humidity, cold temperatures and excessive wind gusting all contribute to a reduction in gas mileage as well, if only a little. It's not something that you'll immediately see during any one trip but over time you'll probably notice, like I did, that the Maxim-X prefers warm, dry days with stagnant air for better gas mileage and performance.
	#4-Load Naturally, extra loads (like a passenger, etc...) will also reduce gas mileage but the Maxim-X has enough power to keep the losses due to load to a minimum. Even with my own 92.5kg (204lb) body, my wife on the back, the saddle bags loaded and a few extras strapped to the front and back, with a little effort my 750 Maxim-X can still achieve about 20km/L (5.0L/100km, 56.5mpg CDN, 47.0mpg U.S.) during a casual, long distance cruise. Weight is undoubtedly a factor, but the more powerful the engine, the less the effect of load on gas mileage. Load will effect the gas mileage of the XJ700X just slightly more than the XJ750X.
	#5-Air Filter Obviously, an engine that can breathe well will perform more efficiently & get better gas mileage and therefore it's important to always have a clean air filter. What's surprising is just how much impact a dirty air filter can have on gas mileage and performance. On one occasion, I was getting a consistent 116km (72 miles) or less to reserve with a 1-year-old, stock, paper air filter. I really didn't expect that a filter which was only a year old could have any appreciable effect on gas mileage or performance but I found out otherwise. When I replaced the dirty, paper air filter with a brand new K&N cotton air filter, I suddenly found that it wasn't at all difficult to exceed 150km (93 miles) before switching to reserve. Of course, I'm aware that the mileage difference was probably effected by more than just the changing of the filter but I did my best to limit other causes. It appeared that simply replacing a dirty, paper air filter with a new high-flow K&N cotton air filter could result in a 30% to 40% increase in gas mileage. However, making room for other factors, I think I can confidently say that a 20% to 30% increase in gas mileage, with obvious performance increases as well, can be expected. Of course, that level of increase would only be seen where the paper filter is heavily congested as mine was. That won't be a typical result but nevertheless, there will be some level of increase in gas mileage and performance.
	#6-Aggressiveness It didn't take long to realize that, like any other bike, the single greatest contributing factor to Maxim-X gas mileage is driving style. When I drive through town like a bat outta hell and let rip with a blitz or two, I get gas mileage as poor as 13.53 km/L (7.39 L/100km, 38.2 mpg CDN, 31.8 mpg U.S.). I usually drive hard and therefore I average 17.5 km/L (5.7 L/100, 49.4 mpg CDN, 41.2 mpg U.S.) but with an easy, laid back cruise of 50-70km/h (~30-45mph) on a calm, warm summer day without a lot of stops, I was able to reach an astounding maximum of 23.4 km/L (4.3 L/100km, 66.2 mpg CDN, 55.1 mpg U.S.). No question, the Maxim-X is a "cruiser" because it absolutely prefers casual cruising speeds of 50-70km/h (~30-45mph). At higher sustained speeds of 120-140kmh (~75-85mph) gas consumption truly sucks (pun intended).

The bottom line - if you want your Maxim-X to get good gas mileage and good performance, after a thorough tuneup, don't buy gas which contains Ethanol, use 89-91 octane fuel only, keep your air filter clean, hope for calm, warm and dry weather, leave your wife and luggage at home and don't be heavy on the throttle.