JD X748 Sucking Fuel Like Candy

[KennedyDiesel]

I run it with the throttle at 100%, the pedal is floored (8 - 8.5 MPH) and cutting grass at typical height (4.5 inches not 8 or more inches), but the grass can be thick. Running both my X748 and my uncle's X748 this way and they both eat fuel. Run the X748 like my mom does at 50% throttle and 3 MPH, the tractor seems to sip the fuel.

All I can say is let Mom mow the grass or get a Ztrak.

 

[eagle107]

All I can say is let Mom mow the grass or get a Ztrak.

Yeah, I know. Nonetheless, I purchased the tractor for her and she finds it easier to use than the Scag ZTR, so that is what counts in the end.

 

[JDTank]

I run it with the throttle at 100%, the pedal is floored (8 - 8.5 MPH) and cutting grass at typical height (4.5 inches not 8 or more inches), but the grass can be thick. Running both my X748 and my uncle's X748 this way and they both eat fuel. Run the X748 like my mom does at 50% throttle and 3 MPH, the tractor seems to sip the fuel.

..Are you serious? Your trying to cut grass at 8 MPH? Please tell me that is a typo. You will never get the kind of performance you want if your trying to cut at 8 MPH. The number one problem I see with people who cut grass, almost everyone, is that almost everyone drives too fast. You shouldn't be going any faster than a slow jogger/fast walker.

I didn't know you were trying to cut grass at full ground speed, no wonder your eating through fuel. That is far too fast. Also, you will not see cut quality with speed that quick. The faster you pass over grass, the less time your deck has to suck it up vertically and cut it.

Of course the tractor sips fuel at 3 MPH, it has power to spare. The faster your ground speed, the heavier the load on the hydro pump, which leaves less available power for your PTO, in this case, your mower deck.

 

[Carl Bert]

I run it with the throttle at 100%, the pedal is floored (8 - 8.5 MPH) and cutting grass at typical height (4.5 inches not 8 or more inches), but the grass can be thick. Running both my X748 and my uncle's X748 this way and they both eat fuel. Run the X748 like my mom does at 50% throttle and 3 MPH, the tractor seems to sip the fuel.

There's your problem. These machines were designed to cut at 4 to 5 MPH, and at full throttle. You bought the wrong type of mower if you need to mow at that speed. The problem with mowing too fast and at lower RPM's, is that you're ripping the grass rather than cutting it, which results in poor cut quality. Fortunately for you the 7 iron deck spins faster than a regular deck or you would really be taring in your lawn.

 

[JDTank]

There's your problem. These machines were designed to cut at 4 to 5 MPH, and at full throttle. You bought the wrong type of mower if you need to mow at that speed. The problem with mowing too fast and at lower RPM's, is that you're ripping the grass rather than cutting it, which results in poor cut quality. Fortunately for you the 7 iron deck spins faster than a regular deck or you would really be taring in your lawn.

Not trying to split hairs, and you are correct Carl Bert.

Still, even with the slightly higher blade tip speed of the 7-Iron, it's still way too fast. Also, as you said, if you want to cut at that speed, you need a seriously high end commercial zero-turn.

 

[eagle107]

..Are you serious? Your trying to cut grass at 8 MPH? Please tell me that is a typo. You will never get the kind of performance you want if your trying to cut at 8 MPH. The number one problem I see with people who cut grass, almost everyone, is that almost everyone drives too fast. You shouldn't be going any faster than a slow jogger/fast walker.

I didn't know you were trying to cut grass at full ground speed, no wonder your eating through fuel. That is far too fast. Also, you will not see cut quality with speed that quick. The faster you pass over grass, the less time your deck has to suck it up vertically and cut it.

Of course the tractor sips fuel at 3 MPH, it has power to spare. The faster your ground speed, the heavier the load on the hydro pump, which leaves less available power for your PTO, in this case, your mower deck.

Yes, I am totally serious. From what the dealer told me, cutting at speeds like this should not be a problem. As I explained to the dealer that I cut at 10Mhp with the Scag Tiger Cat (this is a commercial mower with the velocity plus deck's blades running at 18000fpm). It was explained to me that cutting at full speed with the standard JD Xtra (X48-X62) residential decks would be problem because the blades run at 12000fpm to 13000fpm. The 7 iron deck is a completely different animal as it is a full commercial deck like the Scag's velocity plus deck; the 7 Iron's blades speeds are at 16500fpm and running the tractor at 8Mhp should not be problem for this deck. To be honest, cut quality is very good after I am done cutting (for the few times I cut with this tractor) and cutting at full speed (at full throttle - not mom's speed) should not be a problem for the deck. It just seems that the hydro pump load with the AWD system is putting more stain on the engine which is making it more hungry. To me that makes sense and now that I know what is happening, I can deal with it. I know we are not in agreement on everything here, but nonetheless, think this was a good discussion and I appreciate the help with this issue.

 

[arlen4720]

Yes, I am totally serious. From what the dealer told me, cutting at speeds like this should not be a problem. As I explained to the dealer that I cut at 10Mhp with the Scag Tiger Cat (this is a commercial mower with the velocity plus deck's blades running at 18000fpm). It was explained to me that cutting at full speed with the standard JD Xtra (X48-X62) residential decks would be problem because the blades run at 12000fpm to 13000fpm. The 7 iron deck is a complete different animal as it is a full commercially deck like Scag's velocity plus deck, the blades speeds are at 16500fpm and running the tractor at 8Mhp should not be problem for this 7 Iron deck. To be honest, cut quality is very good after I am done cutting (for the few times I cut with this tractor). So cutting at full speed (at full throttle - not mom's speed) should not be a problem for the deck, it just seems that the hydro pump load with AWD system is putting more stain on the engine which is making it more hungry. To me that makes sense and now that I know what is happening, I can deal with it. I know we are not in agreement on everything here, but nonetheless, think this was a good discussion and I appreciate the help with this issue.

I agree completely. The 7 iron IS a different animal than the "yellow deck" that JDtank has. I have the yellow deck, on my x748, but I have the 7 iron on my 997. The 997 has a 31 hp diesel with a 72 inch deck, so the HP to deck size ratio is close to the 62 inch deck on my 24hp x748. The 997 is 1700 lbs so it's taking more power to move the machine also. There is absolutely no comparison to the cutting speed of the 7 iron on the 997. If you can hang on, the 997 is fully capable of mowing at 12mph. 8mph is childs play for the 7 iron.
So, if you have a smooth yard, and the cut quality is good, you are good to go at 8mph. Of course, just my opinion based on cutting 7 acres per week with both a yellow deck, and a 7 iron.
eagle107...you would love the 997. What a beast.

 

[jenkinsph]

I can mow at full speed with good results as long as I don't let the grass get out of hand. If I cut the grass when it is about 6 inches and cut it down to 4 inches it works out well for me. I use an x48 deck on my 749 so the power isn't an issue and no drop in rpms. While I would have preferred the 7 iron deck it wasn't an option on the x749 and I can't fit the larger decks everywhere I need to go.

 

[JDTank]

You are all correct that the 7 Iron can handle that speed.

My point is merely that the tractor can't handle that speed. The X700 series wasn't built to mow at 8.5MPH.

On the bright side, we found your problem. The speed combined with the big 7-Iron deck is too much demand for the hydro system once you get into any kind of long grass. Not trying to sound like a smart arse, but either mow slower or buy a zero-turn. Myself, I would never buy a zero-turn. Tractors can do just about anything. Zero-Turns are useful for one thing only, cutting grass like no one's business.

 

[BBO]

Everything will clear up when the mowers get broke in.
Until then I WOULD mow at a slightly reduced engine speed.
Some operator manuals tell you to not run at full speed until the break-in period is over.

Break it in, change the oil and report back.