I had to make an adjustment like this on my
B2400. I haven't checked my 2910 to see if it needs adjusting.
Fortunately, the machanisms are the same and it's easy to adjust. The WSM describes an adjustment to ensure the lift reaches max height. I presume if it reaches max height with the control at position 8, then the lower setting all fall into place. If not you may have a different problem. Regardless, you might try this adjustment to see if it corrects the problem.
Here it is from the WSM:
1) Set the position control to the lowest position
2) Start the engine and set at idle
3) Set the position control to the uppermost setting
4) Move the lift arm to the upper end by hand and measure the free play
5) If the measurement is not within spec, adjust the free play by changing the position control feedback rod setting length.
Factory spec for free play is 0.2" to 0.4"
In step 4, with the 3PH lift fully raised, walk around to the back of the tractor and lift up on the lift arms by hand. You should be able to raise them approximately an additional 1/4" to 1/2". I suspect in your case you will find that you can lift it a couple of inches. This was the case on my
B2400. If it's off, you'll find the feedback rod under the seat on the right side of the lift housing. It's a threaded rod with adjustable nuts that goes through an eye on one of the lift arms. You can losen the nuts and thread them forward and backwards to get the lift up to the specified height when the control is at it's max setting.
All in all, it's a pretty easy adjustment to make.
If your's has been sagging, you might find the nuts are not tight, or maybe it's just part of breaking in.
Hope this fixes it.
Peter