Gear ratio change on shaft drive?

I was wondering if anyone knew if the final drive can be changed to a different ratio on a shaft drive 750 LTD. I'm doing near 5k rpm at 70MPH while in 5th gear and I would like to get a bit more MPG.

Anyone have any input?

You can make a small change with a different rear tire, taller ratio. In metric this usually means wider at the same time.
What rear are you running now?
Otherwise the final drive or the engine bevel gear would have to be swapped, and that could prove expensive depending on what would fit and how much you could get it for.

For the rear tire I'm running the OEM spec size 130/90/16. I was hoping I could get a different bevel gear set to keep the stock look. I've searched around but I can't find anything and I don't have the time or the energy to go compare the sets on other bikes in a boneyard.

Unfortunately, that is one of the pitfalls of a shaft drive. You are stuck with the ratios the engineers gave it at the factory. Seems like it would be a lot of work and probably money to make any sort of changes.
For the record, 5k at around 70 mph sounds about right for a 750, which is a motor that needs to keep the revs up to make any power.
Best of luck.

83KZ750LTD wrote: I was wondering if anyone knew if the final drive can be changed to a different ratio on a shaft drive 750 LTD. I'm doing near 5k rpm at 70MPH while in 5th gear and I would like to get a bit more MPG.

Anyone have any input?

These engines were born to spin at their designed road speeds, and they happily do so.

Ideally, there's a sweet spot where the engine is performing at maximum efficiency, where the rpm is "just right" for the load and road speed.
Neither over-revving (such as constant cruising in a lower gear), nor under-revving (such as more lugging effort resulting from too tall gearing).

Stock gearing usually produces the better compromise between acceleration and cruising.

Consider that the maximum road speed of a stock Z1 is about the same in either 4th or 5th gear.

Imo, ideal highest gearing produces top speed just as engine rpm meets red-line.
In other words, where a properly performing engine will barely pull red-line in top gear.

Taller overall gearing may require less rpm for a more relaxed feeling at cruising speeds, but at the expense of reduced acceleration.

Conversely, lower overall gearing may afford quicker acceleration, but at the expense of a more frenetic unnecessarily higher rpm at cruising speeds.

Taller gearing doesn't necessarily result in higher mpg. And may result in lower mpg.

Where the engine is running in its sweet spot at a given cruising speed, changing to taller gearing that moves it out of its sweet spot -- although at a lower rpm -- requires the engine to work harder at the lower rpm, and actually perform less efficiently.

Just my 2¢.

Good Fortune!

All of that's good information.

In addition, fuel economy is more of a function of the amount of work the engine has to do to get you and keep you at speed. Changing the gearing for your bike to get better MPGs at highway speeds isn't going to work the way you want it to.

Even if you go for a lower RPM, you're still going to have to provide EXACTLY the same horsepower to the wheel to stay at a particular speed. You are overcoming resistance (roll, mechanical, and wind) at that speed.

Changing the location in the power band that the engine is running at when at your desired cruising speed is the only way to affect fuel economy without changing other resistance factors. This is deep science, and is dependent on the particulars for your engine.

For other considerations (acceleration, etc.), changing the gearing can be very effective, but for your stated purpose (better MPG) I don't think you are going to see a difference and there's a 50/50 chance that you actually make your mileage worse.

Ok this is all good information. I think I need to find the root issue as to why my fuel is empty just after 125 miles. I'm running stock on every thing and a spark plug inspection tells me the air/fuel mixture is perfect. The engine runs smooth and only has 8000 miles on it.

I guess I expect better than 27 mpg on a bike.

That does seem low. I would have expected low to mid 40s.

I'd also expect about 50% better mileage.

Check your carb float height. If you are running too high, you could lose a considerable amount of fuel to the overflow.

Check your fuel line for leaks. You could be losing gas when you're moving, which would cause this kind of fuel economy problem.

Check your valve lash. Marginal valve clearances can rob you of mileage by robbing you of power.

Check your timing. If you're running with your timing retarded (not you personally), you'll have to supply a lot more gas to get to the same level of power from the engine.

83KZ750LTD wrote: Ok this is all good information. I think I need to find the root issue as to why my fuel is empty just after 125 miles. I'm running stock on every thing and a spark plug inspection tells me the air/fuel mixture is perfect. The engine runs smooth and only has 8000 miles on it.

I guess I expect better than 27 mpg on a bike.

That is pretty low unless you're really running hard. I've always gotten 34 - 42 depending on how hard / fast I'm riding. Check the fuel level using the clear tube method. Ed

83KZ750LTD wrote: Ok this is all good information. I think I need to find the root issue as to why my fuel is empty just after 125 miles. I'm running stock on every thing and a spark plug inspection tells me the air/fuel mixture is perfect. The engine runs smooth and only has 8000 miles on it.

I guess I expect better than 27 mpg on a bike.

Are you calculating the mpgs correctly?

I'd guess the tank is ~3.2 gallons total including a reserve of about 0.7 gals.

3.2 gals x 40 mpg = 128 miles

If your bike has a low fuel warning light, it would illuminate at 100 miles when getting 40 mpgs.

You can get a 140 tire, that will add a bit of both height and width, small increase in gearing.
That fuel mileage if right is terrible unless your hammering on it. You should go do basic maintenance first, paying close attention to things like posted already. Carbs, Ignition including Voltage to coil check, Filters, Tire pressures, and such. Look close at the ignition advance and make sure it is moving freely and in spec. My shaft drives, I have been running synthetic gear oil to help cut friction.