GT750M fuel milage

[pennell]

Hey there,

Just seeing what others are getting for fuel milage? Mine seems to be quite horrible at 80-90miles per tank. I think that its the needle jets in my carbs, looks like someone took some plyers to them trying to get them out at some point.

[tz375]

Needle jets on BS40 carbs are in the float bowls and do tend to corrode in place. If yours look bad, oredr a set from SUDCO or your local supplier, but remember that they are not normal VM 22/210 type. They look similar but are actually very different. They are BS30/96 .

http://pinkpossum.com/GT750/carb/BS40carbs.htm" onclick="window.open(this.href);return false; for details

[pennell]

Damn... I wish I had of found this clarification a month ago when I was going crazy looking for needle jets. I emailed mikesxs wondering if the Z6 would be similar but he didn't know. I ended up finding 3 used needle jets in good shape on ebay for 15 bucks.

[VintageKiwi]

Your mileage seems about right my 750A does 160 kilometres to a tank which is about 100 miles , that is before running on reserve.
Jim

[tz375]

Of the three needle jets that MikesXS carries only one will work. It is a Z-6 and that is several sizes richer than stock. All the others are too short or the wrong style. That Z-6 is the same style as a Z-0 but should only be used when you want to richen the whole fuel curve from bottom to top. They are not suitable as a replacement for stock needle jets on a basically stock bike.

The same applies to needles. They carry one needle that can be made to work but it's much richer than stock and is suitable under certain circumstances, but not as a replacement on a stock bike.

[pennell]

Wow... this is crazy. My bike uses more gas than my car. So if I rebuild my carbs my milage won't get any better? If I do some highway driving I can squeeze 100mi on a tank before the reserve comes on.

[oldjapanesebikes]

Wow... this is crazy. My bike uses more gas than my car.

Well - is your car also close to 35 years old ?

A bit over 100 miles per tank (prior to reserve) is about what I get on my 'A' - typically between 45 and 50 mpg, and I get about 40 mpg on my 'custom' (and those would be the larger imperial gallons, not the US ones )

[rbond]

Maybe you should switch to US gallons... You might go farther.

[markj]

Compared to it's Kawa H2 cousin, which got about 22-25 mpg it's practically a Prius.

[Buffalo-guy]

My J gets about 175 mi to reserve, with 16/43 gearing. It's even more impressive when it gets about 280 kilometers on the same amount of fuel. Your 100 mile range is low, but not particularly uncommon. My hotrod is sucking fumes at 85 miles, and I haven't even scratched the surface on the mods yet. Much bigger carbs are yet to be adapted, plus other enhancements, so there goes the old mileage down the toilet But the grin factor will be worth it. Al Gore won't be happy with me. Tough!!
If your spark plugs read good, and your bike runs nice, don't sweat the details. Enjoy it. Cheers.
Fred

[pennell]

So why the huge difference is fuel consumption? 100miles vs 175miles? I find this is the case when reading online as well, some say it was pretty good on fuel others say it was horrible.

[Suzsmokeyallan]

A lot was going on over the years with the Buffalos; carbs were changed, port timing was altered, crossovers were removed, internal gearbox ratios and final drive ratios were fiddled with constantly.
If you have an M or A model expect no more than 120miles from main to reserve and thats riding conservatively.
The J and K models with the VM carbs and different port timing do way better at fuel efficency than the later offerings simply because the torque delivery was shifted lower and the VMs are worlds better than the quirky BS40 carbs.
Raising the gearing on an M or A model to lower rpms in an effort to increase mileage defeats the cause because the port timing is not designed for lower rpm power delivery so you end up lugging on inclines or dropping down a gear for more rpms to get back to the where the power comes on strong.
For an A model 15/43 is about as good as it gets for most touring riding and even so, anything under 3500rpms in fifth means literally soft power.
Back in the 70s gasolene was how much a gallon again? the mileage was not that bad in reality compared to some other bikes from the same time era.

[pennell]

Thats for all the help folks.

[oldjapanesebikes]

..... and the VMs are worlds better than the quirky BS40 carbs........

While it is a fact the porting, exhaust characteristics and gearing changed, what is less clear is what the actual 'facts' are about the carburettors, as generally when this discussion comes up all you hear is opinion. I think you also would first have to decide what it was you planned to measure - performance or fuel economy as (and this is my own opinion not supported by fact ) I don't think you can get both at the same time with these engines.

I would dearly like to see some actual data showing a test engine with the carburettors being the only variable changed, in the same way it would be interesting to know how only changing from points to electronic ignition changes things. Has anyone ever actually done some science on this topic ?

[markj]

That's interesting. The L is sort of a good comparison for this. It has the earlier port timing and the CV carbs. Anyone fimiliar with the miliage it gets or how it compares to the other models.