gas mileage not so good

[Gene]

My 85 NH 650 had the stock jets, and because of a stumble just off of idle, I boought the complete kit from carbjet kits. I also cleaned the carbs.

Fast forward...

It runs great, but the fuel mileage is about 20-25 mpg. From what I've read it should be higher. This makes me wonder if I did the right thing. Perhaps the bike didn't need the kit, but the carbs just needed to be cleaned and the pilot jets adjusted. Plugs look normal, so I know it's not running too rich.

Anyone have the same experience as me? maybe reinstall the smaller main jet, or put the needle jet back to the stock position?

BTW, I haven't synced the carbs yet, (but I will tomorrow).

[Bob H]

It runs great, but the fuel mileage is about 20-25 mpg.

Yeah, that is pretty low.
Have you run through a few tanks to see what a consistent number is?

Were you riding hard - testing out the new jets? That will tank your mileage.

I don't have the same model, but a search says 50.4 mpg for your bike, which I would take with a grain of salt.

The specs for my 1993 NH 750 says High/Low/Average 54/28/35
I am not very concerned with MPG, and know that carbs are much less efficient than fuel injection.
Nonetheless the few times I checked it over the years it NEVER got anywhere near 54, and was usually around 40.

I rejetted and completely rebuilt my carbs a year ago, decided to track my MPG for a few months. Did a spreadsheet and for each fill up the results were 42.19  46.51    36.95    40.95  40.75  40.66  41.71  36.63

So despite very accurate miles to fill up noted to the tenth, and gallons to the tenth, some tanks were 36 some 46 and I attribute that to some conservative long distances at steady speed vs getting it on in the twisty canyon roads.

[Pete in PA]

The little bit I checked mine after rejet I got 38-40 mpg.

Carb sync being out can really mess up mileage.  might improve.

What gas are you using?  Nighthwaks only require 86 octane. Any higher you lose power/mpg.

I'm using 87 E10.

[mollusc]

I use fuelly.com to track the mileage in all my vehicles.  My 700S sits at around 35mpg over almost 10,000 miles, with best ever being almost 55.  Lowest was around 22.  So yeah, things can vary a lot.  Synching and tuning your carbs is essential, of course.
I also only run mid-grade or premium, mostly because it stores for longer but also because I get slightly more power and better mileage out of it.
I think your rejetting may have been unnecessary.  CV carbs are known for a stumble off idle because it takes a moment for the slides to respond.


As an aside, my NC700X averages over 60mpg with best ever tank being above 78.