Got a HSR42 kit from Shane @SSC about 2 months ago, set up as follows:

Main- 170
Pilot- 25
Pump- 50
PMS- 1.75
Needle- 97 on 2nd clip

Overall very happy, back road cruising 55-65mph nets 50-52mpg. But as soon as I jump up on the super slab mpg tanks, bad, way worse than the CV40. I'm not talking 80-90 mph either, just 70-75.

My question is, do you think going to a #98 needle will significantly improve 70-75 mph mpg?

I have a air fuel gauge and a 98 needle was to lean for me. I went to a 172.5 main, 35 pilot, 97 on the 3rd clip and i get great gas milage but for whatever reason im richer than most jetting profiles but my meter says im on the lean side. I would raise the needle a clip.

I get 50mpg at 75mph btw. City is mid 30's but alot of stop and go and im not easy on the throttle

smokescreens wrote:
I have a air fuel gauge

Smokes, will you start another thread and explain how you installed an AF gauge?

I'm clueless how mine is jetted.
Bought it as set up for an HD and works great.

Warden wrote:
smokescreens wrote:
I have a air fuel gauge

Smokes, will you start another thread and explain how you installed an AF gauge?

Sure. When i get home from work.

You guys are awesome. Im like on, off, oil, and gas. Anything past that and im like durrrrrr huh

Interesting that Shane sent it with a 170, I kept an email from him on how he sends the carbs out.
from his email:
50 pump
25 pilot
1.75 turns out
97 needle 2 clip
167.5 mains

at 80 you can get 40mpg, if you are still looking for 50, you would be running too lean. Just like cars, if you really want to see what max mileage potential can be, then you really need to do a controlled run, can be boring and mundane too. No heavy wrist action, it doesn't take much wrist to kill mpg's. I've done runs at 65mph for 150 miles at got 50mpg, done runs at 80mph for 120miles and got 40mpg both groove 2. going to groove 1 65mpg 50mpg (notice, no change from groove 2) 80mph 45mpg 5mpg better, but a seat of the pants performance loss

according to the Mikuni tuning manual, needle clip position won't affect mpgs below approx 70mph, and since the only difference between needles is the cruise portion (65mph) then the leaner needle won't affect it either since at that point on the needles the diameters are the same. You can lower the needle to groove 1, however, you will lose some acceleration performance, and even at 70mph you will want to downshift to pass. On a side note, if you cannot get the bike to perform in groove 1, then you more than likely have a air leak. I ran the carb for 6 months without an issue on 1st groove. I gained 5mpg at 80mph, but lost performance. Only other thing I changed was 1/4 turn in on pilot screw for 1st groove. After 6 months, and barely running hwy speeds, went back to 2nd groove, would rather have my performance than to gain 5mpg at speeds are hardly rode at. There was only 2 that I know of that ran 1st groove. Those who said they could not get it to run, all had an air leak at the manifold to heads.

Erbman02 wrote:
Interesting that Shane sent it with a 170, I kept an email from him on how he sends the carbs out.
from his email:
50 pump
25 pilot
1.75 turns out
97 needle 2 clip
167.5 mains

at 80 you can get 40mpg, if you are still looking for 50, you would be running too lean. Just like cars, if you really want to see what max mileage potential can be, then you really need to do a controlled run, can be boring and mundane too. No heavy wrist action, it doesn't take much wrist to kill mpg's. I've done runs at 65mph for 150 miles at got 50mpg, done runs at 80mph for 120miles and got 40mpg both groove 2. going to groove 1 65mpg 50mpg (notice, no change from groove 2) 80mph 45mpg 5mpg better, but a seat of the pants performance loss

according to the Mikuni tuning manual, needle clip position won't affect mpgs below approx 70mph, and since the only difference between needles is the cruise portion (65mph) then the leaner needle won't affect it either since at that point on the needles the diameters are the same. You can lower the needle to groove 1, however, you will lose some acceleration performance, and even at 70mph you will want to downshift to pass. On a side note, if you cannot get the bike to perform in groove 1, then you more than likely have a air leak. I ran the carb for 6 months without an issue on 1st groove. I gained 5mpg at 80mph, but lost performance. Only other thing I changed was 1/4 turn in on pilot screw for 1st groove. After 6 months, and barely running hwy speeds, went back to 2nd groove, would rather have my performance than to gain 5mpg at speeds are hardly rode at. There was only 2 that I know of that ran 1st groove. Those who said they could not get it to run, all had an air leak at the manifold to heads.

Niel, thanks for the info. I've read the HSR tuning manual several times and believe I'm starting to grasp it. I know the #98 needle is the leanest for the hsr42 and seems to be the most popular on the forum. Will using a 98 improve 70-75 mph cruise mpg without being too lean?

Shane ships a 167.5 main for the 1600s and 170 for the 1700. He also includes one smaller and one larger

I tuned mine with the 97 needle groove 2 for 40mpg at 65mph, with 22.5 pilot then changed to the 98 needle same groove without touching anything else, then got 48 to 50mpg at 65mph and Barons BAK filter. I should say that was my final jetting that I had for about 2yrs till I changed pipes then eventually air kits. prior to that, I jetted quite a few times with 20, 22.5 and 25 pilots, and 97 and 98 needle, some tweaks here and there, did about 8 afr runs, this was over about a 6 month period. I always ran a jetting thru a couple of tanks, before making changes again. I was also running the Nemesis manifold and Yost tube, the manifold because of a longer throat makes for a big difference. Even the smallest air leaks at manifold to heads will make a big difference too Once I got rid of all leaks, I had to drop to a 162.5 main, was at 11.4 afr with a 167.5 wot, didn't need to be that rich for wot