Average MPG low
HDF Community Team
Joined: Aug 2018
Posts: 3,011
Likes: 1,190
From: New Hampsha
[Edit - If your carb has an accelerator pump, not all of what follows is applicable]
If you have a Keihin CV carb, the biggest factors affecting acceleration (hesitation) from low throttle settings are the pilot jet, float setting, and pilot screw setting, in that order. The size of the main jet doesn't come in to play until near full throttle and higher RPM. Between those two ranges, the size of the needle jet and the taper of the needle are the biggest factors.
Popping on decel indicates the closed throttle mixture is too lean on over run. This is common since the higher RPMs are pulling more air across the pilot screw, which has been adjusted for idle air flow. You can try backing the pilot screw out 1/4 to 1/2 turn if you feel the need to "correct" it.
Shimming the needle will also often cure hesitation, but it does so at the expense of cruising fuel consumption. I would leave that as a last resort. A typical #4 washer is about 0.7mm thick. Two of them will make a huge difference in fuel metered, from about 1/4 to 3/4 throttle. (Try one washer first.) After that, the needle is up as far as it can go and fuel delivery is controlled primarily by the main jet.
Mikuni CV carbs operate on the same principles.
If you have a Keihin CV carb, the biggest factors affecting acceleration (hesitation) from low throttle settings are the pilot jet, float setting, and pilot screw setting, in that order. The size of the main jet doesn't come in to play until near full throttle and higher RPM. Between those two ranges, the size of the needle jet and the taper of the needle are the biggest factors.
Popping on decel indicates the closed throttle mixture is too lean on over run. This is common since the higher RPMs are pulling more air across the pilot screw, which has been adjusted for idle air flow. You can try backing the pilot screw out 1/4 to 1/2 turn if you feel the need to "correct" it.
Shimming the needle will also often cure hesitation, but it does so at the expense of cruising fuel consumption. I would leave that as a last resort. A typical #4 washer is about 0.7mm thick. Two of them will make a huge difference in fuel metered, from about 1/4 to 3/4 throttle. (Try one washer first.) After that, the needle is up as far as it can go and fuel delivery is controlled primarily by the main jet.
Mikuni CV carbs operate on the same principles.
Last edited by John CC; Oct 18, 2018 at 01:05 PM.
Supporter
Joined: Jan 2007
Posts: 15,787
Likes: 5,609
From: along the shore of Mishigami
Google Joe Minton Tuning the Keihin CV carb. He has also done articles in the Mikuni carbs. I did his tune up tricks on the "K" carb and the bike ran pretty good along side the 96" engines when they first came out, they would pull away with the 6th gear. We used the 02 Dyna as a two-up touring before we got the Road Glide Ultra. Windshield and bags are detachable.
HDF Community Team
Joined: Aug 2018
Posts: 3,011
Likes: 1,190
From: New Hampsha
Ah! Good point. The ones I have the most familiarity with do not. If it does, my comments about hesitation are not as applicable.
Stellar HDF Member
Joined: May 2015
Posts: 2,902
Likes: 443
From: West Tennessee
My 2011 with 96 got an average of 42mpg until I made the mistake of completing the Stage 1 with a Power Vision tuner that for whatever reason froze up constantly never allowing me to do an autotune. 27 mpg average was the result! Sucked having to stop and fill up every 100 miles or so. My new RG often goes over 300 miles on a tank. Not touching this motor!!! Apples to oranges with a carb but tiny changes can make a huge difference.
Last edited by tnriverluver; Oct 19, 2018 at 11:29 AM.
Tourer
Joined: Jun 2018
Posts: 356
Likes: 47
From: freedom
yea they are super lean and fuel efficient from the factory. just run hot. when i tuned mine after stage 1 with a thundermax i also went from 42 and 43 down to 34/36. wasnt thrilled but it sure does run cooler, smoother, and much better all around.
Outstanding HDF Member
Joined: Mar 2015
Posts: 2,840
Likes: 900
From: Philly Suburbs
Now making a little over a hundred HP at the wheel, my originally-88-now-97 with Mikuni, cams, headwork, etc. fluctuates between 31 and 38 mpg, depending on my right hand...
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Southpaw Super Glide: A Left-Hand-Drive 1979 Harley FXE Built to Fit the Rider
Verdad Gallardo
The Best and Worst Harley-Davidson Moves of 2025
Verdad Gallardo
Elite HDF Member
Joined: Sep 2008
Posts: 4,440
Likes: 148
From: Northwest
My own intake, V&H BR2-1 and Andrews 26h cams... with TTS, I still get ~45 on the road (set at 14.3afr).. in town - it's probably around 32 in town but then stoplight to stoplight what do you expect?
The ECM is only operating at 14.3 ( or whatever you have your AFR set at) when cruising. All other times, throttle positions...etc... it's running on the different maps.
The ECM is only operating at 14.3 ( or whatever you have your AFR set at) when cruising. All other times, throttle positions...etc... it's running on the different maps.
Supporter
Joined: Jan 2007
Posts: 15,787
Likes: 5,609
From: along the shore of Mishigami
For the OP, is the bike yours originally? How many owners has it gone through? If a previous owner put in a Dyna-Jet kit on the carb it's quite possible there in lies your mileage. The accelerator pump on the carb is on the right lower half of the carb looking into the throat, look in the carb with no filter (don't get to close) and twist the throttle, there is a tube where the spray comes out, that is the accelerator pump nozzle.