Gas milage

[Pierre]

Hi, i have a Road King 06 with carb, when stock it average about 42 MPG, now we make a 95C.I. flat top,Andrews37B,Mikuni Hsr 42,Screaming Eagle A/C, Hooker Tuned Flow turn to Torque slip on.he bike run great,it have 88HP and 101 Torque but the fuel milage drop to 28, i go down to 22.5 pilot jet from 25, and put a leaner needle. I have the 160 main do you think i must go to the 157.5 main ? I read the tuning manual from Mikuni ,i make mark on the throttle and i try to ride the bike at 1/4 throttle opening without good result. Can you help me? Thanks ... Pierre (i'm from Quebec, Canada)

[Pierre]

i'd like to add this one

[Mike]

At peak torque you are actually lean when at 100% throttle but the chart does not show (and cannot show) what the AFR is when at steady state (cruising). To check steady state, have the dyno operator apply a 25% load with the bike in fifth gear and check AFR when held steady at 50, 55, 60, 65, 70, 75 and 80 mph or hold the throttle at 1/4 as you are doing on the street. You may find that lowering the needle (raising the clip to a higher groove) will be required, you want an AFR of 14.5-14.7 under these conditions.
Without the dyno, I would lower the needle two grooves but go to a 165 main (based on your dyno chart). I would also adjust the accelerator pump stop screw in as far as possible until you experiance hesitation or stumble with sudden throttle changes (this is the small screw on the top of the Mikuni that stops the white plastic accel. pump arm), this will reduce the accelerator rod stroke lenght and give an improvement in milage when combined with lowering the needle. Also make sure that the accelerator rod actuating arm has a small air gap above the rod when at rest (throttle closed), this is adjusted by the small phillips head screw, with the spring on it, attached to the cable turret, facing to the air cleaner. If there is no air gap between the actuator arm and rod, it will pump fuel all the time due to vibration, reducing fuel milage. The larger main should give better mid range torque at WOT. So you get better milage and power!!! More power can translat into better milage since the bike does not have to work as hard to do the same job. Last, if you have a programable ignition, you can try adding more timing at low load/rpm (small throttle opening and mainfold pressure {MAP}), this also helps milage.
Let me know if this helps!
Thank you for using our forum,
Mike

[Pierre]

Thank Mike i'm going to try this today... I let you know the results for sure...Pierre

[Pierre]

Hi Mike, i try what you tell me for the needle and the main jet,i drop the clip 2 notches and put a 165 main i'm now at 41 MPG from 28 MPG ,i'm really happy about it. I also adjust the small gap at the accelerator rod actuating arm but i have trouble reaching the accelerator pump stop screw on top . I don't have access to a dyno for now because it's about 150 miles from home and it's start to be really cold here in Canada but next spring we check it for sure. The bike run great. I try lowering the needle one more notch to the lower one but the motor ping when leaving at a stop 2 up so i reverted to what you tell me.From your experience,how much do you think the 165 main will afect my air/fuel ratio at WOT ? Do you think it can be too rich ?With these mods the air/fuel ratio line on the graph mus surely be straighter? Thanks for your help....Pierre i also include this print from the dyno ,it goes with the run i post before.

[Mike]

I suspect the 165 is about right from the 160 you had earlier. Each 2.5 jet size change is about .4 on AFR, so two size changes (based on 2.5) would equal about .8 AFR. Your old AFR was near 14.0 so .8 would put you at about 13.2. It will not necessarily flatten your fuel curve at WOT since this is mostly a function of the exhaust gas flow. Though increasing the low speed jet can help with that but will affect fuel milage in a negative way. Another thing to consider is when the needle is lowered it is more difficult for the fuel to climb past it through the emulsion tube casuing the mixture to go slightly lean vs. the needle in a higher position. The main jet often has to go up one size (2.5) to acount for this. You may actually need a 167.5 main, which is pretty normal based on dyno's.
Thanks, Mike

[Pierre]

Hi Mike, i put a D&D Fat cat on the bike, how do you think it will affect the A/F Ratio? How do you set the needle clip and main jet as a starting point ? I have access to a dyno in a couple of months from now..Thanks

[Mike]

Main 170. Needle third from top.
Mike