Will give you insight into whats happening, Recently we have installed a S&S 128CI with 550c Cam into what was a 2018 114CI Fat boy, Ever since doing the upgrade we had a hell of time getting the tune right, only in the bottom scale what is happening is when at cursing speed at 5% throttle 1500rpm till around 2200rpm the motorcycle sounds like it is dropping a cylinder and jerking but if you go anything above 5% throttle it disappears, it is not spark plugs or leads but seems like more of a tuning issue, we are currently using power vision with auto tune, and have got a base map from dyno jet that is suited for a 475c cam, we ran the auto tune and built a map from that, but the jerking still seems to be there to the point of not even been able to ride in that area, the motorcycle pulls bloody hard in every other rev range but just this bottom scale is a night mare to smooth out, we changed the cam back to stock just to check and the motorcycle ran perfect in that rev range, is the the 550c cam that aggressive that it is basically not ride able in that rev range? or is this more of a tuning issue?

Throttle body and injectors are stock with PM air filter
We are getting 47KPA at idle with the 550c cam and around 26kpa with stock cam
Could the throttle blade position be a problem at that rev range?

We do not have any dyno tuning places around the area so are stuck with auto tune for the mean time.

 

I also live in an area that has no tuners. I know how you feel. Pretty much screwed.

 

baz70 has the 550 cam in a 124" in this thread:
https://www.hdforums.com/forum/milwa...kit-124-a.html

 

No expert me but.... stock tb & injectors on that build !
Stock plastic tb can have issues, poor flange seal leaks/cracks, would have at least upgraded to the SE55mm alloy intake 27300167
Bigger injectors required
Have you tried S&S for a map sounds like your running their Kit with the 550 cam

 

The tuner I use doesn't like that 550 cam. He's tuned a couple of those S&S kits with the 550 and they are hard to tune especially on the low end. He's talking the dealer that brought him the last kit with the 550 in it to change to the 475 instead. Might be worth a try.

 

Done some research on stock throttle body and manifold with stock injectors, it does hold them back HP wise but shouldn't cause a low end miss should it? have also checked for intake leaks and nothing has appeared.

 

I am really starting to lean towards that issue of the cam just being too much cam a shame because the cam pulls so nice to red line

 

Even the S&S chart shows a nasty dip in the torque curve low down on their site ,for that set -up !

 

I thought this guy is running the 550, see post #30
https://www.hdforums.com/forum/milwa...o-numbers.html

 

Thank you everyone for the feed back, What I done on the power vision is played with the throttle blade % and has made a huge improvement but now we are starting to think that the throttle body is actually causing this by not giving us enough air for the 550C cam maybe we are wrong about the concept but it seemed to smooth it out alot at the bottom scale.