HarleyTechTalk

Y'all are getting me worked up with some old posts I've searched through and several mentions of finicky tuning when it comes to Ductile Iron Axtell cylinders on the street with a Super G. 

I've witnessed one 88ci XL ridden HARD, Super G, no T-jet, 1 3/4" drags, "small" valve lightning heads: this bike ran a happy life beat hard and I think it had OEM ignition redshift 575 cams. Bike ripped hard real stump puller. Extremely crispy bottom and mid range power due to small ports, valves, and high compression. No buttons, bike would beg to crank the starter over and then fire right up.

106ci XL, Super G, no T-jet, S&S large port/valve heads, drag pipes maybe 2"?...... running a happy life but I never been in the motor before. Bike doesn't run much but idle and wide open. redshift 643 cams. Compression releases. Blows 180+

Got a 106ci Big Twin with a G on it, WITH T-Jet. Never ran it yet. Hoping to get through this project someday but the 3 13/16" builds are a blast from the past and a challenge to build I say. Considering AFR for tuning so I don't burn it up. I have the other 106 XL for jetting reference, both top ends are very similar, but the T-jet makes the jetting quite different.

I've only owned one bike with a T-Jet and have little experience other than that. We do have some members that have used and still use them.

Below is a mile high tuning chart that is really just a place to start. You can also get a copy of the ThunderJet tuning / installation guide from Zippers Performance at the link below.

Link to: Zippers Performance - Thunderjet Tuning Guide

IME the starting points are way rich, and the air bleed will bring in fuel too soon.  BUT how I do it is to set idle and this will get me the correct intermediate jet.  Go and tune WOT with a jet I have plugged for tjet. From what I have seen is with correct main. It will support well into the 5000's and Tjet is only needed to carry through the 6000's. Even with a bit leaner main for part throttle tuning.  It seems this can just take a bigger Tjet and not an earlier air bleed.  But this is all changes based on reading frt rr afr.

Heads and cams will affect carb tuning more than cylinder wall material.  Wall material or out of a chunk will not affect signal in venturi.  High velocity heads and high manifold pressure will affect signal in venturi.  My 4.25 Hyper cylinder with a G still runs a .029. 

My g on tc in oz 107" 33 inter 50 air 82 main. Gives very close economy to the new  injection bikes nice plugs colour. Also yost discharge tube. Maybe a fraction rich in high country. Very little umidy here