High elevation VM34 jetting

[kwhy3000]

‘79 engine, 750cc big bore just installed, stock cam, HHB CDI charging and ignition kit, straight pipes, velocity stacks with foam inserts.
At 4450ft in elevation and started jetting at:
Needle jet- 159 P-6
Needle- 6F9
Slide- 2.0
Air jets taken out
Main- 175
Pilot- 22.5
A/F screw- 1.25 turn out
Needle clip- 3 from top
Seemed rich as hell, plugs immediately covered in soot. Idle seemed fine, air screw caused stumbling both ways so I think I’m close there but anywhere 1/4-3/4 throttle caused major missing/stumbling.

Main- 160
Pilot- 20
A/F- .75 out
Clip- 1 from top
Worked my way down to these numbers and the 1/4-3/4 throttle cleaned up quite well. My concern is: plugs are still immediately covered in soot. Do these jet numbers seem reasonable for my elevation of 4450ft? I’m kind of worried my ignition isn’t working well enough which is why plugs are black? I have no evidence to support that. All testing of the ignition seem to be in good order. Is my pilot too rich and that’s what I’m seeing? Would really appreciate any input. All components are brand new. It’s a new build. I’m diligent when it comes to the details but starting to get nervous and don’t want to burn this new top end up. Thanks.

 

[Gadjo fandjo]

I just saw your post a year later, shame no one replied. I think it has been many posts regarding the jetting of big bores, and most of them are old and their links are obsolete. I am looking for the best tuning for my 840 bore. So far I should have the original VM34 jetting and the plugs are showing too charcoal black. After some 20/30 milles, it doesn't run smoothly and if more it stops on the idle and is hard to start. Until I clean the plugs.
From at least 5 guys in the known, all have different options! LOL.
In my humble opinion, you seem a bit too low with your Main as the original is 220 (I understood) and may be put the clip in the mid notch for a start.
I will soon get on mine and post my findings. (when longer and nicer days)