Advice on next jet change - Mikuni 44's

[inline6]

I've been working on the jetting of the Mikuni 44's on my engine.  Attached is a plot showing RPM and AFR.  Here are my notes from that session:

 

3rd on interstate.

 

Downshifted to third and stabilize RPM (about 4800 RPM)

Squeezed throttle slowly until near full throttle, shift to 4th, end recording.

 

I've read that main fuel jet adjusts the fuel mixture at all engine speeds, and main air jet adjusts the mixture at "high" engine speeds.  

 

Current settings:

 

Main 180

Air 230

Pilot 57.5

Pump 45 

Choke 37

 

 

 

What I am seeing rather consistently in 3rd gear runs like this one is a bump up in the AFR in the 5000-5800 territory...(from steady state AFR I am seeing when on the pilots) which is then followed by a descending AFR trend until I short shift to the next gear.  

 

Thoughts?

 

I am just trying to get the jetting "close" so I can make the most of my time at a dyno session.  

Edited March 1, 2015 by inline6

[madkaw]

I would say the mains are not involved at all speeds. You are just running on pilots at partial throttle. I've had a main jet fall off the emulsion tube and the car ran fine around town until the throttle was opened enough to pull it in.

I think I would start backing off the main air jet sizes and see how that affects your AFR. You might find that you will need to drop the main jets sizes after that..  

[Tony D]

Make a pull n 4th from 1000 RPMs at low throttle opening. Make another pull at 1/2 throttle, and one at WOT. It will be a boggy one until 3,000/3,500 on the last two. Don't mash it and mask the jetting with accel pump jet (disconnecting the pump for these three passes might be an idea.)

 

Don't upset it by a downshift. Let it climb slowly and steadily.

 

The transitions from pilot to main, and then emulsion/air bleed/main will be seen above 3,000 RPM's.

 

It looks like your pilots are right.

Edited March 2, 2015 by Tony D