what could cause popback on ITB 3.0?

[pampadori]

Trying diligently to get my car running again before the end of summer! Luckily, i have some time left.
Over the last handful of months I rebuilt my 3.0 motor and used 9.3:1 CIS pistons and had the cylinders coated at EBS and used their ring kit. I couldn't tell for sure what the cams were but i recall narrowing it down to either 83 SC or 3.2 cams. I followed all the procedures in the book to time things and measure clearance etc. I felt confident when done that I had the cams installed and timed correctly.

I combined this motor with Triumph ITBs and an AEM Infinity 506 with the EPM replacing the distributor. I got my timing sync'd - Locked ignition to 5 btdc and had cyl 1 sparking exactly when the mark just to the right of Z1 was lined up with the fan housing hash mark.

It starts and idles pretty well. Got my itbs all sync'd up as well.
AFR at idle dances around 13.5:1 and my timing maps are calling for around 7-8 degrees at idle and goes up to about 15 degrees by 2000 rpm.

The issue - when i try to open the throttle just a touch to rev the motor, i'm getting popback thru the throttle bodies and it doesn't rev up smoothly. I have tried more fuel, more timing, less fuel, less timing. It still popsback.
Is this indicative of cam timing not being correct? I guess i could remove the valve covers and check for when the intake on 1 and 4 open if you all think that is where I should look next.

I appreciate any feedback to help me get this thing running well.
Thanks,

[jpnovak]

This is lean tip-in. acceleration enrichment is not correct.

[pampadori]

I tried fattening up the VE table but didn't get anywhere.
Maybe I'll give tuning with throttle input for load instead of MAP and see if that gets me some improvement.
I'll also try to log it some and share the data. People, they like the data!

Edit: I'm learning just how above my head this tuning stuff is. Found some good explanation on what the "wall wetting" tables actually are for. From what I read this is basically my acceleration enrichment where I tell it how much extra fuel to inject on top of the VE map if the throttle opens x amount in x amount of time. The table has an axis representing how quickly I open the throttle. I'll play with this tomorrow and see if I can get the lean pops to stop.
It's really blowing my mind how much I can adjust and tweak on this EMS.

[Jeff Alton]

Think of it as an acceleration pump feature on a carb. Needs more fuel at tip in...

[pampadori]

Jeff - that made complete sense!

Update - I adjusted the wall wetting and immediately it was improved but still seemed like i couldn't find the sweet spot.

So then I changed the fuel method from MAP based to throttle based and bingo! Revs up much cleaner now without the popback. There might be a little popback due to a vac leak on cyl 2 but it isn't that bad. I suspect there is a leak somewhere in my brake boost which is directly hooked to that cylinder. For now, i might just adjust that individual cylinder trim.

GLad that I can put the fear of a botched cam timing issue behind me!

My lord does this engine rev up fast now!

[otto in norway]

Glad to see you are making progress!

Here's another tip for you:
I have experienced that the injector angle (Timing setting for when the injector fires in the cycle) can also lead to hesitant throttle response. Don't know if you have the possibility to adjust it with your setup though...
And you should really fix the leak, it may proove nearly inpossible to tune away.

[safe]

MAP is tricky with ITBs, you need to connect all throttles to a "chamber" and measure MAP from there.
For the brake booster you almost need an external pump or skip the booster.