Intake distribution issues
First question that popped into my head was "What manifold are you running?" At the end you said "M1", but that doesn't help, since MP probably released a dozen manifolds under the M1 designation.
etc. etc.
So I ask, single or dual plane? Open or divided plenum? And then, what type of spacers- open or divided?
TBI systems like an open plenum so they get a better vacuum signal; and arguably work better on a single-plane manifold.
My swag is that you've got a a dual plane with a divided plenum, and you added open spacers to it- and as you added more spacers you stabilized the vacuum signal and it ran better.
If this is the case (I'm making a lot of assumptions here due to a lack of info) you could get rid of the spacers by having about an inch of the plenum divider removed. I've read the exact recommendation somewhere, but can't find it right now- but an inch is about right if my feeble old brain recalls correctly.
First question that popped into my head was "What manifold are you running?" At the end you said "M1", but that doesn't help, since MP probably released a dozen manifolds under the M1 designation.
So I ask, single or dual plane? Open or divided plenum? And then, what type of spacers- open or divided?
TBI systems like an open plenum so they get a better vacuum signal; and arguably work better on a single-plane manifold.
My swag is that you've got a a dual plane with a divided plenum, and you added open spacers to it- and as you added more spacers you stabilized the vacuum signal and it ran better.
If this is the case (I'm making a lot of assumptions here due to a lack of info) you could get rid of the spacers by having about an inch of the plenum divider removed. I've read the exact recommendation somewhere, but can't find it right now- but an inch is about right if my feeble old brain recalls correctly.