'72 1.7
Pulled the FI off several years ago and installed a set of EMPI 40s.
Basically pulled them right out of the box and bolted them on.
Car runs pretty well and plugs all look good.
Over the weekend I was messing around and noticed the vents were 28mm.
Just did the calc and it said I should have 30mm vents.

So... should I?
How much of a difference will it really make?
With new vents goes new main and idle jets too?

28mm sounds about right for a 1.7L. You want the smaller venturis to get higher air speed.

If your off idle throttle response is OK, don't mess with it. Larger venturis can create a "flat spot" where the main jets kick in.

Thanks Andy. She runs out pretty good. For a 1.7 with 100+k miles on her.

if you're pleased with the way it runs leave as is.

40mm IDF's with 28mm vents should be fine for a 1.7. I had 40mm IDF's with 28mm on my 2.0 with a mild street carb cam and it ran well and had very good gas mileage as well. Low end and mid-range were good, very drivable. Go with it.

Thanks guys. Just making sure I wasn't leaving lots of power on the table.

No biggie. Maybe 40-50 hp if you get it wrong.

You might be down 1 or 2 HP at 5500 rpm. The bigger venturis work well at high engine speed. Most of us don't stay at that rpm for long.