Hello everyone. I could really use some help.

When I pull two shots back to back, with time enough between to clean and fill the the PF, the second shots pulls 10-12 secs faster. Not a nice stream either. First pull is 22-26 secs. This has been consistent over a long period of time. I have a system that I follow to reduce the variables.
I have tried grinding the 2nd shot finer. Also increasing the coffee volume. Still.....problems.

Any ideas or suggestions? My equipment is about 2 yrs old. Works the same as it did when I got it.

Macap is M4?

Do you leave coffee in the hopper?

Is this at the start of the day?
If so, do you grind a few grams to clear out the detritus?

I've noticed the same sometimes, and have suspected that hotter temps pull faster.

Thanks for the tips and the link. My issue is the same.

I only grind the exact +/- amount that I need for each shot. I do not weigh. I typical use the same grind setting, quantity allocation and tamp method. (reducing the variables)

I still don't see the difference since my methods are the same for both shots. The only difference could be the wet PF. I have tried both wet and dry and found no noticeable dif.

I had suspected PF or group temp. I flush the group before the each shot.

My grinder did not come with a built-in grind marker so I made one. I grind a variety of beans and the marker allows me to color co-ordinate the grind points for quick reference.

I assumed the grinder was consistent. I'm surprised to hear otherwise though that was my suspicion. Just seems strange.

HB wrote:Let me back up. Do you have a bottomless portafilter? A pour time difference of 10-12 seconds points to massive channeling.

BPF? Yes. Channeling is common. Sometimes just a very fast, sloppy pull that splatters the backslash of the machine.

HB wrote:I think Ian was alluding to inconsistent usage of the grinder, e.g., a mixture of old and new grounds or two different coffees.

"Old and new grounds"? Sometimes. Only on first shot. It will slow down the pull time. "two different coffees? Seldom. I will experiment once in a while

If you are filling the grinder on a per shot basis, try grinding half a dose before the first shot of the day to clear out the detritus. There is a LOT of coffee hanging about that has dried out and will end up in your first shot. Use a chopstick or BBQ skewer to remove the last of the dose from the throat on each shot. Use a bottle brush to clear the throat after the last shot of the day to remove as much as possible.

ANY time you change beans, grind a full dose straight into the bin and start dialing in from there.

The MC4 is VERY consistent. Beans are VERY inconsistent. SO often require a much different grind than a blend. Changing back and forth between several coffees is going to use a LOT of coffee to get consistent results.

Definitely sounds like you've got old coffee trapped in the grinder.

Other possibility... do you per chance put the coffee for both shot into the grinder at the same time, grind and dose and pull one, and then repeat for the second?

Just ran this little test on the MC4 with the heel of the roast we've been using all morning:

With just enough coffee for two shots [using BBQ skewer to clear schnoz each shot]:

1st Shot : ~17g to get the same pour time as ~14.5g
2nd Shot : ~15g time is ~15 vs ~30

for shots ground with ¼+ pound in the hopper