Mercedes was pleased to report "no bouncing" during the first of three days of testing at Bahrain as it has sought to eliminate the porpoising phenomenon that dogged it last year.
But the second day of running was blighted by persistent mid-corner balance issues for both Hamilton and team-mate George Russell before the latter parked up in the afternoon with a hydraulics failure.
While the team was satisfied that overnight tweaks had settled the handling problem, Hamilton said that "underlying" issues from the draggy W13 had carried over to the new car.
Speaking on Saturday, the seven-time champion reported: "It's difficult to sum [progress on new car] up.
"We've had a couple of difficult days and yesterday particularly was difficult. The first day didn't feel too bad. Yesterday was a little bit more of a struggle.
"George has had a much better morning today [running to second in the times behind Ferrari's Charles Leclerc], so things are going up, so hopefully we've got the set-up in the middle of the place."
Asked to compare the W14 to its problematic predecessor, Hamilton continued: "Right now, for example, the bouncing that we had has pretty much gone. That's a huge step for us.
"It's nice to drive it without the bouncing in the corners. But there are still some underlying things that we are working through."
The Briton played down expectations for the season opener in Bahrain in a week's time but reiterated his willingness to dive through the data with the team to troubleshoot the car.
He said: "It's going to be tough for everyone with this short period of testing.
"We're trying to make sure we hit the ground running in understanding the car, the tyres and the ability to respond. There are things we're working through.
"Some of the balance limitations that we had last year are present. I'm really proud of everyone in the team for continuing to remain positive after a tough year last year.
"Amazing work through the winter to arrive and have the mileage that we've had. Every single year they arrive with the same mental focus and determination to fix whatever issue we have.
"I enjoy being in the offices just chugging away going through the data. We will hopefully get there."
