Cheeseburger! Cheeseburger! Cheeseburger!
When that doesn’t work, bolt lead weights to the seat of the kart. You can buy them from kart shops. They’re available from 2 to 8 pounds. If you know of a local plumbing supply near you, they should have 5 pound lead bricks. You’ll have to drill them for a 5/8’s bolt and either double nut them or drill the bolt for a cotter key. On the 8 lb weights, you’ll probably be required to use two bolts. Most track I know of require the weights to be painted white.
You can move the weights up or down the seat for to help in chassis tuning.

I have used weights from a dive shop, they are covered in a yellow plastic and come in many sizes.

Make sure you check with the organization that you’ll be racing with on the size of the weights that can be used and how they must be attached.
Another option to bolting the weights to the seat is weld on tabs such as this, https://cometkartsales.com/Weld-On-Lead-Weight-Tab-Steel.html. There uses to be a perch that was bolted to the chassis frame that you could stack weight on. But couldn’t one this morning.

Also it is better to add some small weights on the kart rather than large heavy ones so you don’t stress the seat. Try to spread them out of you can.

We have weight in the front of the kart, on the seat, and then on the frame so the kart is balanced all around rather than having 40lbs attached do just the seat and putting all the stress on the seat

I’m about the same weight as you. Is it possible to use a weight in between the seat and the frame? Like a spacer?

No need to use weight as a spacer between the seat/chassis.

I’ve had to add 50lbs+ my whole life.

Hang six 5 pound weights on the back of the seat and one 5 pound weight on each side of the seat. Make sure you do this on the scale though to make sure your weight distribution is correct. That’s the most important thing when adding weight to the kart.

Shoot for around 42% front weight.

I run Master so 50# is normal for me.  I put 5# each under the front wings of the seat and a 10# curved diver’s weight in the middle of front of seat.  I put a 5# on each side and the rest I place on the back of the seat.  When I’m feeling anal, I put a 3/4″ washer between the seat and the weight, which keeps the contact to the seat down to a minimum.  My thinking is that clamping the entire surface of the weight to the seat will stiffen it, especially with so many weights.

I’ve also removed two 5# from the rear of the seat and placed them on the left and right rear corners of the belly pan.  (You do need to watch the F/R balance)  This might be worth it because it lowers the polar moment of inertia and improves the responsive of the kart during turn in.

Someone above mentioned 5/8″ bolts.  Don’t use 5/8″.  I think they meant 5/16″ or 8mm.  More smaller weights seems to allow the seat to flex more.

I’ve used 2-1/2 Lb. weight lifting weights painted white with a bushing to make the hole 3/8″ and my take is that they take up allot of space and look like crap. If you make bushing for these kind of weights make sure you put a heavy washer that covers the original hole or the bushing could pop out from vibration. Don’t put more than 5 Lbs. on a 5/16ths bolt. If you mount more than 5 Lbs. on one bolt go up to a 3/8″ bolt.

MM