Check around and see where your local Jiffy repair shop is. A lot of small engine shops can do it. If you wish to do it yourself, you'll find a number or letter/number identifier on the side of carb mount. (Mine has an "F") Take that to the shop along with the engine serial/model number, they will give you the diaphram. Ask specifically which way the diaphram goes. One side has a larger diameter disk than the other, it's important. I have a 1991 Jiffy 3HP, I've changed the diaphram 3 times, in 20 years, they get brittle. Secondly, I just use regular gas with Amsoil synthetic, I mix at 50:1. I only mix a litre at a time, I have never ever used more than 2 litres in a whole winter. No point in letting gas get stale, I find it's easier to make small fresh batches. Good luck.