I have been guilty of enlarging jets on many engines. I usually go up one or two drill sizes and try it if I am working with the stock jets. Yes, it usually yields more power depending on the situation. You can do it, then after driving a while, pull some spark plugs and see if they are blacker than they should be. If you see this, or blacker than normal smoke out the exhaust, then maybe you went too far. If quite white, you can go another drill size. If I go too large, I then carefully lead the jet shut and re-drill it to the smaller size I want to try. There are those who yell out that you cannot do this leading in and drilling out but they are welcome to come down and see how it has worked on my power units in tractors and vehicles. The new alcohol content fuels are a key cause here. To get an older engine to perform like it did jetted for the pre-alcohol blend fuel, more fuel needs to be put into the air/fuel mixture. Many times bringing the timing ahead of factory spec, but not to the point it rattles, helps power greatly also on the alcohol blend fuel. I cannot see it affecting shifting or anything else.
I have an M880 I modified the carb with jet drilling out to run E85 with good success. E85, and to a big extent the 10% blends eat up the rubber in lines, fuel pumps and carbs made for the original fuel so I despise alcohol blends in older vehicles. Leave one set too long with it in them and see how the inside of the carb is literally destroyed with corrosion. I run the 91 octane alcohol-free fuel in all older motors. Yes, it is more expensive but I think that balances out over the cost and frustration over the many destroyed components I have had to constantly repair/replace due to the alcohol. On the farm many vehicles like combines and tractors will sit idle for months so this kind of damage is unacceptable. The bean oil content diesel is no better.
