Put the boots on the engine first. This way theboots are pointing perpendicular from the engine where the carbs fit in. Boot to carb first creates an angle situation which is difficult.
Sometimes I use WD40 which helps slide the carbs in.
The best time to re-attach the carbs is in warm weather because the rubber is softer. Out in the hot sun, the black rubber is more pliable, easy to push into. Obviously, now, in the winter, it is cold and the rubber is really hard. Recently, I re-attached the carbs and picked a day where the temp was 40+F and used a hair dryer to warm the boots.
Usually, I used a rubber hammer to carfully pound the carbs into the boots. Go from side to side and work the carbs in; #1 then #4, and #1 and so on.
Even if the boost are new, they are hard in 70F weater and even harder when colder. I bought new ones and decided that the old ones are no worse to use with sufficient heat.
