When I worked for a Volvo dealer, we used GM Top engine cleaner. They had a special canister for introducing it into the system. On my 79 Vette, I just slowly poured 2/3 of the can down the throat of the carb while it was running, keeping the rev's at 1500 rpm or so. Then when there is only 1/3 of the can left, instructions say to dump the rest of the can in fast enough to stall the motor. Let it sit 15 min, then start and run motor until it stops smoking.