In 1992 and 1993 he won the bronze medal in the junior race of the IAAF World Cross Country Championships. At the Track - Africa Championships 1992, he won bronze in the 5000m and 10,000 m gold. In 1995 he finished fifth at the World Athletics Championships in Gothenburg in the 10,000 m and won gold at the Pan-African Games in Harare. The following year he finished tenth at the World Cross Country Championships and won with the Kenyan team gold. At the Olympic Games in Atlanta, he was fifth in the 10,000 m.
Doubtful achieved fame Machuka by an incident early in his career. At the Track Junior World Championships 1992 in Seoul, he was on the final lap of the 10,000 -meter run in, as he was overtaken by the Ethiopian Haile Gebrselassie on the home straight. Machuka was upset because Gebrselassie had done no leadership during the race, and smote the Ethiopians on the back of the head. However, he could not prevent his defeat by and was subsequently disqualified.
- 3000 m: 7:39,32 min, July 12, 1996, London
- 5000 m: 13:04,04 min, July 8, 1996, Stockholm
- 10,000 m: 27:10,34 min, August 25, 1995 Brussels
- 10 - km road race: 27:52 min, 29 May 1995 Boulder
- 15 - km road race: 42:23 min, November 19, 1995, Nijmegen
- 10 -mile road race: 45:19 min, 22 September 1996 Zaandam