Air Box Boots

by Alan Buehner

In the last “Tech Tips” (Still Keeping Track – Spring 2012, issue #54) I showed the different styles of intake manifolds used on the KTM cylinder, from 1972 thru 1980. In this issue, I am showing the different style of air boots used on the KTM's from 1972 thru 1980. My intention is to make you aware of the different styles and lengths of boots that are available.

With the introduction of the Chrome Moly Framed bikes in 1972, one style of air boot was created – part no. 51-06-026-200 (see photo “A”) to connect the carb to the fiberglass air box. This was a one-size-fits-all boot used on the 125cc to 400cc bikes up until 1976. Since the mouths of the Bing Carb have different diameters, a rubber adapter was needed for the Bing 27mm carburetors use on 125s – part no. 51-06-029-000 (see photo “B”) and Bing 30-32mm carburetors used on 175s – part no. 52-06-029-000 (see photo “C”), so that the small end of the air boot would fit snug.

In 1976 the new MC5 frame was introduced with an alloy air box that required a new style of air boot – part no. 55-06-026-000 (see photo “E”). The 125's used a 28 or 30mm Bing 84 Carburetor that required the used of a plastic adapter - part no. 51-06-029-600 (see photo “D”)– to fit this new air boot.

In 1977 the new GS6 frame was introduced that used the same alloy air box used on the MC5 frame. The same “straight” air boot was used on the 250s and 400s but 2 new air boots were used for the 125s and 175s. The air boot for the 125 – part no. 51-06-026-000 (see photo “F”) is offset and measures 70mm long. The 175s came with Lectron carburetors and used a large bellows style air boot – part no. 52-06-026-500 (photo not available).

In 1978 both the MC5 and GS6 were equipped with plastic air boxes. This was also the year that KTMs came with a new generation of intake manifolds that were “cocked” and came in different lengths (see Tech Tips in Still Keeping Track issue no. 54). To compensate for these different lengths of intake manifolds, different lengths of air boots were also introduced. The KTM 125 used a 91mm long air boot -part no. 510-06-026-500 (see photo “J” ). The 250 and 400 MC-5s used a 51mm long “cocked” air boot – part #55-06-026-500 (see photo “ I”) to match the “cocked” intake manifolds.

The GS cylinders still used the straight style intake manifolds and depending upon the length of the manifold used, came with a 70mm long boot - part #51-06-026-000 (photo F); a 61mm long boot – part #52-06-026-100 (photo H); or a 35mm long boot – part #54-06-026-500 (photo G).

In 1979 a new frame was introduced – the MC80 and GS80 which replaced the MC5 and GS6 frames. The MC80 and GS80 were the same basic design with the GS80 having a removable rear frame loop. This new frame also came with a new style plastic air box.

The 125GS used a 62mm long air boot – part #52-06-026-600.

The 125MC uses a 91mm long air boot – part no. 510-06-026-500 (see photo “J”).

The 175GS used a 70mm long air boot – part no. 51-06-026-000 (see photo “F”).

The 250 and 400GS & MC used a 35mm long air boot – part no. 54-06-026-500 (see photo “G”).
see photo “K “), mounted on the bottom of the air box.

In 1980 the 175 and 250 used the same air box used on the 1979 frames. They both used the same 62mm long air boot – part #52-06-026-600. However, since the 175 used a smaller carburetor, it used an adapter – part no. 52-06-029-000 (see photo C “ ).

The 125 and 420 used the same air box used on the 1979 420MC80 frames. They both used the same air boot – part #560-06-026-000. However, since the 125 used a smaller carburetor, it used an adapter – part no. 52-06-029-000 (see photo “C “).

In 1981 the 250. 350, and 390 use the 1979 air box but used a “cocked ”51mm long air boot – part no. 55-06-026-500 (see photo “I”).. The 125, 420 & 495 used the same air box and air boot used on the 1979 420MC80 frames.