Selection Of The Transmission Ratio (Fr 125 Max) - Bombardier-Rotax FR 125 MAX FR 125 Junior MAX Installation And Operator's Manual

Operating Instructions FR 125 MAX, FR 125 Junior MAX and FR 125 Mini MAX

4.2. Selection of the transmission ratio (FR 125 MAX)

Because of the special tuning used, the engine performance is very good in the speed range from
6000 to 12000 r.p.m.
Peak performance will be achieved at 11500 r.p.m. but over-revving of up to 14000 r.p.m. is
permitted.
Note: The maximum engine speed in kart operation will be controlled by the ignition unit.
At engine speed above 13800 r.p.m. the ignition timing will be controlled such that
the engine performance will drop significantly (see diagram 1).
performance drop will result in the intersection of performance graph 1 and drive
resistance graph (see diagram 1, in this particular case at approx. 14100 r.p.m.)
Attention: Never run the engine without load. By revving the engine without load, speeds of
above 14000 r.p.m. can be reached and this excessive engine speed will drastically
shorten the life span of some components (conrod, conrod bearings etc).
If the speed range of 6000 r.p.m. to 12000 r.p.m. should prove inadequate due to a particular track
routing, target 13500 r.p.m. as the maximum speed.
In this situation you can profit from an additional performance rise fom 12000 to 13500 (see
diagram 1, performance graph 1). This increase of performance will be achieved by the advance of
iginition timing to 30° B.T.D.C at 12400 r.p.m.
Note: A basic requirement for use of the speed range from 12000 to 13500 r.p.m. is that
the carburetor has optimal jetting (refer to Section 4.1 Carburetor calibration
diagram 1).
Note: Diagram 2 shows clearly that it is not always the best to use the speed range
between 12000 r.p.m. to 13500 r.p.m.
Seite/page 86/108
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Ausgabe/edition 09.2003