Engine braking strength is based on….
- Maximum engine vacuum
- Primary spring start force
- Secondary spring start force
- Primary clutch ramp angle (first 1/5th of the ramp)
- Drive belt width (wider = stronger, narrower = less strength) More belt gap, less strength,
Adjusting those details above change the de-clutching speed.
The engine should idle at 1100 to 1200 rpms.
Logic statement;
IF the engine is idling higher than 1200 (ie 1400),
THEN engine braking strength will be lower than 1200.
Maximum engine vacuum is at the lowest idle speed. (etec can only be adjusted by BUDS laptop)
Open the throttle plates more, vacuum drops, engine braking strength lowers.
If there is an air leak (reed boot or crank seal) causing engine speed to idle high like over 2000 rpms, there will be nearly no engine braking whatsoever.
Secondary spring – can increase the start force for stronger engine braking. Can lower start force to reduce strength.
Belt tension – Maximum engine braking is when you can make the belt deflection be not quite as tight as this but dang close.
https://www.youtube.com/watch?v=VNVv-jOzaIE
Right now with a stock 800etec and 850etec, about the only details you can do to lower engine braking strength is...
1] dial in a little bit more belt deflection (make the belt sit slightly lower in the secondary) by turning the belt adjuster about 1/12 of a turn - like turning it from 1200 to 100 (drop the belt a little)
2] lower the start force of the secondary spring (but i would not on a summit, 160 start is low enough
3] Get someone with BUDS to increase the engine idle up 200~300 rpms. [easily done on a carb jobby]
4] Go from the 417300531 or 571 @ 38.3mm to the narrower 572 belt @ 37.7mm
On my clutch kits...
- Dial in a little bit more belt deflection; make the drive belt ever so slightly more loose tension between the pulleys.
- I also have secondary clutch spring start force options from 225/XXX to 195/XXX
- I can also provide a shim to raise engagement speed by 200 rpms.
My latest testing of the new 966 ramp with 31~3200 engagement when i was out in Revelstoke first week of Dec, tree riding; I could come down a fairly steep hill on someone else's track and the engine braking held till about 12kmh (8mph) before de-clutching....hahaha.