iconic558 Posted December 12, 2014 Report Share Posted December 12, 2014 My SWM has a working decompresser, so far I've been using it as an aid when kicking starting her by engaging whilst kicking thereby making life much easier, also I kick her thru whilst operating the decompressor to prime her when cold, and lastly to stop her. Now I'm fairly sure the decompressor is also there to help on hill decents but I'm not sure why, when and how to use, be grateful for advice. cheers as always for any help Quote Link to comment Share on other sites More sharing options...
vonhazza Posted December 13, 2014 Report Share Posted December 13, 2014 (edited) I rode a couple of Ossa's back in the 80's with de compressors that seemed to there as a substitute for brakes and they worked quite well giving a strong 4t effect ie engine braking when going downhill, the best thing would be to find a gentle downhill slope and test it out for yourself, just let her roll down slowly and apply the de compressor to slow you up, it may take a few goes to get the feel of it and use your normal brakes if its not working for you, Edited December 13, 2014 by vonhazza Quote Link to comment Share on other sites More sharing options...
feetupfun Posted December 13, 2014 Report Share Posted December 13, 2014 Why it works is because the air going in and out of the little hole in the decompressor causes the motor to do work on the air. Quote Link to comment Share on other sites More sharing options...
laird387 Posted December 13, 2014 Report Share Posted December 13, 2014 Hi, Way back in the day - as we say - the decompressor on a twostroke gave a much more controllable gentle deceleration on slippery descents, quite often you were able to stop the rear wheel from locking under engine braking just by a touch on the decomp. lever as you felt the tyre lose grip. Don't forget also that, in the day, the brake linings gave far less control than modern brakes - a tendency to grab was not unusual - and using the decomp to control speed down a slope had a much finer degree of control 'cos you could always use a slightly higher gear and the decompressor as long as you kept your weight as far back (over the point of contact of the tyre) as possible. Quite a few people would have their cylinder head drilled and tapped to take an after-market decompressor (same thread as a spark plug) fitted, some of the works bikes had a refined decomressor fitted that 'blew' into the exhaust port, so you couldn't hear it.............. 1 Quote Link to comment Share on other sites More sharing options...
jon v8 Posted December 13, 2014 Report Share Posted December 13, 2014 The other advantage of the decompressor going into the exhaust is that it cant suck dirt into the engine like the ones that go to air can do. 1 Quote Link to comment Share on other sites More sharing options...
woody Posted December 13, 2014 Report Share Posted December 13, 2014 (edited) Hi, Way back in the day - as we say - the decompressor on a twostroke gave a much more controllable gentle deceleration on slippery descents, quite often you were able to stop the rear wheel from locking under engine braking just by a touch on the decomp. lever as you felt the tyre lose grip. I've always found the opposite.... They act as a great rear / engine brake as long as the rear tyre has traction. If it is used on a slippery surface, the engine braking affect just stalls the engine as the rear wheel is unable to bite into the surface and overcome the engine braking to keep it rotating, the wheel skids and the engine just stops. There is less engine braking affect without the decrompressor. Pull the decrompressor in on ice and see what happens. I became pretty good at using them as I used to use those fitted to my Bultacos and Ossas a lot back in the 70s, but only if the surface gave the rear tyre something to bite into, otherwise it was front brake only and a whiff of rear with engine braking on slippy descents. Most fun use on the Ossa was on the road and pulling it in on high revs whilst passing bus stops or crowded pavements as the noise scared the cr@p out of people Edited December 13, 2014 by woody 4 Quote Link to comment Share on other sites More sharing options...
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