Maybe i am putting this in the wrong topic (mod's?) But i am planning to do my summer trip on my jawa 350 twin. Aside from not closing the throttle at instant when reaching a top, of giving every 30 sec's (?) some throttle when descending, are there more things to do to keep the engine healthy?
I always mixed my fuel a bit rich, and carried some spare spark plugs. With just a touch of smoke out the tail pipe, I never fouled a plug.
Ummmm - if you mean you upped the oil in the premix, that's making it leaner (less fuel for the volume of air). Whatever, obviously worked for the thinner air up high in the mountains.
I always though more 2-stroke oil provided better lube for the motor. I never thought about it in terms of fuel/air, only fuel+oil/air. Maybe best if the OP doesn't follow my advice, since it is worth what he paid for it...
Keep the mixture as it is. The premix will not getting leaner when you rise the oil amount. No changes has to be done, the engine gets fatter as higher you will go, so best is not to change anything. (You can do a fine adjustment at the valley level where you are riding if you are at home at sea level). You should not have any power loss between starting point up to +3000 feet, between +3000 and +6000 there is some power loss and the exhaust fumes will turn blue if they haven't done before. From +6000 to +9000 the power loss is remarkable also acceleration is getting slower too. For going down long sequences, keep the engine idleling without any gear engaged and use the brakes, best way to do. Do a very good brake maintaince, look up the cable if they work proper, clean the inside of the drum brakes, grease the brake shaft with heat resistant grease. new pads or grinding the old ones so any debris that might have already left a layer is removed. Having very good brakes in the mountains is in my own experience very important.
From my experience with two different, piston ported two strokes at higher altitudes is that they suffer from quite a bit of altitude power loss compared to similar four strokes. My experience was that above 5000 feet you really start noticing a lot of power loss. Since this bike is a 350 Jawa, I'm betting it starts riding like a heavy 175 above 5000~6000 feet. I'd pay particular attention to getting the jetting right if you plan on riding above 4000 feet for extended miles, because two strokes are much more sensitive to altitude and mixture. If this is the 'modern' oil injected California Jawa I'd expect it's oil lube needs are met if it's oil injection system still working well.
rode my dt400 on some pretty narly trails in the mountain trails of Utah, just keep attention to you're bike and bring some extra plugs and make sure you have your tool kit, you will do fine
