Steve Cooper shows you how.
One of the quickest ways to restore two-stroke performance is to de-coke the exhaust system.
Ican still recall the endless hours spent chasing my tail sometime in early 1977. My previously devastatingly effective Yamaha RD350 had turned into a total and utter slug; nothing seemed to be able to restore its performance. Carbs, timing, points and the like had been checked and double checked but all to no avail. Asthmatically crawling to work one morning, the ‘Lightbulb of Logic’ finally illuminated – baffles – it had to be the baffles. Ripped out of the bike while still smoking they were hastily dropped into a live steam tank the engineers used for degreasing. Augmented by some caustic soda the malevolent black tubes sat stewing all day until refitted at 4pm. Nothing, absolutely nothing I have ever done to any bike before or since has had such a dramatic effect upon a machine’s performance. That one, unintentional, wheelie out of the car park proved to me beyond doubt that two-stroke exhausts should never be taken for granted. On any stroker I fettle these days my primary focus, once I’ve had the bike running, is the exhaust system. Yes I’ll sort out the timing and service the carbs but none of this is worth a tuppenny damn unless the exhaust system is free-flowing. Everyone has their own pet methods but what follows is a methodology that has worked well for me over the years and as I no longer have access to live steam tanks, this is now my ‘default-decoke’ MO! Among my project bikes is a ratty Yamaha AS1 that will need some TLC to its exhausts. My local chromer will strip and replate them for me but between the two processes I need to get some damage sorted out. I’ve a good mate who can cut and weld as necessary but, quite reasonably, he doesn’t want his workshop filled with lots of oily smuts and grey smoke. So, on that basis I need to evict as much crud from the pipes as humanly possible. So it’s workshop clobber on, dig out the industrial gloves and goggles and on with a de-coking session.
If you have a drain-cleaning mole that fits your pressure washer this can be used to give the insides one final rinse cum blast just to be sure. And that’s it, your two-stroke exhaust should be as clean as you can possibly get it within a DIY environment. Trail bike exhausts may not necessarily take too kindly to being exposed to paint thinners but it’s a call only you can make: some nice satin black paint or a free-flowing exhaust? Life is always about compromises so why not clean the crud from the inside, then give a nice fresh coat of paint? Chrome systems will just need a good rinse in hot water followed by a clean with some solvent and then a bit of TLC with some polish. Don’t forget to fit the baffles please. Leaving them out doesn’t make the bike any faster whatsoever and you are no longer 17! With the silencers fitted back on the bike you can now fire it up and marvel at just how much better it sounds. Enjoy the sounds and all that extra power you’ve suddenly liberated.
87/ With the rubber bung removed this is literally just a snapshot of what’s been lifted out of the exhaust’s gizzards over 48 hours and there’s more to come! 8/ Once rinsed through the same exhaust has deposited this little lot in my rinse bucket. A solvent and caustic de-coke; the gift that keeps on giving!