tonk Posted January 25, 2012 Report Share Posted January 25, 2012 Removed the headers from my bike t'other day and had a good look inside the exhaust port. It feels rough and is blackened on the short radius and around the valve seat Both are identical (it's a twin). I've only had experience with 2-strokes before in this area and they were always smooth and shiny. So is this normal for a 4-stroke? It's dry and isn't crumbly, nor does it leave too much on a clean finger. PS there's another valve out of sight above this one, couldn't bend down far enough to see it, but I've given it a good fingering. (Pic taken on phone so not the best quality) Link to comment Share on other sites More sharing options...
tonk Posted January 25, 2012 Author Report Share Posted January 25, 2012 It runs great Zak, pops and bangs a lot on a closed throttle and sometimes between gear changes (but only on the quickshifter). I was just amazed amazed at how rough it is. Are they cast like that or is it a carbon build-up? I take it there's nothing to be gained from it being smoother? As you can tell I know fuck-all about gas flow. Link to comment Share on other sites More sharing options...
speedy sie Posted January 25, 2012 Report Share Posted January 25, 2012 exhaustible post need to be polished like glass... ...even on the old deisles Link to comment Share on other sites More sharing options...
Superdunc Posted January 25, 2012 Report Share Posted January 25, 2012 Looks normal to me Tonk. On a race bike some people like a shiney finish others prefer a smooth matt finish. Being a production bike yours probably a bit of finishing, but mostly would of been as cast. A lot of tunners will tell you that carbon build up is agood thing as it makes a good insulator and keeps the heat in the exhaust and away from the rest of the cylinder head. Link to comment Share on other sites More sharing options...
tonk Posted January 25, 2012 Author Report Share Posted January 25, 2012 Thanks SD, it all feels nice inside, no lumps or ridges and the pipe is clean and dry. Would it be safe to assume the engine is vulnerable while the pipes are off and at least one valve is open? I've bagged the intake tubes, would clean rags be ok stuffed into the exhaust? Link to comment Share on other sites More sharing options...
Superdunc Posted January 25, 2012 Report Share Posted January 25, 2012 Thanks SD, it all feels nice inside, no lumps or ridges and the pipe is clean and dry. Would it be safe to assume the engine is vulnerable while the pipes are off and at least one valve is open? I've bagged the intake tubes, would clean rags be ok stuffed into the exhaust? That's a good idea, don't want mice stealing your exhaust valves! Link to comment Share on other sites More sharing options...
tonk Posted January 25, 2012 Author Report Share Posted January 25, 2012 Popping on the over-run is unspent fuel burning in the exhaust, either from leaky exhauist joints, or more likely, the air-injection system bleeding air into the exhaust. The air-injection has two functions- 1) it burns unused fuel that would otherwise escape out the tailpipe, which would increase the hydrocarbon emission of the engine, 2) unburnt fuel knackers the catalytic converters in standard exhaust pipes, so this prolongs the life of the cat. Didn't know it had air injectors, I'll load up the CD manual for a butchers. Definitely not leaking from any exhaust joints. There's a servo-controlled flap between the cat and the silencer and two sensors screwed into the headers - one on each side, just before the balancer pipe, before the cat. @Zak - mice?! They've all been eaten by the SAS commando spiders, big tattooed fuckers who nick my spanners. Link to comment Share on other sites More sharing options...
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