knocky sound at idle

[mad marc]

does anyone  have any ideas as to my engine  idle problem.......when i start the bike up the engine sounds fine  ticking over at about 1200-1500 revs, but  it will suddenly  drop revs  and a  knocky sound can be heard from the engine,  the engine will  immediatly  return back to idle  and sound fine again,  when i rev the engine  no sign of the knocky sound can be heard.

  i cant seem to determine if its head or base of the engine the sound is coming from,  the engine  sounds fine apart from the slight knocky sound  , this happens  now and again  and its not constanly there,  the engine pulls well  sounds fine and goes well,  also there seems to be slight back pressure into the carbs,  as ive noticed a sort of backfire  although  its not from the exhaust its from the head into the carbs,  ive changed the plugs for new  standard ones  and   :dunno_white:regapped them,  and ive cleaned the air filter....   ?

i  was told  its the  cam shafts  moving  side to side  causing the knocky sound... and that  its  normal.... but i dont think  the  knocky  sound  is normal  is it  ?

the  plugs  seem to  indicate the engine is running  fine   ive checked the  pilot screws  and  im  about to  ballance  the  carbs.  but i dont  really  want to have to take the  engine  apart   . does  anyone  have any  ideas  as to what it my be.......i  hope  its not the  main shaft  shells  or  crank shaft.......   the  bikes a   gs 500 e    0n a   2003  plate   done  12,000  miles

[annguyen1981]

The GS does have a knocking noise, which according to Suzuki is not a problem, but they do have a fix.
Suzuki released a bulletin on 3/21/06 regarding this matter.  I have yet to find out from the dealer if this is a free fix.

And Welcome!!

[gsJack]

Welcome gw0wvl, you describe it slightly differently here than on the other forum but it still sounds like the harmless camshaft knock to me.  I've only experienced it at slow idle with a hot engine; never heard the camshaft knock with a cold engine when the oil is thicker.

Sooner or later you need to check your valve clearances so you might want to check your camshaft endplay when you have the valve cover off, I did when I first had the knock on the 97 GS and found considerably more endplay on one camshaft than the other.  Never bothered to check it on the 02 GS but have heard the same knock on occasion.

If you click on search above and search for camshaft knock or engine knock you will find much discussion of this problem has taken place here.  Others will probably jump in to express opinions and ask questions regarding your knock problem.

[MarkusN]

Welcome!

Since you experience a drop in RPMs as well I rather think it's something to do with combustion. Might be an upstream backfire. Which might be related to valve clearance issues. But then, it might just be choppy ignition at idle, causing the chain to knock.