knocking under acceleration

[russomf]

not sure what it is but the engine sounds OK when idling or when coasting down the road but once i get on the throttle it starts to knock a little.  also gets worse as the biek warms up, not so soticable when it is cold.  i have not had a rod bearing or main bearing go in an engine so i am not sure if that is the problem or not.  

any info would be great as i just got this dam thing back together and now this i am not a happy camper.

[Jace009gs]

If you threw a bearing it's going to knock and carry on at all the rpm's in the range. From idle to redline. It would be more so of a violent vibration in the bars. Have you changed the oil? See if little metal bits come out when you tap into the drain plug...Hopefully not.

Did you pull the plugs? What color are they? [make sure you run the bike for a bit get it real warm. Come back to the garage wait for the engine to cool off then pull the plugs and note the color.] I would go ahead and put new plugs in anyways since their cheap.

I think you just need a valve job IMHO. Sounds like one of the exhaust lobes is a little out of spec. There is a FAQ about how to do a valve check.

[russomf]

define valve job?  if you mean check their clearances they are at .005" or .002" over spec.  

I will check the oil and change spark plugs just did not  think that would be the issue.  

if there is anything else that comes to mind let me know
mike

[gsJack]

Hard to tell about a noise without hearing it, but if it is heard on acceleration and is worse as the engine warms up it could be gasoline knock/pinging.  Can be bad on a GS as carbon builds up with many miles on bike.

What grade of gasoline are you using?  If regular 87 octane, try a tank of premium 91/92 octane and see if it's better.  If you are using heavier than 10-40 or 15-40 oil, that could make it much worse.  Change to the lighter oil if it's the 15-50 or 20-50 and see if that helps.

It's much worse on 2000 and earlier GS500s than on the 2001 and later GSs that have the 3 circuit carbs rather than the old 2 circuit.  If it's one of the older type and it pings badly when you open the throttle a small amount try opening it more.  That usually stopped the pinging on my 97.

Running 15-50 Mobil 1 synthetic in my 97 GS I went from reg grade gas to mid range and then to premium grade gasoline over a couple years as milage added up at 15-20k miles/year to reduce gasoline knock.  After changing from the 15-50 oil to 15-40 Delvac 1300 oil I could run it on regular gas again.  Heavier oil makes the air cooled engine run hotter.  Good oil flow is necessary for cooling the head.

[russomf]

jack would the timing advancer do that as well?  i am running 10-40 oil just put a tank of 93 in and running a advancer.  i am playing with the carbs as well i am currently 140 main with 2 washers.  3 turns out with pilots.  definately runing rich i can head it popping in the exhaust can.  will cut back fuel and see if that helps at all.  just really hope it is not the rods.

[gsJack]

If it were possibly a mechanical knock, it would be more likely a main bearing rather than a rod bearing.  Main bearings knock under heavy load while rod bearings generally knock when backing off the load.  I doubt if it is either in this case.

Advancing the ignition timing in a gasoline engine definetly makes gasoline knock worse, one of the things generally done in past years was to retard the timing to reduce the knock.  A little light pinging under acceleration is harmless but heavy gasoline knock can do serious engine damage.  Can you put the standard ignition setting back on to try to see the effect?  Both of my GSs are stock engine wise and will probably remain so although I've considered rejetting the 97 to make it more suitable for winter use.  Someone like Srinath could give you better advice on your carb mods but it sounds to me like you bike is much too rich if it's popping back in the exhaust.  Ignition missfiring will also cause backfiring, are your plugs good?

[The Buddha]

jack would the timing advancer do that as well?  i am running 10-40 oil just put a tank of 93 in and running a advancer.  i am playing with the carbs as well i am currently 140 main with 2 washers.  3 turns out with pilots.  definately runing rich i can head it popping in the exhaust can.  will cut back fuel and see if that helps at all.  just really hope it is not the rods.

Advancer makes it knock easier yea. But 140's are too rich with stock air box, and too lean with K&N pods. 3 turns out with pilots - you mean air screws ... Popping in the exhaust does not mean rich, it could very well be lean, or even normal. Misfire could also be lean. Not just rich. Rich misfires are sorta wet sneeze like, lean misfires are much more louder and sharper pitched.
If you got stock air box and UNI or stock paper - you need 125 mians and 1 washer along with 40 pilots.
With K&N pods you need 150 mains in place of the 125.
Cool.
Srinath.

[Jake D]

I'm saying main bearing, but I'm a glass is pretty much empty kind of guy.

[russomf]

srinth
i have uni pod filters, full system 2 into 1 yosh exhaust, advancer, 3 turns out with air screws, jet needles are probably equal to 3 washers, and 140 main jets.  also milled heads .020", web cams, and the engine does not have more than 300 miles on it since the rebuild.

did not make this noise at first (122.5 main jets) but since i richened the air/fuel it started to make this noise.  i will do new plugs soon and any suggestions for air screw and main jets?

[The Buddha]

OK a stock motor will need 150's ... milled and modded cams =        ... but 140 still sounds wrong ... 122.5 was better ... I doubt it ... but no real Idea, if you make the heads flow better you'd need to jet up I think ... but hey no real definite idea.
Cool.
Srinath.

[russomf]

i know.  i bought the bike from a friend who did not have the time to put it together.  he was setting it up for a track bike so i have a lot of different things on it to help improve performance.  i will start with plugs and 150's and go from there.

[davipu]

dump a whole bottle of octane boost in there and it should fix the problem for now.  with the intake and exaust you are running about lindsay lohan lean, on 140 mains, you need atleast the 150's.  and if you want to run 87 gas with the advancer get a stock head, and if you want to run the milled head, retard the timing from stock.  if you want to run both, atleast 92 octane.  btw i got a set of pistons so when you blow a hole in one of yours let me know and I'll sell them for a good price.

[russomf]

davipu
appreciate the info even with the sarcasm.  i will jet to 150's and run 93 octane.  i removed the advancer but now it stumbles pretty bad off the line, what pilots should i be running?  how do i set them up once i get them in.

again info is much appreciated.

[The Buddha]

With stock motor 40's ... the one guy I knew from way back when, that ran a pumped motor (dont remember the details really ...) with stock carbs I believe used 45 pilots and 155 mains ... 40/150/1/3 is a starting point for a modded motor ... yea and run it too lean and you'll have to take up davipu's offer ... I'd actually start with ~160/45's and get leaner ... going lean to rich is the risky way to jet. Besides, 1 jet size too rich and you'll know right away. 1 size lean and you may never find out. I'd jet leaner from 160/45, and see what change gave you the best bump in performance and go back 1 step. say it ran much better with 155's than 157.5's ... you'd go back to 157.5. You also need to jet it in the dead of winter, not in summer. But that back 1 step will work just fine.
Cool.
Srinath.

[davipu]

if you want to get it right the first thing to do is find a shop that has a dyno with a exaust sniffer. and they will tell you aprox what to go to then do the trial and error.  Srinath's suggestions 99% of the time are right on the money, if you didn't want to spend the money on the dyno run I'd follow his suggestions.

[russomf]

160/45/1/3 OK i know the 165/45 but what is the 1 and 3?  is 3 the number os turns?  what is 1 then.
thanks

[davipu]

one shim on the needle.

[russomf]

ok so i went 155/45 3 turns and no change to the washers.  now it hardly idles.  i sounds like it is firing on 1 cylinder and gets a huge puff of black smoke every time it fires.  i can hardly get it to 5k then it starts to sound normal and take off.  do i need to go back to a 40 pilot?  i even tried turning in the air screw to 2 turns and it got better but not perfect.  this is really starting to wear on my nerves i work on the f-ing thing more than i get to ride it anymore and that is starting to upset me.  little help please i just want to go riding and not have to work on this thing.

i have a fuel injected bike and never had these kind of problems.

[The Buddha]

OK back down to 40 or 42.5 pilots, and over 5K it runs fine ?? then try 160 mains ... you need to jet it down from "crappy rich" ... not up from "fine but lean" Yea you mod the motor ... you're in un charted waters buddy, I worked on my jetting for almost a year ... you start on this 2-3 days ago and expect it to all be peachy ... yea ... FI is good, but over bore it, over size the valves, flow it and mill it and see how much harder it is ...
Cool.
Srinath.

[russomf]

i bought the engine form a friend i thought he had all this sorted out before he gave it to me,  that is why am upset i did not choose to have the engine work done.  just frustrated is all i seem to be in the bike more than i am not.  why go to 160 mains if i am getting black smoke?  should i just go to 40 pilots and see from there?  think i am changing too much each time to get a base line.  also what does the air screw do and how is it supposed to work on our carbs?