Topic: Knocking at low idle

[narcoticrex]

I think this may have something to do with carb syncing, but I just wanted some opinions.  When I bought this bike a couple weeks ago, it ran great at low rpms.  it would idle at 1100 with no problems or strange noises.  It has slowly gone bad though, to the point where when it is warm, it wouldnt idle at less than 1800 (by this i mean the main idle screw was all the way out, and the rpms wouldnt drop below 1800).  And when it was warming up, if i dropped rpms below that, it makes a "knocking" noise - I say knocking because I dont know what else to call it. The noise went away as the rpms raise.

I cleaned the carbs today, the slow jets were clogged on 3 of 4 carbs, so now I can get my rpms down low again, but at 1200, there is that noise coming from the engine. Sorry, Im not as experienced as you guys, so I cant really determine where exactly the noise is coming from - it sounds like the middle of the engine i guess. Sorry, I know that sounds stupid, maybe tomorrow I will post a youtube video.

Havent adjusted tappets yet, but I have adjusted the timing, and I thought I did it right. I am going to check that again tomorrow too. 

I really think it might be a carb sync issue, but could it be something else?  Sorry, I know Im not giving out a lot of info, but ill answer any questions you have to the best of my ability, thanks for any ideas.

[scunny]

a carb sync is  good,when the cylinders are out of balance it tends to rattle everything else.
but....... before you sync your carbs everything else must be adjusted: timing, valves etc

[kayaker43]

I agree with valve adjustment first, then carb syncing to smooth out the idle. but I would give the carbs a thorough cleaning first. It sounds like you have sediment clogging your pilot jets?

Finally a cam chain adjustment.

[mystic_1]

It sounds like you have sediment clogging your pilot jets?

Sediment comprised of blue paint pigment, I'd bet 


Rex, poor carb sync and other issues will cause some extra chatter both in the cam chain and in the clutch basket.  This is common on 750's.  Does the sound change if you pull in the clutch?  If so it's the clutch chattering, otherwise the cam chain.  Possibly you have noise from both.

Follow the tune-up procedure in the sservice manual in order, front to end.  Tuning the carbs is last, because so many other things can throw this off.  Cam chain adjustment, valve adjustment, plugs and timing adjustment, then carb tuning.

mystic_1

[narcoticrex]

Sediment comprised of blue paint pigment, I'd bet 

Naw, this is my 550, my daily rider.  I just took off the carbs yesterday, and totally worked them over, they are spotless.  Hers some vids, the first is startup, then the second is the low idle one....it seems you cant hear the noise im describing in the vid too well. 

On a side note, today I noticed a fuel leak coming from 4 or 3 splashing onto 4. Looked like it was coming out near the gasket, near the top.  I tapped the bowl and then raced home - and when i got there, it had stopped. Leak didnt restart when i started her up to take the vids you see, so i dunno whats up.

[youtube=425,350]0Y5km8gMKbE&hl=en[/youtube]
[youtube=425,350]1vhjEkG1v3A[/youtube]

[TwoTired]

Do a full tuneup, followed by a carb sync.  It should idle much better.

Does the offending noise you hear change when you pull in the clutch?

How many miles on the engine?

Possibilities:
The primary chain has no tensioner.  This is allowed to whip around and make noise if the cylinders aren't firing smoothly and allowing the crank to change rotational speed. (carb sync)  Then the chain alternates which is the slack side, top or bottom.

The trans gears are always meshed, even if not engaged.  Some of them are loaded with the weight of the clutch parts.  When the crank changes speed, the inertial weight of the components forces the gear teeth to alternate tooth face contact front or back.  This "gear clacking" occurs on all the gears, and can be quite loud.
While its not a major problem, per se.  I feel that this action probably wears out the trans faster than if they were smoothly engaging. 

My 77 CCB550 F makes quite a racket at idle if the cylinders aren't running just perfect and equal across the bank.  Ignition timing also needs to be spot on, too.  I'll force it to idle higher, when the "gear clack" becomes noticeable.

Cheers,

[narcoticrex]

I think it has to be carb syncing or timing (i had recently adjusted this, i shouldve checked and made sure everything is still aligned, doh) - i am so broke right now, i dont even have the cash to buy the parts for a DIY manometer    All my cash is going into the smurf.

the motor has ~12k original. clutch doesnt change anything, and this was obviously done in neutral...i also think im running lean (would that have any bearing on this particular problem?) as today was warm and the girl  ran great, and as I was coming down a hill with the clutch in and in first gear, i was popping/light backfiring out of 3 or 4 (noise coming from my right).  Im also in lynchburg, va in the blue ridge mtns - 1000 feet above sea level.  Im going to turn my screws out about a half a turn, and maybe take a short ride here in a couple minutes.

after writing this all up and rereading your post, I think you are onto something twotired, as the noise im hearing would fit that and make sense, regarding its location and sound.

[TwoTired]

If it is "gear clack", you are hearing.  Pulling in the clutch, even while in neutral, should change the Clack sound.  Won't stop it, but the intensity/tone will change, as pulling in the clutch changes the mass or loading in the gear train.

Remember, the gears are always meshed in the trans.  But, not locked to a shaft until engaged.

Cheers,

[narcoticrex]

If it is "gear clack", you are hearing.  Pulling in the clutch, even while in neutral, should change the Clack sound. 

well, i guess that not it, pulling clutch = no effect.  will check the timing again tomorrow and try to adjust tappets (never done that before!) tomorrow after I install my phenolic piston I bought from kevin400f