slidevalves vs. cam chain tensioner

I finally got my Yamaha Radian resto running .Using slidevalve Mikunis from an FZR 600.Bike started up great after 10 years in storage,Idles good ,runs good,seems like plenty of power.However,at idle (900rpm or so),makes a Godawful rattling noise.Noise goes away at 1500-2000 rpm.I had 2 thoughts:cam chain tensioner versus the slides in the carbs rattling.Any way I can tell the difference (isolate the noise source)without replacing the tensioner or tearing the carbs down again?Thanks.bj

put your fingers on the slides with engine running and see if the sound goes away or lessens if so it's the slides.

Thanks.Will give that a shot.Sorta major surgery to get the airbox hoses et al out of this bike,but will keep u posted.bj

Old school method...take a big old screwdriver(or somthing) and touch one end to valve cover near cam chain area or the tensioner and touch the other end (handle preferrably!) to your ear...listen. Now do the same with the carbs. Hopefully you will be able to distinguish where the bad vibes are originating. Also on alot of bikes that rattle could be from the clutch basket. Does it go away when you pull the clutch in? If so, it's the clutch basket and can sometimes be remedied by carb sync.

Would it be feasible to attempt reaching the slides through the air box with thin dowels or coat hanger wires to press against the slides at low rpm and possibly dampen any clacking? (But even if straight shots, might be screens between air box and hoses.)

Just guessing. :S

Good Fortune!

Edit: Mechanic's stethoscope as suggested by seanbarney41 would seem a better first effort.

Actually I have a physicians stethoscope from another life so could use that.The rattle does not lessen appreciably on pulling in the clutch(tried that first).Patton-the airbox on a Radian is even more shoehorned in than any Kawi I have ever seen so to get to slides the box and intake airbox manifolds have to be removed (also the battery and tool tray).Carbs were both bench synched and vacuum synched with my new play purty synch tool and seem spot on-plus the bike runs and idles really well-just clatters like an old Chebby V-8 with mechanical lifters-same sound.I am really leaning toward the cam chain tensioner as the culprit,but I have never had a set of slide valve carbs so cant rule that out either. I assume that if it a. is the carbs, and b. they are in sync=live with the noise and be grateful bike runs well-- correct?I really dont mind the noise as long as some really essential function is not going to decide to leave the engine at 75mph and hit me in the huizingas.Thanks for the input gentlemen.bj

hocbj23 wrote:

...never had a set of slide valve carbs so cant rule that out either. I assume that if it a. is the carbs, and b. they are in sync=live with the noise and be grateful bike runs well-- correct?I really dont mind the noise as long as some really essential function is not going to decide to leave the engine at 75mph and hit me in the huizingas....

Regarding rattle/clack of flatslides, here are some excerpts from topic rs34's:

kzrider.com/index.php?option=com_kunena&...ew&catid=3&id=162987

...running great. The only problem I have is the noisy carbs. These flatslides are clacking around like crazy! The carbs are brand new and now have a total of 31 miles on them. The engine is tuned perfectly, cams degreed, and it still clacks at idle and while riding... don't know if I can take that noise. I'm thinking of going back to 33 smoothbores. Thoughts??

Well, they aren´t called RattleKunis or ClackSlides for no reason. They will clack on idle then it quiets down when revs go up. Syching the carbs helps a lot but they will clack.

Are your RS34s clacking while cruising above 3000rpm?

If your carbs are constantly clacking while you are cruising, that's not a good sign and not necessarily related to the carbs. IMO carb clacking has little if anyting to do with jetting or ignition timing.

My carbs clacked and my bike ran so-so until I got everyting tuned just right. Now it pulls like a truck all over the rev range without a clack or ping...but it took a while.

The clacking is the noise of the flat slides banging back and forth against the carbs body as the piston changes direction in the cyl. The cyl pressure changes from pos to neg and this actually pushes and pulls on the carbs slides, and causes this clacking noise. My carbs are fairly quiet at idle up to 3000rpm then they are a little noisy at criuse, about 4000. not bad though.

glad to hear that the clacking can be limited with tuning. That is really annoying me.

Have you ported your head? Opening up your intake ports will also make a difference. Bigger intake ports will tend to produce more clacking. Your carbs/engine will not respond too well while the carbs are clacking...

By the way, I was able to see (hear) that only the #1 carb is "clacking". What could be causing that? Getting everything synched really helped, but it is still rattling and I can actually see it moving around with the carb tops removed. The other 3 cylinder are nice and steady.

Anything else that could cause only 1 cylinder to "clack" like that?

can hear carb "clacking" and and it was suggested that I test the compression. The clacking seems to be much better now that I have synched the carbs, carbs are way better since they've been synchronized. I don't hear any clacking at all except at idle...

No clacking while cruising is good. Don't worry about the clack at idle. You'll drive yourself nuts trying to get rid of it. It's normal to have this at idle even if it's only one carb that's clacking...

one thing i have noticed with flat slide carb's is that they can be very noisy you outa hear a zx7rr with the airbox off you can barely hear yourself think.same thing with dry clutches just part of the package i guess.i think that is one of the main reasons that mikuni went to roller bearing slides on there big harley flatslides.

finally have the RS34's dialed in pretty well. The bike is running really well but the slides still clack more than I'd like...RS34 Flatslide smoothbores

that is one of the problem with flat slide carb's is the noise from the slides themselves i did a zx7rr engine job ad when i fired it without the air box to set every thing it sounded like it was coming apart as soon as i put the air box back it became quiet. but i can handle a bit of noise if it means the bike is going to make stupid power.

mine are probably as quiet as they're going to get. You don't really notice it except at idle. I still wonder how it would run with my old 33 or 29 smoothbore roundslides?

I'd like to pick up a pair of round slide Keihin RS carbs someday, but those are pricey. I wonder if the Keihin flatslides rattle too??

about the only flatslides that dont rattle alot are the ones everybody is putting on there harleys the 42,45 mm mikuni flatslides are supported by roller bearings up and down bothsides so it keeps them quiet.

If it's any consolation the RS recently removed from the KZR clacked at idle as well.

A slight clack at idle is normal for RS carbs. They shouldn't clack while cruising. If they are clacking it's a sure sign that air and fuel from the cylinder is reentering the intake port - reversion. The engine will be low on power and the carbs will be difficult to tune. Interesting things is that this situation cannot be tuned out through, jetting, ignition timing or changing carbs (changing to a round slide carb will stop the clacking but won't stop the reversion).

I know it's going to disappoint you guys but I gave up on the RS34's. I have my Mikuni 33 smoothbores back on for now and I enjoy riding it much more. It really runs well and doesn't have that annoying flatslide sound. I plan to install Keihin CR35 specials very soon.

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Good Fortune!

Patton: Thanks for the informative post.IF I can get the stator cover off (frozen screws) and get the bike to verified TDC, I am going to adjust the cam chain tensioner (on this bike it can be adjusted) and see if that helps.If not will just live with the noise as it only occurs at idle and the little bike runs great otherwise.Thanks again for all the input.bj