Throttle Shaft Seals

Hello All,

I have a hanging idle. Once the bike reaches operating temperature the bike will hang at 2000ish RPM then drop down to a nice 1000 after about 5-10 seconds. I can also get it to come down with the clutch or by popping the throttle.

Checked the intake with some contact cleaner and low and behold, my throttle shaft seals are leaking... great...

Is there any quick/temp fix for them without pulling the carbs? I would prefer to have another few weeks before I make time to pull the carbs.

I also noticed via the Spark Plugs that cyls 1,2,4 are good mixture if not a touch lean. And cly 3 is very rich. So I turned in the mix screw on carb 3 by 3/4 to set it at 3 (1,3,4 are at 3 3/4 turns)
I will see tomorrow if that helps the cyl at all as it didn't change much from me running the bike at idle for a few minutes. Will see after the ride to work tomorrow.

Inspecting with the contact cleaner it seems that the outer seals are the worst. seal from 1-2 is slightly leaking, seal 3-4 is fine (no RPM change via spray)

And input on the mix or the seals would be appreciated.

Cheers
Dave

 

You can only get to the outer two without pulling and breaking the rack. Besides, if you're going to do one, you might as well do all eight.

On that note, I'll just leave this here.

 

Carb rebuilds are fun

 

No temporary fixes I can think of amigo, gotta do them right or you are just wasting time. Of course you could flood them with some combustable liquid as you ride down the road but that would probably be impractical.

 

That is great, thanks

I have no issue with doing the rebuild, it is the down time I don't like as I rarely have a straight shot of time to do it.

That is what I figured... and this whole issue is because I didn't think of them when I had the carbs out over winter.. So doing it right is how it'll be done this time...

Cheers
Dave

 

Either its a hole in one of the rubbers under your hats or dirty slide bores.
I had the hanging idle too till I polished the slide bores. It came back after one riding season so again i polished again. Cured mine.
While you are in there, blow them out seven ways to sunday with a few cans of carb cleaner. Set the floats at the proper level.

 

The float level was set but I will check again, My diaphragms shouldn't have holes as I checked before assembly, bores were also polished. I would think that the leaking shaft seals would cause it to run lean under load(high vacuum) but when the vacuum faids they'll re-seal, such why the idle runs, then drops and stalls. But who really knows, I just know that they leak, and while it is apart I plan on cleaning everything regardless.

Cheers
Dave

 

Nah....they leak the whole time. BUT they can only leak a tiny amount which makes very little difference above 3k rpm but makes it impossible to get the rack synced or adjust the mixture since depending on the exact position of the shafts and seals SOMETIMES they leak a lot, the next blip of the throttle and they don't leak so much.
One second #1 is leaking like mad and #2 is sealed up pretty good. You sync to that and then #1 seals and #2 leaks and your sync is way off.

But now you get to completely reset everything! but it's a definite requirement and it won't run right until you do it.
I would surely double check the float levels while its out just to eliminate that potential problem which will require the rack to come off AGAIN...

 

" I would think that the leaking shaft seals would cause it to run lean under load(high vacuum) but when the vacuum faids they'll re-seal, such why the idle runs, then drops and stalls."

Actually Azrael it is quite the opposite.

When you release the throttle and the butterflies close you are creating a restriction in the path of the airflow causing an increase in vacum.

The motor still wants X amount of airflow per revolution. If it can not pull that airflow through the throat of the carb it will start pulling it through the next weakest point. That being the shaft seals.

What this surge of air throught the shaft seals does along with the increased vacuum is pull a surge of fuel through the idle circuit in the carb. This temporarily increased fuel/air mixture is what causes the erratic idle problems.

That being said. Replace the shaft seals and you should be good to go.

Ghost

 

did you do a running sync? a temp fix might be to pack the cavity with grease but i don't know how long it would last

 

That makes sense. I still need to pay attention to what our teacher always said "Engines suck!"

I did, thought admittedly with no YICS tool. Might try the grease but do you think it could harm the engine/carb if it gets pulled in through the carb?

Cheers
Dave

 

Back in the "Golden Days of Rock-'n-Roll", ... all you needed to do was put a couple of Drops of TEAC Rubber Pinch-roller Conditioner in the Shaft Tunnel and rejuvenate dried-out Seals.

The latter-day equivalent is probably this stuff:

http://www.mcmelectronics.com/product/2 ... rm=200-200

 

Wow. That I will certainly try before tearing the carbs out. Thanks a lot Rick

 

Rick:
Do you think this would be the same? (local distributor)
http://www.rpelectronics.com/408b-125-r ... 100ml.html
Cheers

 

That is what I'm using on my rubber parts, it works pretty well. Smells good too!!!! (What are all of these pink elephants in the room for???)

 

It's likely the same; or better.

Browse. Look for the ones that have Precision Applicators.

Hold the rack vertical and put three of four drops of that Rubber Conditioner, work the Throttles and let it work.

Invert. Same; same!

 

So then if I brush this on and/or inject it into the seal it would stand a decent chance of re swelling the seal to make it good for a little while again?

Might it also be a good idea to brush on the boots before they crack?

Cheers
Dave

 

What, does that stuff smell like ditto machine fluid?

Where I work we usually have a gallon can of contact cement sitting in the fire cabinet for use in various places. Its distinct aroma caused one of the other mechanics to refer to it as "the happy can".

 

Wait whoa stop hold on.

TEAC tape decks and other electronic equipment's rubber parts aren't exposed to over 200*F operating temps like the various components attached to the bike's engine are.

What happens when everything gets nice and hot? What does the "magic elixir" do then? Make things better, or worse?

-Order all 8 seals.

-Since you know the outers are done for, replace those immediately (10-minute job, if that.)

-Don't apply anything to the seals that isn't at least "automotive" grade; I wouldn't apply anything myself.

-Finish the job correctly as soon as you can.

 

I would agree for most parts but my understanding is that carbs don't get hot. And printer rollers do actually get pretty damn hot. Nothing like the rubbers on the block itself, but comperable to the carbs I should think.

I have a parts carb so I will be repairing that one up vs fixing the one that is on the bike, but I would like to try something to temp fix the ones on the bike till I can afford the seals for the new carb ($90 for the kit)

How hard is it to get the butterflys off the shafts?
I was talking to our head tech at work and he was saying that yamaha peened over the back of the screws so you need to file them down or you'll screw up the threads on the throttle shaft... But no write-ups mention that.

Cheers
Dave