Author Topic: carb throttle shaft repair  (Read 956 times)

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Offline batboy

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carb throttle shaft repair
« on: August 28, 2019, 12:54:42 pm »
On my rack of 36mm Ninja carbs, I have a problem. Carb #1 throttle shaft (holds the butterfly plate) has excessive free play that is causing a vacuum leak and prevents me from synchronizing the carbs. I have spent hours researching how to repair this issue. I assumed the bushing was worn, but I've found out that it's actually the throttle shaft that is worn. I bought a throttle shaft for a #1 carb from a ZX1000A on eBay. Then, I found out the felt seals are toast which is why I have a vacuum leak. Seems like when people replace Keihin felt seals, there is only a 50% success rate of fixing the vacuum leak. Some people had good luck replacing the felt seals with a rubber o-rings.

Now I need to de-rack the carbs and replace the #1 throttle shaft and convert over to o-rings. So I do more searching and find a post from SISF that basically says the throttle plate screws are staked and once removed the carb is essentially ruined because the screws won't hold when reinstalled. The standard procedure is to replace the rack of carbs rather than repair the old carbs (according to both Steve and the service manual). But, I want to try and fix this if possible, realizing I only have a 50-50 chance.

Anyone try this before? Once the throttle shaft and butterfly plate are reassembled, I plan to re-stake the screws to prevent them from loosening up in the future. That seems to be the obvious solution. I figure I can't break it if the dang part is already broke, so why not give it a try? The worse thing that can happen is I still have a vacuum leak. If so, then I will find another set of 36mm carbs, I reckon.
« Last Edit: August 28, 2019, 01:20:18 pm by batboy »
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Offline connie_rider

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Re: carb throttle shaft repair
« Reply #1 on: August 28, 2019, 01:29:49 pm »
Before I retired; I sometimes used special "O", "X", or "square"-rings to act as seals.

Maybe; Seal the shaft by packing the felt with High Vacuum grease.
             {It is a silicon based, heavy/sticky grease that stands up to heat pretty well}.
                  Doesn't flow when vacuum is applied to one side.
                           We use it on our antique cars.

NOTE: Before seals were designed, they used to use felt {or other} as "packing" and sometimes had a way to compress it as it wore. 
             Might try putting the vacuum grease on the felt, and also find a way to compress the felt slightly.

https://www.ebay.com/itm/DOW-CORNING-Laboratory-High-Vacuum-Grease-976V-Stopcock/280617417916?hash=item415619fcbc:g:SW4AAMXQ~c9RG6bj

Ride safe, Ted
« Last Edit: August 28, 2019, 09:20:44 pm by connie_rider »
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Offline m in sc

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Re: carb throttle shaft repair
« Reply #2 on: August 28, 2019, 02:25:37 pm »
ive done it on different carbs, but also used a lathe and brazed the shaft and then turned it back down, etc. (keep in mind i was a clock maker for 10 years so i have a lot of experience doing this, its delicate work). however, i like connie-riders idea as well. i mean, are you sure there's a significant vaccum loss at the shaft? 

Offline batboy

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Re: carb throttle shaft repair
« Reply #3 on: August 28, 2019, 06:05:40 pm »
Any vacuum leak is bad news for me when I'm trying to tune for performance with a wideband. Besides, a vacuum leak makes that cylinder run lean, which is not good.

I reamed out the throttle shaft bushing of a 4 barrel quadrajet carb once, which means little for this project. A few people have repaired throttle shafts on Keihin CVK carbs (google search).

Ted, that vacuum grease is an idea I hadn't thought about. The throttle shaft I got on eBay even comes with one good felt seal. I heard they're sort of expensive to buy from Keihin. When I put it back together, I'll give that vacuum grease a try, maybe it'll help seal the felt seal. Order was placed with Amazon.

I'm also working on Plan B, which is, find a good rack of 36mm carbs.
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline m in sc

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Re: carb throttle shaft repair
« Reply #4 on: August 28, 2019, 06:27:24 pm »
we've also fitted small lipped oil seals to shafts on SU carbs. just depends how deep you want to go.  >:D like said, are you sure there's a verified leak there?

Offline Lee

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Re: carb throttle shaft repair
« Reply #5 on: August 28, 2019, 08:07:22 pm »
Plan B and a good rack? Why does that sound so good?!?!!?

Seriously though we used to use appropiate sized bronze bush
glued with loctite red or a bearing press product after reaming to carb to size.
This on Corvair carbs. Worked better and longer than new.

Good luck!

Offline m in sc

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Re: carb throttle shaft repair
« Reply #6 on: August 28, 2019, 08:28:49 pm »
this..and it takes a correct reamer to do right. after i used to braze the shafts we did this on really bad ones. ( and one was a q-jet) :beerchug:

Offline MAN OF BLUES

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Re: carb throttle shaft repair
« Reply #7 on: August 28, 2019, 08:58:00 pm »
this all sounds wacky.. and way out of proportion.. in the 1000 carbs i've seen, never would I have said the throttle rod leaked enough on a bike carb, that it made any difficulty "synching" them... now, if getting really techno, and expecting this "tuning" using a finite metering device, like an Air mixture anylitcal thingamabob... well.. maybe.. but all I can add it remove the nut and washer from the end, smoosh some chopped up bar soap shavings in around the shaft, and replace the washer and nut.. if that doesn't seal it, buy more carbs.   :great:

anything you add as a seal, will effect the return function on the assembly.. jamb grease in there... maybe, and top that with a small "home made" cellophane washer, or saran wrap disc..

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Offline batboy

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Re: carb throttle shaft repair
« Reply #8 on: August 28, 2019, 09:26:13 pm »
I have confirmed a small vacuum leak. Don't make me admit I found the leak by spraying carb cleaner while it was idling.

If you open the throttle butterflies and wiggle them gently with a finger tip, the #1 shaft has visible free play on the right side (closest side to #2 carb). The rest of the carbs seem to be okay.

I'm still waiting on parts and had not planned to remove the carbs again until Friday.

Like I said, I figure repairing it will be a 50% gamble. I'm actively looking for another set of carbs. Worst case, I put the 32mm stockers back on, they work fine.

MOB, what brand soap would you recommend for something like this?
1988 Kawasaki Concours ZG1000 - Ninja Edition
Bike has the usual accessories and modifications

Offline MAN OF BLUES

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Re: carb throttle shaft repair
« Reply #9 on: August 28, 2019, 09:32:10 pm »
I have confirmed a small vacuum leak. Don't make me admit I found the leak by spraying carb cleaner while it was idling.

If you open the throttle butterflies and wiggle them gently with a finger tip, the #1 shaft has visible free play on the right side (closest side to #2 carb). The rest of the carbs seem to be okay.

I'm still waiting on parts and had not planned to remove the carbs again until Friday.

Like I said, I figure repairing it will be a 50% gamble. I'm actively looking for another set of carbs. Worst case, I put the 32mm stockers back on, they work fine.

MOB, what brand soap would you recommend for something like this?

 :)) :)) :))

Lifeboy...  (just a Christmas Story joke.. sorry)

Irish Spring, bar soap.. or, any small soap bar, accumulated from many stays at Holiday Inn Express'... they all work.

Ask TED... he's the soap expert...  :rotflmao: :rotflmao: :rotflmao: :rotflmao: :great: :great: :great: :beerchug:

actually, pure paraffin, wax, like used in sealing canning jars of jelly and such, works great also.. gas has little effect on it..

my dad, rest his mechanical soul, always had blocks of it in the garage, he was a mechanic that taught me things you will never see in books.. he showed me how to make fibre/paper/cardboard gaskets, and impregnate them with paraffin, to seal many many things..

oh, and spraying carb cleaner, just got that sucked in, and removed the greases that sealed that shaft prior.. spray enough on the other ones, and they will suck air also.. might want to re-lube those seals, with some 90wt lube, let it soak in, and reassemble..  when I check for vacuum leaks, I use a propane torch, unlit, and wave the tip around openings.. when the propane gets sucked in, and changes "idle" characteristics, then I look at those spots..  mind you, propane is a large complex molecule.. oxygen is not.. if it changes with induction of propane, meh.. it may be a factor..  if it doesn't change, and O2 is being ingested, well I say if Propane doesn't effect the idle, it isn't worth calling it "a leak".  Going back to my dad's system, we had an acetylene tank, and hose for brazing stuff, so he used that for his "does it suck this in" analysis.. .Sometimes the hose wasn't long enough, and I had to hold the tank up while he was running the tip around.. I sad screw that daddy, here, use this Bernz-o-matic I have..  :rotflmao: :rotflmao: we agreed, it worked as well.
jmho/ymmv/lsmft/ some settling may occur in shipping.. don't try this without protective gear, and all those other warnings.   
 :great:
« Last Edit: August 28, 2019, 10:03:17 pm by MAN OF BLUES »

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Offline connie_rider

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Re: carb throttle shaft repair
« Reply #10 on: August 28, 2019, 09:51:49 pm »
I was under the impression that the carbs were off the bike.  :-[

Here is a thought;
Before you pull the carbs, use a long Q-tip/etc and heavily coat the area around the shaft area with the vacuum grease.
Then crank the bike and attempt to sync.

If you have leak there, the grease should stop/slow it e'nuff to see if that is your problem area.
But, I find it doubtful that the felt seal is your problem/cure.
ie; Felt seals are porus and don't seal air. They primarily act as dust filters.
    The grease normally helps capture the grease.
     in this case the heavy grease might seal the shaft to help you troubleshoot.

NOTE: My thought was to pack/coat the felt with grease.
          The grease alone will not act as a packing.
           The soap {used with the felt} just might work too.

Ride safe, Ted
« Last Edit: August 31, 2019, 11:31:13 pm by connie_rider »
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Offline MAN OF BLUES

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Re: carb throttle shaft repair
« Reply #11 on: August 28, 2019, 10:06:21 pm »
he has to remove the nut, and washer, to get to the sealing / leaking area, to apply any goobi stuff, meaning off the bike, and seperation.
just mentioning. :truce: :truce: :truce:
 or...
« Last Edit: August 28, 2019, 10:10:10 pm by MAN OF BLUES »

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Offline GeorgeRYoung

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Re: carb throttle shaft repair
« Reply #12 on: August 28, 2019, 10:22:04 pm »
Had the same vacuum leakage problem with a pair of ZG550 downdraft carbs. I removed the butterflies, replaced the lip-type seals with suitable O-rings, reassembled and it worked fine.

Offline m in sc

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Re: carb throttle shaft repair
« Reply #13 on: August 28, 2019, 10:40:00 pm »
you do know that if its a legit minor  leak, when you synch the carbs with a vacuum gauge it will compensate for it at that low of a level. i very, very seriously doubt at anything over idle its going to leak that bad where its notable.  sorry, it just just isnt. and if it is, there are other issues and the rack is probably trashed and the shafts rusty. i agree with the others on this, on the hundreds of carbs ive worked on, the only ones ive ever had to really get into to rebush on a bike was some old CB450 carbs. the rest were car carbs of various sizes, and those things are sloppy as it is, and take a bigger load then the bike ones do, and they typically are just not as precisely made. i think you're splitting hairs on this

Offline MAN OF BLUES

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Re: carb throttle shaft repair
« Reply #14 on: August 28, 2019, 10:49:59 pm »
thank you M

I didn't really want to come off and seem as condescending, about the issue. As that would not really be effective, but as you note, and I have also, over many years... it's just not seeming to be "a real" issue, with form fit function.. there may be some other underlying things contributing to the whole "analysis", of this minimal air ingress.. that far exceed what is being seen, and taken as a "problem" with his air/fuel program and tools/readings

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Offline connie_rider

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Re: carb throttle shaft repair
« Reply #15 on: August 29, 2019, 01:31:41 am »
He has to remove the nut, and washer, to get to the sealing / leaking area, to apply any goobi stuff, meaning off the bike, and separation.

I'm referring to the area around the OD of the bushing "boss". Not down at the shaft itself.
   Not sure what to call the area? {The cast aluminum material that supports the OD of the bushing}
By sealing the Carb "boss" to the throttle quadrant, the shaft to bushing area is effectively sealed for a test.
  As a test, he can try to sync the carbs, and/or spray carb cleaner to see if it is still sucking air.

Wondering if the sync problem is other than the shaft though. Lots of possibilities.
         Pinhole in diaphragm/O-ring not on air mixture screw/valves not seating properly/etc.

Ride safe, Ted
« Last Edit: August 29, 2019, 12:51:44 pm by connie_rider »
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Offline m in sc

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Re: carb throttle shaft repair
« Reply #16 on: August 29, 2019, 02:08:51 am »
its a bushing seat.

Offline tdbru

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Re: carb throttle shaft repair
« Reply #17 on: August 29, 2019, 03:21:03 am »
would RED loctite keep butterfly tight on the shaft?  or is re-staking mandatory?
thanks,
tdbru

Offline Lee

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Re: carb throttle shaft repair
« Reply #18 on: August 29, 2019, 03:55:28 am »
Interesting series of posts here over a wide range of expertise and experiences. Just to add to this and not to disagree with any post would share this.

On a Virago that was running terribly to not at all on rear cylinder, I found it failed the propane test at the outer throttle shaft juncture on rear carb. This after frustratingly checking everything over a period of weeks.

Upon disassembly found a peculiar profiled seal ring that had torn or split if you will on the throttle shaft. It was unattainable anywhere.  Not even listed as a part if I remember. I was able to place two thin traditional o-rings with enough pressure to seal but not slow the throttle after experimenting with single and then double combinations and sizes.

The bike was unusable without this point sealed properly. Can not tell you why that bike was so sensitive to a vacuum leak at that place but it was. The fix was not simple in time spent looking for the why, but for this bike it was an elementary fix. The problem was finally resolved.

Please note I do not have hundreds of carbs under my belt. But enough to know they are designed to work within parameters. For some there can be little room for deviations, for others the parameters are so loose it is a wonder they perform period even new.

Good luck with this issue.

Oh, think it was Ted who offered the thick grease as temporary fix as a diagnostic tool/trick. Next time I am in the situation will try that with some string as packing.
Might clue me in faster along with propane to check sealing.

Got to love COG! A world of help even if differing thoughts at times, Oorah!
« Last Edit: August 29, 2019, 03:59:08 am by Lee, Reason: spelling »

Offline batboy

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Re: carb throttle shaft repair
« Reply #19 on: August 29, 2019, 12:31:29 pm »
The carbs have been on and off several times. They are currently on the bike and must be off to do any of this throttle shaft surgery. I might have extra time this morning to remove them again. I will at least pull the tank back off so I can eyeball them and maybe pull all the spark plugs out for a look.

A guy in another forum recommended applerubber dot com for O-rings. They supposedly have 300 million o-rings in stock. That's in case I decide to convert from felt to rubber seals.

I was feeling guilty about the carb cleaner because it was a dangerous flammable liquid. I didn't even think about it dissolving packing grease. I only gave it a couple quick squirts in that the one spot.

tdbru asked if staking the screws was mandatory. That's how it was assembled by Keihin. There could be other options, I guess. Is Locktite gasoline resistant?

At least this is something different to discuss and brainstorm. I know some of you are thinking a small vacuum leak is a minor issue, but I can tell the bike is not running right. There is way too much free play movement of the shaft and butterfly. I suspect the felt seal has pretty much disintegrated.
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Offline m in sc

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Re: carb throttle shaft repair
« Reply #20 on: August 29, 2019, 12:55:32 pm »
if theres physical free play the body or shaft is probably trash.

ive used red loctite on LOTS of choke plates and throttle blade screws, no issues.

Offline batboy

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Re: carb throttle shaft repair
« Reply #21 on: August 29, 2019, 01:18:22 pm »
Right, I agree. If it's worn down into the body, then game over, because I'm not going to try and re-bush it. If it's the shaft and seal, I have a replacement to try.
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Offline connie_rider

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Re: carb throttle shaft repair
« Reply #22 on: August 29, 2019, 01:33:01 pm »
Instead of grease, maybe try placing a drop of heavy rear differential oil at the gap.
It should flow down, and seal the area temporarily to do a test.
    If so, it would allow you to see a change on your gauges.

Ride safe, Ted
« Last Edit: August 31, 2019, 11:32:44 pm by connie_rider »
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Offline batboy

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Re: carb throttle shaft repair
« Reply #23 on: August 29, 2019, 11:50:13 pm »
Plan B was starting to look like my best option. So, I bought another set of ZX1000 Ninja 36mm carbs. I should get them early next week.
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Offline strum

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Re: carb throttle shaft repair
« Reply #24 on: August 30, 2019, 11:54:20 am »
I can see why they staked those screws instead of lock tite. It would not be a good day when the loc tite gives and and the screw ends up hanging a valve open.
 getting another set of carbs is a good plan. Lots of parts now :great:
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