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Discussion Starter #1
Hey folks, new here.

Working on a buddy's 96 TB with Mikuni CV BST 36mm flat slides.

(I think i am going to buy this bike - I love the look.)

The number three carb has a VERY stiff throttle plate. it loosens up if you hit it with a ton of carb leaner and work it open and closed for a few minutes, but no matter how much carb cleaner and compressed air I use, it always stiffens up again.

Any ideas? Looks like there is no way to easily disassemble the plate.

Boil in lemon water?

Ultrasound?

Never saw a throttle plate on a Japanese carb behave like this.
 

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Including yours, I now know of at least 3 sets (of Mikunis) that have had this problem so I guess it's a common-ish issue.

I wouldn't recommend boiling them in water because they have thick felt washers on the outsides of the shaft and these will retain it and make the problem worse I would think.

You might have to take the whole lot apart and clean the shafts with fine wet & dry, then repack them with a good sticky grease.

I can't remember if it's the #3 carb but one has a round metal plate punched into the shaft hole, you could try removing that, hitting it with lots of WD40/CRC and then putting packing it with grease.

Dissassembly is not too hard and the throttle butterfly screws come out quite easily, just remember to make a not of which screws and butterflies went where so you can put them back together properly.

Remove the screws slowly and carefully and don't try to make the threads loose. They will go back in nice and tight which is what you want.

I used Loctite on the butterfly screws and it has worked well so far, although other (more experienced) users on this forum say that it's better to re-pein the screws. Although that's not easy to do without bending the shafts.

And of course you're going to need a carb balancer (Manometer) to get then synched when you're finished.
 

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Discussion Starter #3
I can't remember if it's the #3 carb but one has a round metal plate punched into the shaft hole, you could try removing that, hitting it with lots of WD40/CRC and then putting packing it with grease.

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Thanks for the tips. And yes, it is indeed the No 3 Carb that I have the problem with and removing that cap on the extreme right hand side looks like a huge PIA.(Of course, if it is just cosmetic, I could leave it off, but I am concerned air would leak through.)

I'm going to keep fiddling. I have the offending No 3 carb off the rack and I am going to experiment to see how much heat affects it by putting it on a luke warm wood stove to warm up slowly.

Also, a buddy siggested trying WD40 instead of carb cleaner in the butterfly shaft to see if that works better. (I have to wait a few days for that one missing silly little pilot air screw washer to show up, anyway.)
 

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....I have to wait a few days for that one missing silly little pilot air screw washer to show up, anyway.)
While you're in there I recommend replacing the pilot screw O-Rings and make sure all those "silly little washers" are in there too, you'll have endless problems if they're not right!

They go in the order - O-Ring - Washer - Spring - Screw (just in case you needed that info), and set the idle screws to 2 1/2 turns out, should be right.

And make sure you get the proper (fuel resistant) O-rings too and one trick is to grease the pilot screw threads on reassembly, it will prevent them seizing up (another common and VERY expensive problem), and it also helps seal them too. I used copper grease.
 

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Discussion Starter #5
Thanks. I have the little pilot air screw O rings - they came in a rebuild kit. Smallest things I have ever worked with. Had to use a dental pick to get them out.
 

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Discussion Starter #6
Update:

Heat - did not work.

WD40 - did not work.

BUT

Liquid Wrench - PERFECT.

Stuck it in the firdge to check for cold temps - still spins perfect.

(But some of the food smells pretty funky.)
 

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lol, oh well the main thing is you got it working again.
 

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Update:

Heat - did not work.

WD40 - did not work.

BUT

Liquid Wrench - PERFECT.

Stuck it in the firdge to check for cold temps - still spins perfect.

(But some of the food smells pretty funky.)
We will be needing a taste test report on liquid wrench flavored milk. Might be the new drink of choice for serious mechanics everywhere...

Merlyn
 
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