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Discussion Starter #1
Getting closer to getting my bike back on the road (replaced oil gallery cyl. head o-rings, new fuel pump, rebuild carbs......) and find that I can't bleed either rear brake and clutch MC Both are original fitments.

Looks like the rear (10mm?) MC rebuild kits are availale on flea-bay but not much for the clutch.

A remote reservoir set-up/swap seems readily available but it looks like the carb choke lever is integrated into the MC. Right? Wrong? Any suggestions/guidance?

Much thanks.
 

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On my 92, the choke lever was not part of the master cylinder, it was separately removed when I switched to FCR carburetors. For the rear brake have you tried elevating the caliper so that it is above the master cylinder when you bleed it? The coffin master cylinders frequently get an air bubble trapped. Once you bleed the caliper or clutch slave, wrap a rag around the banjo at the master cylinder and crack open the banjo while squeezing the lever. Close before you release the lever. This usually gets the air bubble out. I put bleed banjos on my master cylinders, but no one makes them the right size so I had to have then shortened by a machine shop. If this doesn't work, check Bevelheaven, the new replacement master cylinders aren't very expensive and can save the time and hassle of a rebuild, IF you can find rebuild parts.

There are some good threads on here regarding replacing with radial master cylinders if you want to go that route.
 

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I just changed my clutch mc yesterday, from coffin to remote reservoir. The choke is held to the side of the mc with 2 little screws - a real little bugger to get off ( I broke a little piece of plastic off the choke lever :( ). Both mc's have the threaded holes for the choke, so no problems there, just a challenge to remove and refit.
 

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It is rare enough that one master would fail I do not see it happening to them all unless someone put the wrong fluid in .

I would also recommend elevating them and keep at it they most likely have some air trapped at the banjo fitting . It was not uncommon to lean the bike over far enough to make the upper banjo lower and then you could get the air out, cracking the banjo while also holding the lever also helps some times. If you do take the lines off consider adding banjo bleeds and it will be easy after that.
 

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Discussion Starter #5
Thanks for tips and info. Bike has not had love and attention for quite a while...... (a couple of years). At some point I had replaced the front brake MC with a remote reservoir Nissin unit and that is still working well.

Even with a vacuum pump on caliper/slave cylinder, no fluid comes through at all. Also, levers never develop any resistance some I'm thinking the pistons are leaking grossly.

When this annoying job stops taking away my precious free time, I'll look closely at clutch MC and choke assembly.
 

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If it has sat and you are not getting pressure it is more likely that there is some Mung (build up crud) in the ports. if you look in the reservoir make sure those little pin holes in the bottom are open and pushing fluid in both directions. Also make sure the bleed down adjuster in the lever has not been mis-adjusted so the ports are not opening.
 

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I have been having issue with my clutch MC as well. It keeps pumping up. After a few pulls it gets very stiff - so I pop the bleeder screw on the slave without any lever action and fluid spits out. Clutch works great again for about 3-5 pulls then here-we-go-again.

Gonna take it apart while I have fairings off for LED headlight conversion. I am thinking there is some crud in there which is covering up a fluid port.....
 

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It’s incredible how much muck can be in there. I fitted a braided clutch hose, just for bling, and when I bled the system I used a mountain bike bleed kit (syringe) to push fluid up through the system from the slave end. The amount of brown gunge that came up into the reservoir was staggering. I “wasted” a lot of new fluid flushing it until it came clean. It was probably worth it by the sounds of it though.
 

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It’s incredible how much muck can be in there. I fitted a braided clutch hose, just for bling, and when I bled the system I used a mountain bike bleed kit (syringe) to push fluid up through the system from the slave end. The amount of brown gunge that came up into the reservoir was staggering. I “wasted” a lot of new fluid flushing it until it came clean. It was probably worth it by the sounds of it though.
Same here. I went through an entire pint of fluid just to get it "more" clean running out the bleeder. I went the other way with the flow. As with gravity most of the muck tends to settle in the slave. But there is still something wrong with my master, still pumping up and not letting go. Gonna take it all apart again, may have missed a tiny smidge which is still covering the return flow hole.
 

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But there is still something wrong with my master, still pumping up and not letting go. Gonna take it all apart again, may have missed a tiny smidge which is still covering the return flow hole.
Bummer! There are so many tiny things (literally) that can cause us grief.

I’m currently having carb issues. I rebuilt them (original Mikuni’s), replaced fuel filter and she ran sweet for a while. Suddenly yesterday she’s sluggish and unresponsive, especially when I throttle blip on down changes. It’s horrible! I have a new set of FCR 41’s sitting on the bench. It’s time to put those bad boys on!
 

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Bummer! There are so many tiny things (literally) that can cause us grief.

I’m currently having carb issues. I rebuilt them (original Mikuni’s), replaced fuel filter and she ran sweet for a while. Suddenly yesterday she’s sluggish and unresponsive, especially when I throttle blip on down changes. It’s horrible! I have a new set of FCR 41’s sitting on the bench. It’s time to put those bad boys on!
Two things right off the bat it could be and these are 50/50:

Vacuum leak - and it can be anywhere. I use ether and spray it all over the outside of the carb and its intake runner to the head. If no change in idle it could still be vacuum leak into the chamber.

-OR-

There is muck which got sucked into the idle circuit and the muck is plugging those #85 holes where the mixture exits aft of the butterfly.

The latter was the problem on mine. It is so hard to clean the idle passages. But I have seen those wax paper intake gaskets fail. They are so thin those can be easily missed.
 

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I suspect part two of your 50/50. The last day of good riding before the bogging down issue sprung up, the weather got quite dusty (mini dust storm out here in the desert). My OEM air filter is in need of changing and I am dubious of the seal it makes with the air box, so it is highly likely to be some dirt somewhere. Another reason to install my FCR41 kit now (including K&N filter). I mean, why bother messing around with those Mikuni’s any more when I now have the FCR kit waiting to go?

I owned heaps of carby bikes through the 80’s and 90’s and have never had one give me grief like this thing does. It’s a special case, that’s for sure. But I still like the bike. Temperamental Italian!
 

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P.s. Sorry to drift this thread.

Back to your master cylinder rebuild. All the best!
 

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Discussion Starter #14
Thanks again for all the info. I've got a 10mm piston rebuild kit for the rear MC on the way.

Clutch slave cylinder had leaked so I have replaced with an aftermarket unit. Oberon? I still could imagine gunk might abound but the tiny input whole in the coffin reservoir is not clogged.

JAFA, what unit did you use? The choke lever assembly is definitely integrated into this coffin style MC.

Hot air, no worries!
 

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Just joined the group, but quick add as I have had issues bleeding clutch circuits. Secondary (slave) internal ports can also become clogged, if you are unable to pump fluid and air through the secondary then might be a good place to start.
 
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