Carburetor nightmare; wasps+ wrong broken mixture screws on top broken mixture screws…

SpiderWrench

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The 81 XS400 has been parked since late August when I rode it to its new home and parked it in my basement. It has never run particularly well, and has always had idle problems according to PO because it had to be tuned to the 2-1 exhaust. When I went to remove the carbs, I thought they looked a bit overly dirty. I figured it might just be a clump of mud that stuck up on top of the carbs.
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Nope. It was a wasp nest!
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At least I know the bike can move faster than the wasps, as there were just a few dead larvae inside. I do wonder how long those wasps were chasing me as I rode off with their babies.

Through the wisdom on this form, I determined my next step had to be a good carb tear down and cleaning.

Removing the carburetors, I made my next horrific discovery, one of the mixture screws was missing. I found it soon enough, lodged in an engine fin, with the tip bent and broken. I looked down the port, and to my delight saw the little brass tip lodged in the bottom, great!
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I removed the mixture screw from the other carb to discover that it too was bent into a curly que shape.
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At the bottom of that port was a bit more brass. The mixture screws were replacements for the originals which were broken off in the carbs and cranked down on top of the originals to break themselves, so it seemed I had two broken tips in the bottom of each carb. I found myself blissfully reminiscing when my problems were only a wasp nest.

Anyhow, this is really more of a thank you to this forum, because it took several attempts, and many long hours to remove those broken mixture screw tips. I used combinations of techniques posted by drewpy and Greasey Fingers plus a bit of creativity and a lot of patience. I used a heat gun to heat the area first, and wore leather gloves (after I had the first pick I made from sewing needles break off and go through my finger) The first one came out using a ground down HF pick pushing up. The second larger one was removed by a ground down nail pushing down which removed a tiny piece of one tip then followed by a 0.025 drill bit that I twirled in my fingers (No, I didn’t use a power drill because I don’t have a chuck that would fit this bit and I figured I would do the least damage by just manually twisting the bit) for hours. I don’t think I would have had the patience if I hadn’t read all the success stories on this form with the same problem. Thanks All!
 
Good for you!! The trials of old bike ownership. These sort of things are a constant reminder to do the job right so WE are not the guy being blamed down the road. It is a good idea to spend the time rather than short cut to a future failure.
 
Gross. Found mud wasps all under the seat of my '82 when I got it.
Still need to wash some of the mud out of the tail light area.
 
Yeah, the wasp nest kind of freaked me out when it broke open. The mud/nest was super hard to clean off as well. Hope your's is easier to clean up than mine, I never realized wasp saliva (or whatever bodily fluid they use) is like epoxy.

I also wanted to mention that after I got the mixture screw tips out, I measured the size of the port opening with my drill bits ( I figured I could do no more harm than what I had already done) and a #68 bit (0.031" / 0.7874mm) slid through with no resistance, and a #67 (0.032" or 0.8128mm) did not fit through, so if you use a drill bit or grind down a pick, use something smaller than #68 bit (0.031" or 0.7874mm) to be safe, I used a #72 (0.025" or 0.635mm).
 
They wont work in those carbs. You can tell the 77-79 from the 80-82 in a few ways. The easiest is the aluminum tops that are only on the 77-79. The 80-82 used tin ones. Post more pics of the carbs so we can have a better look.
 
Its best to get genuine Mikuni parts, especially when it comes to jets. The aftermarket stuff is a lot different from the way the parts are machined. Heres what you might need. Part number: 2A2-14923-00-00. https://www.partzilla.com/product/y...?ref=1c71f7bc81e7db7c358e18f268535cff92631a9b

Youre probably gonna need to rebuild the whole setup anyways. Thats what I ended up doing. All the brass stuff gets worn out and doesnt provide proper mixing and sealing after a while.

That hole for the idle mix doesnt look so good. I hope its not marred up and stripped. You should still be able to find carb bodies and maybe complete replacements. Its seems everyone likes xs360 carbs for their 400s.. They run richer than the 400s.
 
Those are 77-79 carbs. Have you removed the main jets and the pilot jet screw plugs? Those are missing from your pics. There are videos from a member that show how to clean and take apart these year carbs. It maybe in the tech section and on you tube.
 
Thanks everyone. I've been working on the bike and done a lot to it now. I am just about broke so the new pilot screws will have to wait, in the mean time, I did something with the old pilot screws which might make some peoples head explode, or maybe it will give someone who is also in a jam some ideas. I honed the bent up pilot screws back into points so that I could use them temporarily. I took a diamond stone and a piece of fuel line to act as a tension er, and rotated the screws until they came to nearly a point at the same as the original angle (similar to sharpening a knife, but in the round.). It worked alright, and my bike is running better than it ever had before I took it apart. I also did a ton of other maintenance, valve clearance, oil change, starter delete, idle adjustment (I know, not much good with makeshift screws, but still better than before), carb sync, tire change, and a bit of paint. In the process I have been burned, crushed and cut up (xs fell on me, luckily no damage to the bike, ha). Before:
After (but not done):
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