'80 XS1100 MS leaking float valves(?)

[cajun31]

These are the ones without the holes which are not oem or correct. Genuine Mikuni jet N151.067 - Jets R Us

[cajun31]

These are the correct pilot jets for the bike with those original oem carbs. Genuine Mikuni jets BS30/96 - Jets R Us

[cajun31]

Thank you for that info Phil! And I did confirm that the MS currently had the six bleed hole type #42.5 jets installed, and the new Yamaha #42.5s I have installed in my other set of '80 carbs on my 78E are of the no-hole variety. Very interesting. Well, I guess the search for the flooding-out culprit continues. I will try and see how the MS carbs run with my new no-hole pilot jets swapped over, just to eliminate that as a variable. Who knows maybe those old #42.5s got micro-drilled to something larger. I did also once again reconfirm that all seems well with floats and float valves.

If it were me, and it's not, I would leave everything stock including those pilot jets. I have three MNS and all of mine have the original type pilot jets with 6 holes and are 42.5. Of course I also run everything else OEM other then the air filters which are K&N. Make changes if you think they are necessary after you get the bike working correctly. Otherwise you might be chasing your tail.

[DEEBS11]

I have never run these so I can't comment from experience but this is the part I was referring to. If you have something like this in your carbs from the previous owner and you don't know about it, this can play havoc with trying to solve jetting problems.

https://www.ebay.com/itm/25556877974...Bk9SR56_-8bCYw

[DEEBS11]

There was a discussion some time back about these bleed holes in the pilot jet. After some testing, the no hole type worked exactly the same as the 6 hole type. You want to stay away from the 8 hole type, as they are for the VM type carbs and have a different type spray nozzle on the end.

This is true Phil. I had issues with my KZ750B carbs when re-jetting. They almost look the same. They were so rich that it ran terrible.

[DEEBS11]

Also check these air jets. I have seen these made in smaller size to richen carbs across the rpm range. Always better to leave stock and modify the separate circuits as needed.

[DEEBS11]

It's a good idea to put in a known good part to eliminate issues.

[gtem]

Thank you for that info Phil! And I did confirm that the MS currently had the six bleed hole type #42.5 jets installed, and the new Yamaha #42.5s I have installed in my other set of '80 carbs on my 78E are of the no-hole variety. Very interesting. Well, I guess the search for the flooding-out culprit continues. I will try and see how the MS carbs run with my new no-hole pilot jets swapped over, just to eliminate that as a variable. Who knows maybe those old #42.5s got micro-drilled to something larger. I did also once again reconfirm that all seems well with floats and float valves.

[bikerphil]

There was a discussion some time back about these bleed holes in the pilot jet. After some testing, the no hole type worked exactly the same as the 6 hole type. You want to stay away from the 8 hole type, as they are for the VM type carbs and have a different type spray nozzle on the end.

[gtem]

Very intriguing, I will definitely be checking what showed up from partshark as OEM Yamaha, I could have sworn they had bleed holes. Now, within the context of how these pilot screws sit in the BS34 carbs, how do they seat, and does it *matter* that they have the bleed holes or not? as I recall the pilot jets that are on these MS carbs in question *DO* have bleed holes, but I will reconfirm. I went down a similar rabbit hole with a set of I think BS32s on a GS650G a few years ago. Presumably the jets seal between the chamfer between the jet tip and the carb body. BS30/96 style pilot jets have the metering orifice down at the tip, does air from the air jet travel past and interact with those bleed holes?

[DEEBS11]

Here is another Chinese kit. No holes.

[DEEBS11]

However, when examining a photo of a cheap Chinese kit....well well well. Lookee here.

[DEEBS11]

Looks like no bleed holes.

[gtem]

One more question for the crowd: is this the *Correct* style of pilot jet for the 1980 BS34s?
Yamaha part number: 4G0-14142-42-A0
Some google image searches show it has having solid walls with no bleed holes along the sides at all, I need to check and see what the ones I bought from partshark for my '78 E (that's running '80 carbs as well) have.

[gtem]

When you cleaned the carbs did you install new float needles. I thought I read that you did. The reason I ask is, and you are probably already aware of this, that the pin in the top on those needles sits on a spring that can allow the pin to compress a bit then expand as the float rides on it. If the are stuck in the compressed position and you set the float heights from there then you are not stopping the fuel flow quick enough and they can flood. Probably nothing but I thought I would mention it. Those choke plungers can't be completely removed and inspected unless you take the rack apart.

Yep I got full sets of float valve seats/needles, OEM Yamaha, with new o-rings for the seats. Floats have been checked and rechecked for proper height and not hanging up. No issues with overflow when tested on the bench, I even checked with low pressure compressed air to confirm that the new float valves don't let a few PSI's worth of air by.