'80 XS1100 MS leaking float valves(?)

[gtem]

All testing on the bike so far was done just with some roughly 6" fuel lines attached to the two fuel "T" and the bowls filled. So I'm excluding any sort of petcock factors, plan is to delete the OCTY all together in favor of a pair of manual petcocks. I did drain VERY fuel-diluted oil from the engine when I first got the bike (refilled with rotella 15W-40) , I'm glad I checked before running it for more than a few seconds. I've heard of gas-diluted oil actually affecting jetting before.

The MS luckily came to me with a pretty fresh set of carb boots. I haven't done any checking for vacuum leaks, as I assume that would cause problems in the form of a lean condition, not this current super rich scenario.

I'm going to look for that hole vs no hole discussion, per Phil in this thread, his conclusion from the same thread(?) was that it didn't matter, but if it does, that would be very useful info indeed!

[DEEBS11]

Good tip vs. bad tip (ignore the side holes).

[DEEBS11]

Correct pilot jet specs.

[gtem]

Thanks Deebs. Yep I learned a while ago on my XS500 about those VM style pilot jets where the metering orifice is down at the thread end of the jets, totally wrong for the BS carbs! All of mine both hole and no-hole have the metering hole at the tapered end.

[cajun31]

I think I found a logical explanation for the pilots with or without the side bleed holes. On the xs650 forum there was a discussion about whether the pilot shared with the main and had rubber plugs. If they did then the bleed holes are required because that is where the air gets in versus not plugged where the air is coming in from the top. So if that is the case then the non holed pilots should be no different in operation in the later carbs from those with holes in them. The only other things I have found related to the venturi effect of atomizing the fuel and some seem the think that those holes help with that process.

[jetmechmarty]

I think I found a logical explanation for the pilots with or without the side bleed holes. On the xs650 forum there was a discussion about whether the pilot shared with the main and had rubber plugs. If they did then the bleed holes are required because that is where the air gets in versus not plugged where the air is coming in from the top. So if that is the case then the non holed pilots should be no different in operation in the later carbs from those with holes in them. The only other things I have found related to the venturi effect of atomizing the fuel and some seem the think that those holes help with that process.

FWIW, I have several BS34 XS650's. They all use the rubber plug over the pilot jet. All have the six holes. My XS1100 does not employ the rubber plugs and all the pilot jets have six holes. My XS11 has a K&N in the air box and the exhaust is a four into one Jardine. My jetting is stock. It's stock not because I'm lazy and left it. It's stock because that's what I came to. It operates better than fine and has over 100,000 miles on it.

[cajun31]

FWIW, I have several BS34 XS650's. They all use the rubber plug over the pilot jet. All have the six holes. My XS1100 does not employ the rubber plugs and all the pilot jets have six holes. My XS11 has a K&N in the air box and the exhaust is a four into one Jardine. My jetting is stock. It's stock not because I'm lazy and left it. It's stock because that's what I came to. It operates better than fine and has over 100,000 miles on it.

Couldn't agree more Marty. I have learned over the years to not stray too far from the way those Japanese engineers built these machines. With few exceptions mine are all stock with OEM parts. The only things I changed were, like you, the K&N air filter and I also have installed Vmax cam chain tensioners on all of mine. Nothing wrong with the original tensioner, just don't put a lot of miles on any of my bikes so thought that change would be more convenient for me in the long run not having to worry about remembering to adjust them. I always advise everyone to leave things stock until you get things running right. Causes a lot less confusion that way.

[gtem]

A final update on the Midnight Special: I replaced all of the o-rings on the idle mixture screws and replaced one of the screw assemblies entirely, the spring and washer were completely rusted out underneath the screw. With all of the float heights rechecked and various leakdown and pressure tests on the (new) float valves done, I put it all together and got it on the bike. It runs and rides beautifully! I made some minor tweaks to the idle mixture screws to dial them in a bit better, the bike starts up, idles, pulls hard through all the gears, etc.

The bike happens to have the "updated" "no hole" #42.5 pilots, and new OEM 110 mains installed (came to me with 117s). So it's all stock, stock exhaust, and runs like it.

Thanks all for all of the advice, wow I really got a second education on these Mikuni BS carbs between this Midnight Special and my '78 E.

[cajun31]

A final update on the Midnight Special: I replaced all of the o-rings on the idle mixture screws and replaced one of the screw assemblies entirely, the spring and washer were completely rusted out underneath the screw. With all of the float heights rechecked and various leakdown and pressure tests on the (new) float valves done, I put it all together and got it on the bike. It runs and rides beautifully! I made some minor tweaks to the idle mixture screws to dial them in a bit better, the bike starts up, idles, pulls hard through all the gears, etc.

The bike happens to have the "updated" "no hole" #42.5 pilots, and new OEM 110 mains installed (came to me with 117s). So it's all stock, stock exhaust, and runs like it.

Thanks all for all of the advice, wow I really got a second education on these Mikuni BS carbs between this Midnight Special and my '78 E.

I guess because all I own are my three MNS's setting everything up stock has always served me well and is why I always advise folks to get things back to oem and work from there as the address modifications. Glad to hear the bike is running well.

[gtem]

I guess because all I own are my three MNS's setting everything up stock has always served me well and is why I always advise folks to get things back to oem and work from there as the address modifications. Glad to hear the bike is running well.

Yup, it's the most sure way to get things right. Unfortunately on the '78 I don't have that luxury, with the 4-1 exhaust and '80 carbs that it came to me with. But as I posted in my other thread, I'd say I see the light at the end of the tunnel on that other one as well.