'80 XS1100 MS leaking float valves(?)

[gtem]

Hi all,

For once, this isn't about my '78E with the '80 carbs. No, I'm helping out a friend who bought himself a somewhat shabby '80 Midnight Special, with all the usual things going on (gunky carbs, dragging brakes, ancient tires, etc). Anyways, as a favor, I volunteered to at least go through the carbs for him for just the cost of parts. Thankfully looks like all stock parts inside. Upon reassembly, I set the float heights to 23mm, all the usual precautions etc. Initially, I didn't mess with the floats/valves at all, as the tip on one of the float "towers" on carb #2 was broken and miraculously the pin was still held in place and I'm a fan of "do no harm." Well, an initial leakdown test on the bench showed the not-unexpected wetness at the air jets from the bowls overfilling. So I then proceeded to take the float valves out, and replaced with NOS Yamaha parts. Thankfully that carb #2 pin still functions and the float sits correctly. Once reassembled, I rechecked float heights, and as a precaution, even set them at 24mm (ie lower fuel level in the bowls).

Frustratingly, I'm *still* seeing a bit of wetness in the smaller of the two air jets (the pressed in one). Mind you, no actual leaks. This isn't correct, right? I shouldn't see *any* signs of any fuel in any of the air jets. These are the viton-tipped style of float valve needles (and that's what was in there originally too). Could NOS rubber have gotten oxidized? They look and feel fine, then again so did the ones that I took out. And I was hoping that sitting in gas would "bring them back."

What I haven't done yet is to check the "wet" float level ie with a piece of tubing coming off the bowl drain... any handy tips for how to make an adapter for that? What I can see for sure is that the float gaskets are getting wet with fuel so the fuel level is at least at the gasket level, a clue that fuel level is for sure at least at gasket level, ie higher than the float level *should* allow. Thanks for the help as always!

[DEEBS11]

I want to make a comment concerning your issue that may or may not be a factor. I have been having many issues with counterfeit OEM parts. Sometime the parts are pictured with an OEM parts tag filmed next to them and what you actually receive is a Chinese crap part packed in a clear zip lock bag with no OEM tag. Classic bait and switch to fool you into buying a cheap, low quality Chinese part that will make your bike run like sh*t.

To all: If and when this happens, you will certainly have strange issues similar to what gtem is having. As I have stated before, the bike will run, but not correctly. There are literally millions of these sub-standard parts being sold to us and installed in all sorts of our infrastructure systems. It is something to be aware of, especially if you are doing a repair with new parts and are have issues. The lure here as always is low prices/maximum profit for vendors out to make an easy buck.

That being said, gtem, was your fuel weep only on the #2 carb? if so, you already know what the issue is. Imagine when you add the heat and vibration of a running motor to the situation. That broken tower is a red flag. However, if you having issues across all carbs I would say you possibly have defective parts or a hung up float(s) touching a bowl gasket. I believe you have non-brass floats so there is no chance of a breech in one of your units.

[gtem]

No these were definitely OEM packaged as far as I could tell and visually identical to the OEM parts I took out, unless the fakes have gotten that good! I'm seeing the tiny bit of wetness when I shine a light down the air jets evenly across all 4 carbs, and this was the same as it was before I replaced the valves. Again, it is very minor, not enough to actually leak fuel out of these air jets. But the fact that the gaskets are seeing fuel certainly implies the fuel level is higher than it should be.

[DEEBS11]

New gasket too?

[DEEBS11]

You can also check your fuel level like this:

[gtem]

My '80 carbs have the press in style float seats but yes I put new viton o-rings in. I'd love to do that level check from the float drain, where did you get that handy fitting for the drain screw?

[DEEBS11]

eBay.

https://www.ebay.com/itm/27488126072...AAAOSwOA5g~xxQ

[Ranger_xs1100]

I'd love to do that level check from the float drain, where did you get that handy fitting for the drain screw?

As an alternative to purchasing drain plug fittings, I bought clear tubing at home depot that was about the same size OD as the drain plug threads (maybe just slightly bigger. You can then thread the clear tubing directly into the carb bowl’s drain plug opening. I like to do all four carbs at once, with four pieces of tubing. The soft tubing becomes self threading as the threads cut into the plastic.. I’ve done this several times, but only with the carbs off of the bike and filled with water rather than gasoline, in case of a leak. It worked well for me.

[LAB3]

You can also check your fuel level like this:

I've had one of those for every carb I've worked on over the years, a very affordable and invaluable tool.

Water and gasoline have different densities, it would make sense to me that the this would affect the float level.

[bikerphil]

As for the slow leak, my guess is dried crud where the seat O ring sits down in the tunnel. It often gets overlooked and hard to see down in there on the sides.

[Ranger_xs1100]

I've had one of those for every carb I've worked on over the years, a very affordable and invaluable tool.

Water and gasoline have different densities, it would make sense to me that the this would affect the float level.

Lab3, Thank you. You make a good point. And now that I am thinking about it, I did use gasoline to check the float levels.
At other times, I have used water when I was checking to see if the float valves were shutting off and not leaking. I was more cautious with the leaking valve issue.
It would be an interesting experiment to find out if there is a measurable difference in float levels between the two liquids.

[LAB3]

Lab3, Thank you. You make a good point. And now that I am thinking about it, I did use gasoline to check the float levels.
At other times, I have used water when I was checking to see if the float valves were shutting off and not leaking. I was more cautious with the leaking valve issue.
It would be an interesting experiment to find out if there is a measurable difference in float levels between the two liquids.

The easiest way to test that would be to do exactly as you mentioned, otherwise it could be done mathematically.

Water weighs eight pounds per gallon and gasoline is about six and a half pounds per gallon so a float placed in water would sit significantly higher than it would in gasoline.

[gtem]

As for the slow leak, my guess is dried crud where the seat O ring sits down in the tunnel. It often gets overlooked and hard to see down in there on the sides.

I did a pretty darn thorough job cleaning those out before popping in the new seats with new o-rings, but that's definitely a good thought! I might recheck the make sure the o rings didn't get damaged while being pressed in there.

[DiverRay]

A thin coat of dielectric or silicone grease will help the O-rings go in without binding. The grease will NOT harm the rubber material of the O-ring.

[gtem]

On DiverRay's recommendation, I pulled a few of the float seats out and recleaned the bores a bit (they were fine), confirmed my new o-rings didn't get damaged getting inserted the first go-around, then applied some dilectric grease and pressed them back in. They definitely go in a lot smoother this way. I refilled with gas, I'm still seeing my usual bit of wetness around the pilot air jet, could it be that this is just normal capillary action or something? To clarify, I've not had any actual fuel leaks from the carbs, I can just see a glimmer of fuel down the pilot air jet. I've done plenty of sets of Mikunis before (around 7 in the last two years), I've just never scrutinized these air jets to this degree. In the past with sticky/dirty float valves I'd see actual leakage.