Replace Throttle Shaft Seals. Can See Light in Butterfly Valves

I replaced my throttle shaft seals (following the ideas found in the comments found in this long thread). I used a small dremmel HHS cutter to remove the back of the threads on the two screws and then used a Philips head screwdriver. These screws came out flawlessly.

I'm concerned that when I removes the butterfly valves themselves, that I didn't take them out gently enough and messed something up. I did not do anything crazy to remove them (no pliers or anything). It just took a little bit of encouragement with my fingers rather than them just sliding/slipping out on their own. Did I damage them by doing this?

I ask because when I put them back in (after replacing the shaft seals), and doing to re-centering pull and release of the throttle, I can still see the smallest bit of light when holding them up to the light. It is a very small amount e.g. can only see it when held up to the light and rotating the carb body and at certain angles...
When I look at the other side carb, which I haven't taken apart yet, I can't see any light. So I'm concerned that I may have messed things up on this one? Is the smallest bit of light OK? The light can be seen in the bottom left side of the valve/body. You can't see light anywhere else on the top etc. As mentioned, only at certain angles. There is no binding in them.

Did I mess them up? If so, what did I mess up the valve themselves or the carb body? Is there a fix (new valves? - I didn't see any online with a quick search). Does it matter? Because when it is all assembled, there will be a small gap because of the idle adjustment and sync adjustment screw will have them open the slightest amount anyway.


thanks!

What you describe, IMHO, is completely normal. BS38s, right? Ideally, after you do the other side, the light pattern will be the same.

I can't believe I forgot to write which carb model!
These are bs34's



I am curious what will happen on the other side but didn't want to finish up the first carb before I was sure I did it correctly.

Typically way more light will shine through BS38s, which is why I made my assumption, but I otherwise stand by my first post. The light that you see can really be different from one side to the other on BS38s, but on BS34s any difference will be minimal and can easily be tuned out using the sync screw.

I think they'll be fine. When doing the alignment thing, do open and snap them shut several times to insure they have centered themselves. As you said, when you set the idle and sync them, you will end up with a slight gap anyway.

I'm sure you're aware of not aggressively cleaning the butterfly plates when they're out, especially at their edges. I just gently hand polish the fronts and backs with a little Mothers or Blue Magic and a rag.

When pulling the plates out and putting them back in, they have to be aligned as they will be installed (with the screw holes) or they'll bind. They're not perfectly round.

Something I found useful that I don't remember being covered in the threads. When you snap them to center the plates, the screws holding the plates should be not loose. They should be a bit snug but not final tightness. Because if you don't , after the snapping centers them, they will just fall off center again.

They have to be loose enough that the snapping can move them, but tight enough that they will stay the way that snapping moved them. After you're satisfied you can tighten them a bit more and snap and check again, and so on. Finally, when they're close to final tightness, take one screw out at a time, give it blue locktite and give that screw its final tightness. Continuing to snap and check it all the while...

What are you doing about the fuel T? A replacement from somewhere? The bracket that holds the two carbs together should be final tightness before you finish the plates. I actually squeezed that area of the carbs together with my knees while I tightened the four bolts there.

thanks. This makes me feel better.

I don't remember how the gap looked when the bike is running properly. How big is this gap, a couple millimeters? So the butterfly valve is never truly closed when set up correctly, right?

xjwmx
Yes, I had then tight enough so that they wouldn't fall out of place after snapping the throttle. I did this many times and continue to get the same result - the ever-so slightlest bit of light in the bottom left corner when holding the carb up to light and rotating around a bit. I've been kneading my blue locktite for an hour now making sure I'm ready

For the fuel T fitting... I've read about this being a problem on the forum but I have not had any trouble. I had these carbs apart before (before when I cleaned them up and tried to get away with not changing the throttle seals) and put them back together. I did not have a leaking issue at the fuel T fitting. Is this the big concern of people, fuel leaks?

rjz1 said:

I don't remember how the gap looked when the bike is running properly. How big is this gap, a couple millimeters? So the butterfly valve is never truly closed when set up correctly, right?

Click to expand...

The idle adjustment screw will hold them both open quite a bit.

You have to put some pressure on the "T" when assembling the carbs so it's tight and won't rotate easily by hand. Being pushed into both carbs tight is what seals it. The stock "T" is coated with rubber which also helps it seal. If that rubber has deteriorated or come off then yes, guys do have issues with them sealing. I use a pipe clamp on the carbs, making it just tight enough so the "T" won't rotate before I tighten the angle bracket screws fully. The top butterfly shaped plate needs to be in place too .....



When the idle is set, the gap will be small, maybe 1mm. Yes, the butterflies aren't closed completely once the idle is set. That's what controls and sets the idle speed, the plates being open. Having them matched and open exactly the same amounts is what the sync is all about.

Only a couple days old, but a T that was flopping loose before dis-assembly got swabbed with pure wintergreen oil a couple times and a bit more flowed in the gap after the now snug fitting T was installed in the carb bodies, no fuel leaks at all. FWIW I don't press the bodies against the ends of the T when I assemble, they seal just fine, shrug.
Really fuel swells the rubber once the gas is on, but it's nice to start dry and not have to wait for the leak to stop.

Wintergreen oil?!? Is that the new wd-40?

5twins. Nice idea with the clamp. I don't have a pipe clamp but think I can use my large welding clamp to do the same.

thank you all. I'll have it back together just in time for some... snow...

You don't need or have to clamp it really hard, just enough to get the "T" fitting tight. I like it so it will just barely rotate if pushed on really hard. That pipe clamp came from HF I think. You just need a length of pipe threaded on one end to put it on. I happened to have that short length and it turned out to be perfect for clamping carb sets.

My tee was loose as well when i put my 34's back together. tried putting pressure on the carb bodies so the tee bedded in, but the holes wouldn't align when i tried to put the bottom bracket on........

Tee was loose so i got fuel resistant o'rings and cut a groove between the 2 humps on the end of the tee and sat the rings in...........worked good...........then gggGary come up with the evergreen to swell the dried out rubber on the tee

When you squeeze the carbs together, you have to have the brackets that hold them together loosely mounted or they will press in too far. Then the bracket holes won't line up.

I did that as well......then the tee was loose because it wasn't pressed up hard in the hole and i had lateral play in the tee.

there's a riff on wintergreen oil in mailmans resto thread. Been using it on rubber parts in my recent carb overhauls, got a really stiff diaphragm with a couple ratty sets of carbs that came in today. Going to try wintergreen on that...........

Some info on early BS38 throttle plate gaps in my album.
Start at this pic, then progress backwards for another 4 pics.

http://www.xs650.com/media/71xs1b-b...d-wider-than-38mm-by-about-0-005.23256/#media