Butterfly Removal

All,
Does anyone have any tips on removing the small screws holding the brass butterfly in place? A screwdriver won't budge them and I'm afraid of stripping the head with too much force. I have a small easy-out, but I only want to use that as a last resort.

Plan C would be to boil the carbs with the butterfly assemblies in tact. Is there any risk of damaging the gaskets/o-rings inside the butterfly assembly. I'm sure those o-rings are 35 years old, too. If they are cracked now or are damaged during boiling, is there a big risk of air leakage in that area? Those assemblies fit pretty tight.

Thanks for any insight you can provide!

I don't have any tips but I am pretty sure i have read that you shouldn't boil the carbs without removing those.. So just hold off a bit until someone else who knows better chimes in.

I was going to attempt this myself but my carbs are decent enough I deemed it not necessary and plain and simple chickened out. Having been through enough of these scenarios I would suggest soaking them with some PB or WD (which you have likely started with). It is important to make sure you have the exact size and shape bit, and instead of a screwdriver it may be a good idea to use a ratchet with a screwdriver bit... it is easier to keep centered and monitor how much of a turn you are giving it and how much if any the screw is releasing. With some good steady pressure you only want to try for 1/32 - 1/16th of a turn at a time. I have seen from time to time if the screws are in decent shape that a hair of a turn tighter may be enough to free it up. or if you have a punch you can center it on each screw and give it one quick whack with a hammer, not full out but don't go to easy on it either, that may free it up.

If you are trying to save the butterflies you will be in good shape either way even if you extract the screws, if you need the pins then be a little more cautious with the hammer or avoid this route. Those screws are likely in there with some locktight glue as if they were to come loose the damage they cause would be pretty bad. Its nice to save the hardware when you can but in most cases its not worth the battle ...

and we all know we are going to end up at the hardware store eventually anyway. I have made a ton of my own hardware for my bike, cutting bolts to fit and such. I even made my own choke pin mounting bolts. I feel for ya though as I would guess these butterfly mounting screws are likely a PITA to get out, and just as hard to find quick replacements.

Still would be good to hear someone chime in who has successfully removed these.

oh yah forgot to add, its never a good idea to boil any rubbers or O-rings with the carb. Always disassemble and set aside plastic and rubber parts from the carb. Those can be cleaned on the side with soap and warm or hot water.

On my carbs they were clean enough they didn't require them to be removed,howevere on other carbs I have removed them also strip the heads of the screws and broke the heads off.I don't think they are meant to be removed.Im in agreement with the rest of the posy about boiling your carbs making sure you remove any rubber or plastic pieces.I would just boil them with the butterflies in place.Your carbs will be clean enough with them left in place.

Thanks, all!

I'm sure they will be plenty clean if I boil them as is, I'm just concerned about the rubbers and air leakage if they degrade in there. I'm sure that gasket is there for a reason... I hate to put all the time into cleaning them if I ruin or damage something in the process. It sucks that the butterfly fits in the slot and the screws pass through it. The screws HAVE to come all the way out to disassemble it.

I'll take another crack at it with a ratchet and bit. If that's unsuccessful, I'll just boil them as is and hope the seals and fit are tight enough that I can compensate with the mixture screws if it's not air-tight. Although the more I think about it, the seal the butterfly makes with the carb body itself isn't perfect.

Thanks, again. I'll let you know how it turns out.

Your butterfly valve don't seal because the bike needs them to be open a bit in order to idle Like tim said use a well fit bit and go slow. I have removed dozens of these and only had one or two strip (only because of rust)

The screws won't just come out that easy; i'm pretty sure the backside is pressed and knurled so they don't come out (look from the other side of the carbs through them). I'm not sure how to remove them, but you can't just unscrew them.

I boiled my carbs with the butterflys in and they weren't damaged as far as I can tell. Generally I just stick with carb cleaner and compressed air to clear the passages out.

Look at the other end of those screws: They are staked, i.e. crushed or stamped. I would think that the only way to remove them would be to grind off the tips; but XSchris says he's unscrewed them successfully. When I cleaned my carbs for the first time last week, I scrubbed them in the kitchen sink with Simple Green, a toothbrush, Scotchbrite pads, and lots of hot water rinses. Then I shot carb cleaner through the various tiny passages. I'm happy with the result.

Boiling and solvents will damage the seals on the ends of the butterfly shaft, leading to air leaks.

Well, I chickened out. After I inspected the back of the screws I couldn't determine if they were staked, so I set out to do a through passage cleaning with carb cleaner (taking care around the butterfly o-rings). I picked up these carbs as a second set and I'm guessing it's been a long time since they've seen gas. The carb cleaner just melted the varnish like I've never experienced and everything is shining up very nicely. The varnish from current/modern gas seems to be much more stubborn than this stuff. Anyway, a couple more days of stealing away to the shop for an hour or two should have everything clean and ready for installation as soon as the mercury rises above the -16 F we're stuck in today.

I've removed my butterfly valves too. I just used a smaller driver and a bunch of penetrating oil. I slid a crescent wrench on the end of the driver for torque, then pressed down with my body weight...carefully. Worse case, get a smaller impact driver (the kind you tap/hit with a hammer) and gently tap them until they're free.

I never removed mine. If you don't boil the carbs and are not too aggressive with solvents, you can get the carbs clean without taking the butterfly shaft out. Well, for me it worked at least

These Suzuki part numbers are the cheapest of the 4 UJM's that will work to rebuild the BS34 throttle shaft after butterfly screw and shaft seal removal. They have a nice fit to the butterfly shaft as well as the body of the carb. McMaster Carr does not carry the correct screw for the butterfly shaft rebuild. It is close but not correct.

13604-44080, SCREW

13651-51010, SEAL

esmith87 said:

These Suzuki part numbers are the cheapest of the 4 UJM's that will work to rebuild the BS34 throttle shaft after butterfly screw and shaft seal removal. They have a nice fit to the butterfly shaft as well as the body of the carb. McMaster Carr does not carry the correct screw for the butterfly shaft rebuild. It is close but not correct.

13604-44080, SCREW

13651-51010, SEAL

Click to expand...

So what I hear you saying is that the part numbers above will work to replace damaged butterfly screws in our XS?

I have removed these from quite a few sets now with no issues, as mentioned use a tight fitting phillips head bit, also using a small T wrench is a good idea so you can put a bit of downwards pressure on them so the bit does not slip as you undo them. They really do have to come out for best cleaning results. I have found removing the actual butterflys and reinstalling them is the trickiest part, without scratching them up as they can be quite tight.