Carburetors hanging open

[Mailman]

I mentioned this in my long running thread " My 60th birthday present" but I know not everyone reads it and I am looking for some input.
Yesterday I had my BS38 carburetors off and apart for cleaning and to fix an intake leak, the leak was making my idle erratic and I thought it was making my throttle hang up
So everything cleaned and re assembled, back on the bike and fired it up. Intake leak was gone , the bike started easily and idled well, and runs good. Then this morning I took it out for a little test ride and before I got far at all the throttle started hanging open, making the motor race.
When I got home I disconnected the throttle cable and worked the throttle manually and it doesn't snap shut like it should, it hangs open and you have to wiggle the throttle shaft to get it to close.
I will probably pull the carburetors off next weekend and take a look, but not sure what could be binding.
When I pulled the carburetors apart, I didn't touch the throttle shafts or butterfly's.
But could it be maybe the butterfly's dragging on the carburetor body? I can't think what else might cause the linkage to hang open.
A little background.
This just started happening PRIOR to tearing down the carbs, it has worked perfectly before.
I have a Pamco E ignition and the electronic advancer.
The throttle cable is new and routed exactly the way the manual shows to route it.

 

[Mailman]

One more detail, the inside of the left carburetor has a spot where the butterfly has worn into the body. But this has not caused any issues before.

By the way these are old photos taken prior to rebuilding.

 

[TimeMachine]

Dang Mailman, OK lets assume it is the carbureators at fault ? And that the slight wear damage next to the butterfly valve is not the reason. I am suggesting you loosen slightly the top butterfly shaped bridge up top. Slightly loosen the 90° angle brace. And attempt to let the carb bodies "float" into alignment. Though this was easy to accomplish with my carbs in hand, clean, and on the bench. Being very particular actually , ya Im not just a simple lucky one, I am quite certain by "floating" my own carbs into alignment while moving what components I could. IE: choke shafts, butterfly shafts, and linkages. Tightening fasteners as I went. My BS38's found a very "true" alignment and work well ! I hope this isn't just another "rat hole" I really don't want to lead you on. Hang in there Mailman. Oh and I can't see that Arizona heat helping you either... Good Luck -RT

 

[Mailman]

Yeah, my hunch is that I'm not going to see something and go AHA! But rather more like what you just described.
The way it feels is just like that. Like something is binding and once that pressure has been removed , all will be well.
I'll know more once I get them on the bench and can get a good look at how everything operates.

 

[robinc]

Hey Bob, just posted this in your " My 60th birthday present" thread.

Couple thoughts:

I had a similar problem on my 77D with the 74/75 BS38's that it came with. If I over tightened the carb mount clamps the butterflies would bind and not fully return. I could over tighten to the point that they were hard to even move. Always took a little fiddling to find the 'right amount of tight'. Try backing them off a bit.

Also, I seem to recall that you replaced throttle shaft seals. Maybe you didn't get the butterflies properly installed in the throttle shafts and properly centered in the carb body? See if that's what's binding.

Good luck going back in buddy!

Edit: And Bob, everybody reads that thread.

 

[Mailman]

Hey Bob, just posted this in your " My 60th birthday present" thread.
Edit: And Bob, everybody reads that thread.

Hahaha! I sometimes imagine someone new to this forum stumbling across that thing and going My God! That's longer than War and Peace!
I never imagined it would grow so long, and it's a shame that a lot of good stuff has been covered in there but you have to read so much to find it. I am planning to edit the very first post to include an index that has post numbers for some of the project repairs such as charging systems, Pamco install, steering head bearings and such. Some hot day when I'm sitting in the house, bored. Haha

 

[TimeMachine]

A+ on effort ! You've contributed to the world over ! Lol

 

[mrtwowheel]

I've worked out butterfly drags on four bank carbs before, there are procedures available, but in the end it is still "hit and miss" with a lot of tries, but possible. And, those little screws can loosen up and destroy a cylinder.

I feel for you, good luck.

Scott

 

[robinc]

And, those little screws can loosen up and destroy a cylinder.

Hey Scott, any suggestions on how to stake those throttle shaft screws?

Replacing with stainless allens seems to be the popular fix, but how to stake them?
gggGary suggests to use blue Locktite when installing them, and I know 2M suggested 'bombsight' drilling and then using a spring loaded center punch to stake. My drill press quill/spindle are too worn and aren't accurate enough for those small screws. I tried using a pair of pliers on the end of a sacrificial stainless screw and it just shattered.

Any suggestions as to how this can be done?

Thanks.

 

[mrtwowheel]

Hey Scott, any suggestions on how to stake those throttle shaft screws?

Thanks.

Like Gary said, Locktite. Staking might bend the shafts, never done the staking. Heard stories of pros rebuilding carbs and screws coming out and entering the engine. If I did one tomorrow, it would probably be stainless allens and big gobs of Locktite.

Scott

 

[robinc]

Ok, thanks for the reply. That's what I have done but wondered if staking as well was important.

I appreciate the confirmation.

Take care.

 

[weekendrider]

To "stake" all you really need to do is deform the threads. A pair of sidecutters/nippers could do this. I apply a little blue locktite to the flare of the screw head, open the throttle shafts and from the intake side hit it a couple of times right at the shaft/thread junction with a spring loaded punch. Does it go without saying the slides need to be removed for this?

 

[TwoManyXS1Bs]

Ditto on the blue loctite on the throttle plate screws.

Having a throttle plate rubbing on the throttle bore, as you show above, is a definite sign. On my '71 carbs, after getting the butterfly plate fully closed and aligned in its bore, I'll shuttle the throttle shaft left/right a couple times, final shuttle to the outside (return spring side), and hold a little pressure on the shaft end keeping it shoved outward, while tightening the plate screws. The return spring applies a little outward pull on the shaft, the shaft stopped by the staked washer on its opposite end, so the butterflys need to be centered for this shaft position. Dun't know how this would apply to yer carbs...?

 

[Mailman]

When I first rebuilt my carbs I actually spent a pretty fair amount of time trying to carefully center and seat the butterflies. I did notice the other day when I had them off that I could see a little daylight around the bottom of one.
The more I think about it, they seem like the most likely culprit. I will take more time with them when I have them apart again. I was in too big of a rush to get them back together because my free time is scarce lately.
I need to apply the old carpenters adage
" Measure twice, cut once."

 

[robinc]

Or like the confused carpenter says, "I cut it three times and it's still to short"

 

[5twins]

You should see a little light at the bottom of the plate, that's normal. That's your idle setting. You don't want to see it on the sides, that shows the plates aren't centered. When I center the plates, I do so only after the return springs and other linkage bits have been installed on the ends of the shafts. That way, the shafts are experiencing that pull towards the springs when I do the centering. So far, I've had no problems with any.

I think TM may have it figured. The carbs aren't quite mounted right in the brackets that tie them together and that's causing something to bind.

 

[mrtwowheel]

You should see a little light at the bottom of the plate, that's normal. That's your idle setting. You don't want to see it on the sides, that shows the plates aren't centered. When I center the plates, I do so only after the return springs and other linkage bits have been installed on the ends of the shafts. That way, the shafts are experiencing that pull towards the springs when I do the centering. So far, I've had no problems with any.

I think TM may have it figured. The carbs aren't quite mounted right in the brackets that tie them together and that's causing something to bind.

Yeah, all of that. Springs and linkage all together before positioning the butterflies. I use the top of my table saw to get the carbs in position to each other while tightening the bracket that holds them together, never got it all right on the first try.

Scott

 

[Bob Kelly III]

Or like the confused carpenter says, "I cut it three times and it's still to short"

robinc: did you know that little joke was from an actual situation on building the observatory at the top of the mountain in Hawaii ?
the workers building the buildings up there had to work for short times then go back down because of Oxygen deprivation.
one of the scientists in charge was talking to one of the workers and he was all upset..and the scientist asked him what the problem was...
and he responded with " I cut that board 3 times and it's still too short" the scientist looked at him and said time for you to go down the mountain ! ......NOW ! LOL ( they had had a few collapses on the job by then and his job was to make sure the workers didn't stay up there too long...)
Just so you know... if you didn't already.... it's become one of my favorite funnies of all time !
I can't even imagine the look on the scientists face.... there's no doubt about that one !!!!!!!
LOL
.....
Bob.....