Twisted off pilot screw(ed?)

[2XSive]

As I wait for new carb parts to arrive, I've been doing a bit more research on this issue and the concern now is that when the PO jacked the mixture screws in so hard, he most likely ruined the seats and the result will be that tuning these carbs may be near impossible on the pilot circuit. Carbs are probably toast at this point, but I'll give it a go and report back.

 

[5twins]

It may not have ruined them, it just may take a different setting than recommended on the mix screws if jamming the points of the screws in there enlarged the holes any. It may take less turns out on the screws now to achieve the same level of flow.

 

[xjwmx]

Typical shop air is 100 psi. I'm guessin' the diameter of that tip is about a tenth of an inch... or less?
Lessee..... π x r² gives us about .008" of area.... times 100 psi. So we'll apply less than a pound of force to the pin with shop air. I don't think that's gonna do it.

still 100lbs of pressure on it. imagine the tip of the hose tapers to the size of the piece to blow out and it's plugged up. it'll have all 100lbs trying to blow it out -- it doesn't get harder to blow out the smaller it is, as it approaches impossible... but if the tip is anywhere near 1/10 inch, i'm probably thinking of a different problem anyway...

 

[Jim]

still 100lbs of pressure on it.

No... 100psi is pounds per square inch. That means it exerts 100lbs of pressure on 1 square inch of area. If you're talking only a fraction of the area of that inch, the force exerted is reduce by the same amount. Conversely, you can apply 100psi of pressure to a piston 12" in diameter and lift a 10,000lb truck 5ft in the air to work under it. Happens everyday in garages around the world.
I used to teach this stuff for a living. Look up Blaise Pascal.

 

[xjwmx]

you're saying the smaller the plug in the end of the hose, the harder it is to blow it out, approaching impossible to blow out. that's a misapplication of some kind. you're the expert, so tell me what kind

 

[Jim]

so tell me what kind

Look up Blaise Pascal.

 

[Jim]

so tell me what kind

Tell ya what... since you want me to spoon feed you, make it worth my while...... let's play a game. I'll ask the question, you give the answer. Fair enough? First question:
If 100psi exerts a force of 100lbs on one square inch, how much force does it apply to 2 square inches?

 

[2XSive]

Perhaps another way of thinking about it is that in order to exert the equivalent of 100 psi to the needle, one would theoretically need an airhose that is the exact same diameter of the needle tip and apply it directly to the needle in a way so as not to lose any pressure. Editing this...to end with a question mark "?"

 

[Jim]

Perhaps another way of thinking about it is that in order to exert the equivalent of 100 psi to the needle, one would theoretically need an airhose that is the exact same diameter of the needle tip and apply it directly to the needle in a way so as not to lose any pressure. Editing this...to end with a question mark "?"

That's the intuitive way of thinking about it Larry, but it doesn't actually work that way. Big airplanes have a 3000psi hydraulic system. That would overwhelm the braking system and cause the brakes to immediately lock the wheels when applied. They use a deboost valve to lower that pressure to a more manageable 5 - 800psi. the valve operates exactly like you described.

 

[2XSive]

Ahh, so even though there is 3000 lbs of pressure, the volume is regulated down based on diameter...

 

[Jim]

Ahh, so even though there is 3000 lbs of pressure, the volume is regulated down based on diameter...

Actually, that was a bad analogy. Let me think of another.....

Think of the remnants of the pin as a piston, a very small one. Above I said 100psi on a 12" dia. piston would lift a 10,000lb truck. that's because the area of the piston is 113". 100psi times 113" of area is an applied force of 11,300lbs. If we reduce that piston to say... 6" in dia, it's area is a tad over 28". 100psi times 28" is 2800lbs of applied force. Bring the piston dia. down to about 1-1/4" and we're at 1" of area. Now, 100psi exerts a force of 100lbs. Cut that area in half... .5 square inches.... times 100psi and were only pushing at 50lbs of exerted force. Reduce it down to the size of your broke off screw tip? Prolly less than a lb. of exerted force.

 

[xjwmx]

Tell ya what... since you want me to spoon feed you, make it worth my while...... let's play a game. I'll ask the question, you give the answer. Fair enough? First question:
If 100psi exerts a force of 100lbs on one square inch, how much force does it apply to 2 square inches?

more interesting question. if the wall of the hose is composed of infinitely small points, each with zero psi exerted on it, how can there be any pressure in the hose at all? there is an answer

 

[Jim]

more interesting question. if the wall of the hose is composed of infinitely small points, each with zero psi exerted on it, how can there be any pressure in the hose at all? there is an answer

Yeah well... at least I tried to teach you something. Have a nice day.

 

[xjwmx]

if you're paddling upstream in a canoe and a wheel falls off, how many pancakes fit in a doghouse?

 

[Jim]

if you're paddling upstream in a canoe and a wheel falls off, how many pancakes fit in a doghouse?

That's an easy one.... DFTT.

 

[xjwmx]

how much wood could a woodchuck chuck if a woodchuck could chuck wood?

 

[Rasputin]

Well, finally achieved success! Thanks, all, for the tips. After removing the throttle shafts and seals I then heated the area up good and hot with a heat gun. Was then able to use a push pin and hold it with a pair of pliers, and then used a 1" bar to get good perpendicular leverage. Didn't take much force and the tips popped out. You guys were right....heat is the way to go. I couldn't figure out how cooling these in the refrigerator would help, given what Gary said re the rate of expansion between both metals. Pics attached in the event they help if anyone else runs into this issue. Now, time to order new shaft seals and pilot screws, etc. Will see if I can get this XS1100 running and determine if it's worth restoring. Will post up other pics soon. Thanks again everyone! Love this forum.

I had a similar problem on a CB750F2. Luckily the tip was pushed out with a piece of 3mm brazing rod sharpened to a point and bent in a curve. Good job with the collective input.

 

[gggGary]

Last year at Barber Vintage weekend guy was checking out madness, got into a discussion about decreasing master cylinder bore to increase braking pressure. He claimed he was a "hydraulic engineer". Asked him what products he "engineered" on (so I could avoid them).

 

[ckahleer]

Last year at Barber Vintage weekend guy was checking out madness, got into a discussion about decreasing master cylinder bore to increase braking pressure. He claimed he was a "hydraulic engineer". Asked him what products he "engineered" on (so I could avoid them).

I think he's right. Smaller master, same size slave, will increase force, at the expense of greater lever travel.

 

[gggGary]

I think he's right. Smaller master, same size slave, will increase force, at the expense of greater lever travel.

That was NOT the side he was arguing, .