Diaphragm pinholes concept

[Peder_y2k]

So I post a question about a throttle response issue, and the concept of pinholes in the carb diaphragms come up...again....as in numerous articles posted on this forum.

 

I just don't get it. Someone enlighten me, please. BTW, I have a degree in mech engineering, so I'm not ignorant.

 

The factory manual clearly states on examining the diaphragm for issues, to look for rips and tears, No mention of holes or pinholes at all.

 

So in examining the piston valve (slide), there is a large designed in hole in the piston itself that passes vacuum through to the other side of the diaphragm. Duh? So what difference do a few pinholes make? Should be negligible. The built in hole is so large as to be some 20-30 times the size of a pinhole or 3.

 

The engineers at Yamaha would mention 'holes', or 'pinholes' in the diaphragm if it were an issue, but they don't.

 

I can understand the rips and tears as these can easily be much larger than the built in hole, but the pinholes concept seems vacuous at best.

 

I'm wondering if the pinholes concept isn't someone's invention.

 

Attached is an image of the manual section describing the diaphragm inspection, and a diagram of the piston (slide) with the hole designated with a red line.

 

-Pete, in Tacoma WA USA

[cowpuc]

You pose a very good question there Pete.. While not being an engineer of any sorts and probably not the best person to even voice an opinion on the subject I will,, just cause I dont mind being wrong and I LOVE to in these discussions and learn:cool10:

I theorize that the hole in the slide works in unison with the vacuum being pulled on the rear of the diaphrams and serves as a venting device to allow them to move, maybe the area where the diaphrams are located form there own vacuum area in response to the intake vacuum environment they are sitting in and they have to have this venting action in order to operate.. Any holes, pinholes included, in the surface of the rubber diaphrams will interupt this delecate balance and cause issues.. It seems like it woudnt take much of a hole for vacuum to be lost and the diaphrams to, at least lose quick response to vacuum change...

 

There,, I contributed,, I hope someone much more intelligent than I responds to this one

[GeorgeS]

The material the diaphrams are made off, is Very Thin. Over the years many of us have found the material Torn, or Ripped, and also many small holes develop in the material.

 

It happens !! Whatever the reason for it. Mainly on the old 1st Gen Bikes.

I am not sure about the 2nd gen carbs, they are different carbs.

 

If you have an " Old Venture " Check the diaphram covers for the " tamper proof " screw, ( one of 4 ) If its still installed, then the cover most likley has never been removed. And the Original diaphrams, are still installed.

 

Bottom line, is , The material fails !! thats just the way it is !!

Irregardless of any Engineering Practice's !!!

 

IF, you have bad diaphrams, you can tune and adjust till the cow's come home, and you " Ain't " going to get it running correctly .

 

:whistling:

[Prairiehammer]

At first glance, the hole in the slide seems counter intuitive. Especially if you think the sole vacuum source is outboard of the diaphragm. However, if you consider the primary vacuum source is the venturi, then the hole in the slide becomes obvious. When there is high velocity through the carb throat, a vacuum is forming outboard of the diaphragm due to the low pressure at the throat, causing the slide to move outboard, lifting the needle. If the diaphragm is leaking, whether due to pinholes (less detriment, but still a detriment to pulling a vacuum) or tears ( a larger vacuum leak, thus more detrimental) then the vacuum pulled by the low pressure in the throat, through the vacuum port in the slide is reduced and the slide does not lift as much because the weak vacuum cannot overcome the spring.

The key point is where the vacuum to lift the slide is originating. It is originating from the venturi.

 

http://www.chinesescooterreference.com/manual_images/CV_Carb_Diagram.gif

[cowpuc]

Oh,, by the way Pete,, after trying many many things to get more life out of my Venture Diaphrams thru the years I finally discovered a product that works FANTASTIC for resurfacing that rubber.. Yamabond #5 seems to be doing the trick.. Its pretty neat stuff to work with, totally a different critter!! I have one diaphram on Tweeks right now that I patched up with the stuff and its still going strong after 40k of usage.. Dont know why it works or whats in it BUT it does seem to work well...

I honestly think that a tube of Yamabond #5 and an old diaphram to be used for patching material in case of an actual on the road tear wouldnt be a bad addition to anyones maintenance department on their bike, if you ever have a diaphram self destruct during a trip you will be GLAD you have this - had a buddy that had it happen and it cost him 4 days of riding while waiting for a shop to get his parts.. The Yamabond can also be used for MANY other purposes as it is rubber,, after it dries,,, I think...

[Huggy]

I agree with GeorgeS and puc. The pinholes will change the dynamics of the slide. the main hole is engineered to allow the slides to operate at there optimum ability. Any additional holes offset this and the result is the slides can no longer work in unison. The ones with pinholes will never be in sync with the ones that do not have pinholes.

[Flyinfool]

All of that, the hole on the slide is a calibrated leak. any holes in the diaphragm are letting in more outside air than the system was designed for.

 

AND, the pinholes are probably the beginning of a tear. If you have pinholes, the diaphragm is going to be junk soon anyhow. While you have it apart anyhow is always a good time to fix it right.

[Peder_y2k]

OK.......... If the system is so sensitive (presuming that it is very sensitive) to vacuum, then there ought to be serious driveability issues with altitude change, but there aren't. It is a known fact that 3000ft. elevation change from sea level will make a 10% reduction of vacuum............that's significant, yet the bikes can tolerate 10,000 ft mountain passes easily enough with only a slight loss of power due to less oxygen.

I'm suggesting the system is not that sensitive to be affected by a few pinholes in the diaphragms

So, please convince me otherwise..........or am I missing something here.

-Pete, in Tacoma WA USA

[EasyRider]

So have we examined the diaphragms and determined no pinholes? If so next thought on issue?? However if only fixing or replacing the diaphragms has fixed the issue then the issue is purely belief. Because I don't understand something does not mean it doesn't work. I'm still working on a square wheel.

[cowpuc]

OK.......... If the system is so sensitive (presuming that it is very sensitive) to vacuum, then there ought to be serious driveability issues with altitude change, but there aren't. It is a known fact that 3000ft. elevation change from sea level will make a 10% reduction of vacuum............that's significant, yet the bikes can tolerate 10,000 ft mountain passes easily enough with only a slight loss of power due to less oxygen.

I'm suggesting the system is not that sensitive to be affected by a few pinholes in the diaphragms

So, please convince me otherwise..........or am I missing something here.

-Pete, in Tacoma WA USA

 

You might not be off base in your thoughts Pete.. One of us should pick up a set of pin hole infested diaphrams, stick em in our bike and make a video of how they compare to good ones, on a set of vac gauges at a variety of R's and in performance..

I still think that the area inside the diaphram housing is forming its OWN vacuum, or, as mentioned earlier, is being formed by Venturi action,, either way, if this were true ambient pressures would have little affect on the diaphram vacuums and that any vacuum loss across the face of the diaphram is gonna cause issues of some sort.. It may not be as critical as an actual tear or separation but it seems like it wouldnt help in making an effecient running engine.. If it did nothing but cause an imbalance in syncronization,,, well,, we all know what a poorly sycronized 4 carbed Yam motor runs like,, icky..

[Prairiehammer]

OK.......... If the system is so sensitive (presuming that it is very sensitive) to vacuum, then there ought to be serious driveability issues with altitude change, but there aren't. It is a known fact that 3000ft. elevation change from sea level will make a 10% reduction of vacuum............that's significant, yet the bikes can tolerate 10,000 ft mountain passes easily enough with only a slight loss of power due to less oxygen.

I'm suggesting the system is not that sensitive to be affected by a few pinholes in the diaphragms

So, please convince me otherwise..........or am I missing something here.

-Pete, in Tacoma WA USA

 

CV carburetors have the reputation being, unlike non-CV carbs, altitude compensating. That is, their mixture ratios do not change dramatically with altitude. A CV carbed machine can be ridden at 12,000 feet with nary an evident mixture change. That is because pressure differential, the principle that raises the slide, is the same proportion no matter than altitude. The pressures are different, but the proportions of each to each other are the same.

This does not mean however that CV carburetor equipped bikes will not lose power at altitude. They will. But it is because of a lack of oxygen to fill the cylinders and provide combustion pressure, not due to any significant changes in air/fuel mixture.

Obviously, if the diaphragm or slide is leaking vacuum, the pressure differential (Delta P) will be affected whether at altitude or not.

[Yammer Dan]

Only answer I have is if you have diaphragms with holes replace or repair and you will become a believer!! Yammy #5 Puc?? I've heard of that stuff but for some reason don't have it. I'll have to try that stuff. Most things are too stiff for this repair and once applied Diaphragm is ruined. I have a few of those......:whistling:Bike will run on them....if you push it out of a tree....

[Peder_y2k]

OK..I accept the concept that a vacuum imbalance differential between carbs can be an issue of improper fuel mix, but then the return springs MUST be exact matches, and that is highly unlikely. A few millinewtons (1oz. = 278 millinewtons) difference in spring pressures would make for an imbalance between carbs. A perfectly balanced set of return springs would be very costly due to selective tolerances, but the springs are relatively cheap. I suspect spring pressure differences are actually in the many tens of millinewtons making balanced carbs impossible.

Still open and receptive to input.

Inquiring minds want to know...........

-Pete, in Tacoma WA USA

[cowpuc]

Only answer I have is if you have diaphragms with holes replace or repair and you will become a believer!! Yammy #5 Puc?? I've heard of that stuff but for some reason don't have it. I'll have to try that stuff. Most things are too stiff for this repair and once applied Diaphragm is ruined. I have a few of those......:whistling:Bike will run on them....if you push it out of a tree....

Give it a shot Dan, YOU WILL LOVE IT!! Clean em real good with a little carb cleaner, apply Yamabond 5 to cover side of the diaphram, small smear goes a long ways - stuff is really really amazing to play with!! If only a few pinholes a light smear - let sit for 24 hours, a little larger smear over the first one, dry for another twenty four hours before use.. YOU CANNOT TELL THE PATCH FROM THE ORIGINAL RUBBER IN FLEXIBILTY OR TEXTURE!!

I am dieing to try an actual patch over a complete tear out, cut a patch from an old diaphram, seal between the two pieces of rubber with #5,, I dont expect it to work perfect but far better than a dead jug on a cross country trip.. It must have been a good a epifany cause I carried some #5 and an old diaphram all over America and never had a chance to prove my theory.. You and I both know that if you conquer ol Murphy and his law you are probably onto something!!! Hows THAT for engineering thought you guys.. :rotf::rotf:

[cowpuc]

OK..I accept the concept that a vacuum imbalance differential between carbs can be an issue of improper fuel mix, but then the return springs MUST be exact matches, and that is highly unlikely. A few millinewtons (1oz. = 278 millinewtons) difference in spring pressures would make for an imbalance between carbs. A perfectly balanced set of return springs would be very costly due to selective tolerances, but the springs are relatively cheap. I suspect spring pressure differences are actually in the many tens of millinewtons making balanced carbs impossible.

Still open and receptive to input.

Inquiring minds want to know...........

-Pete, in Tacoma WA USA

But,, arent you forgetting that this is one of the reasons that the system is designed to be adjustable,, or, sycronized.. Its not a perfect system in itself so by adjusting those little balance screws we are probably compensating for issues like you are pointing out Pete.. This is also why after tuning I like to run my bike up to normal running R's (careful doing this if your still using Mercury Sticks) - around 3800, just to see what my gauges look like in that range.. I usually tweek Tweeks in that range cause I hang out that alot.. If nothing else, differences in balance at those R's can be affected by a lot of things, spring weaknesses included, and I like to at least know whats happening even if I dont totally understand it..

Good thread!!!

[Prairiehammer]

OK..I accept the concept that a vacuum imbalance differential between carbs can be an issue of improper fuel mix, but then the return springs MUST be exact matches, and that is highly unlikely. A few millinewtons (1oz. = 278 millinewtons) difference in spring pressures would make for an imbalance between carbs. A perfectly balanced set of return springs would be very costly due to selective tolerances, but the springs are relatively cheap. I suspect spring pressure differences are actually in the many tens of millinewtons making balanced carbs impossible.

Still open and receptive to input.

Inquiring minds want to know...........

-Pete, in Tacoma WA USA

 

Consider the fact that the slides barely move (or are pertinent) at idle where most people synchronize their carbs. The diaphragms and springs are not in the picture at idle when synchronizing.

The differences in spring rates CAN affect the mid to upper range of operation, but usually there is such a small difference as to be imperceptible. Some have discovered fatigued springs (too much sag) and have simply stretched the fatigued spring back to specification. You should note that the springs are of a very light rate and don't have much effect upon the slide. The vacuum is much stronger than the spring. The primary reason for the spring is to return the slide to a 'closed' position.

[Yammer Dan]

Moved #5 to top of pick-up list Puc!! I've spent some time burning up brain cells on this in the past. Can't afford to do much of that!!! When you replace a set of bad Diaphragms it makes a believer out of you. And the Springs.....Not the correct way but I took all 4 and laid them side by side and there was quite a difference in two of them. I as carefully as I could made them match the others. And I use my special cleaner regularly. Keeping carbs from having problems I'm convinced is the right approach to these things. I HATE CARBS!!"Brown Sugar" eats Hardleys and 2nd Gens so I must be doing something right. And don't get called stupid TOO OFTEN!!!

[Flyinfool]

As was mentioned above.

New diaphragms do not have any holes.

Once the pinholes start, it is the pinholes that a tear will grow from.

Why would anyone go through the effort to tear something apart, and then not repair a found problem, and then go through the effort to reassemble with parts that they know have started to fail and they will have to do it all over again when they finish failing?

 

And yes a few pin holes do make a difference in drive-ability. When I replaced my diaphragms there were just a few pin holes in them. I noticed an immediate improvement in how the bike ran with the new diaphragms. There was another member present that had running issues. His diaphragms each had 4 to 5, 1/4 inch tears in them. his bike ran really bad. We put my old diaphragms in his bike and he never knew the bike could run so good. As soon as he got home he ordered new diaphragms and was again amazed at how much better still it ran.

 

As to all of the science as to why it works the way it does, I am not 100% sure of. All I know is that if you have a leak, you will not have the correct amount of vacuum that the system was designed to work with. That can never be good. And has been proven by testing to not be a good thing.

 

I can understand you want to know the science involved, But because you do not understand the science involved does not mean that it is not there. I do not understand the science of how blood gets oxygen out of the air and into the blood and then again releases the oxygen into the target tissue. But I do know that I will not work well if it does not happen, and while small leaks in my systems will not stop me from functioning, my whole body does work much better when it is totally leak free.

[Venturous Randy]

Many, many years ago, I had a cylinder that would occasionally foul a plug. I tweeked on the air fuel mixture and synced and still fouled a plug. I pulled the diaphragm and found pin holes. I cleaned the diaphragm with alcohol and used some liquid rubber and no more plug fouling.

I have since replaced all the diaphragms and also reset the slide needle depths and routinely get 43mpg's or better riding 2-up and that is with a V-Max final drive. If your slides are not opening good because of pin holes or tears, the bike will run more rich on that cylinder.

RandyA

[MiCarl]

If you're a mechanical engineer you should understand this:

 

The bottom of the diaphragm is exposed to atmospheric pressure - through a port to the air box. More correctly, exposed to the pressure in the air box.

 

The top of the diaphragm, via the hole in the slide, is exposed to the pressure in the carburetor throat.

 

Pressure is the way we measure potential energy of a fluid.

 

When air from the air box enters the carburetor throat it accelerates - giving it kinetic energy. To keep the laws of nature in balance that energy has to come from somewhere - so the potential energy (pressure) decreases. That drop in pressure is communicated through the hole in the slide to the top of the diaphragm. The slide will rise in response to the pressure difference.

 

As the slide rises the air under it slows down - increasing the pressure (potential energy). When everything (pressures and spring force) come into balance the slide will stop at a new position.

 

If there are leaks in the diaphragm the pressure on top will be too high for the air speed and slide position. The slide doesn't rise as high as it should and restricts air flow and fuel to the engine.

[Yammer Dan]

If you're a mechanical engineer you should understand this:

 

The bottom of the diaphragm is exposed to atmospheric pressure - through a port to the air box. More correctly, exposed to the pressure in the air box.

 

The top of the diaphragm, via the hole in the slide, is exposed to the pressure in the carburetor throat.

 

Pressure is the way we measure potential energy of a fluid.

 

When air from the air box enters the carburetor throat it accelerates - giving it kinetic energy. To keep the laws of nature in balance that energy has to come from somewhere - so the potential energy (pressure) decreases. That drop in pressure is communicated through the hole in the slide to the top of the diaphragm. The slide will rise in response to the pressure difference.

 

As the slide rises the air under it slows down - increasing the pressure (potential energy). When everything (pressures and spring force) come into balance the slide will stop at a new position.

 

If there are leaks in the diaphragm the pressure on top will be too high for the air speed and slide position. The slide doesn't rise as high as it should and restricts air flow and fuel to the engine.[/QUOT

 

You tell em Carl!! I understand it but couldn't have said it.....

[zoey04]

i have fixed a few pin holes in my diaframs clean real well let dry and what i use is called amazing GOOP if u let dry over nite and put back in they will go along time before u need to totally replace . i have over 15,000 km on the two that i fixed and still going strong zoey04:whistling:

[EasyRider]

If you're a mechanical engineer you should understand this:

 

The bottom of the diaphragm is exposed to atmospheric pressure - through a port to the air box. More correctly, exposed to the pressure in the air box.

 

The top of the diaphragm, via the hole in the slide, is exposed to the pressure in the carburetor throat.

 

Pressure is the way we measure potential energy of a fluid.

 

When air from the air box enters the carburetor throat it accelerates - giving it kinetic energy. To keep the laws of nature in balance that energy has to come from somewhere - so the potential energy (pressure) decreases. That drop in pressure is communicated through the hole in the slide to the top of the diaphragm. The slide will rise in response to the pressure difference.

 

As the slide rises the air under it slows down - increasing the pressure (potential energy). When everything (pressures and spring force) come into balance the slide will stop at a new position.

 

If there are leaks in the diaphragm the pressure on top will be too high for the air speed and slide position. The slide doesn't rise as high as it should and restricts air flow and fuel to the engine.

 

I almost understand it!! Now to go get some yamabond#5 as cowpuc said to prevent future leaks

[saddlebum]

So I post a question about a throttle response issue, and the concept of pinholes in the carb diaphragms come up...again....as in numerous articles posted on this forum.

 

I just don't get it. Someone enlighten me, please. BTW, I have a degree in mech engineering, so I'm not ignorant.

 

The factory manual clearly states on examining the diaphragm for issues, to look for rips and tears, No mention of holes or pinholes at all.

 

So in examining the piston valve (slide), there is a large designed in hole in the piston itself that passes vacuum through to the other side of the diaphragm. Duh? So what difference do a few pinholes make? Should be negligible. The built in hole is so large as to be some 20-30 times the size of a pinhole or 3.

 

The engineers at Yamaha would mention 'holes', or 'pinholes' in the diaphragm if it were an issue, but they don't.

 

I can understand the rips and tears as these can easily be much larger than the built in hole, but the pinholes concept seems vacuous at best.

 

I'm wondering if the pinholes concept isn't someone's invention.

 

Attached is an image of the manual section describing the diaphragm inspection, and a diagram of the piston (slide) with the hole designated with a red line.

 

-Pete, in Tacoma WA USA

Your questioning seems to be based on the assumption that the holes in the barrels cause a lose of vacuum to the diaphragm's. But if you look at the position of the holes in relationship to the venturi were it narrows and then widens again, I would suggest that they actually sit in the low pressure zone of the venturi and therefore actually contribute to the vacuum acting on the diaphragms, Where as the pinholes are in affect actual vacuum leaks. If you want a good example of this effect just look at the back of any tractor trailer going down the road on a snowy day. as the rig passes through the air going down the highway it creates a low pressure area at the back of the trailer commonly known as a vacuum and all the snow gets sucked up and clings to the back doors of the trailer. Edited July 15, 2014 by saddlebum

[cowpuc]

Your questioning seems to be based on the assumption that the holes in the barrels cause a lose of vacuum to the diaphragm's. But if you look at the position of the holes in relationship to the venturi were it narrows and then widens again, I would suggest that they actually sit in the low pressure zone of the venturi and therefore actually contribute to the vacuum acting on the diaphragms, Where as the pinholes are in affect actual vacuum leaks. If you want a good example of this effect just look at the back of any tractor trailer going down the road on a snowy day. as the rig passes through the air going down the highway it creates a low pressure area at the back of the trailer commonly known as a vacuum and all the snow gets sucked up and clings to the back doors of the trailer.

 

I knew it,, I just KNEW that some how, some way, someone would find a way to bring SNOW into this subject... What is it with you people? Why cant we all just sit around the perverbial campfire and have an easy, fun loving, gearhead to gearhead discussion about our bikes without someone making it personal?

Take this particular saddle bum for instance. He reaches deep into his pocket filled with all kinds of perfectly useable nouns to use in his very well thought out example, so what does he do? He reaches into the depth of that pocket and has to pull out the most dreaded noun known to man, SNOW.. I mean,, really... Talk about .. If he had to use something cold and something that melts he could have used the word ice cream instead of the word snow.. I suggest we all think about the point I am trying make the next time we gather around the campfire to discuss these sensitive issues..

Oh well,, at least this winter when a truck goes by each one of us forming a vacuum around its tailgate we might pause and ask ourselves this question,, is that snow we see gathering or, is that in fact, vanilla ice cream?

 

Heyyy, Saddlebum,, seriously, GOOD example!!!!!!!!

Edited July 15, 2014 by cowpuc