Hello again. I'm making a new thread on this subjeckt.
This is the issue; ny fuel vacuum valve (-95 3. gen) was stuck and i had to fix it. While doing the manual tests before putting it back I discovered that the valve opens as it should when applying vacuum. What I did not expect was that the valve remains open after cutting off the vacuum. There is actually a tiny one-way air-valve in the housing, in the part where the vacuum hose enters the valve, and this air-valve restricts air from flowing back into the vacuum camber. The fuel valve spring inside the chamber is for this reason not able to shut off the fuel when vacuum is cut off.
Anyone know why this is? I left the thing for 2 hours and it did not close during this period. What would be the idea with a vacuum valve that opens once and never closes?
The inner part of the housing, where the vacuum hose enters, has a small aluminum "lid" with a tiny hole in it. Inside that hole I can se a small "rubber ball" or something similar, and this is the "return valve" restricting air from flowing back into the housing. Why is this thing there, if not to restrict the returning air? I was thinking, maybe it's there to delay the returning air, and not to totaly restrict it? Anyone?
Found this paragraph in the general shop manual from Honda. Hope it helps.
[attachment deleted by admin]
You are talking about this, correct?
I had an issue with mine not allowing gas through to the carbs, have you clean it well?
(http://i203.photobucket.com/albums/aa214/TLRam1/Motorcycles/Magna%20Tech/DSCN8151.jpg)
(http://i203.photobucket.com/albums/aa214/TLRam1/Motorcycles/Magna%20Tech/DSCN8152.jpg)
(http://i203.photobucket.com/albums/aa214/TLRam1/Motorcycles/Magna%20Tech/DSCN8153.jpg)
Yes this is the one. And I have taken it all apart and cleaned t.
You can see the aluminum circle shape inside the rightmost part of the housing in the 2 last pics. There is a small hole in the aluminum part, where the vacuum is applied. Inside that hole there is a rubber ball (on mine anyway), and that is what restricts air from entering the vacuum chamber when vacuum is discontinued.
The question is; should I take the rubber ball away?
So you are telling us there is a check valve inside the housing where the vacuum line attaches? The diagram does not show this "feature". I do not understand why it is there.
To provide a delay before shutting off the fuel valve? Why would one need this? I don't get it.
I've got a replacement valve set (part # 16953-MN5-023) which consists of the three parts in the last picture that Terry posted (flapper diaphragm center, spring and vacuum cover) that I have yet to install. The vacuum cover does appear to have some sort of one-way valve in it (only allows suction). I don't know that this would prevent the diaphragm from shutting off fuel flow though once suction is removed. There does appear to be a vent in the center diaphragm part, perhaps yours is clogged?
Quote from: lragan on March 16, 2010, 04:08:09 PM
So you are telling us there is a check valve inside the housing where the vacuum line attaches? The diagram does not show this "feature". I do not understand why it is there.
To provide a delay before shutting off the fuel valve? Why would one need this? I don't get it.
Me neither :-?
Quote from: LIMagna on March 16, 2010, 05:54:29 PM
The vacuum cover does appear to have some sort of one-way valve in it (only allows suction). I don't know that this would prevent the diaphragm from shutting off fuel flow though once suction is removed. There does appear to be a vent in the center diaphragm part, perhaps yours is clogged?
You have discovered the same thing on your part as I have. Have you tested it to see if it closes when suction is removed?
The vent in the center is open and ok. It can be seen in the shop manual page posted by Iragan.
Quote from: Cannon on March 17, 2010, 02:26:32 AM
Quote from: LIMagna on March 16, 2010, 05:54:29 PM
The vacuum cover does appear to have some sort of one-way valve in it (only allows suction). I don't know that this would prevent the diaphragm from shutting off fuel flow though once suction is removed. There does appear to be a vent in the center diaphragm part, perhaps yours is clogged?
You have discovered the same thing on your part as I have. Have you tested it to see if it closes when suction is removed?
The vent in the center is open and ok. It can be seen in the shop manual page posted by Iragan.
No, I haven't tested it. I purchased the parts a while back after reading that the diaphragms can become problematic with age but have yet to swap them out. I'm not sure if holding them together will be enough to simulate installation but I can try it when I get home later today.
Okay, as best I can tell (holding the parts together with my fingers), the valve slowly closes when vacuum is removed. It doesn't snap shut but within two or three seconds, it's extended the plug which should shut off the flow of fuel.
That is what one would might expect it is supposed to do. There must be an orifice somewhere that admits air at a slow rate into the vacuum side of the chamber. If you can identify where it is, perhaps Cannon can clear his and he will be back in business.
I would bet it just leaks back through the check valve. The check valve prevents pressure above ambient from being applied to the diaphragm but does not completely seal the unit in the absence of vacuum. I don't remember seeing any other means of venting short of the center section vent.
Here I go again -- speculating about something I have not experimented with, and really don't know much about. So I beg your forgiveness in advance. :cool:
As a designer, I don't understand how one could be assured that all the produced units would release in a timely manner through the check valve -- unless maybe you created a series of grooves in the ball? If I want the device to close within a prescribed time frame, I am going to have to create a path with a controlled leak rate. Is there not a tiny hole somewhere that establishes this leak path?
The designer had to care that the valve would shut off -- otherwise, there would be no need for a valve at all. How about in the diaphragm? Is there a hole in it's center, maybe?
You may very well be right ... I'll need to inspect the diaphragm a little more closely when I get home. It may draw air slowly through the center of the diaphragm from the vent in that center section. By the time this is done, we're going to understand exactly how this thing works :-)
Okay, I've looked this thing over nine ways to Sunday and can't see any deliberate path to vent the vacuum side of this device. I thought that there might be a small hole in the middle of the diaphragm but if there is I can't see it. I've attached two pictures I took but I don't think they help much. The vent in the middle section appears to vent only the center section between the two diaphragms.
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from what i know about that device, this is my take on it: when the bike is off, there is no vacuum applied to the 'in' side, aka the little tube that connects to a small black vacuum line that connects to cyl#4 (right front) when the bike cranks over & fires, it creates a vacuum and pulls the diaphram tighter and tighter allowing fuel to start to enter the other side of the diaphram. the fuel is held back by the large black rubber stopper on the opposite side. the purpose of the little rubber 'ball' i think is to block the flow of vacuum, or to keep maximum vacuum applied to hold back the diaphram during operation. if it were not there, i would assume that the diaphram would pulsate with each vacuum pulse from the engine and cause sporatic fuel flow. when the engine is turned off, there is no more vacuum source, so the diaphram closes off the fuel flow via the return spring, and blocking the fuel from flowing down to the carbs. i've tested mine (when i actually rode with it on the bike, have since removed 2 years ago) and it did not shut off instantly--it took like 4 or 5 seconds to completely shut off the fuel flow. if yours does not shut off after 5 seconds or so, something is wrong, either a torn diaphram and fuel is leaking into the vacuum chaimber and allowed to drain into the engine (i've read about this last year) or the return spring is weak, not shutting off the fuel, or the vacuum 'in' port is obstructed in some way. this is just a saftey precaution valve, you don't actually need it for the bike to function.
Quote from: LIMagna on March 18, 2010, 06:05:03 PM
Okay, I've looked this thing over nine ways to Sunday and can't see any deliberate path to vent the vacuum side of this device. I thought that there might be a small hole in the middle of the diaphragm but if there is I can't see it. I've attached two pictures I took but I don't think they help much. The vent in the middle section appears to vent only the center section between the two diaphragms.
In the bottom picture, there is a spot, or dot, or hole, or something I cannot make out at about 8:30 in the ring around the center port. What is it?
QuoteI cannot make out at about 8:30 in the ring around the center port
Is that 8:30 am or pm :D :D :D.. sorry i forgot to take my meds continue on :???:
Charles, there are still a few of us who remember what an analog clock face looks like!! :lol: :lol:
Quote from: lragan on March 18, 2010, 10:14:49 PM
In the bottom picture, there is a spot, or dot, or hole, or something I cannot make out at about 8:30 in the ring around the center port. What is it?
I noticed that too but it did not appear to be a hole. It was some sort of raised nub or something. Why should it be there, I don't know but even under my 200 mm telephoto lens, I could see no passage way. Oh and I tried both positive and negative pressure on that side of the cover but it behaved just like the outside vacuum line connector, only passing air in one direction (out).
Quote from: LIMagna on March 19, 2010, 07:17:24 AM
I noticed that too but it did not appear to be a hole. It was some sort of raised nub or something. Why should it be there, I don't know but even under my 200 mm telephoto lens, I could see no passage way. Oh and I tried both positive and negative pressure on that side of the cover but it behaved just like the outside vacuum line connector, only passing air in one direction (out).
OK, thanks. I remain stumped, having pose all the questions I could think of. :???:
OK guys lets try this on for size the hose for the vacuum runs to the right front cylinder correct OK now where does that go into the cylinder and gets it's vacuum signal from there not sure how it works.
But I sure know it is not a closed system so once the engine is shut down the vacuum stops and the valve releases the valve it's self can be a closed system because the crankcase is not so closed right again once the engine shuts down the signal stops and the hose loses suction and the valve is supposed to open. CASE CLOSED send donations to 1-800-GET-VALK :lol: :lol: :lol: :lol: :lol:
Allen, it really doesn't matter where the vacuum comes from. There is a one-way, check valve in the vacuum inlet of the fuel shut off valve that holds vacuum in the chamber after the hose to the cylinder comes to ambient pressure. There must be a relief "leak down" somewhere, from what is posted above, but in Cannon's valve, it leaks way to slowly to allow the valve to shut off in a timely manner.
The same malady may very well be one of the problems with Jennifer's bike. It appears her fuel shut off valve is missing or stuck.
the release of vacuum is when the motor shuts off, there is no one way valve that i can see that needs to bleed off pressure. when the motor shuts off, the vacuum is gone, the return spring then pushes the valve closed and forces out whatever air was left in the system back into the cylender. he could have carbon or some foreign material blocking the port on the motor or an obstruction in the vacuum line that would cause this symptom.
in jennifers bike, her vacuum diaphram could be torn, allowing fuel to seep from the fuel side to the vacuum side, draining down the vacuum tube and flood the cylender.
i tested my valve when i had it off the bike before i sold it. i sucked on the vacuum hose and then pinched it off with some pliers. the vacuum would hold and allow fuel to pass. when the pliers were removed the fuel would slow down to a trickle and stop after 4-5 seconds. if there were a one way valve, this would not be possible. when full vacuum is reached/applied, the diaphram is pulled to the right, and that little rubber ball plugs up the port for the vacuum. it's that simple. stretch the return spring some and reassemble. you could bench test it in a similar way. suck on the vacuum hose to open the fuel passageway then pinch it off. attempt to blow through the fuel ports, it should flow nicely. now do the same, but remove the pliers and watch the resistance get harder and harder to blow air through there. it should stop eventually.
Quote from: roboto65 on March 19, 2010, 08:18:11 PM
OK guys lets try this on for size the hose for the vacuum runs to the right front cylinder correct OK now where does that go into the cylinder and gets it's vacuum signal from there not sure how it works.
But I sure know it is not a closed system so once the engine is shut down the vacuum stops and the valve releases the valve it's self can be a closed system because the crankcase is not so closed right again once the engine shuts down the signal stops and the hose loses suction and the valve is supposed to open. CASE CLOSED send donations to 1-800-GET-VALK :lol: :lol: :lol: :lol: :lol:
the vacuum is created by the piston moving down. when it moves down, it pulls air from the intake, which that hose is connected to and builds up pressure, and when the pressure is high enough, that little rubber ball plugs up the opening and keeps it held there until the bike shuts off.
I dunno, Chad. What I think is true is that the "little rubber ball" is the check valve, one way valve, whatever you call it. LIMagna tested his valve, and it shut off in four or five seconds, as you say. If the ball were removed, it should shut off immediately. That air enters the chamber at some slow rate keeps the valve open for a few seconds and shuts it slowly. Conner's apparently doesn't shut off at all, or takes way too long.
It seems to me that there must be a very small orifice somewhere that allows air into the chamber when vacuum from the engine goes away.
Certainly a tear in the diaphragm would result in the unit not operating properly. What I think would happen is that the vacuum would never open the valve at all. It is air pressure on the other side of the diaphragm that causes the valve to open, and the spring that causes it to close.
If there were a crack or tear in the fuel valve itself, then fuel would flow all the time, regardless of the position of the diaphragm. The same would happen if the fuel valve did not seat properly.
Lawrence is right, without the ball/check-valve/whatever, the flow of fuel would stop immediately after vacuum is removed. The spring would snap the valve closed instantly. I did indeed test the new valve I've got sitting in my spare parts cabinet and it does not allow positive pressure from the outside (vacuum port) nor does it allow negative pressure from the inside (can't suck in any air from the diaphragm side).
I know that none of you know me from a hole in the wall but I do have a background in engineering (BS in Aerospace Eng. & MS in Systems Eng.) and have done quite a bit of "wrenching" on my own over the 30+ years I've been playing with cars (and to a lesser extent, bikes) so I'm not a complete neophyte when it comes to stuff like this. That said, I'll admit I don't completely understand, in light of the above observations, how it does bleed out vacuum on the diaphragm side and shut off the valve but again, when holding the parts together as tightly as I could with my fingers, that's exactly what it does. My only guess is that the one-way valve is not completely one-way but does allow for pressure to reach equilibrium on both sides ... when it's operating properly.
I replaced the vacuum valve on my bike over the weekend and thought I would post a few observations. I believe it was the original valve so even though there are only 15K miles on the bike, the "innards" looked as you might expect for something that's been sandwiched together for 14 years (had to peel the rubber diaphragm from both sides of the device). Although the diaphragm appeared to be intact, there was a small amount of fuel on the vacuum side of the device. The parts appeared to be identical to the replacement kit I had ordered a couple of months back (part # 16953-MN5-023), right down to the little nub on the inside of the vacuum chamber cover. Speaking of the cover, the old one did not appear to have a functioning one-way or check valve ... air moved freely in or out of the vacuum line attachment port. I couldn't tell if it's just not there or simply no longer operates. It's possible that the check-valve function could have been added as a later revision to the part but again, the outward appearance of the two items was identical, down to every last detail so it's most likely that it simply stopped working at some point.
I tested the operation of the device again after reassembling the new parts and confirmed proper operation of the shut-off valve. Fuel (well in this case air) flowed freely for a second or two after removing vacuum, gradually tapering off completely.
Quote from: lragan on March 18, 2010, 08:12:14 AM
The designer had to care that the valve would shut off -- otherwise, there would be no need for a valve at all. How about in the diaphragm? Is there a hole in it's center, maybe?
That could be the case, but I doubt it. Reason; While balancing the carbs, the vacuum hose must be removed from the no 1 cyl to connect the balancing "tool". In order to keep the engine running without the vacuum supply, the hose must be clamped off with the engine running, in order to "trap" the vacuum before the hose is disconnected. I did this on my bike (some years back) and i let it run for quite some time while doing the balancing routine. If there was supposed to be a hole in the diaphragm, the "trapped" vacuum would escape and the engine would stop during this procedure (I think... :?)
Good reasoning, Cannon. I have pinched off the same line whilst balancing my carbs, but just didn't "make the connection".
Perhaps there is a small groove, or channel, in the seat for the ball valve?
I would really like to know how this thing works like it does, but (so far at least) am unwilling to take a good one off a running bike to check it out. :smile: