Is this the sound of an apex seal gone bad?
05-08-08, 03:39 PM
#101
Dave I'll take that coasting valve, thank you! I do want to get a good one in there.
Although I have to say the car ran just fine this evening with the valve corked off on the 50 mile round trip to OGTA (the leading ignitor was toast, I replaced it). Just one big backfire on a long highway deacelleration.
The White One is Back!
Although I have to say the car ran just fine this evening with the valve corked off on the 50 mile round trip to OGTA (the leading ignitor was toast, I replaced it). Just one big backfire on a long highway deacelleration.
The White One is Back!
05-09-08, 07:50 AM
#104
All Hail the mighty 7! For posterity, here's the link to the White One looking and running better than the day she came off the showroom floor (with movies):
https://www.rx7club.com/1st-gen-general-discussion-207/white-one-rises-again-754460/
https://www.rx7club.com/1st-gen-general-discussion-207/white-one-rises-again-754460/
05-12-08, 03:05 PM
#105
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Ray,
First of all I'm glad you found a fix and that she's running good again. I came across your post while researching a similar problem on my latest project, a black '83.
I'm wondering, is the coasting valve also referred to as the anti afterburn valve #2? Whatever it is, it's the mushroom shaped guy on the back of the carb, that has a large hose going down to the intake manifold, and a smaller one that goes to the shutter valve solenoid on the rat's nest. Well while poking around under the hood the other day I noticed that the smaller hose was plugged up with a bolt, and the small nipple on the valve was sucking air like crazy. I was thinking to myself, "a vacuum leak like this can't be good". So I took the bolt out and hooked the hose back up to the valve. My idle stabilized, and I didn't have the whoosh of that vacuum leak anymore. So then I proceeded to take the car out for a spin. Guess what happened? All of a sudden my idle went to crap and it started acting like it was going to stall. I could barely pull out of my driveway because of a severe loss of power. I was running on one rotor! I limp around the block and come back home, pop the hood, and a few seconds later the idle returned to normal. I removed the air cleaner cover and didn't hear the famous honking sound of the shutter valve being bad. While researching your problem did you come across anything that might clue me in to what's going on? I need to find out how these valves work together and how to correct the problem.
First of all I'm glad you found a fix and that she's running good again. I came across your post while researching a similar problem on my latest project, a black '83.
I'm wondering, is the coasting valve also referred to as the anti afterburn valve #2? Whatever it is, it's the mushroom shaped guy on the back of the carb, that has a large hose going down to the intake manifold, and a smaller one that goes to the shutter valve solenoid on the rat's nest. Well while poking around under the hood the other day I noticed that the smaller hose was plugged up with a bolt, and the small nipple on the valve was sucking air like crazy. I was thinking to myself, "a vacuum leak like this can't be good". So I took the bolt out and hooked the hose back up to the valve. My idle stabilized, and I didn't have the whoosh of that vacuum leak anymore. So then I proceeded to take the car out for a spin. Guess what happened? All of a sudden my idle went to crap and it started acting like it was going to stall. I could barely pull out of my driveway because of a severe loss of power. I was running on one rotor! I limp around the block and come back home, pop the hood, and a few seconds later the idle returned to normal. I removed the air cleaner cover and didn't hear the famous honking sound of the shutter valve being bad. While researching your problem did you come across anything that might clue me in to what's going on? I need to find out how these valves work together and how to correct the problem.
05-12-08, 04:18 PM
#107
Thanks Bliffle, and now she's running like the Proverbial Rotary Rocket!
dj, here's a nice labeled photo of the different valves on the Nikki carb, courtesy of 74RX4. The "shutter valve diaphragm" in this photo is the coasting valve:
Here's a nice diagram I stole from somewhere showing the difference and relationship between the shutter valve and the coasting valve:
And here's a photo of the shutter valve and coasting valve, corresponding to the diagram:
So no the coasting valve is not the same as the #2 afterburner valve, but both can cause vacuum leaks and similar rough running symptoms.
The coasting valve is attached to the intake manifold at the base of the carb on the driver's side. It is hard to see if your rat's nest is still in. There are two rubber hoses running out of the coasting valve, a large one that goes up to the breather and a smaller one that connects to the coasting valve solenoid port on the rat's nest.
I'm still learning about the coasting valve/shutter valve set up, but basically from experience two things can go wrong.
1) the shutter valve can stick closed, permanently cutting off fuel to the rear rotor and making the engine run very rough. This is what happened to cause my original symptoms in this post, so bad I thought it might be an apex seal.
2) the coasting valve can leak causing it to suck air through the breather tube even when idling, in effect causing a vacuum leak and poor running, although not as bad (at least in my case) as the shutter valve sticking closed. You can detect this by putting your thumb over the coasting valve port inside the breather, if it is pulling any suction at idle that is a vacuum leak (it should only pull vacuum when quickly de-accellerating, if you feel it then it's working).
The cork marked "W" shows the coasting valve port in the breather:
So it sounds like your coasting valve probably went bad at some point and somebody put the bolt in the tube to eliminate it from this system - this is a common fix. Then later on one of the small hoses got disconnected, causing the vacuum leak you discovered.
When you reconnected the coasting valve you got back your old problem, probably a vacuum leak through the coasting valve (you can verify this by doing the test at idle above, if there is a vacuum at the breather that's the problem).
If so your choices seem to be:
1) replace the coasting valve with a good one
2) disable your bad valve again but be sure to eliminate the vacuum leak by properly blocking off the tubes that were connecting it to the coasting valve solenoid.
Hope this helps and somebody who really knows what they are doing will correct any errors I might have made.
dj, here's a nice labeled photo of the different valves on the Nikki carb, courtesy of 74RX4. The "shutter valve diaphragm" in this photo is the coasting valve:
Here's a nice diagram I stole from somewhere showing the difference and relationship between the shutter valve and the coasting valve:
And here's a photo of the shutter valve and coasting valve, corresponding to the diagram:
So no the coasting valve is not the same as the #2 afterburner valve, but both can cause vacuum leaks and similar rough running symptoms.
The coasting valve is attached to the intake manifold at the base of the carb on the driver's side. It is hard to see if your rat's nest is still in. There are two rubber hoses running out of the coasting valve, a large one that goes up to the breather and a smaller one that connects to the coasting valve solenoid port on the rat's nest.
I'm still learning about the coasting valve/shutter valve set up, but basically from experience two things can go wrong.
1) the shutter valve can stick closed, permanently cutting off fuel to the rear rotor and making the engine run very rough. This is what happened to cause my original symptoms in this post, so bad I thought it might be an apex seal.
2) the coasting valve can leak causing it to suck air through the breather tube even when idling, in effect causing a vacuum leak and poor running, although not as bad (at least in my case) as the shutter valve sticking closed. You can detect this by putting your thumb over the coasting valve port inside the breather, if it is pulling any suction at idle that is a vacuum leak (it should only pull vacuum when quickly de-accellerating, if you feel it then it's working).
The cork marked "W" shows the coasting valve port in the breather:
So it sounds like your coasting valve probably went bad at some point and somebody put the bolt in the tube to eliminate it from this system - this is a common fix. Then later on one of the small hoses got disconnected, causing the vacuum leak you discovered.
When you reconnected the coasting valve you got back your old problem, probably a vacuum leak through the coasting valve (you can verify this by doing the test at idle above, if there is a vacuum at the breather that's the problem).
If so your choices seem to be:
1) replace the coasting valve with a good one
2) disable your bad valve again but be sure to eliminate the vacuum leak by properly blocking off the tubes that were connecting it to the coasting valve solenoid.
Hope this helps and somebody who really knows what they are doing will correct any errors I might have made.
05-12-08, 05:41 PM
#108
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Ray, thanks for the pics and info. I had seen those when searching but I did not notice the coasting valve named in there, I thought that the whole assembly was the shutter valve. So basically the shutter valve is the butterfly that connects to the coasting valve via the rod and lever.
Well, the AAB#2 is what had the small hose disconnected and was pulling in air. You can see the larger one with the red mark drawn from it going to the manifold in the pic above. The smaller one just to the right of that is what I'm referring to. The tube that comes from it goes to the rats nest, connecting to the shutter valve solenoid. That tube was blocked off with a bolt. I'm guessing that once I hooked it back up, the vacuum was sufficient to activate the shutter valve after I attempted to drive. That makes sense. It did not activate it at idle (no suction from where you have the cork) but when I put it in gear to get to the edge of the driveway and then stopped to check traffic, that created a deccel condition. So my guess is that perhaps the diaphragm in the coasting valve is not up to spec. That's what was getting me confused, not having the suction from the valve at idle, which seems to be a telltale sign that it is bad. I don't have the same problem when I cap off that opening on the AAB #2 valve body, so I'm not sure why the bolt was in the tube going to the nest, and the opening left as a vacuum leak. Oh well, the PO was at least on the right track. I am still curious as to how it's supposed to work though.
I will be taking off this carb, mani, and rats nest soon anyway, to make way for the Sterling Nikki and matching ported manifold.
I've just got to do the supporting mods first. I've got a new fuel pump, regulator, and gauge... I've just got to find a suitable exhaust and I will be all set.
Well, the AAB#2 is what had the small hose disconnected and was pulling in air. You can see the larger one with the red mark drawn from it going to the manifold in the pic above. The smaller one just to the right of that is what I'm referring to. The tube that comes from it goes to the rats nest, connecting to the shutter valve solenoid. That tube was blocked off with a bolt. I'm guessing that once I hooked it back up, the vacuum was sufficient to activate the shutter valve after I attempted to drive. That makes sense. It did not activate it at idle (no suction from where you have the cork) but when I put it in gear to get to the edge of the driveway and then stopped to check traffic, that created a deccel condition. So my guess is that perhaps the diaphragm in the coasting valve is not up to spec. That's what was getting me confused, not having the suction from the valve at idle, which seems to be a telltale sign that it is bad. I don't have the same problem when I cap off that opening on the AAB #2 valve body, so I'm not sure why the bolt was in the tube going to the nest, and the opening left as a vacuum leak. Oh well, the PO was at least on the right track. I am still curious as to how it's supposed to work though.
I will be taking off this carb, mani, and rats nest soon anyway, to make way for the Sterling Nikki and matching ported manifold.
I've just got to do the supporting mods first. I've got a new fuel pump, regulator, and gauge... I've just got to find a suitable exhaust and I will be all set.
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