Weber 32/36's burning the eyeballs!

dang

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Also, just to double check, when you say the carbs were used, do you know if they were previously used on a BMW m30 engine? If they were used on another engine, you may need to start from the beginning with your tuning.
I got them from @Mike Goble and he usually finds all his stuff on BMW's at self service wrecking yards. I'll ask him if he remembers where mine came from. Pretty sure they were on an M30.
 

shanon

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These books are very helpful. They list base jetting and tuning info. Each motor is different. Ultimate fine tuning is best done with a guru, AFR gauge and or dyno session. Then they are 'set & forget'.
 

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TedS

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I got them from @Mike Goble and he usually finds all his stuff on BMW's at self service wrecking yards. I'll ask him if he remembers where mine came from. Pretty sure they were on an M30.
I would assume they're from his car. I think he's using 38's now. I'd also wager the jetting is:
Primary- idle 60; main 140; air corrector 145
Secondary- idle 55; main 170; air corrector 175

Based on these assumptions I'd check the choke plates are open (per Ohmess) since it sounds like you made a change there and then check your mixture screws-- while it's running (chokes open) start turning them in and see if it raises the idle. Sorry if I'm stating the obvious but I can't tell if you've tried this yet.
 

dang

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Drove without air filters and it seems about the same. Choke plates are opening all the way up. Front carb idle mixture is at 1 1/2 turns and the rear carb is at 2 turns before they start to make idle go lower while turning them in
 

Gazz

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Not yet, but I like to drive with my head out the window. Do you think that might be making my eyes burn?
Only if you are following a car that's running rich.

I was serious about the painted carbs bit though. New paint is really fumey when you first use it on a hot engine .
 
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TedS

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Did you turn the mixture screws out until the idle stopped increasing? About how many turns was that?
Do you have the cut off solenoids? If so, when you unplug them does the car die?
Last one- plugs are sooty?
If all that is fine I’d move on to ignition and make sure baseline settings.
Was there a problem with the zeniths?
 

dang

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Okay, a little more info. I got the top off of one carb last night and here's the numbers.

Primary
Idle: 60
Main: 140
Air corrector: 160
Emulsion tube: F50

Secondary
Idle: 60
Main: 140
Air corrector: 170
Emulsion tube: F50

I also checked the power valve per what I found online. I covered the exit hole and pushed down on the plunger and there was no resistance on the return. Zero. This is suppose to mean it's bad but I didn't have time to take if off and inspect the diaphram yet. It was also "dry" since the gas had evaporated. Not sure if that matters. I think I should figure out the power valve before doing anything else.
 

dang

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I got the power valves off to inspect. I have four total with two parts carbs and they all look the same. The diaphragms work as far as move up and down freely without any obvious damage but I really don't know how to tell if they're good. I tried using a vacuum on the orifice connected to it and couldn't get it to move, on all four. Not sure what to do now.
 

shanon

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Have you checked the float bowl levels/adj float heights? Checked fuel pressure PSI? Should be 3-5psi.

HTH
 

dang

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Have you checked the float bowl levels/adj float heights? Checked fuel pressure PSI? Should be 3-5psi.

HTH
I'm using a Facet electric pump right now and it's only suppose to provide 3-4psi I think. I need to get numbers for setting the floats. They need to be checked.
 

Ohmess

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So, I understand the "power valve" is used to enrich mixture at full throttle. I would think this is unlikely to be your problem because it looks to me like the spring would act to keep the valve closed most of the time. Are you finding information on the net that indicates that they might leak?

Otherwise, I would think you should initially concentrate elsewhere. I like Shanon's suggestion to check your float levels, and while you are at it make sure the floats are empty. Sometimes they develop pinholes and fill up with fuel (this is more likely with brass floats). If they don't float they won't stop the flow of fuel into the bowls, and having too much fuel in the bowls messes up everything.
 

dang

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So, I understand the "power valve" is used to enrich mixture at full throttle. I would think this is unlikely to be your problem because it looks to me like the spring would act to keep the valve closed most of the time. Are you finding information on the net that indicates that they might leak?

Otherwise, I would think you should initially concentrate elsewhere. I like Shanon's suggestion to check your float levels, and while you are at it make sure the floats are empty. Sometimes they develop pinholes and fill up with fuel (this is more likely with brass floats). If they don't float they won't stop the flow of fuel into the bowls, and having too much fuel in the bowls messes up everything.
So far all I know is the floats don't leak. I need to get baseline numbers to check/set the float level.

As far as the power valve goes, they're new to me so I'm just now trying to understand them. The way I understand it is, the shaft of the power valve sits on top of the valve at the bottom of the bowl. When the shaft is down (fully extended) the valve is open. This means the valve is open while the engine is off. When the engine is running and has normal vacuum the shaft is lifted off of the valve so the valve is shut (no extra fuel), but as soon as the vacuum drops, like during WOT, the shaft drops back down and depresses the valve and allows fuel to be drawn through the venturi with the main jets. If this is the case, if the diaphragm is bad, the shaft doesn't get pulled off of the valve at the bottom of the bowl so the extra fuel is always present.

EDIT: I have a couple extra power valves and I think they're bad anyway. Seems like I could shorten two of them and see if it makes a difference, since this would presumably close the valve for extra fuel.
 
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'69 2800cs

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I think it was sreams who mentioned bad power valves causing a rich mixture years ago.

I replaced mine prior to my tuning journey and it stopped the “stinking rich” at idle symptoms I was experiencing.
 

bfeng

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I think it was sreams who mentioned bad power valves causing a rich mixture years ago.

I replaced mine prior to my tuning journey and it stopped the “stinking rich” at idle symptoms I was experiencing.
Exactly. A leaky power valve diaphragm will cause the power valve to be ‘on’ all the time. That’s why you are right to check it if you have an over rich idle or progression phase.

FWIW, I would adjust the idle mixture screws about half way between the too rich and too lean point as a starting point, and not that the richest good-idle setting as mentioned above. But what you really want to do is optimize your AFR not at idle but as you drive. Adjusting the idle mixture only helps if the rest of the setup is already dialed in (eg good jetting selections).

For this reason I use an aftermarket wide band O2 sensor tool that provides real time AFR and adjust idle for leanest good driving characteristics. By the way, if you are way rich in easy going driving around town, the main circuit can still be a contributing cause. It was in my case (DGAS38/38).
 

Ohmess

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Dang - thanks for the power valve explanation. It appears I was mistaken about the way the power valve functioned. I now understand it is "on" unless it experiences a certain amount of vacuum.

Nonetheless, I believe its ability to function properly depends not only on having a functioning diaphram, but also on the fuel level in the bowl, and thus on float settings.

I've looked at this only briefly, but I think a high level of fuel in the bowls can diminish the effect of engine vacuum on the valve.

If I am right (and even if I wrong about this, proper float settings can't hurt), making sure your float levels are correct should be the next step.
 

dang

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If I am right (and even if I wrong about this, proper float settings can't hurt), making sure your float levels are correct should be the next step.
I checked them last night and one was set too high. I've also rigged both power valves to be shorter so they'll be taken out of the equation as far as richness goes. I'll be firing it up tonight and hoping for progress.

Here's three of the power valves I have. The one of the left has about half of the rubber membrane left and the other two just have the fabric material exposed. There's no way any of these can work properly. I'm ordering two new valves but in the meantime I'll test without them working.

IMG_20210421_171610890_HDR.jpg
 

bluecoupe30!

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This is so familiar. I look at those power valves, and from here, they all look expired. But I would do the very same thing you are doing. Swap, experiment, evaluate, obsess, and finally spend the money. But we are all very entertained at the sequence of events here. Carry on, Dan! ;)
 
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