Idle shut-off solenoid and Webers

CookeD

CookeD

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Hey all,

I'm troubleshooting my rough-running Webers, and a couple of things are suspect. Specifically, I don't have power going to the idle shut-off solenoids, and have a few questions about this:

1. First and foremost, if there is not power going to the solenoids, will I have symptoms that include poor running/will not idle? I've read on-line about snipping the pins off the solenoids that go into the jets, but this doesn't sound like the best thing to do....
2. I have power going into the relay (that's mounted on the rear of the vacuum booster), but there is not power coming out of the lead where the solenoid wires attach. Should this lead have power with the key on, or is this heat-activated (i.e.: Gets power via the temperature lead @ the thermostat)? If I should have power going through the relay with the key on, I've got a relay issue.
3. In bench testing the solenoids, they will not pull themselves in. If I push them in with 12V current going to the solenoid, they will hold themselves in. When I cut the current, they pop out, seemingly as they should. So, should the solenoids pull themselves in with a 12V signal applied? Of course, I need to get the relay problem repaired, but once that is eliminated, I need to make sure the solenoids are operating properly.

Thanks in advance for any help-- I need to be motoring in my "one of the 25 most beautiful cars."

John
 
You don't mention the type of Weber you're running. If you have the 38/38 models, it's unlikely the solenoids would be the cause of your problem since they only work on one of the chokes. The other choke does not have provision for a solenoid. Assuming you're idle jets are adjusted properly it's hard to imagine a faulty solenoid would be the cause. To answer your question, yes, you should have 12v going to them in order for them to be "pulled in" and open. When you turn off the ignition the lack of 12v causes the solenoid to close, theoretically preventing fuel from reaching the combustion chamber.
 
Shutoff solenoids

Further to TJ's post, if you don't have power to the shut off solenoids then you are trying to run on half of the carb when idling or running at low throttle inputs. They are closed. Good luck with that or even trying to tune it at all.

I had one pin that was sticking, depriving one of the four chokes of any fuel and it drove me nuts trying the adjust it until I clued into the problem.

I have eliminated both of the solenoids with the weber large idle jet holder appropriate to the larger diameter and have found that as good or better than the solenoid shut off's - very little run on if you idle for about 5-10 seconds before turning the engine off. Cutting just half of the fuel off seemed a bit dodgey anyway. Of course now I have two different types (same orifice diameter) of idle jets in the same carb but it runs well.
 
Hey TJ/de,

They are 32/36's, and yes, you guys are correct-- With the solenoids not working and permanently extended, there is no chance of making things happen correctly on the primary side. After analyzing the situation and applying a 12V signal to the solenoids without the pins extracting, etc., I got pissed and cut the pins off with side-cutters-- I was fairly certain that the solenoids weren't working correctly anyway. Because I would have to replace or eliminate the solenoids all together, this was more or less a test to see if the malfunctioning solenoids were the problem. As you can probably guess, with the pins eliminated, the car runs beautifully.

So, I'm going to just eliminate the solenoids and forget that whole relay mess. Also, this is good fodder for the forum, as I couldn't find anything on-line that detailed how the solenoids were suppsed to correctly function.

Johnny in Providence
 
Nothing mysterious about the solenoids. They should have 12v when the ignition is on. When the 12v shuts off, the pin extends to cut off fuel flow to the primary circuit. They keep the car from dieseling.

IIRC, this was a problem TJ struggled with for a while.
 
Are there any problems I HAVEN'T struggled with? = )

Years ago I had a problem with my CS dieseling after I turned it off. I attempted to fix it with the solenoids, but I ended up with only a partial fix.
 
Okay, look, testing the solenoids is easy

The function of the solenoid(s) is to cut off gas flow when you shut off the engine. Faulty solenoids (that don't shut off) can lead to dieseling. Faulty solenoids (that don't open) can be overcome through jetting and setup, I believe. But mine work, so I'm not messing with them.

So to test:

1. take em out.

2. put a bit of snugly fitting aquarium tubing over the business end, not on all the way so it covers the holes in the side of the brass end.

3. try blow through the tubing. The needle should be extended and air should not flow.

4. apply 12v to the connector, and ground the body of the solenoid. With power applied to the pin, and functioning ground, you should hear it click, and be able to blow through the tubing.

5. now you've checked the solenoid. Do as you will from this point forward.
 
Faulty solenoids (that don't open) can be overcome through jetting and setup, I believe.
Click to expand...

Sorry :( this isn't the case. The solenoid cuts fuel to the IDLE circuit only. There isn't enough air speed at idle for the engine to draw fuel properly from the main jet. Sure it will draw some, but the car will run rough so in answer to this a small jet is incorperated into the bottom of the venturi underneath the butterfly valve, this jet also (normally) incorperates the mixture setting screw so the idle mixture can be adjusted.

The only way the need for this extra circuit could be bypassed would be to decrease the size of the venturi which in turn would speed up the flow of air over the main jet, but this in itself would strangle the engine at higher rpm. If this wasn't allready pointless enough you still need to jet the carburettor in such away that the engine can't draw off enough fuel at idle so that you can add just the right ammount via a metering screw, so you're back to square one.
 
Yes, the solenoids shut the fuel off when the ignition is turned to off, thus preventing dieseling. I understand the concept, and understand why the car was running poorly with the relay/solenoids malfunctioning. I just ordered new jet holders that are the same as the secondary side to eliminate the solenoids all together, but since I snipped the pins, they're already effectively eliminated. No dieseling, by the way...

My original questions were regarding the proper functioning of the relay (i.e.: Is it heat-activated, part of the cold start circuit, what the Hell is it, how much did I drink last night, etc...?), and how exactly the solenoids were supposed to function via a correctly-working relay. I now know that my relay is bad, in addition to the solenoids being unresponsive to 12V-- The little things that occur when parts are old I guess... There is a lot of information available via Google about what the solenoids do, but not how they are acutated and/or exactly how they function in practice (on/off, in/out). Alas, the board provides...

Fellas-- Thanks for all the help.
 
I wouldn't bother replacing anything now that you've cut the pins leave them alone as long as it runs ok. Personally I've never understood the point of them anyway, in my opinion it would be far better to know that there was a problem with the car ie carbon build up, bad timing, wrong plugs etc and get it fixed than to be blissfully unaware and melt something.
I don't know where the solenoids draw their current from (via a relay or from ignition switch) as I've never had much to do with the carbed models. Personally if I had to re-wire the circuit from scratch I'd use a relay that was triggered by the ignition being turned on, having said that they probably don't draw that much current (you'd have to check) and could probably be connected to an ignition fed point of the fuse box just remember to put a slightly stronger fuse in at that point. Its that simple, you want the engine on and running sweet? feed the solenoids 12v all the time no timer no nothing else.
One thing to bear in mind is that if your carbs are mounted to the manifold via rubber insulation blocks (to prevent heat soak from manifold to carb) then each carb needs an earth wire to the manifold.

Regards
 
This just wouldn't be a complete Weber topic if I didn't weigh in and say "Throw those crappy things in the trash and install some proper Zeniths to return to your car the performance and economy you deserve and desire!"

OK, I feel better.
 
One thing to bear in mind is that if your carbs are mounted to the manifold via rubber insulation blocks (to prevent heat soak from manifold to carb) then each carb needs an earth wire to the manifold.
Click to expand...

1. Never seen BMW carbs mounted on iso blocks, just with gaskets.

2. Don't those 4 big mounting bolts provide a pretty reliable ground path?
 
velocewest said:
This just wouldn't be a complete Weber topic if I didn't weigh in and say "Throw those crappy things in the trash and install some proper Zeniths to return to your car the performance and economy you deserve and desire!"

OK, I feel better.
Click to expand...

Didn't Zenith make really bad TV's and stereo's as well? Or just carburator's.

Couldn't resist.
 
1. Never seen BMW carbs mounted on iso blocks, just with gaskets.
Click to expand...

As I said in my post. I've never had much to do with carbed models but some manufacturers did mount carbs this way and when they did the rubber block completely isolated the carb from the manifold. It was just a thought as I have seen cars come in with running faults where someone has changed the carb and left the earth wire off.
 
Yeah, the carbs are on plastic blocks-- I think Gazzol has M30 ESP...? The blocks are not solid like phenolic spacers; more of a hollow plastic block. I'm assuming the function is to keep heat away from the carbs, and maybe build a bit more velocity? Probably the hot ticket in 1980...

Like Tony said, I also would think that the mounting bolts would provide sufficient ground for the solenoids.

I've been looking for a set of Zeniths, and would be more than happy to convert the car. Tony, can you donate a sorted set to my cause?

John
 
Carburator Choices

The following is from a posting in 2003 on the old Forum concerning the performance of the Webers and Zenith carbs. Tony is correct about the Zenith and 32/36 Webers based on these numbers.

Date: May 02, 2003 at 18:00:17
From: mike, [000-160-092.area1.spcsdns.net]
Subject: Re: Your 38/38 vs 32/36 math needs revision

there is a great many things that covern flow outside of just the diameter of the holes. the shape of the venturi, carb configuration............

on a flow bench at 28 inches of water, the zeniths flow 268-279, the 32/36 flows 248-259, and the 38/38 flows 322-330 cfms. the variations are attributed to casting differentiation as well as age on the zeniths ( vacuum secondary)
according to weber, they do not use a cfm formula and have no published cfm numbers available.

If you go to the 38/38 Weber, you can expect better performance, reduced gas mileage in city driving but should be combined with at least a more aggressive cam. I'm not sure the 38/38 is appropriate for a stock CS set-up - it is a performance upgrade. I have this set up and am very pleased with it.
 
I've been looking for a set of Zeniths, and would be more than happy to convert the car. Tony, can you donate a sorted set to my cause?

John
Click to expand...

I don't have any spares now, though I have been looking. I rebuilt a set a couple months back for a local guy to use on his Bav. All the factory rebuild info is in the Tech Info section of this board. It's a pretty easy rebuild, actually. The biggest concern is wear around the throttle shafts and warping of the bottom plate from overtightening. There's a guy on eBay.de that posts new throttle plate sections for sale once in a while, but in a pinch you could bush a worn shaft with brass. I've done that on Webers, it's not too hard. I always check the flatness of the bottom surface with a straightedge, and if needed do a little hammer massage and filing to get them nice and flat.
 
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