Webers won't behave

[Bob Ashlock]

Long story… the subject is a ’70 911T 2.2L engine with Weber 40IDA3C carbs. For several weeks I have read and re-read these posts but now I'm throwing in the towel and submitting my questions. Before going further, let me express my thanks to all the contributors to this forum as it is very helpful!

Here's the background: I don’t have any history on this engine as the previous owner had it sitting in his garage for many years. I cleaned it up and set it up on a “test stand” so I could check it out before installation in my car. It appears to have had a top-end job at some point and had the chain tensioner modification.

Here’s the problem: These Webers continue to spit and pop. When they are cold, that’s expected. After warm up, they will idle without too much shenanigans, but as soon as I give throttle to push the rpms up to 1500 – 3000, I get a lot of spitting and popping on the #1-3 bank. If I really push the throttle to get up on the mains, the engine responds well with no popping… so this just occurs during “transition” or in what I would call the “level cruising” zone, where you would be cruising at 3000 rpm with a light foot on the throttle to maintain a fixed speed.

I have gone through these carbs and they are clean. The shafts are not loose as I had them zinc plated to build them up a few thousandths. The butterflies seat nice and there is no ridge in the barrels. The accelerator jets all squirt into the barrels OK. If I release the cross-linkage, I can rev up bank 4-6 without any popping and the engine sounds good. If I do the same with bank 1-3, I get bad popping, most especially on #1. I swapped the carbs and the problem follows the “bad”carburetor, making bank 4-6 have the same problem, while the “good” carb fixes bank 1-3. Using a uni-sync, the balance between each throat and side-to-side looks reasonably close. I have tried precision balancing using the air bypass screws and even using a manometer. This doesn’t help. It just seems like #1 is always too lean during transition. So I disassembled that carb again today and carefully verified that all the idle circuit and progression passages are clean and clear.

I have also verified the following:

(1) Compression: All cylinders at 145-155 psi.
(2) Checked valve clearance cold … all are .004”.
(3) Installed new spark plugs and set them at .028”
(4) Points are gapped correctly and set static timing at TDC.
(5) Verified distributor is advancing and returning properly.
(6) Timing around 5 degrees at idle and at high rpms around 33 degrees.
(7) Plug wires all measure good.
(8) Fuel pump pressure is 3 psi.

It seems to me that the “bad” carburetor runs leaner (especially on #1) even though all the jetting matches the other (“good”) carburetor. From all my readings on this forum, it seems that these values should be suitable for this stock 2.2T engine:

Mains 125
Idle 55
Air Correction 180
Emulsion Tube F26
Venturi 30

Spark Plug read: shows #1 looks like it is burning leaner than the others, which are mostly black as I have been spending a considerable amount of time idling this engine.

I tried installing a #60 idle jet in #1 and this decreased the popping. I installed #60 in #2 and #3 and I could see a small improvement. It just seems to me that this is wrong. Why would this particular carb need larger idle jets than the other one? Perhaps I could just bite the bullet and install #60 idle jets in both carbs, but it seems like this is an overkill or might be ‘masking’ some other problem.

I suppose it is possible that these Webers are just not well-suited for this engine. Perhaps their previous life was spent on a 2.0L engine. They do have fairly low serial numbers ... (1358 I believe.) I also understand that the 2.2T engine typically arrived in the U.S. with Zenith’s. My goal is to get this engine set up for good driveability. I am not necessarily looking for maximum power. I saw one post that stated the "pecking order" is PMO, Zenith, then Weber as a last choice in this regard.

Any ideas about how to resolve this problem? Should I just bite the bullet and set up the idle circuits in an over-rich condition? --Bob

[jpnovak]

Did you make sure the secondary venturis are installed correctly?

They have a hole on only one side. Its like they are not delivering fuel. If installed backwards the engine will have the problems you describe.

I would have originally suggested that your linkage was set incorrectly but since you checked each bank individually this might not be the case.

btw, great engine stand.

[Bob Ashlock]

Thanks for the reply. Yes, I did check to be sure the secondary venturis are installed correctly so that the port can feed the side-hole. The secondary venturis don't really come into play until you lean hard on the throttle. What I am experiencing is more related to the idle/progression circuits that are in-play under light throttle conditions.

[Trackrash]

Assuming your motor is stock.
Nice looking car BTW.
First make SURE the carbs are getting clean fuel. A GOOD new fuel filter and CLEAN gas tank are mandatory.
Unfortunately you will have to run the idle rich on these carbs to get them to behave, especially with the crap gas available now days.

60 or even 65 idles may be needed.

One trick I learned is that your motor will run better with a re-curved distributor. This is not the cause of your carbs spitting, but something to think about doing. The original T distributors did not have enough advance at or near idle. Weber motors will run better with about 7 deg advance at idle an about 35 deg advance at 6K rpm.

[Tooth911]

What about the float levels and there condition. Try doing a float level check with motor running with a float gauge attached to the drain plug.Each one should be at the middle level.cheers Chuck

[Bob Ashlock]

Thanks Gordon, thanks for the compliment on the car .. 66-912. Yes the fuel is well filtered. I am well-aware of how easily the idle circuits on Webers can clog from my experiences with my Weber carbureted 912.

You make a good point that these carbs were designed for fuel that was available 35+ years ago. Thanks for the tip on the distributor curving. --Bob

[Bob Ashlock]

Regarding the comment about float levels. I forgot to include that in my original post. I have set the levels correctly. In fact, I have even experimented with raising the levels as much as 5mm just to see if that would give more enrichment. This spitting/popping problem seems to be pretty immune to the float level setting.

[joeblow]

I would suggest swapping the acceleration jets from one carb to the other. I know it sounds strange but it seems like if it is a transitional issue you should focus there. If the problem follows the jets then you have isolated your issue.

It does not seem like a jetting issue if it only happens on transition.

[Steve@Rennsport]

Bob,

Your symptoms are due to leanness and if the carb is really, truly clean (understanding that you'll rarely ever see the offending dirt), I'd recommend looking for a vacuum leak between the carbs and manifolds. I'm assuming that the throttle shafts and bushings are not worn.

Both can be checked by careful and precise use of carb cleaner in some areas.

Your jetting is just fine and I would not change anything.

[Bob Ashlock]

Thanks for the input Steve, I understand the comment about hidden dirt. I had even considered removing the lead plugs to give clear access to all the passages, just to make sure nothing is hiding in there. I was reluctant to do that considering I didn't have any lead to put back in (although I suppose I could use JB Weld). I hesitated because it seemed like the passages are clear based on my observations when spraying carb cleaner and compressed air through them. None the less, the condition is definitely lean on that cylinder and there must either be air getting in somewhere, or not enough fuel is getting sucked through the fuel feed passageway to the idle jet. This is just one of these deals where I will have to continue playing with it until I have the "ah-hah" moment.

More info: When I observe the behavior of the little indicator on the uni-sync, even though it rises to the same basic level as the other cylinders, on this problem cylinder it seems to bounce up and down a bit more than the others... as if there is more reversion, or some kind of manifold leak. I already installed fresh manifold and carb base gaskets and made sure everything fit flat and nice. I would even suspect a valve leak, except I just ran the compression again yesterday and saw good numbers on that cylinder, although it was the lowest (145) versus 150 for the others.

[Eagledriver]

Air can be leaking into the carbs around the idle mixture screw or the idle jet holders (o-rings should be on both of these. You can also try swapping the idle mixture screws between carbs.

-Andy

[Bob Ashlock]

I do have those little suckers O-ringed, although these early carbs don't seem to have the depression area to accept an O-ring. (I had read or seen that the O-ring was something Weber added later.) I think I already tried swapping the mixture screws amongst the same carb, but did not compare them or swap them with those on the other carb so I suppose that's an easy one to try!

[74er]

You might want to consider opening up those lead ports. I've done so with good improvements. Maybe just do the #1 first to check it out. Once opened, squirt carb cleaner through where the fuel enters the carb near the butterfly by taking out the screw in fitting...squirt up where the fuel enters this port. Make sure you see fluid pass through all of it's passages. You may need to hold your finger over one or two passages so that you know it can travel in all directions. I melted some solder into a ball and semi-shaped it to a good plug and tapped it in to refill the lead ports. You don't want to refill the lead ports too deep or you'll block the flow. JB weld may seep into the hole and block flow before it dries.

[Bob Ashlock]

Thanks ... good idea to just use solder balls to re-plug the passages.

[Trackrash]

You may also want to check the by-pass orifices. I had one plug up once and it acted just like a plugged idle jet.

[Bob Ashlock]

And where are those "bypass orifices" located?

[c0metdot]

Had the same problem. A good soak and a pertronix flame thrower coil did the trick.

[Trackrash]

Remove the plug at the red arrow. You will see three holes.

[Steve@Rennsport]

Those are the Progression holes and like everything else, must be perfectly, absolutely clean.

Unlike other brands of carburetors, Webers do NOT tolerate even the slightest dirt (or water) inside any passage tor jet so "Cleanliness is literally next to Godliness",....

I would also recommend very carefully removing all the lead plugs to get all the passages spotlessly clean. I use old lead shot to reseal the holes when I'm done.

[Bob Ashlock]

Thanks much to Steve, Gordon and all others for the suggestions and recommendations. I will pull out those lead plugs to inspect the passages. I know there has to be a good explanation for this bizarre behavior and when we get down to the bottom of it, it will make perfect sense. Since today is my wife's b-day, and we are leaving on a little trip tomorrow for a few days I probably won't get back on this subject until late next week sometime.