Help - Weber 38 Starts and Stalls Instantly / No Idle

I recently installed a Weber 38/38 with an electric choke and can’t get it to idle. I am running the factory fuel line straight into the carb, no FPR, and blocked off the vacuum port on the rear of the carb.

I’ve checked for vacuum leaks where the carb meets the intake manifold/adapter and there doesn’t seem to be any. With choke full open, I’ve tried adjusting mixture screws, idle speed screw, and I changed both fuel filters. The engine starts and revs for a few seconds and dies. The only way I can keep it from stalling is if I keep pumping the gas pedal. If I leave my foot on the gas instead of tapping the pedal repeatedly, it stalls. Since it’s starting and I’m able to rev it when I pump the gas, I’m thinking the fuel pump is working (I hear it whir when I turn the key in the ignition).

I’ve been messing with it for a week and can’t get it to run. Really need some help on this! Thanks!

Is the vacuum advance still connected

From the distributor, no it is not connected to the carb. But even when it was I was having the same issues.

Yup I just tried reconnecting that vacuum advance and still stalling. I removed most of the vacuum lines from the stock carb, do I just plug all the ends (like the ones on the back of the intake manifold)?

How did you connect the advance? There should be a line to the lower advance port to the manifold. Other than that, all ports on the manifold and carb should be plugged... That should be enough to run.

Is this what you mean? The one I circled is where I have the advance connected.

Yes. But you didn't have it connected initially? Did anything change when you hooked it up?

Is the choke closed when you try to start?

Thanks for the replies, I've been double checking my connections and tried adjusting the choke (it's electric). The choke is closed when I try to start it. It seems to run when I increase the tension on the choke. If I prevent the choke from opening all the way it seems to idle. The idle is at about 1200 RPM and if I try to go lower, the idle is very rough and the tachometer is bouncing. Could this mean low fuel pressure or vacuum leak? And should I be letting the car idle without choke fully open?

It seems like there is still an underlying issue...

Have you done any basic tuning on this carb?

It's obviously going to need the choke open to run. Open the choke all the way and then mess with the mixtures, idle shouldn't be more than 1000

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Originally Posted by 87revival

I recently installed a Weber 38/38 with an electric choke and can’t get it to idle. I am running the factory fuel line straight into the carb, no FPR, and blocked off the vacuum port on the rear of the carb.

I’ve checked for vacuum leaks where the carb meets the intake manifold/adapter and there doesn’t seem to be any. With choke full open, I’ve tried adjusting mixture screws, idle speed screw, and I changed both fuel filters. The engine starts and revs for a few seconds and dies. The only way I can keep it from stalling is if I keep pumping the gas pedal. If I leave my foot on the gas instead of tapping the pedal repeatedly, it stalls. Since it’s starting and I’m able to rev it when I pump the gas, I’m thinking the fuel pump is working (I hear it whir when I turn the key in the ignition).

I’ve been messing with it for a week and can’t get it to run. Really need some help on this! Thanks!

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It doesnt sound like its getting much fuel, I would see where he float adjustment is and what he fuel level in the float bowl is.

Hey yall, thanks for the replies, it's been a really busy month and I've only had so much time to work on the car. I got the car to a running condition at a cold start (above 1100 rpm), but it still doesn't idle when warm.

But after hours of testing, I made sure my carb is tuned at least at the base setting (1 1/2 turns out), and I installed a pressure gauge, a new pump, and a regulator. My problem seems to be getting more complicated now that I can monitor the setup. So, when I start the engine the fuel pressure is around the 2-3 psi mark. However, when I leave the engine running, eventually the fuel pressure is building up and approaches 5-6 psi at which point I shut off the car because I know the carb is not designed to take that pressure. Something else I noticed is that, regardless of the position of the choke, when the engine is warm the car will stall or not start.

Now I am realizing there are a few maybe unrelated issues:
1) fuel pressure
2) doesn't idle when warm

I am thinking that the first issue can be solved with a return line. Do the carb'd versions of these cars come with fuel return lines from the factory? If not, has anyone here done it and know the best way to go about adding a return system.

For the idle, I am thinking it may not be vacuum related, since I have my vacuum advance from distributor connected to carb and brake booster still connected to intake (to my understanding the only two sources of vacuum needed). Then, I am thinking, do I need to change the jets and if so, what size jets are typically used for this car?

There is no fuel return line, but I dont see a problem with 5-6psi, I think thats what the factory carb and pump ran at. If it actually creeps too high all it will do is push out of the jets, that is what I would look for to determine too high fuel pressure.

http://www.redlineweber.com/html/Tec...as_tunning.htm
Follow this. You HAVE to get it to run with the choke OPEN, then you can sit the idle screws. Take note at the bottom, if the idle screws have to be turned out more than 1 1/2 turns to idle then yes you need larger jets.
Follow the set up adjustments to a T!

To my understanding the correct fuel pressure for these Webers is lower than most carbs, and I believe it is not supposed to exceed 3.5 psi (or be in the 2-4 psi). The pressure does start out between 2-3 psi when I first start the car, but it increases to the 5-6 psi mark after a few minutes. Also that is the sheet I have been following for adjustment, but as I mentioned with choke fully open it would not run. I will try this again later today.

My speculation was also that the jets are simply not pushing out enough fuel so it’s causing the pressure to build…, but after talking to a tech advisor at Redline, he thinks that the fuel pressure increase would not have anything to do with jets and that was why he recommend the return line setup. What do you think?

Does anyone run the Weber kit straight out of the box or is it necessary to adjust jets for our cars?

Is this a new kit from redline? Not sure about the jetting with the kit, but I would have gotten a jet kit along with it. Maybe you should cap off the brake booster vacuum line, verify timing is way off the line with the vacuum line plugged up, and on the lines wih the line disconnected (dont actually care about timing, as these engines will run on a very wide range as long as the advance works)
For fuel pressure, do you have anything to regulate it? Yes, a return style would be better, but good luck converting to that. And no, not everyone who has a weber went return style.

Yeah converting to return style is something like a last resort, bc I do think it will fix the fuel pressure issue but I don't think its going to be so easy. And yeah it was a new kit, Kit # K 728-38 to be exact. I do have a deadhead FPR after the filters and before the carb, that's where I attached the gauge too. But turning the screw out doesn't seem to help. What is the purpose of capping off the brake booster line, to test vacuum?

a 30 year old brake booster could easily leak. Just a variable, as is a working ignition advance

Some 32/36 or 38/38 weber have a fuel cutoff solenoid in the back. If it is not connected or receiving power with the ignition on it will not idle. It has a single wire male spade connection 12v ign positive. It is the only electrical connection to the carb besides the electric choke on applicable models. Not all weber have this, but it sounds like this is your issue or your idle screw is all the way in

This is an extremely late reply, but I figured out what the issue(s) were, in case someone else has similar issues.

1) There was a small fleck of dirt stuck in one of the emulsion tubes, preventing enough gas from being mixed.
2) Adjusting float helped.
3) Adjusting choke helped.
4) The stock jets (at least the one my kit came with) are not the best air/fuel ratio. I think putting a larger main jet or a smaller air jet may help. My current main jets are 45 and air jets are 165/170, for reference.

It runs, but I will mess around with a jetting kit to try to fix the pressure issue. Thanks for everyone's guidance, I definitely needed to rule out all of the things you guys mentioned first!

Glad you made some progress on it. On the subject of jets: is your engine stock? I’m running a Weber 38 on an engine with a 272 cam, and even then I had to reduce the size of the jets the carb came with. Mentioning this because I am doubtful you would need to increase your main jets, unless your carb came with tiny jets. I recommend getting an AFR gauge & installing a wideband O2 sensor in the exhaust, it will make tuning the carb a lot more convenient.

Edit: your Main jets are likely 145 instead of 45. I don’t think they make a 45. Unless you’re talking about idle jets?