Yet another carb question...

[MrWrench]

1984 here.

Yesterday while I was driving and being a little heavy on the throttle. The car started hesitating and then began dying at idle. It dies at idle both cold and warm.
It'll start and run fine and drive down the road with no issues and no misfire or anything noticeable. But once it gets back down to idle, it'll hesitate and fluctuate RPMS and then die.
Previous known issues I haven't addressed is dieseling at shut off and it seemingly is running pretty rich. Exhaust is rich and smells like fuel. Here's a list below of what I've tested so far. There's probably something small I forgot to mention.

Does anybody have any ideas as to what I should search for or test next? I was considering just replacing every single vacuum line on the car.

So far I've tested the following items and found them to be good.

- Float level is in sight glass when car stalls. Which leads me to believe it isn't pump related.
- Fuel cut off solenoids can be heard when sending power to them through the harness.
- I spray tested all vacuum lines, carb baseplate and intake manifold and found nothing.
Found vacuum advanced disconnected - fixed this.
- I changed a handful of little vacuum lines that seemed too short and kinked.
- Checked timing. It's at 10°
- AAP. When cold, I crimped the line off with a pair of hose clamp pliers - fuel came out. I let it warm up-ish (difficult to do but it was running for probably 8-10 min) Crimped off the same vacuum line and turned the car off. No fuel came out.

[dlb]

Is it still cold when it dies at idle, or has it warmed up by then? Depending on which it is, it may be as simple as adjusting either the idle or fast idle.

[MrWrench]

It dies both cold and warm unfortunately! I haven't adjusted the idle or fast idle at all.
Prior to it randomly failing and leading to the fluctuating idle and other issues I've had as of late. It would idle around 850rpm.

[Nordical25]

I had similar issues with my 4wd Tercel. A fix to my issues was a remanufactured distributor. My original distributor had a failured vacuum unit, which caused Aisan to have wrong timing advance at idle both warm and cold.

Simple check to verify functionality of vacuum unit is to check if timing advance unit ports can withold vacuum. If the unit is original, that is very unlikely.

[MrWrench]

I did notice my vacuum advance was disconnected and I couldn't tell you how long it wasn't connected for.. but at least the last 1,200+ miles since I've owned it.

How can I test if they hold vacuum?
Thank you!

[Nordical25]

I see. I assume, that you have several lines to distributors at vacuum advance canister? I know that different Tercel 4wd models could have from one to three vacuum lines to vacuum advance canister at distributor. First line is from disributor vacuum advance to carb, second line should be from distributor to thermal switch valve and third one could be height compensation vacuum line. We have only one here in Europe, that is the carb one.

Basic idea of vacuum advance canister is explained here, it works primarly on low engine loads, while spring mechanism works mostly on higher loads:
https://www.youtube.com/watch?v=msHlcjrnjV0

I have heard that officially you should have a vacuum gauge, which tests that vacuum advance canister is good. I don't know if you have here a Tercel 4wd service manual, which specifies this test.

However, manual and very simple exam is to test vacuum advance canister with clean unused vacuum hose. You will attach clean hose to distributor vacuum canister and block remaining vacuum canister ports. When you suck the air through the canister port, a vacuum advance canister arm attached to distributor should move and you should feel the vacuum. Air will flow just through without any bigger distributor advance movement if the thing is broken. Do this test to all vacuum advance canister ports. There are a rubber membranes inside the canister, which are becoming weaker similarly to all aging rubber parts. When the membranes suddenly break, you will have no longer vacuum advance but a vacuum leak instead.

[MrWrench]

I do! I just went out and looked and it has 3 vacuum lines to the distributor. The upper one is the one I found disconnected.

I just went and re-sprayed everything down with starting fluid and found nothing that changed.
It seems to fluctuate between 800-1300 RPM and the idle is not steady. It'll smooth out and run steady at around 1100-1300 for a brief moment and then continue to fluctuate. Which was not the case before. It used to idle around 900rpm and fluctuate RPMS from there and stall. Maybe I created a vacuum leak I cant find? Or possibly it has been altered with the leak at the vacuum advance port to run smoothly and now that it's connected, the RPMs have increased?


With all that being said, it isn't stalling nearly as often as of my last test drive. It's also 20+°F colder today which might be playing a factor?

I also realized I do have a vacuum tester, but nothing small enough to securely snug onto the ports of the distributor. I will see if I can't source some 3.5MM vacuum line to test it out (it would be a good idea to replace them all anyway)

Thank you for your help!

[NWMO]

Hey Luke,

I was fighting a similar issue on the Rusty Frog and found it to be “rust” particles in the idle circuit. Even with a fuel filter, some crap may by and create an issue. At speed it did fine, but it wouldn’t maintain idle.

Chris

[MrWrench]

There's a very good chance that is a possibility. I drove this car the entire way home without a fuel filter. I added one about 400 miles ago. What was your remedy? I'll look up in the FSM where this is located.

[dlb]

I also realized I do have a vacuum tester, but nothing small enough to securely snug onto the ports of the distributor. I will see if I can't source some 3.5MM vacuum line to test it out (it would be a good idea to replace them all anyway)

Replacing vacuum lines is usually not necessary. It's very rare for them to split or disintegrate. The most common sources of vacuum leaks are hoses that are not attached, and vacuum diaphragms that are broken. Incorrectly routed vacuum lines is also more common than broken ones.

You don't need a tester to test the diaphragms, like the ones on the distributor. Just leave the hose connected to the diaphragm you want to test, disconnect it at its other end (only do one hose at a time so you don't get them mixed up), wipe it off and suck on it. If you can suck air through it, the diaphragm is broken. In that case, cap the port or hose that goes to the broken diaphragm until you can replace it. You should do this with all the diaphragms since they do wear out eventually.

[MrWrench]

Thank you very much! I will try this tomorrow after work and see what I come up with.
I believe I have a distributor with a broken rotor that I could replace the vacuum advance with, should this be the problem.
I will test it and hope for the best!

Thank you all so much for your help! This forum is amazing.

[MrWrench]

So, patience isn't a strength of mine... I decided to run out to the garage tonight and test this. I removed the longest piece of vacuum line I could find on a spare 3A engine.
I pulled one port off at a time at the distributor vacuum advance. they all seemed to hold vacuum when sucking on the end of the hose connected directly to the distributor vacuum advance port.

[dlb]

Ok that's good about the vacuum advance holding vacuum.

Back to your original question of dying at idle/rich exhaust/fuel smell -- how is the choke butterfly valve, does it turn to almost vertical after a few minutes of the engine running?

You mentioned the timing is set to 10*. Is that with the vacuum advance hoses disconnected and plugged?

[Nordical25]

It is good to hear that you have a functioning vacuum unit, it helps a lot with original carburetor and is kind of a requirement. As dlb mentioned, it is worth of thinking timing angle next.

You may want to clean the carb as NVMO mentioned and also a fuel tank if the RPM fluctuation is caused by dirt at carburetor. Dirt at carburetor can originate from dirty fuel tank.

Last thing to check after these suggestions are to check distributors rotor, spark plugs, spark wires and distributor cap surfaces. Especially distributor cap oxidation and rotor oxidation tends to case weaker idle. As a quick fix you can clean distributor caps metal surfaces with a screwdriver and rotor with paper to gain metal surface visible again.

[NWMO]

Post by MrWrench » Sun Feb 13, 2022 6:16 pm

There's a very good chance that is a possibility. I drove this car the entire way home without a fuel filter. I added one about 400 miles ago. What was your remedy? I'll look up in the FSM where this is located.

As I recall, if you look at the break-out on FU-6, I pulled the "slow jet" and cleaned it. There should be I believe two very small holes at the bottom of the hollow tube that provide fuel at slow speeds, etc. I'm sure I sprayed down everything else with carb cleaner, but I remember finding some debris in the slow jet and felt like that was the issue.

Chris