choke breaker jet not working

[Rickety Rhino]

Hi,
Both my 84 4WD's have the same warming up problem - when it's cold outside, around 5 or 10 seconds after starting, the engine RPM's go down, the engine runs rough, then dies. I have to put on gas to keep it going, which causes smoke. I've narrowed it down to the choke breaker jet not passing vacuum to the choke breaker, which is supposed to slightly open the choke after a few seconds delay after starting. If I open the choke slightly with my finger, it warms up fine, and eventually the choke opener opens the choke all the way like it's supposed to. The choke breaker jet fails the repair manual test, so I bought a new one from the Toyota dealer. It failed the test too, and also didn''t work when I put in on the car. I changed its direction in case I got it on backwords, still no vacuum goes through.

Has anyone else had a problem with a choke breaker jet? Do you know any other source for a vacuum delay valve of a few seconds which would work? I don't want to buy another ($30) from the Toyota dealer, since the one they sold me didn't work.
Thanks for any advice!

[ARCHINSTL]

How about installing a manual choke control? Lots of cars used to have this. I believe takza (and possibly others) did this; believe it was from JC Whitney, and not expensive - possibly AZ, ADV, O'R, or NAPA would stock it as well.
Tom M.

[4wdchico]

Toyota parts have a one year warranty. Just return the bad vac delay valve and have them get you another.

[Highlander]

You might check the TVSV, the vacuum to the choke breaker is controlled by the TVSV, so it may explain the bad new jet form the dealer. Just my .02

[4wdchico]

Actually the inner CB diaphragm that the vac line with the jet (AKA vac delay valve) goes directly to manifold vac. The outer diaphragm of the CB is controlled by the TVSV.

OP: Hard to imagine that you have two bad jets. They probably flow a very small amount of air so I would put a hose on the end of the jet that you are not blowing thru and put the end of the hose in water so you can know for sure if it flowing air when you do the blow thru tests.

The inner CB diaphragm holds vac and will break the choke when vac is directly applied, right? The vac line from the carb to the jet is in good shape and supplies full manifold vac all the time? Sorry, just had to ask...

[danzo]

I think I inadvertently discovered a gas mileage enhancement that may come in handy for a few peeps. I am about to become takza's new best friend.

Last week I was in a j-yard helping a friend remove a tranny from an old BMW. She was stuck in the grill. I started looking at '80's Toyotas for the 'choke breaker jet' referenced above since mine was clogged and I didn't want to spend $30 on a new one. Mine didn't flow either in either direction like the FSM says. I noticed that every carb'ed Toy I came across had no such jet, just a straight factory vacuum line. So I decided to simply remove my jet and see how it ran.

I measure my mpg with every tankful, and it's always hovered right at 30 mpg for combo city/highway driving. Really nobody does one or the other exclusively unless they are on a cross-country trip. But after removing the jet my mileage jumped to 36 without changing anything else. This even included quite a bit of idling while I was trying to get my a/c working. I suppose the choke breaker wasn't getting enough vacuum to fully open the choke, so my car was running a bit too rich. I have always been able to get more than the EPA estimate (even with the old est system) on all my cars since age 16, so I feel I have a pretty good handle on how to drive efficiently and consistently.

Of course I will continue to monitor my mpg and report any changes, but for now I'm pretty stoked. Hello mutual funds!

[ARCHINSTL]

I think I inadvertently discovered a gas mileage enhancement that may come in handy for a few peeps.
I am about to become takza's new best friend.

HAW ! !

[takza]

Well....hold on a minute there pardner. (spoken as John Wayne)

3ACPower (early member) is the one that talked me into giving up on my perfectly working auto choke because he found that by disconnecting it he got better mpg...though he had to mess around trying to keep it running when cold.

In my case going to a manual choke did nothing mpg wise...so my choke was working OK. I left all the vac tubes on it.

That's why you always want to check your choke plate when engine is warmed up to be sure it is fully open?

There are two vac diaphragms that pull the choke open? One that opens it slightly after it starts (breaker?) and the other one that keeps it fully open?

There might be something else going on with this? Might be not fully choke related...as in allowing vac to some other part of the carb.

That is a serious mpg jump....good buddy.

[danzo]

Partner, I can't speak for what 3ACpower did or your results from his advice (seems that your choke was OK), I'm just saying that if one's choke breaker jet isn't flowing then it could be hurting your mpg. The choke breaker actually does have two diaphrams inside as detailed on page 138 of the FSM.

Hopefully this will help me pass emissions in a coupla months. Wish me luck, good buddy.

[takza]

Pretty sure the choke is fully closed when set...and the choke breaker (unloader?) immediately pulls it back some...I know from experience with the manual choke that the car will not run will the choke fully closed...even cold. Then as it warms up it's the TVSV that controls the choke? The default for the choke is fully closed...only the vacuum keeps it open?

Hope you keep seeing the 36 mpg...like to hear if you do.

[Gokhan]

I have exactly the same problem with a 1985 Corolla 4AL-C engine, which is very similar. I am still troubleshooting it. So far, this is what I know.

First, the theory of operation. (Read the theory carefully before posting any reply.)

(1) Choke valve is fully closed when you pump the accelerator pedal before you start the engine, which also sets the fast-idle cam.
(2) Choke breaker is supposed to open the choke valve 38 degrees from the horizontal (39 degrees on non-carburetor-feedback models) through carburetor vacuum applied to diaphragm A. This action is delayed 1 - 5 seconds by the jet, which is at the vacuum hose and restricts the vacuum flow. It has nothing to do with TVSV.
(3) TVSV further applies vacuum to choke-breaker diaphragm B (in addition to vacuum directly applied through carburetor to diaphragm A) if the coolant temperature is above approximately 12 C, which further opens the choke by about an additional 17 degrees to a total of about 55 degrees from the horizontal (50 degrees on non-carburetor-feedback models). If one of the diaphragms is faulty, the total opening angle will be less.
(4) When the coolant heats above 53 C or so, TVSV applies vacuum to the choke-opener (not choke breaker) diaphgram, which fully opens the choke (90 degrees from the horizontal). It also turns on the EGR. Both are accomplished by the TVSV port M vacuum.
(5) You can only test the choke-breaker jet by blowing air into water by attaching a hose to it, as it restricts the flow quite a bit, even when it's brand-new. When you do so, you will see a few bubbles a second if you blow hard. It also has filters installed on both ends inside to protect the tiny jet opening. I did have a bad jet in the past, which was about 24-years-old, with which I saw no bubbles at all.

Now, the experiment:

I thought I had a problem with the jet again, and got a new one (for a little under $20 from the dealer), and replaced it. However, I tested the old jet later, and it turned out fine. The problem didn't go away as expected.

I will start the engine with the air-cleaner cover removed to see what's happening. There are several things possible. It could also be that the choke-breaker diaphragm A is the culprit. Perhaps both the jet and diaphragm A are OK. I had a bad TVSV in the past, which would open the choke fully with a cold engine, in addition to turning on the EGR with a cold engine (both done by giving vacuum through TVSV port M). This would cause stalling when driving with a cold engine. I doubt TVSV is the problem in this case. Nevertheless, I am fairly confident I will be able to troubleshoot it. A bad choke-breaker diaphragm would be hard to fix.

PS: Regarding the MPG vs. choke breaker and/or jet mentioned by a third poster, no, that can't happen. Chances are that there was something else wrong with that engine. Choke is supposed to be fully open (90 degrees from the horizontal) in a hot engine through the choke opener, even if the choke breaker is completely broken. Chances are that in that engine either the TVSV or the choke opener is faulty. Check to see if the choke opens to 90 degrees from the horizontal when the engine is hot. If not, it could either be that TVSV is not putting any vacuum through port M or the choke opener is faulty. It should be easy to figure out which by checking the vacuum at port M and applying vacuum to the choke opener.

[dlb]

welcome, gokham. yes, the 4A-LC is very similar to the 3A-C so you can use our FSM to test your various emission components. that section starts on page 81 so take a look. here's the link to it.

https://tercel4wd.com/forums/viewtopic.php?f=2&t=8103

[Petros]

welcome to the list gokham.

I agree with you, I can not see how altering or removing the jet for the choke opener would make any difference for a fully warm engine. Its only function is to open the choke when you stomp on the throttle when the choke is closed or activated. Once the choke is fully open, the opener does nothing.

I have owned a number of the Tercel4wds, all have gotten similar fuel economy, about 30-32 mixed highway. But there have been a few on this list that claim they have a dead stock Tercel4wd and they get 36-38 mpg. I want to know what is different about those cars! There was even a list member that had three, two got 32 mpg, and one got 36. He did not know what was different with that one. Go figure. choke breaker jet? not likely.

[Gokhan]

Thank you for the warm welcome, guys! I actually do have an original hardcopy of the 1985 Corolla FWD OEM repair manual. I've also downloaded the PDF for the Tercel manual for the fun of it. It looks very similar. It's great job by the person who scanned it!

As I said before, the problem I am having is identical to the one described by the original poster. I know it's not the jet (and it wasn't the jet with the original poster either), as I have replaced it with a new one and tested the old one as well. (You need to test the jet by blowing into water through a hose.) I will troubleshoot the system when I get a chance, perhaps in a couple of weeks, and hopefully find an easy fix. The original poster seems to have been unable to isolate the malfunction, as he didn't post about it.

[Ace]

I will just say that a good-working automatic choke works good, and is better than a manual choke IMO. I've had my '83 Tercel since 1984 and the only thing I have had to do with the choke is very occasionally spray some WD-40 (what I had available at the moment) on the associated linkage if it was hanging up, as evidenced by the choke not closing when the engine was started cold. It is also worth checking for cracked vacuum hoses that might mess up starting or operation.