3AC Carb Troubles

GTSSportCoupe · Post by **GTSSportCoupe** » Thu Apr 01, 2004 11:23 am

As some of you may recall from a couple months ago on the yahoo tercel4wd group, I was having trouble with my 87 tercel 4wd's carb. Originally I had the following problems: choke didn't work very well (if at all), rough idle, not very smooth when driving at operating temp, really bad fuel mileage, and leaked gas into the primary when engine turned off hot.

I had tried working on adjusting and troubleshooting the carb as per the factory repair manual, but eventually realized that a new carb was in order.

I went up to the wrecking yard last weekend and picked up a carb in good shape with the same tag number as my original (15300), cleaned it up really well, and installed it on my engine with new gaskets. The wrecking yard told me they had driven the car it came off for a while, and it ran just fine, so I have to assume that the carb is good. On my car it fixed most of my previous problems, but I still have the rough idle (really rough), and poor fuel mileage. I double checked all the vacuum line connections as per the factory repair manual, as well as did a visual for vacuum leaks. Everything appeared fine.

Previous to all this, my car has a new fuel filter, new air filter, new spark plugs, new distributor cap and rotor, adjusted lifters and even compression. Timing is set to 13 degrees BTDC at idle with all vacuum lines connected as per normal. Idle speed is set to 950rpm. The car also has good tires, non dragging brakes, and synthetic oil in trans, diffs and engine. The carb float is at the right level

This is a pretty frustrating problem, as I would really like to get good mileage out of this car (especially for the 62hp that it provides me with). I'm thinking that my problem might still be a vacuum leak somewhere that I cannot see. This weekend I'm going to replace all of the vacuum lines with new vacuum hose.

Does anyone have any idea what else the problem might be? Have you had any carb problems on your tercel? Is this the way a carb might perform with a vacuum leak? Thanks for any help.

Nick

icE · Post by **icE** » Thu Apr 01, 2004 1:26 pm

My 87 4WD does the same thing, probably needs a new carb too. It burns oil and idles rough. Can't really say much to ya tho, except a hidden vaccum leak or a bad fuel pump.

GTSSportCoupe · Post by **GTSSportCoupe** » Thu Apr 01, 2004 2:07 pm

I was wondering about the possibility of a bad fuel pump too...I thought the symtoms would be different, but it is always a possiblity. I'll check into it...

GTSSportCoupe · Post by **GTSSportCoupe** » Fri Apr 02, 2004 10:26 am

Well, I replaced all the vacuum hoses last night with absolutely no change in engine operation.

My idle is really strange, not only is it rough, but it wanders a fair amount. I have it set to 950 rpm, but it will sometimes almost stall out, and other times wander as high as 1200 rpm.

Any ideas out there?

sacwac · Post by **sacwac** » Fri Apr 02, 2004 1:46 pm

I have just about the EXACT same problems as the parent post describes. One thing I found on my 86 was the vacuum advance on the distributor was bad. Was supposed to be advancing the timing around idle speeds, but was not.

Found a replacement at a junkyard, $6. Wasn't even off the same car. A 4A Corolla I think.

It made only a SLIGHT improvement.

Also, I drilled out the carb mixture screw cover so that it could be adjusted.... Adjusting that screw is a big pita.

Still, I have slightly rough idle..

1

GTSSportCoupe · Post by **GTSSportCoupe** » Fri Apr 02, 2004 2:27 pm

Interesting! I have noticed that my vacuum advance doesnt seem to be working correctly. When I pull any combination of, or all of the vacuum lines off the vacuum advance unit and plug them, my timing doesnt change at all. The timing advances with rpm, but that must be a different system (I have to read up some more on it). Maybe I'll replace my vacuum advance unit and see what happens. I want to try to avoid having to drill out the plug and adjust my mixture screw, but it has crossed my mind.

Thanks for the help.

sacwac · Post by **sacwac** » Fri Apr 02, 2004 3:13 pm

hmm. To really check, you could pull off the distributor cover, and visually check that the advance advances when vacuum is applied. Get a vacuum pump, and connect it directly to the advance... Then, see if you can get it to change. Thats what the factory manual says to do... I can take pics of that section if you want.

I get the feeling this is more of an emissions thing, as the manual states that it "retards" the timing at low rpms to burn more of the air/fuel mixture.

You are right! The advance is controlled by another system... this vacuum thing overrides that only at idle speeds.

GTSSportCoupe · Post by **GTSSportCoupe** » Fri Apr 02, 2004 3:32 pm

Thanks for the info! I'll check out my vacuum advance on the weekend. I do actually own a factory repair manual, so can look up info on the vacuum advance. Thanks for offering to scan pics for me though! I'll let you know how I make out.

takza · Post by **takza** » Mon Apr 05, 2004 4:06 am

My car actually idles OK...when I remove the air bleed that is.

Ocassionally it will act weird when I start it...but I think this is a stuck EGR.

Doing the decarboning thing has cleared up dieseling and starting problems at least temporarily.

Basically, you have to buy a vacuum tester for $25 and a multimeter for $10.......and go thru all the tests for each GIZMO on the engine till you have them all fixed. I'd look at the EGR first though.

Fixing my vac advance cured what remained of my hesitation problems...finding the major vac leak near the carbon canistor helped a lot first though.

Also, it's possible that someone has gotten the vac lines mixed up and on the wrong fittings....good luck with those vac charts though.

Note: I've got the vac tester and multimeter...but haven't done anything with them yet.

He says what?

GTSSportCoupe · Post by **GTSSportCoupe** » Mon Apr 05, 2004 1:21 pm

Haha! Thanks for the help. I do have a multimeter, so should just pickup a vac tester then. I have double checked all of my vac connections, they are all good. Just a matter of taking the time to methodically test each and every system. It's actually just my idle that is a problem now. My mileage appears to have fixed its self.

Thereminator · Post by **Thereminator** » Thu Apr 08, 2004 3:25 pm

Nick,I have a ruff Idle also.It jumps around some(950-1100),Misses(intermitant) and untill it reaches running-temp it will start to die at a light(like its ran out of fuel)and now I automaticly tap the acelerator to stop it.Im going to get a Junk-Yard Carb and compleatly rebuild-it,so Ill be interested to see how you fair.I dont get the 13%-BTDC doesent the manual say 5? Alan.

icE · Post by **icE** » Thu Apr 08, 2004 4:23 pm

mine has a rough idle also, only when cold though

GTSSportCoupe · Post by **GTSSportCoupe** » Thu Apr 08, 2004 4:40 pm

Alan,

You have described the exact problem I have right now. I'll be troubleshooting the problem tomorrow as I have the day off. I'll let you know what I find. I replaced my carb and still had the same problem, so it may not be necessary for you to rebuild your carburator to fix the problem.

My timing is messed (I don't think my vac advance is working right). The book says that the base timing should be at 5 degrees BTDC at idle with the vac advance disconnected (and engine at operating temp with no accessories on). I heard somewhere that the timing should be around 13 degrees BTDC with the vac advance connected at idle. I don't think thats right though. Mine seems pretty advanced as compared to how it should be. It knocks at low rpm full throttle when hot if I don't have high octane fuel in it. But it does have lots of power. Feels like more then 63hp.

icE,

It sounds like your choke is not working correctly. This is one of the problems I originally had until I replaced my carb with a good one.

icE · Post by **icE** » Thu Apr 08, 2004 7:34 pm

Yea, just need to find the time to do it...Probably won't have any till i'm through with school this summer

tercel4wdrules · Post by **tercel4wdrules** » Thu Apr 08, 2004 9:18 pm

My dad's 83 ran like crap in the morning when he used to use it and it would die. The choke on the carb is not working properly is my guess. There are also numerous other problems with it and it would sometimes diesel. Yeah, the RPMs also wander on this one; you start at 700 RPM when cold, rev it up a little and then it stays around 1000 RPMs and we've had this happen before. Cure for this car: replace the engine, rebuild the carb, and fix the locations of the vacuum hoses.