GM feedback carburetors

Sean Owner Cornville, Arizona Posted   Latest  
1981 Chevrolet El Camino 3.8L (A) 3-spd (THM350C)

I had this sweet El Camino get towed in last week as a no start after sitting for 6 months. He inherited it from his dad, so no known history, just that the fuel gauge read half tank 6 months ago when he parked it. Quick check showed no fuel getting to carb after 30 seconds of cranking, and fuel gauge reads half. I hook up a pressure/vacuum gauge, and see it varying between 1 psi, and 1 in/hg, so it appears that the fuel pump diaphragm is intact. I let it sit until Wednesday, then finally I push it in. Pressurized the tank with a small amount of shop air while cranking, and we now have 3.5 psi, still no start, but it will run off of ether. No fuel being squirted by the accelerator pump, and carb looks very clean, like a recent overhaul. Carb is a E2ME Dualjet.

Got the authorization to rebuild the carb, and tore it down, to find it bone dry inside, not even the evidence of evaporated fuel. Check the check valve in the filter, and I can blow through it. I figure if there's a problem, I'll run into it on the reassembly. No issues at all, got the mc solenoid adjusted to spec, the air bleed set, reinstalled the carb, and it fired right up. This morning, I hook up the old brick to adjust the carb, and found codes for tps, and mc solenoid, even thought the solenoid is clicking. wiggle the connector, and it quits. Check the tps, and it's stuck at 4.88 volts. I go, and order a pigtail for the mc, and a new tps, them go back, and decided to perform the base adjustments while waiting for the parts, and found the o2 stuck at .454v, so off to order a new o2 as well. I replaced the ect, and pigtail yesterday while the carb was out, because it had the typical bare wires. 

As I am waiting for parts, I realized that this thing had to have been rebuilt in the last couple of years, and whoever did it only set up the carb, and nothing else, not even testing the tps. Very interesting that they only did part of the job, because these carbs are complicated, and require gauges to set up correctly. I am only 39, and have been in the industry since 2001, so I shouldn't even know how to do these carbs, but 20 years ago, I had an 81 Camaro with the E4ME, and it wouldn't pass smog. I messed with that thing so much, and finally got it to where it was getting 18 mpg, and would pass smog with flying colors.

How many of you out there would be able to make this thing run correctly when done? How many of you would tackle this job as a learning experience, and tool up to do it?

Rusty Owner/Technician
Oakham, Massachusetts

I would and I do a few carb repairs now because few folks know what they are doing. I'm 63 :-)

Your fuel pump test indicates a faulty pump BTW. It should pull at least 15" of vacuum if the outlet is wide open and it should make at least 7 PSI. A compound gauge hooked to either port "cycling" between pressure and vacuum indicates a leaking check valve.

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Jaime Diagnostician
Ocala, Florida

If I rebuilt one I've done a thousand of these carbs. At one point I was doing 3 a day (full rebuilds) and 3 tune-ups (Plugs, Caps & Rotors, if the last 2 were needed) per day. Like Rusty said, you probably have a bad fuel pump. I suspect the pump may have leaked into the engine oil, and not back to the tank though. Either way, change the pump and you shouldn't have the hard/no start condition the next morning.

Oh, and if you have never changed one of those pumps, there's a "trick" to holding the pump push rod in place. Use a 3/8" x 1 & 1/2" coarse threaded bolt in place of the bolt on the front of the block, turned just hand tight, to hold it before you begin.

I commend you for learning the "old" stuff... I believe we must know from where we came in order to better understand where we are at today.

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Sean Owner
Cornville, Arizona

I've done plenty of those pumps, so I already know that trick with the bolt. I pass that one on whenever I can, because nobody ever showed me, and I used to fight the pushrod.

I'm one of the few around that will even work on the older vehicles, and I do probably 6-8 carbs a year. The least favorite one I have ever worked on was the Varijet in the 1984 S-10 I used to own. I could never get that thing perfect, because the throttle shaft was leaking. I now have a lathe, so if I ever come across one like that again, I can just make my own bushings to fix it right.

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Cliff Diagnostician
Santa Maria, California

I would do it in a heartbeat, Though not a learning experience for me. I still have all the tooling to do them. Granted the stuff is in a cardboard box in the nether reaches of my toolbox. I still do about 6 to 8 Carbs a year and I am picky which models I do rebuild do to the lack of readily available parts like the old days. 

Kudos to you for taking it on! I have been in the industry since 1991 and remember the days of doing 3 plus carbs a week here in California.

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John Instructor
Beaver, Pennsylvania

Rebuilt more of those than I can count. How are the throttle shaft bushings? BTW no fuel at all in the bowl? The needle valve was probably stuck in the seat.

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Charles Instructor
Fitchburg, Massachusetts

OH! yes I do recall the process and we actually had a "Clean Room" within our shop so that a rebuild couldn't get contaminated. Really Though it was so that we could keep the odor from the cleaning tanks and we also rebuilt Diesel injector pumps, which the room was set up for. Funny that you ask I was digging into my tool box and when I opened the top left draw I had a flashback and was wondering if anyone still was rebuilding carbs.......and behold their still alive. Funny story if I may.....during the age of feed back carbs we were at the GM Training Center here in Mass., During our tear down the Instructor...ROY ....came and swept all the parts into a barrel and said "lets see how good you guys are!".....Ready! You should have seen his face when one of the techs told him that the carb from his company car was in all those parts.......6 Quadrajet and one Varijet .....simply awesome.......we held him off till 3;30 and he said there was no way it was going to run.......Duty cycle on specs, 3krpm spec right on and tailpipe emissions better than specs ( opened the air adjustment ,as they had a tendency to run very lean) screw. We never got the 20 that was spotted and from that point on he never used his car again........he "borrowed" the Body Shop Instructors for our class and that's another story. It's great to see that a person like Sean has the ability to know how stuff works and can work his way to perfection in the process........great job Sean.......I/we commend you in your abilities and as a senor tech....i've got our Friend Rusty beat by a few know that there are those who can carry the torch forward. The opportunities are all yours.......It's a great Life of which there are no regrets other than what we allow. Good luck and I wish you only the best in your travels.

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Danny Technician
Losangeles, California

I've rebuilt a bunch of them. I'm sure I could put one together blind folded. That said, I would never repair another one for a customer. However, I might do it for a friend as a favor. The last one I worked on was a CO failure. It had a TP Sensor that read reference voltage on the signal line. That put the ECM into WOT mode. Apparently the carb had been taken apart numerous times. The accelerator pump lever was binding because someone hammered on the cover. I had to try very hard not to break the air horn as I removed the pump lever. It should have been an easy repair.

I used to be able to order a kit, float and choke pull off, and have it delivered within an hour. I probably had a half dozen different sources that stocked the parts. Where are you going to find those parts now? This no longer a simple repair, it's a restoration project. If a friend needs this service, they'll have to take the time to find parts, there's a lot of easier ways of making money.

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Glenn Owner/Technician
Houston, Texas

I've got Rusty, beat I'm 70 and still at it. I've done a ton of these also. However in my area in houston tx, i would not consider this job unless the tank is cleaned and fresh fuel added.

I'm pretty sure that even on that old C3 system there is a .450 bias volts on the O2. but if he's keeping the car a new O2 is not a waste. I do have an old Line 9 catalog if you need any part #s and I still have smarts assortment if you need. good luck. glenn …

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Sean Owner
Cornville, Arizona

Both Autozone, and Oreilly's stock carb kits, and floats. Choke pull-offs are usually in Phoenix, so I can order the parts, tear it down, and drop it in the bucket, then be able to reassemble the next day.

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