1981 El Camino hot soak/perculation/hard restart problem

Your car is an ''81. It was built to run on today's gas so that's not the issue.

You believe you have eliminated everything in the carb but I wouldn't overlook it. I still think you have some sort or carb leakdown or overfilling. I would try a different carb on there, even if only to rig it up temporarily just to see if the problem is gone. You can still have base plates leaking or power valve leaking. The problem has to be in the carb somewhere.

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Thanks for the prompt reply.

Yes, it's an '81, but engines and fuel delivery systems have come a long way since then, and so has the fuel make-up to accommodate them. I know that the formulations on current fuels is different than it was 31 years ago.
When I was still driving this car to work 15 years ago, I drove on the average between 180 and 200 miles a day back and forth to work, (I live in southern Arizona, long ways between towns) and I drove more than 600,000 miles over the coarse of 12 years, and I've worn out my share of vehicles. But I would have problems with the car every spring and fall whenever the oil companies would switch their fuel from the "summer" blend to the "winter" blend, (although it was never as bad as the problem I currently have. This particular car I drove for 4 years back and forth and put just over 200,000 miles on it before I retired it from commuter service.)
During that time I had a friend who worked for Unocal, and I had asked him about this once and he told me that it's the fuel, and that the fuel injected cars aren't affected nearly as much as the carbureted ones.
My point to all of this is that the fuel has changed, good or bad, and I need to figure out how to work with it now.

Anyway, I know for a fact that there are no leaks from the carb from any of the plugs, I've pulled the carb off when it was hot just to check for that problem, and it's definitely not coming from an overfull condition. It's a perculation/hot soak issue, as I've seen this with my own eyes. It wasn't easy to detect the signs as the problem is usually with fuel vapors, not necessarily with liquid fuel. But I had the air cleaner off after running the engine to get it hot again, and I was looking at the carb when I just happened to see a drop of fuel coming up to the tips of the discharge jets/nozzles. It was just a very small wet spot, but it didn't go away, it just moved around slightly like fuel does when it's evaporating, as usually just a drop of hot fuel would evaporate right away. And it wasn't dripping out of the discharge jet and onto the throttle plate like you would see if it was a flood issue, just a small droplet of fuel in the hole of the jets/nozzles. Once I saw that I restarted the engine and was finally able to see the fuel dripping erratically out of the discharge jets/nozzles while the engine was just idling, roughly I might add.
If this was a flooding problem, it would have killed the engine as it overflowed into the manifold, but the engine continued to run on.

I have tried a different carb, in fact 2 different ones, (I've also got 4 of carb #17084201, I believe in having spare parts, especially when the vehicle is as old as mine), and had the same result with it as well.

None of the throttle shafts on any of these carbs are completely wear free, but neither are they worn out to the extent that they would cause a problem.

As far as the power valve is concerned, the electronic Quadrajets don't use one. The M/C solenoid, (mixture control) eliminated the need for it.

I even swapped out the oxygen sensor with another known good one just to be sure that wasn't an issue.

Bottom line though is this, it is percolating the fuel in the float bowl once the engine is shut down, and dropping the float level/fuel level doesn't seem to have any effect on this problem. Neither does adding more of an insulating space/material between the carb and the manifold. I added 1/2 an inch with the addition of 4 of the thinner carb base gaskets in place of using the one thicker gasket that is usually used.
The under-hood temperature is more than this fuel can handle, and I need to know what if anything I can do to correct this.

As far as the airflow through the engine bay, there is the A/C condenser that I had cleaned up and straightened all of the cooling fins on when I replaced the compressor, so no restriction there.

The radiator is only a few years old and is a heavy duty unit, and I had flushed and cleaned it out as well when I serviced the A/C system.

The engine has a 195 degree thermostat, which is what it is supposed to have in order for the temp controlled emissions systems to function properly. Although the only thing that really is affected by the engine temperature are the 2 ported vacuum switches, one for the heat riser and the other for the smog pump diverter valve.

The car has a front air dam on it from the factory, which is part of the "Royal Knight" package. The car's color is a very hot maroon here in the southwest, and I know that doesn't help the problem either, but not much I can do to change that.

There is a factory fan shroud in place, and I have a heavy duty fan clutch and a 7 blade fan on it as well. The belts are all in great shape too.

This problem is occurring even without using the A/C too. I haven't been using it just because of this, but it doesn't seem to make a difference one way or another.

That's all I can think of that might play a part in the problem and gives you an idea of what I'm dealing with. I would sure appreciate any and all help in figuring this out.

I don't have time to read that whole book. The car is an 81. They have been unleaded compliant since 71. There's no problem with the fuel.


Thanks for your help.

I don't have time to read that whole book. The car is an 81. They have been unleaded compliant since 71. There's no problem with the fuel.

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You know, I read your thread on how you want to know as much information as possible in order to diagnose a problem, and so I tried to supply as much as I could, and I thought I covered just about all the possible questions you might have had as to what I could try. Now you tell me that it's too much information.
Then you asked about a power valve in an electric Quadrajet.

I realize that the last carburetor installed on a production car was in 1990, (the '90 Cadillac Brougham with the 307 Olds engine) but there are still a whole lot of them running around the country. And I know that me and my carbureted cars are dinosaurs, but I'm still here, and I'm looking for help from another old dinosaur on this problem.
Is there someone here that has actually seen and even worked on a carburetor before?

Is there someone here that has actually seen and even worked on a carburetor before?

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OK smart ass. before you get too cocky, nowhere in your question do you state that is a Quadrajet or even 2BBL or 4BBL. Yes, you posted part numbers but if you expect anyone to recognize those 31 years later, good luck. I didn't even stop to think what carb you may have because you are not the only one I'm helping. I may help 30 to 40 people a day at this and other sites and do a lot of skimming through questions and giving quick answers.
Good luck with your problem.

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Fair enough, you're right, I didn't realize I had failed to mention the name Quadrajet in my original post. I guess it was an assumption on my part that since I knew what I was talking about, everybody else should, or would too. I'm sorry, I apologize for the attitude. And not to be a smart ass, but I did mention it in the second post, you apparently missed it.
So if possible, would you have any ideas on this problem now?

My thanks for any assistance you can provide.

I really don't know. You seem to have covered all the bases. Have you considered maybe trying a spacer plate under the carb? It's a long shot, but have you tried another computer?

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No, I hadn't tried another computer, although I do have one from another '81 I have. Because of the symptoms I didn't think it would help. The original one is still working just fine, and it will self diagnose as it should. I have an OTC 2000 tester that will plug into the ALDL and display all, or at least most of the working parameters on the various sensors, and even that won't give me any idea as to what is really going on. It's not a problem that will set a code, or at least it hasn't done so so far.
As far as a spacer goes, the only thing I've tried so far was the extra thick gasket stack as a test to see if it would really make a difference, but the answer is no, it didn't.
I've also got the factory service manual, and it doesn't even mention anything about a perculation issue or what to do about it.

That's why I'm pulling my hair out, it doesn't respond to anything I've tried so far.


(This post was edited by cadptsman on Aug 27, 2012, 5:08 PM)

The fuel being the issue is your idea. I don't buy that at all. Yes, there are additives in the fuel that will leave deposits and damage fuel gauges but I don't belivee it can cause an issue like that.

So has there been anyone else that has had an issue with hot soaks or hard restarting on a carbureted vehicle? If so, do you recall what they did to resolve the issue? I'm open to any and all ideas on this.

Do you think that changing to the aluminum manifold would cut back on the heat that the carburetor is getting?

Or would this just be a lot of work for a "maybe" solution?

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I would say "yes" to both of those questions. It would cut back on heat but we don't know if that is going to help the situation or not.

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Thanks again for your help, I'm going to see if I can repair this manifold, and if I can, I'll put it on and see what happens. I honestly don't know what else to do at this point. Everything you or I have thought to check I've done, not much left. I'll let you know how it works, or doesn't, as the case may be.

If you are really getting fuel boiling or leaking down on hot shutdown, then you should be able to see smokey fumes rising through the carb throat right after shutdown.
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I know what you're talking about with the fumes, but that won't happen right away, the fuel needs to accumulate some and start to evaporate in the manifold. Most of the time when you actually see a good sized fume coming out of the manifold, it's after you've cracked the throttle to look into the manifold for liquid fuel and there is a pump shot from the accelerator hitting the hot crossover iron.

I've got another theory on what's going on with this thing. Once it's good and hot and shut down, the hot soak begins, making the fuel in the bowl AND in the fuel line expand and even begin to vaporize. The pressure in the fuel line goes up due to the expansion, and then the needle valve and float are hard pressed to keep it held back. Once the engine is started, the fuel pump is adding even more fuel and pressure to the line and you've got a recipe for percolation and fuel overflow from the carb.

I'm thinking what I'm going to try is installing one of those Chrysler fuel filters with the bleed off port on it, and run the line from that back to the fuel line on the car just upstream from the fuel pump. That way the fuel will return to the tank when the pressure goes up when the engine is off, and when the engine is running, it 's basically a recirculating system for anything over the bleed off pressure setting.
The only thing is, I gotta find out what those filters are set at. If I remember right, they were used on the early to mid 80's carbureted Chrysler/Dodge/Plymouths with the 4 bangers in them. I think they did that as a cheap way to return fuel to the tank instead of adding a pressure bleed off port on the mechanical fuel pump.

What think you of this idea?

Didn't even read this whole thing. Fuel pressure is dictated right at the fuel pump with a plain spring. You don't need to alter that if OE designed it that way for any pressure issues.

Fuel will cooperate with a 1981 just some items don't care for the alcohol in current fuel otherwise not any part of the situation and octane rating would be available for what this required - probably 87 octane if not high altitude use only,

T

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I don't mean to be rude, but it would help if you read the whole thing to understand all of the issues we've discussed so far, but I understand you are busy as well. Hammer has been really helpful and patient with me and my problem here.

I guess I forgot to mention that the fuel pump on this El Camino is only a 2 line pump, 1 in, 1 out. So if the pressure in the line goes up due to excessive heat, it really has nowhere to go but into the carb. What I'm suggesting is to add a pressure relief to the line between the pump and carb by using a Chrysler inline fuel filter with a pressure relief port built into it.