QuestionQUESTION: My 1958 Cadillac (bought new) has developed an intermittent stalling problem especially at stop signs. I've re-built the carburetor (Cartr AFB) 2x and re-checked float drop/height adjustments, etc. I replaced the fuel pump, fuel filter, points, condenser, Distributor Cap, Rotor and Spark plugs. Car used to pull a steady 21 lbs vacuum at idle -now pulls 18 - 19 lbs with vibrating needle +/- 1/2 lb despite numerous air/mixture and air horn adjuctments. Wires are good and sometimes it idles very smoothly and then for no reason while watching it, it begins to idle rough and then almost stalls in Park. Reving the engine a little clears it out temporarily. Occasionally, I'm seeing fuel drip from the secondary shaft. Thought I fixed that problem with new secondary venturi gaskets, but the problem re-appeared today. Carburetor "looks" as new inside and out. Fuel bowl is clear and fuel is 1/2 - 3/4 up in the filter which is where its always been. I'm at whits end!
ANSWER: You seem fairly knowledgeable, so we will make assumption that you have checked most of the basics, I will just mention the dwell holding a steady 28-30. If it is not steady, you have internal distributor problems, but I don't think that is what you have here.
Have you checked for an air leak into the intake manifold either at a designated source or a gasket or broken vacuum line. This is most easily accomplished by spraying a flammable vapor around the engine while it is running, especially while it is acting up. I prefer brand name WD-40. The small red tube can help you pinpoint the leak. Don't forget to check the vacuum advance airhorn at the distributor.
If this is not the case, you are going to have to open the carburetor back up. You are not getting complete atomization under differing pressures (minute differences) in the carb. Pay particular attention to the regulating ball under the accelerator pump. Make sure it seats and releases well. Make sure the new gaskets furnished in the carburetor kits have their holes opened well and do not overhang the openings.
Let me know on this one.
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QUESTION: There were a few spelling/number mistakes in my last response - Sorry. "Thanks for the quick reply. Yes, I've checked the basics - Dwell set at 29 - 30 degrees; timing was at the recommended 5 degrees advanced - I advanced it to 7 degrees today - a spec more vacuum, but same problem. I had sprayed the intake manifold with WD-40 looking for vacuum leaks - no affect. I had changed the intake manifold gaskets 2 years ago as well as the valley pan gasket - all seem good. Vacuum advance works fine above 1,000 RPM - 1958's had no advance at idle. I had checked the Accelerator pump ball bearing - it looks like a jet on the accelerator pump side fuel bowl as opposed to the earlier AFBs that sat under the accelerator pump return spring. The accelerator pump primes well and the car starts cold with virtually no cranking. The choke opens normally and I had disassembled the little choke piston assembly, etc. when I re-built the carbretor - everything was clean in there. I have the correct (and fresh) gaskets under the carburetor inclusive of the bakelite spacer and the stainless steel heat plate. No leaks there squirting
WD-40. I'm just wondering about the primary and secondary venturi mounting gaskets. The kit provided 2 types one with a 45 degree slot that lines up with the bottom side of
the venturi and a second set of gaskets were were also provided that did not have the 45 degree slot. I used the 4 45 degree slot ones (2 on primary venturis and 2 on the secondaries. Looking at the shop manual, it shows the non-sloted gaskets in the exploded view. It make logical sense that the non-slotted would provide a smaller orifice for gas flow and if indeed the carburetor was flooding, would reduce the gas flow. Since I noticed gas dripping out the secondary shaft, it has to be going into the hollow chambers outside the secondary venturi area. As the float
levels and drops are to specification and in removing the top of the carburetor,the gas level in the left and right chambers is about 1/3 of the way up, I'm assuming the gas is not overflowing from the chambers, although I did
see gas in the rear horizontal crevis where no gas should be. I believe the carburetor is flooding and reving it momentarily clears it out temporarily. Up until 2 weeks ago and for the past 10 years, the car ran like a top! I do find that sometimes the passenger side air/mixture screws becomes inoperative e.g. I can turn it in
fully with no vacuum or RPM change. Other times, it functions as it shoild. When it becomes inoperative, I see a little puddle of gasoline on top of the aluminum cover that holds the primary metering rod in place. When it works, it remains dry there. I guess the real question is which mounting gaskets are correct for the primary and secondary venturis? The set with the 45 degree slot whick matehes the machined cutout on the bottom of the venturi
or the flat gasket that matches the carburetor base? Beyond this, I am totally perplexed. The car went from
running so well to becoming unsafe to drive. I do appreciate your help!"
ANSWER: I do not honestly know on the gaskets without 'eyes on', but if this were the problem, it would have been instant and continuous. I still feel there is a metering device that is working properly sometime and hanging up sometime.
Don't know the exact layout of your particular carb well enough to be able to say where it is. You might review the schematic from you rebuild kit and be able to pinpoint it.
Also, remember, that climate effects carbs and factor that in on the liquid gas sightings.
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QUESTION: Well, I changed the primary and secondary venturi gaskets to the type shown in the Shop manual and the car "seems" to idle better. However, a new problem has developed. I noticed the top radiator hose was quite swollen and in checking, the lower one was also. I also noticed a buldge in the radiator top cap, so i pulled the Radiator and took it to the shop for repair. They said the radiator is pretty clogged, but the car had never over-heated. When I checked the downflow radiator (1958) with my digital thermometer it had read 200 degrees on top and 130 at the bottom. The thermostat upon looking in the housing was sitting a little off center, although I know I placed it in the little flange properly 2 years ago when I replaced it. There is no rust or crud in the thermostat housing or the removed hoses. I'm concerned as to why both hoses suddenly became swollen. My mechanic thinks maybe a head gasket leak, but the plugs are dry and there is no smoke or sweet smell out the exhaust and the antifreeze level was 1" below the neck where it always is. The drained fluid was bright green. You have provided good responses and I hope you have some recommendations. Maybe it is a bad head gasket and that has been causing my intermittent idling problem or maybe this is just a case of a clogged radiator.
AnswerI actually started to mention head gasket, cracked head or bad valve when I first heard you stalling problem. The shaking vacuum is a minor indicator.
The good thing about a blown head gasket is it is consistant and nearly always progresses to a diagnosable problem, whereas head cracks can be elusive, intermitten and drive you crazy.
A bad valve won't give you your overheat (over-pressure) problem.
A conpression check of each cylinder should tell you alot.
