The Stovebolt Site Forums The Shop Area Engine Shop Truck keeps stalling in the morning

In the evning its fine- in the morning I start it, let it warm up and drive to work. Its only about 2 miles to work and all but the last street are 45 mph zones with stop lights that I mannage to hit every one red usually. My truck is fine untill the last street; its a 55 zone and when I let off the gas at the end the rpms drop and it dies. It starts right back up but its anoying. I havent got a clue what keeps happening but im thinking either the timing is off a bit or the carb is misadjusted? Its a 63' 327 rebuilt a couple months ago with a new holley 4160 and new dizzy hei with 1 gold and 1 black spring from a curve kit. I know its not a vac leak. Only vac lines are the one from the carb to the can on the dizzy and the power nreaks. Both are new and the brakebooster is new. Mannifold is edelbrock airgap and checked for leaks with propane- no leaks. And just to say this again; it drives fine till I have to stop after hitting high speeds. Thanks.

There's your problem. You're experiencing the same kind of carburetor icing that makes airplanes crash. Once you get up to speed in cold weather, the airflow under the manifold cools it enough the fuel is condensing on the floor of the manifold and it's going lean when you slow down and stop. Another possibility is that there's enough of a cooling effect in the carb venturi to form ice crystals inside the carburetor from the moisture in the air because the manifold is so high and cold the engine heat can't get to it. Air gap manifolds look cool, though- - - -they're just lousy performers for street use! Maybe the Chevy engineers who designed the original-equipment parts weren't so dumb after all!
Jerry

Airgap manifold you say? That means the plenum and carb are separated from the engine by an airspace like pontiac and Y-block ford but does yours have heat passages? Since the purpose of it for performance is to keep the mixture cooler and more dense-I would guess not.
My guess the engine water is up to normal temp but not underhood and manifold and carburetor, so the carb is off the choke too soon and we may even have some icing.I've seen carbs and manifold ice up outside at near 50 degrees F in high humidity. You installed a cold manifold and now we see the downside.Icing is worst at small throttle openings because the mixture expands so much across the closed throttle plates.

darn, Hot Rod you beat me to it while I was typing--my 1 finger style aint swift.

Jerry's really on the ball!

You might want to check you're gas fillter also if it's not flowing at 100% when you make that short 55 mph blast it could be draining the carb some.


Pete

Hot rodders are always challenged to provide "workarounds" to work around the problems caused by aftermarket parts mixed and mis-matched.
But we do this to make the machine ours--can we say customize?
Factory designed carburation systems don't allow low idle during warmup by the use of fast idle linkage to the choke.Some carburetors are more tolerant of lack of carburetor heat than others by other methods.
This is not a new problem and makes an intresting study when we look at the methods that have been used to RELIABLY deal with it.
The engineers had a real challenge to make the modern carbureted cars user friendly for women and clueless drivers who wanted to go out at 15 degrees F--kick the accel 1 time,start the car and go back in to drink coffee or get in and drive away.
But WE provide a workaround.
You might try provide longer application of the choke and/or fast idle, or richen the idle mixture as much as acceptable, or provide warm air from the exhaust manifold area, or make the fan(s) inoperative until necessary.Do not use lower operating thermostat.In short, warm that system or richen it up or drive it and smile knowing that YOUR creation has other advantages than a "anybody can drive" warmup system.

Heated air induction systems are unsightly and power robbing if not designed/managed well.
Early Rochester v-engine carbs had a base heated by exhaust directed from one bank manifold through a passage in the head, then the inlet manifold, through a passage in the carb base, and through the other head into the opposite manifold---when the heat valve(heat riser)was closed by a thermostatic spring--if the passages weren't plugged by carbon.
I remember some spacers under the carb from the Blue Oval(also choke housings) heated by water taken from the engine like the heater supply.
This could be managed by a cable operated manual valve and a caring operator if you can find or fab a suitable spacer.
Get creative, and let us know how you did it--we might have the same need.

you really drive 2 miles?

That has to be the absolute last thing I would have ever thought about. Since I got it running during the 110 degree days of summer, I gave a lot of considderation to keeping things as cool as possible, I suppose the 2" phenolol-blah blah blah (you know what im talking about) spacer isnt helping any either. Hmmm. . . And the air cleanner being so high uup and being open element style isnt good ill bet. So I just need to get warmer air if its the prob? whats the down side to running warmmer air all the time? And Enginenut I can assure you that I can rectify this problem with some ingenious bit of craftsmanship. Ill make sure to get some pics and specs when its done!

Just curious, does it want to die the same if you ease off the gas and if you snap it closed? If it behaves differently, is the carb supposed to have a dashpot to ease it down to idle (and is it adjustable?)?
I don't understand the cause but have met engines that wanted to die when snapped closed. Pulses in the intake? rapid change in mixture? Don't understand but would be glad to hear the technical why of it.
Except when needed to get the engine up to stable temperature and aid vaporization in a cold engine, it is normal to want cooler (and as a result denser, more oxygen per cubic foot) air to permit more power per cubic inch.

Grant,I too have seen this action you describe where a sudden return to idle resulted in a stall or near stall before returning to a normal idle.
I think it is because of a residual rich condition--the engine not being able to burn itself clean before going back to idle where less air is available-spark is retarded(ported vacuum)--and the idle mixture is leaning toward the rich side anyway.
In fact I have,rough and dirty,leaned the idle mixture as much as possible and increased the idle speed and advanced base timing,to live with this (should have made corrections to avoid an EXCESSIVELY rich mixture from accelerator pump and power circuit).
Have you ever used the accelerator pump adjustments provided by the linkage to increase or decrease the delivery?Also the power valve tuning can be manipulated to correct within it's field of operation.
These reactions of the engine to a particular carburetor are the reasons Jerry and others tell us of the problems of multiple carburetion where "non-matched" or standard carburetors are used.The original correct mixture management (jetting) provided for a single are not correct when a duplicate (hopefully) is sharing the duties.
I have seen these dashpot applications (can't remember where)to slow the return to idle I think mostly on auto trans cars of the years when the manuf was struggling to reduce measurable emissions.
Come to think of it our current electronic injected engines are modulated in return to idle speed by the computor/idle air controller for this same result.

I learned about carbs with q-jets and never saw one without a dashpot to smooth out the opening and closing of throtle plates, maybey I have a few still laying around I can try it with; but no the carb did not come with a dash pot- not to say thereshouldnt be one. And if I ease off the gas I dont think it will wsnt to die.