I’ve heard rumors that some of you technicians are getting old gray or bald before your time scuttlebutt asset that this premature aging is caused by a variety of engine performance conditions that irritate customers and sometimes frustrate you technicians in all seriousness as emission control standards get tighter carburation and ignition requirements become increasingly critical since we all want cleaner exhaust and owners aren’t ready to accept any reduction in drivability you experts on the tune-up front have your work cut out for you I notice you use the word drivability well that’s a word we’re all going to hear more and more frequently as exhaust emission standards get tougher it’s really a more descriptive term than performance drivability includes everything an owner expects from a good running engine easy starting cold or hot good acceleration acceptable smoothness at idle full power and of course good engine performance is an important safety factor in deciding engines which meet both emission standards and owner drivability expectations carburation and ignition requirements have become increasingly important and the fuel and ignition devices that must be used to ensure clean air performance haven’t made the service technicians job one bit easier solving drivability problems is a bit tougher and more exacting than it was four or five model years ago so stick around while Tech and I pass out some facts fixes and suggestions that’ll help you get the job done now too often the repair order doesn’t give the technician a good clue to the actual condition the owner wants fixed I have some suggestions for the write up man that’ll make the technicians job a lot easier try and get the customer to explain exactly what he’s experiencing if he doesn’t volunteer all the information you need jog his memory by asking specific questions don’t try to pin the owners description of the problem down to one word like die fade stumble sag flat spot hesitation these words probably mean one thing to the customer something else to the write up man and something else to the technician who has to correct the condition do you have any suggestions on what can be done to improve communications from owner to write up man to technician we sure do jack we’ve worked up a glossary of terms commonly used to describe drivability problems if we can standardize on the meanings of these terms we’ll all be speaking the same language and that will go a long way toward improving communications believe it or not I’ve run into more than one case where an owner insisted he had a starting problem a few questions turned up the fact that the engine actually started quite easily and then stalled on a cold start an occasional one time stall or died out as normal repeated stalling isn’t I’m not trying to whitewash actual starting problems but I’ve handled enough complaints to know it sometimes the driver and not the car that needs fixing now if every owner would follow the starting instructions in his operator’s manual half of the starting problems would go away but let’s consider some actual starting problems the choke is seldom well I’ll go further than that is rarely ever the cause of a starting problem unless it has been badly Mis adjusted to compensate for some other fault as a matter of fact of the 1972 models the choke assemblies are not adjustable each choke is correctly calibrated for a specific application and should not be changed or tampered with and serviced on the other hand incorrect vacuum kick adjustment is a frequent cause of cold engine drivability problems the way our carburetors and chokes are calibrated the vacuum kick must open the choke the correct amount as soon as the engine starts so always check to make sure the vacuum kick adjustment is right and operating correctly a ruptured vacuum kick diaphragm a disconnected vacuum line or a leaking vacuum hose will cause a variety of problems one of the worst conditions that have all too often is this reverse distributor vacuum advance and vacuum kick hose connections at the carburetor this causes full ignition vacuum advance regardless of throttle position and no vacuum kick at closed throttle reversing those hoses really creates drivability

problems and it does happen speaking of hoses a disconnected vacuum hose at the rear underside of the air cleaner on cars with heated air intake can cause problems it’s easy to accidentally pull that hose off when the air cleaner is moved and never noticed the difference except an engine roughness and drivability problems unfortunately you can’t spot a disconnected heated air vacuum hose by simply looking you can check the connections at both ends by feel or better yet lift the air cleaner off and check all vacuum hoses to make sure they are properly connected and in good condition but let’s hear what Donna has to say about hot start problems the wrong way to tackle a hot start problem is to blame the choke for the float level before checking the more common causes of hot start problems what do you suggest I look for first take a good look at fuel line routing make sure fuel filter or line from the fuel pump to the carburetor isn’t touching the engine block of the manifold if a fuel line touches hot metal the gasoline in the line will boil and cause a severe hot start problem next check to make sure the fuel bowl vent adjustment is correct if that vent doesn’t open to relieve vapor pressure when the engine shut down you’re bound to have hot start problems and while you’re at it make sure the choke linkage is clean and operating freely dirty oily or sticking choke shaft or linkage is more apt to cause cold start than hot start problems but it pays to make sure nothing in the choke system is binding I keep my hands off the choke unit and the float level until I’m sure all of the easily inspected external possibilities are checked out including ignition timing and dwell however if it’s necessary to check the float adjust the float level to specifications don’t try setting it low to correct a hot start problem or high on a cold start or performance problem experimenting with non-standard float level settings is a good way to create new problems now to avoid possible fuel level problems be sure and inspect the needle valve and seat if there’s any question about the condition of the neoprene tip replace the needle and reset the float level and here are a couple of important precautions use needle nose pliers to bend the float adjusting tab don’t force the needle valve into its seat by lifting the float and pushing the tab against the end of the needle valve doing this will give you a false float setting also on carburetors having the float and needle valve in the main body be sure that the float height adjusting tab is at right angles to the float needle or angled slightly toward the float when the float is at its correct height never slanted toward the needle if the tab slants toward the needle the valve can bind causing erratic fuel shutoff and poor fuel level control this condition can cause some pretty baffling performance problems I don’t have any intention of minimizing hot start complaints but sometimes the problem is wholly or partly the fault of the driver don’t you agree Don I sure do take for one thing many owners don’t differentiate between a won’t start and a slow start condition far too often the driver quits cranking just about the time the engine is ready to start I know that five or six seconds seems like a long time when you’re grinding a starter but that’s what it takes under some conditions I’ve heard you can solve a hot start problem by moving the fuel filter or by installing a flood check yet or a fuel pump with an internal bypass what’s your opinion of those fixes the flood check fix and internal bypass pump lets fuel drain back to the tank side of the fuel pump when the engines shut down under very severe hot start conditions this may reduce hot starting time however fuel drain back will increase the cranking time required to start the engine when it’s cold if a car is going to be driven in both hot and cold weather conditions I would hesitate to install a flood check or bypass pump without warning the owner this possibility moving the fuel filter to the tank side of the fuel pump will reduce cranking time if the hot start problem is actually caused by fuel expansion and vaporization moving the filter takes a bit of doing and I certainly wouldn’t recommend it until I had made sure I taken care of all other possible causes and now will someone turn the record so we can hear the rest of Don’s drivability story before we go any further I’d like to have Don clear up any misunderstanding about a drivability problem we’ve had on some of our 383 engines with a one and a half inch BB D carburetor a Tech’s talking about a performance problem that’s

caused by a warped air horn air horn warpage causes an air leak between the fuel bowl and the venturi section of the carburetor this reduces the pressure on the fuel in the bowl and the mixture goes lean if timing idle mixture and idle speed are correct but performance is below par under most driving conditions you should suspect air horn warpage and if the performance problem continues even after the engine is fully warmed up it’s time to remove the air horn to check for warpage lay a straight edge across the gasket surface and use a feeler gauge to check for a low spot near the center of the air horn a low spot of more than ten thousandths means trouble however it isn’t necessary to replace the carburetor or even the air horn get one of those service packages from the parts department it contains a pressure plate which acts like a bridge and pulls the air horn back into shape that plus a thicker gasket supplied in the kit will correct the air leak and the performance problem the Carter BB D carburetor has been around for a long time how come air horn warpage got to be so much more of a problem these past couple of years there are two reasons Jack first higher underhood temperatures have increased the possibility of warpage second the recalibrated carburetors required meet emissions standards won’t tolerate any air leaks and additional leaning out of the fuel mixture incidentally a new aluminum alloy air horn was introduced as a running change in 1971 models so we’re out of the woods and the warpage problem on present carburetors the main body and new air horn are both aluminum so they looked alike also the new air horn has two distinctive air cleaner locating lugs the previous sync diecast air horn looks entirely different the Holley four-barrel carburetor is another example of where leaks can cause serious drivability problems on these carburetors it is very important to make sure the fuel ball screws are properly torqued loose screws and metering block leakage are common causes of hard starting and rough idle for that matter properly torqued screws are important on all carburetors I haven’t run into it but I hear there were some sag stumble or die out problems on 318 engines with the Rochester to barrel carburetor what’s the lowdown on that if you kept up on your bulletins reading you wouldn’t have to ask that question the fix for a lean condition on the rochester carburetor was covered in a bulletin way last fall if you didn’t say it there’s something wrong with a communication system and your dealership bulletins won’t do you any good if they’re filed without being shown to you fellows that I have to do the work the Rochester carburetor fix called for opening up the idle restriction holds with a number 55 drill enlarging the main jets with a number 54 drill and setting the float level to 2130 seconds of an inch but that’s old news now these changes were made in early production so don’t jump to the conclusion that you should modify the carburetor when you run into a performance problem on a 318 equipped with a Rochester carburetor here’s what you should check on a later production 318 and for that matter or other engines to make sure timing and dwell are correct check to make sure all vacuum hoses are connected and not leaking tighten the carburetor mounting nuts and carefully adjust idle mixture and speed to specifications I found that doing these things will correct most drivability problems that sounds like pretty good advice now what can you tell me about after running well first let’s consider what causes after running an engine continues to run after the ignition is shut off because the carburetor is still feeding the engine enough fuel to support combustion and the combustion chamber temperature is high enough to provide ignition of the mixture after running occurs because throttle valves are open too far when the engine is at curb idle then if idle speed is okay the engine shouldn’t have to run right on that necessarily Jack if mixture adjustment is wrong chances are someone has advanced the idle speed screw adjustment to keep the engine running at a specified idle on that case the throttle valves would actually be open too far at curve idle as a result the carburetor would feed the engine enough fuel to cause after running on two or four-barrel carburetors after running may be caused by incorrect balance between the two idle mixture adjustments if one side is rich in the other leaned the throttle valves are sure to be open farther than they should

be at specified idle absolutely right tech in addition on multiple barrel carburetors in correct balance of the idle mixture adjustment is a common cause of rough idle and pop back when starting so correct idle mixture balance as well as correct idle speed is very important for reasons other than after running as you know the idle speeds in our high-performance engines are in the 800 to 1000 rpm range high idle speeds are used with these engines to obtain acceptable exhaust emissions at idle and when decelerating this high idle speed presents a potential after running problem to eliminate the after running problem on high performance engines the carburetors are equipped with an idle speed solenoid the extended solenoid stem acts as an idle speed screw stop so the solenoid must be energized when setting idle speed also it is very important to adjust the throttle valve stop screw also called the slow idle screw so that the throttle valve can closed far enough to prevent after running when the ignition is turned off another thing to look out for is the ground circuit for the ignition solenoid used on some models make sure the connection is complete at the solenoid and at the carburetor ground switch the solenoid must be energized and timing fully when checking ignition timing how to make sure the solenoid is working disconnect the solenoid lead after setting timing to make sure timing advances then reconnect the lead and timing should 7 to 10 degrees here’s a word of warning the ignition solenoid will not be used on 1972 models instead some models will have a distributor advance solenoid check your service manual before you service a car with one of these new distributors next month will tell you all about the advance solenoid and other 1972 ignition system features on all engines the distributor vacuum advanced line must be disconnected and the vacuum line plug when checking or setting timing also make sure the timing does not advance when the vacuum line is reconnected now I’m anxious to hear what you have to say about spark Nook or engine thing there are two basic conditions which can cause spark knock advanced ignition timing which causes very high combustion pressures near the top of the power stroke low octane fuel having poor anti-knock qualities I’d like to put in my two cents worth about fuel octane both fuel quality and octane standards vary in different parts of the country now we aren’t about to suggest that you tell your customers what gas to buy or what not to buy but if you have any problem gas and your area make it your business to know about it most of the low led and no LED fuels on the market are about 91 octane so under some operating conditions the owner can expect knock with specified ignition timing particularly on older model cars regular grade low LED or no LED fuel must not be used in any engine that was designed to run on premium grade fuel and of course no low LED or no LED fuel should ever be used in any engine unless it contains sufficient LED or other lubricants to protect against valve seat damage if you ever run into a drivability problem on a car with a slant-6 engine now here’s a tip worth remembering particularly if the problem showed up after the carburetor had been serviced or replaced there are four possible ways to install a carburetor in a manifold gasket however there is only one correct way be sure the gasket is installed so that holes provided for manifold vacuum line up both at the carburetor and at the manifold if you install one of those slant-6 gaskets wrong you’ll scratch yourself ball trying to figure out what’s wrong and you never will get the engine running right be sure and take notice of the new emission control information you’ll find in the engine compartment of the 1972 models there is a separate information label for each engine type each label contains timing specifications idle speed recommendations and idle mixture adjusting instructions mixture adjusting instructions are given for the preferred procedure using an exhaust gas analyzer an alternate procedure is given for adjusting the air fuel ratio if an exhaust gas analyzer is not available

I’m sure glad I cornered you two long enough to pick your brains on performance I mean drivability problems I guess I’ve been exposed to a lot of this information but you to have refreshed my memory and sort of pulled it all together for me and some of the tips you passed up or ones I didn’t know about we’ve put it all together and easy-to-use farm for you man out there to you’ll find it all in this month’s reference button keep it handy

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