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Low speed miss or hesitation


plymouthcranbrook

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Although I haven't had any difficulty with my 52 Cranbrook I have noticed as the weather has gotten cooler in the mornings there is a tendency for the car to stumble or have a low speed miss while driving in gear at below 40 mph or so.  Car runs great when cold and also after being used for 15-20 minutes it evens out and runs well again. It is in the area between stone cold and fully warm the stumble/hesitation occurs. I decided that since it hadn't had a tuneup for about 5 years(maybe 1000 miles or so) I would just up date everything to start. So, new plugs, wires, cap, rotor, points and condenser.  One thing I did notice that I did not remember seeing before was a slight variation of the timing mark at idle i.e. a bounce, maybe 1`-2 degrees) . I don't have a distributor machine but did use the  timing light to make sure that the vacuum advance was working. Mark moved about 12-15 degrees or so at mayby 1500 rpm or so.. I don't remember if this is unusual or ? so maybe someone can let me know.  That said even though the issue seems like a fuel problem I checked vacuum(18-20 steady with a good drop when the throttle is opened and a leap upward when closed). Compression on all cylinders is between 100-110 psi.  I replaced the intake/exhaust manifold gasket about 3 years ago and did check for leaks by spraying carb cleaner on the carb, carb base and the intake manifold without a change in speed.  When you push the gas down at almost any speed (over half way) the car picks up speed right away with out hesitation.  The carb was rebuilt by a local old car repair shop in 2014 and has seemed to work well since until the recent issue. I have adjusted the choke according to the manual 3 or 4 times and while watching it from a cold start until operating temp it seems to smoothly  open until vertical.  I have not opened the carb up to check any internals and before doing so I though that maybe someone has dealt with this type of problem and could give me some ideas where to look. Thanks in advance.

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General consensus at the AACA site is carb icing. I had forgotten that it could happen.  Tested the carb today and the base of the carb and also the manifold near it is noticeably cooler than the rest till really hot. Most likely the issue.

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  • 1 month later...
On 11/1/2019 at 10:30 AM, lepic56 said:

COULD IT BE The manifold heat control valve???

IT COULD BE STUCK,  LOOK LIKE IN THE CLOSE POSITION,,

Free as can be. One of the first things I checked.  Thanks though. i am beginning to think that although the icing condition might be it more likely something in the carb is not right.  Looking into a Carter YF to replace it. After doing the rear transmission seal.

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