One for you OLD School Mechanics

Maintenance/Repairs
41

I like the carb for this problem as do the rest of the posters. It may not be something that can ever be tuned away with this carb. It isn’t a very sophisticated design. Edelbrock has the tooling for the old Carter AFB carbs and makes a better than original version that may give better performance at tip-in.

That said, I’ve been bit by the “its a fuel problem” when it really is ignition. This old 6 volt system just may not have enough spark at low rpms to remove the stumble. I don’t know if there are any 6 volt electronic triggers to replace the points but I’d sure look for one. Also consider changing to a 12 volt system. I see many old cars that are “drivers” swapped to 12 volt alternators. There are big ballast resistors sold to keep the instruments as 6 volts.

42

as some have said , a worn distributor or timing gear may play a part

43

is the overheating problem solved?

44

Easy way to test the vacuum advance diaphragm - hook up a vacuum hose to it, try and pull air out with your mouth- if it leaks, replace it.

45

You really need to search around your area for some old, probably retired mechanic or hot rodder who has a garage full of things like feeler gauges, dwell meters, timing lights, and knows how to use them. I know I have those things, mostly sleeping in workbench drawers because “you never know when you’ll need them”. That’s one reason why I started to fool around with old motorcycles.

46

Man I just got an Actron CP7605 dwell meter from sears and got home and opened the packaging and it says “for 12 volt electronic or conventional ignition systems” on the instruction manual. Nowhere was this mentioned on the outside packaging. I wonder if it will still work like my 12 volt timing light still works

47

Customer service says likely wont be accurate…back to sears. Dangit!

48

Heres a carburetor training manual from an automotive mechanics training course 1952. It may help a little with your carburetor issues.

http://oldcarmanualproject.com/books/1952Carbs/index.htm

Now for the distributor. Is the coil the correct one for a 6 volt system? Next, remove the distributor cap and rotor, bump the engine around until the points are on the top of one of the cam lobes. Stick the appropriate feeler gauge in between the points and then push and pull on the rotor shaft to see if the point gap changes. It is easiest to see the changes with a .012 feeler gauge in there.

With a 0.012 feeler in a 0.016 gap, the remaining gap of 0.004 will show small variations more than a 0.016 gap would. A change of 0.002 would show up as a 50% change as opposed to 12-15% change without the feeler in there.

If the gap is changing, then the dwell changes as well. Every 2 degrees of change in the dwell translates to one degree of change in the timing.

Here is a procedure I like to use on distributors, especially when installing one. With the cap on, mark on the distributor body where the #1 spark plug wire is located. Now remove the cap. Set the points to the proper gap and bump or turn the engine to the desired timing mark. Install the rotor and check that it points reasonable close to the mark on the body.

If it is 180 degrees out, turn the engine one turn and align to the desired timing mark. The points should be just opening. If not, adjust the distributor until the points are just opening. If the rotor is not now pointing reasonably close to the mark for the #1 cylinder, the the distributor needs to be pulled out and reinstalled to a different tooth until the rotor is reasonably close to the mark.

Once everything is right, snug down the distributor and install the rotor and cap. Remove and plug the vacuum line, fire it up and check the timing. If it is off, it usually isn’t but it might be a degree off, loosen the clamp and adjust the distributor, then clamp it down again. Rev the motor a little and the timing mark should advance. If it doesn’t, spray a little oil on the mechanical weights. They should be under the plate the points are mounted on. You might want to do this preemptively before starting the above procedure. Turn the rotor to see if it advances, it should move a few degrees.

Once you have determined that the mechanical advance works, then connect the vacuum line. The idle should pick up a little and the timing should advance a few degrees. When you work the throttle, you should see that the vacuum advance retards when you are accelerating the engine (opening the throttle) and advances when the engine is decelerating, (closing the throttle).

One issue with these older cars is the mistaken belief that you can set the idle by ear, that is adjust the distributor without a timing light. You can often get a little better idle doing this, but the engine may have problems when driving because the timing won’t be right for the different RPMs and loads. The timing curve is a compromise and optimizing it for one parameter will often result in poorer performance for other parameters. Do it by the book and the engine will perform better overall.

49

Another thing to consider checking with regard to the engine not always settling down to the same idle speed, the carburetor throttle plate assembly might have worn and shifted slightly. For example, the shaft or shaft bore might have worn so as to become a bit out-of-round. That could cause the throttle plate to be shifted slightly in the direction of the pull of the return spring, which could make the plate return inconsistently to rest as it slightly jams in the opening at the bottom of the carb. This might also cause a vacuum leak around the throttle shaft, possibly accounting for a stumble at low RPMs.

50

Thanks guys. To update: I tried my dwell meter and it actually still worked fine. It read 28. I believe the range is 24-30. Idle read about 450 in neutral, and roughly in that 375 mark for the in gear idle. So really, those things seemed on the money. Oddly, today it seemed alright. A little rough when cold but as it heated it seemed okay. The point gap was just a hair smaller than .016, but I could still get the gauge in there so it seemed ok. Id like to recheck the timing again now that I can read RPM to get a consistent measurement.

The car is kept at my father in law’s father’s house. He passed away a few months ago and the house is currently vacant, and I cant work on it where I currently rent because the HOA gave me trouble. So I do what I can when I can.

So far though I feel like Im making progress.

Every ONCE in a while, I have seen
some bubbley air coming from one of the carb studs in the intake manifold when cold. I had to have the carb studs drilled and retapped bc the old ones rusted out and snapped when I first took off the carb. I mistakenly did not add some gasket glue to the threads. So its possible theres a little air leak there? However I did that a while ago and the problem behavior is recent.

51

I am thinking timing, as a starting point retard the timing until it begins to bog down, then advance 1/4 turn as a starting point. The low idle acceleration fault but high idle fine when centrifugal and vacuum advance kick in lead me there. If it displays the same symptoms 1/8 more turn of the distributor and see if they go away. If that does not work my next step would be checking needle and seat, and float level. If that is all ok my next step a leakdown test for a poor head gasket.

52

With a timing light you can be certain to get the timing back on the mark when desired and that should allow you to experiment with advancing the timing and checking for proper vacuum and mechanical advance. Most would be amazed at the equipment that good tune up shops used. Over the years I have owned some of the now pre-historic Sun equipment and wish I had it back.

53

I concur; that Sun stuff is excellent. Back in the mid 70s a doctor here was a car hobbyist and had a new home built with a 5 car garage. I had the privilege of visiting that house after he moved in and discovered that he had purchased (new) just about every piece of Sun diagnostic equipment in the catalog.

His garage would make a gearhead drool with each and every tool in its surgically clean place.

54

If there’s a sign of an air leak at the carb base, that could cause the problem. I’d check that the carb is secure (not too tight). If it still leaks you need a new gasket.

If the dwell meter’s right, you don’t need to worry about the point gap, it measures the same thing.

55

Check the timing chain. This effects both the ignition and valve timing.

Remove the distributor cap. Have someone get on the crank bolt with a socket/breaker bar.

Have them turn the engine over by hand in the normal direction while watching the rotor in the distributor. Now have them turn the engine over in the opposite direction while watching the rotor in the distributor.

If the crank can be rotated more than a few degrees before the rotor in the distributor starts to rotate, the timing chain is stretched.

Tester

56

Was the car unused or barely used by your father in law for a long period?
That could point to stale gas and/or varnish deposits in the carburetor.

57

Have you already checked each vacuum device for a diaphragm leak? That’s what I’d do first with this symptom. I get a similar symptom show up in my Ford truck from time to time, and it is usually some kind of air leak like that. I’ve had the distributor advance vacuum diaphragm, the vacuum retard diaphragm, and the air cleaner hot air flap diaphragm all spring leaks on me. Not all at once, one by one. And one time it was caused b/c a vacuum hose had split. Checking the integrity of the vacuum operated device diaphragms is a simple check to do. Takes 5-10 minutes. You need one of those hand held vacuum pumps with a gauge. I think I’ve seen them at Harbor Freight for less than $10. Some automatic transmissions have a vacuum operated gadget on them, so if it applies in your case, check that too.

58

The power valve dumps gas in the throttle bore under heavy acceleration,when its bad ,the engine can load up with gas a low rpms-Kevin

59

fender, I hate to be the one to say this but…

you ve been messing around with the old girl for awhile, if you have a diaphragm that is not intact, she just might be pregnant …

60

Hahah wes, please dont tell my fiance!!! It was just a few times!! Im a changed man!!!