Engine: '50 Champion power loss, hesitation and noise when hot.

[Stody]

1950 Champion Starlight
Trying to trouble shoot and looking for a list of possible areas to consider:

Symptoms:

1. Hesitation on acceleration. Replaced the accelerator pump in the carb but did not affect the hesitation.

2 Loss of power. Requires more gas than it should to take off from a stop in first gear. Car's performance is sluggish as though it is running on less than six cylinders. Have to let the engine heat up otherwise letting out the clutch will kill the engine even when giving it modest amount of gas. Gets better after the engine is warm. The heat riser valve is functioning properly.

3. There is an engine noise that only shows up when the engine is under load such as active acceleration. The noise is like a ffft, ffft, ffft kind of thing. Not so much a knocking but rather something that sounds like and has the rhythm of an exhaust leak on one cylinder. The sound is absent when the car is coasting or at idle. I can not reproduce the sound by just reving the engine. At idle, the engine looks to be running fine. It's not tied to RPM variation as much as it it to engine load. The noise is more noticeable after the engine has heated up. Often not audible when the engine is running cold.

Things I've done recently:

Replaced all the usual ignition parts; plugs, points, rotor, cap, wires.
Adjusted dwell and timing to spec.
Replaced air filter
Replaced accelerator pump

Ok guys, I'm ready for your ideas...

[57pack]

Try a compression check on all cylinders along with a vacuum leak check around carburetor and intake manifold.

[nvonada]

+1 on putting a vacuum gauge on it:

http://www.classicinlines.com/Vacuum.asp

[karterfred88]

Since you are likely running unleaded fuel, it might be hard to "read" spark plugs looking for a lean condition. I would look carefully at the manifold gaskets and on your engine, the joining area of the intake and exhaust castings. Looking for cracks and burn through areas. A propane torch, turned on low and moved around intake gaskets and joining areas will cause a difference in engine speed if it finds a vacuum leak. An exhaust manifold crack that lets exhaust gas enter the intake tract will have a severe affect also. Careful examination of the "heat riser valve" chamber for cracks and burn through might also be needed. A vacuum gage might help you to start with, but something increasing with heat usually points to something affected by it, either by warping or expanding past where it should be. Also being a flathead, look for signs of exhaust gas around the outside of the head indicating a partial head gasket failure. As simple as it sounds, make sure the spark plug seal rings are on the plugs and compression is not getting past the plugs as the head heats up and giving you a fffft sound as that cylinder is under compression when hot. Lots of fun, if it wasn't for the noise you describe, I would be looking at the carb and pulling it apart.

[rstrasser]

Need some history on the car. When was the last time that the car ran correctly. Was anything changed between when it ran OK last and now. Or did you just acquire the car and it has always had a problem.. If the last is the case; you need to start checking into the condition of the engine prior to doing anything else.
Ron

[Lothar]

Hesitation on acceleration could be the vacuum advance on the distributor not working properly. Does it hesitate, then, if you back off the accelerator and reaccelerate, actually accelerate?

[Stody]

UPDATE: The main issues were a malfunctioning vacuum advance and a hidden break in the vacuum line from the carburetor. Replaced the vacuum advance unit and repaired the vacuum line from the carburetor. Re-tuned the ignition and now the car runs as it should.