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Drove my 1934 Packard 1100 Standard Eight with a stock (but rebuilt) carburator on the highway today. As I approached 50MPH I could feel the car start to hesitate as if it was losing power. As I pressed the accelerator to increase speed past 50MPH the car started bucking and backfired.

As soon as I slowed down below 50MPH the car behaved normally again. I left the highway and for the next 20 minutes the car continued to drive strongly under 45MPH which is its normal behavior. It idles well with an infrequent light paff but again that's been normal for all the time I've owned the car. The car starts easily, even after sitting in the garage for a couple of weeks, idles smoothly and warms up without issue.

After this behavior on the highway I experimented with the throttle around town. I noticed that in any gear as I increase the throttle past 2/3rds throttle, and the engine RPMs increase towards the higher end of the RPM range, the power drops, the engine power seems to hesitate, and it doesn't seem to breath correctly as if its being held back. I am very gentle with this car and cannot be accused of racing the engine in any gear. I should be able to drive the car faster than 50MPH on the highway with its stock 3-speed transmission and non-highway gears, correct? I know it should not be bucking.

Anyone have ideas for diagnosing the source of this hesitation and the associated lack of power at 2/3rds throttle?

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Assuming the carburetor isn't the source of the problem, it sounds like to me you have a problem with the automatic advance in the distributor, or timing is off a couple degrees. If you're sure the timing is good, perhaps the fuel bowl level was erroneously set during the carb rebuild such that as the engine accelerates to that 2/3 point and as it consumes more fuel, the level drops too much and is being starved for fuel causing the power loss.

Was the backfire through the carb? Then it is a fuel supply problem. Otherwise I would suspect that the points are having a hard time maintaining dwell at that engine speed. Would check their gap and spring tension.

Can't rule out ignition but most likely is a fuel supply issue. I'd start by checking fuel pump delivery volume and pressure, and the fuel bowl level in the carburetor. You might also just put on a timing light and check the timing and a qualitative check to insure the mechanical advance is functioning. On the timing, don't forget you have two independent 4-cylinder ignition systems and each has to be timed separately (assuming you have the stock ingition system).

Fuel filters clean? Condition of the flex fuel line from the frame to the pump?

As to your question about speed, yes - in proper tune your 1100 should be able to accelerate smoothly right up to its top speed (about 86 mph when new). But as to sustained highway speeds, with the original 4.69 rear axle and poured rod bearings you should think of 45-50 mph as your maximum speeds for sustained highway driving. A few mph more if you converted to insert rod bearings. If you want more highway speed capability, consider an overdrive or more advantageous rear axle ratios though these are pretty scarce and no current supplier that I'm aware of.

Also, try a drive without that AIR SILENCER or as many people call it AIR CLEANER

Thanks for the helpful responses. I will update this thread with my progress and the solution, once found.

How are the coil and Condenser?
I recall helping a friend replace his fuel pump, blow out the fuel line, and rebuild the carburetor. The entire time during this adventure I told him I recommend replacing the coil, he ignored my advice, well It was the coil. I know as I had the same thing happen to me on my 1201 Eight, sputtered, ran, stopped, I rebuilt the carburetor, same issues. Replaced my coil and was good to go.
In case nothing else fixes it.
Andy

Hi Christopher,
I had exactly the same problems with my 34 super eight and it turned out to be the twin coils.
Regards
T

i just had my Jaguar XK140 out for a long drive on Monday, started sputtering when I exited the freeway, immediately got back on, drove 35 miles home 75mph, exited freeway and dead, no spark to plugs, 1 mile from home. I checked Fuel, Coil, wires, cap, it was the rotor, the f-in rotor. I put in the old used rotor and fixed. I hope you have fixed your problem.

You know when someone important in your life dies and a friend consoles you by telling you that they get it completely because someone important in their life died, and they assume it's the same experience for you? Just remember, they mean well.

I know a '40 is not a '34, so take this with a grain of salt. I mean well. For what it's worth:

The fuel bowl level may be right at idle, but once you put a load on it, such as heading up hill in first or 2nd gear, if the Float is not set correctly, it will fluff/flummox and die. Stepping on the gas could. make it backfire and you can damage your muffler, among other things.

I had my carburetor re-built at one of the very best places in the country, Daytona Parts Co., and they missed the float setting. I had so much confidence in their rebuild, which was well compensated, that I couldn't believe it was the carb. I checked out everything else. In the end, I put on an old Carter carb that had not been rebuilt and the car ran just fine, so I sent the Stromberg back and Daytona made good on their warranty.

Problem test drive:
mktx.com/packard/5-12TestRun.mp4

Starting at Post#714 on Page 72 of this thread:
mktx.com/packard/5-12TestRun.mp4
and going all the way to Post #750 on page 75, we checked out the usual suspects using other posters as a guide until we had a successful test run.

Successful test drive:
mktx.com/packard/Test4Suckcess.mp4