Lack of power at higher speed

[Guest oakland]

I have a 1929 Oakland AA-6 with a marvel up draft carburetor. The trouble I have is that the car won't go over 40 MPH. At that speed it hesitates. I installed a new fuel pump that I had built at the Antique Automobile Celler. I took the carburetor apart and cleaned it. I installed new plugs and points. I even bypassed the gas tank and feed line by putting a sealed container on the front floor and running a gas line from it, to eliminate problem with the gas tank or fuel line. The car sounds and runs fine at lower speeds, but won't go over 40 MPH. Could someone give me some advice as what it could be. I am taking it in to a garage this week and have the timing checked. I am at wits end. Thank you.

[Guest imported_49packard]

Have you checked compression? Along with that valves.

[Guest De Soto Frank]

Have you checked the throttle linkage to make sure that the throttle butterfly is able to open fully ? ( That the accelerator isn't hitting the toe-board before the throttle is wide-open ?)

Would also check the timing... retarded timing or non-functioning auto-matic spark advance could cause symptoms as you describe...

What kind of temperature is the engine running ?

If your problem were fuel starvation, you should have some bucking or hear some backfiring through the carburetor...

[Guest]

When you cleaned the carb did you remove and blow out the jets? Another possibility is that your float level is too low. I don't know the exact measurement but the top of the fuel level in the float chamber should be just below (maybe a 64th of and inch) the top end of the idle jet. Another possibility is that you distributor is worn and the shaft waves back and forth and changes your point gap. I have had all these problems at one time or another on my Pontiac.

[Guest oakland]

When I removed the carburetor and cleaned it, I did blow out the jets. The temperature is running between 190 and 210, according to the mechanical temperature gauge I have on the car. I check the linkage, and it is working Ok. I am going to have the timing checked. The car is sort of bucking at wide open speed, like it may be starving for gas, but it is not back firing. I did not check the float level. I will do that today. Thanks for the replies.

[Matt Harwood]

You did plugs and points, what about a coil? That could cause the symptoms you're describing and still work fine at lower speeds. Coils don't show any signs of wear in most cases--no way to tell if it's going bad other than to try a replacement.

Hope this helps.

[Guest oakland]

I have not changed the coil. The coil on the car is a Sorensen SC-2 (6 volts). Would any 6 volt coil of that era work, or do I have to buy a specific one?

[Mark Shaw]

All the previous suggestions are good ones. I can only add that high speed jets in Marvel Carbs sometimes develop a crack or split that must be soldered to operate properly. Check it by removing it and apply water under pressure to find the crack.

Also, check to see if advancing the spark (turn the distributor about 1/8" opposite the turning direction of the rotor) to see if it performs better at high speed.

Mark Shaw

[carbdoc]

Oakland,

Just found this thread. I can help you address the more subtle problems which COULD exist as part of carburetion; the rest I don't know about.

Marvel carbs of your era used a crscent-shaped pot metal air valve baffle in the throat. The pot metal quality was poor and the baffle would swell, causing it to bind with the movable tongue-shaped air valve. With the movement of the air restricted, full power could not be developed (and it often caused idling and acceleration problems, too).

Does your car have a Marvel Heat Control Valve above the carb? If so, it will be a separate chunk of cast iron which contains the throttle valve. The steel sleeve insert (or throat) in this heat jacket typically burns out; this causes all manner of problems, too. If the heat contol is still connected to the exhaust, it will cause your engine to gulp spent exhaust gasses. If not, it creates a vacuum leak.

I suggest you remove these componenets and inspect them closely for the above problems. If you find that either one is the cause, you may then contact me at 800-945-2272 and I will advise you on how to repair it.

Good luck.

Jeff

[Guest oakland]

I would like to thank everyone for all the excellent advice you gave me. I took the car to a mechanic and he found the problem. One that I created. I installed a new set of points (first time). The old points had one steel spring on it, while the new points had a brass spring attached and a seperate steel spring. I installed the points using the brass spring only. The points worked fine at low speeds, but a higher speeds the points fluttered and caused the car to miss. He removed the points and installed the steel spring (luckly I saved)along with the brass one. I had the car up to 60MPH today, and everything seemed fine, although I think it is pushing it at that speed. Just wanted to try it out. Thanks again.