Mechanical question concerning Model J Duesenberg

  • Kevin
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02 Jul 2005 02:51 #3307 by Kevin
Kevin created the topic: Mechanical question concerning Model J Duesenberg
Greetings everyone,

Although my questions concerns a problem I am having with a J Duesenberg, I am posting my question in this forum, to hopefully get a broader consensus on what might be my trouble.

I am nearing the completion of a full restoration on the car, which included a complete rebuild of the engine. It has an EE-3 Stromberg Carb, with 1-3/16 Venturi. The engine will start after a few revolutions, but has a random popping through the carb. We have triple checked the clearence of the valves to determine if one is staying open, they check out fine, and because the popping is random, I have eliminated the valve train. When we try to drive the car, the popping increses until higher RPMS, and then seems to smooth out.

The engine also runs rich, and tends to load up at idle. When the idle mixture screws are turned down, it has no effect on the idle, and appears that they have no control whatsoever, normally closing the screws off would kill an engine. We have taken the carb apart and cleaned it out to assure all the passages are clear, but it does not seem to change the way the engine runs.

I am wondering if the 1-3/16 venturi size is to small for the Duesenberg as, I believe the original was 1-3/8? Or could there be a defect with the carb, (enlarged idle passage holes, or leak somewhere) causing the idle circuit to malfunction? Could it be a jetting problem?

We just did a test drive, and the car runs, but barely. It killed and was very difficult to restart, and flooded easily when the engine is warm.

Any suggestions are apprciated, or if anyone knows of a knowledgable carb man I can contact to check this carburator, it would be very helpful.

Thank you,

Kevin

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  • Maurice Randall
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30 Aug 2005 00:36 #3619 by Maurice Randall
Maurice Randall replied the topic:
Hi Kevin,

I'm surprised nobody has responded on here yet.

I'm going to assume your engine is fine, hopefully, because normally popping through the carb is sometimes caused by a leaky intake valve. Of course, it can also be from an exhaust valve that is not opening fully due to a worn cam. But we will rule out a mechanical problem since your engine is fresh.

Now... is the popping due to pressure in the intake manifold from a backfire? This can happen from a fuel mixture that is too lean. But you think it is too rich. So, the popping might not be as serious as a backfire. I'm not there, so I haven't heard it run.

If the mixture is too rich, it could act like there is popping at the carb due to the random misfires that you will get until you get it up to speed where you will consume the extra fuel that is being dumped into the intake manifold. That explains why it smooths out when you get up to speed.

Without actually having the vehicle here, my guess is that the float is adjusted too high, the fuel pressure is too high, or the needle and seat is leaking slightly. Too much fuel pressure can push the needle valve open. The float could also be bad and not able to actually float in the fuel well enough to close the needle valve. Any one of these problems will raise the level of fuel in the float bowl.

When the level is too high, too much fuel will spill out in the venturi area.

Start the engine up and look down the throat of the carb. With the engine idling, you should not see any fuel spraying inside the throat. When you rev it up slightly, you will then see fuel spraying from the venturi (the narrow part of the throat). At an idle, fuel enters below the throttle blade where you can't see it, from the idle circuit. With the throttle open, fuel enters through the main metering circuit and into the venturi area about halfway up from the throttle blade. It will also dribble a little or a lot in the venturi if the fuel level is too high in the float bowl.

I've also seen other problems where fuel leaks from a metering circuit where the carb base attaches to the main body. This is generally a gasket problem.

Maybe you've already fixed the problem, but I thought I would post this just in case you haven't fixed it yet. If the car was at my shop, I could fix it for you.

By the way, the size of the carburetor isn't causing your problem.

-Maurice

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  • balinwire
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30 Aug 2005 21:26 #3620 by balinwire
balinwire replied the topic: Intake popping
Hi Maurice,

If Kevin tries all those suggestions and they don?t seem to cure the miss, check the distributor bushings.

If there is any wear, the rotor shaft will wobble at slow rpm?s, causing similar symptoms of intake miss or backfire. It might balance out at higher revs.

Try an exchange distributor if there is one handy.

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02 Sep 2005 16:25 #3631 by Terry
Terry replied the topic: Engine missfire
Did you check out that the valve springs are strong enough ? Also check the point gap.

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