'47 running very rough

4

47fordv8

Junior Member
'59AB w/ Offy reg dual intake, max-1 cam. offy heads, fenton headers still 6 volt. Barely runs, backfires out pipes at lower rpm, better when faster. I switched back to stock distributor (Rebuilt by Bubba's) from a Mallory so I could go back to stock fan set-up. Over the years, I couldn't ever get the timing and carbs quite right, played w/ jetting and power valves when carbs linked directly, always ran rich, but not this bad. Power valve doesn't appear blown.

Since then I have installed a progressive carb linkage, using the front carb as primary, rear has no idle circuit, plugged off power valve and butterflys shut tight. (Kit from Vintage Speed). Primary carb has .049 jets. and 5.5 power valve, so at lower rpm it is acting like a single carb set-up. Currently showing 11 in. Hg max, but needle is flickering bad. Engine runs equally bad w/ vacuum line to dist. on or blocked. Try a 3.5 power valve (or lower?) I am praying I don't have a stuck valve. Any benefit of having rear carb as primary w/ the regular dual intake? I notice vacuum hole is directly below rear carb location, or doesn't it matter? Any and all suggestions will be greatly appreciated. Thanks!
 
The first thing is we need to know more about the intake manifold. There are basically 3 different types : Supers (where each carb is positioned over one set of intake ports), a Regular, (where the carbs are equally spaced on the manifold, but not directly over the ports), and what I call a "Biased Regular", (where the front carb is in about the same position as a stock single manifold and the rear carb is close to the fuel pump. The last type is the only kind you can run a progressive linkage on, and then it is not ideal.

All of this being said, your problem sounds like an ignition problem. Have you checked or replaced the coil and/or condenser?
 
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Offy "regular" intake, looks like the 3rd one you mentioned, still have stock generator mounted on it. Coil is a few years old, rebuilt by Skip not many miles on it. Condenser is one that was supplied w/ dist from Bubba. Ran very similar just before I took Mallory off to swap back to stock. Different condensers. Can the crab be adjusted except for vacuum brake? I adjusted screw all the way up w/ no effect. (Yes I know it needs to drag slightly) Thanks for quick reply!
 
Google vacuum charts. Flickering vacuum is usually valves. Usually. Could be anything really.
 

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The low and flickering vacuum is your main clue. Compression test first to see if you have sticking valves. Not uncommon if engine sat for months. Often can be fixed by drizzling MMO into the primary carb while jazzing the throttle.
 
I finally got around to the compression check. Highest was #6 at 140psi, lowest was #3 at 115psi. I tried the MMO in the tank and drizzled in the primary carb while running, no help. I had to keep goosing the throttle just to keep it running, will stall when trying to idle. screws are turned out about 1 turn.
Could this be a condenser? When one failed on me a long time ago, the engine just quit. I would hate to think I had a bad one straight from Bubbas!
 
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