| bwhitworth | -- 05-05-2014 @ 6:02 PM |
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I have a 40 Ford that has me baffled. The engine runs smooth at low speed but, when you increase the RPM it pops and runs rough. In an attempt to correct the ignition I made some major changes and didn't correct anything. I converted the 6v system to 12v, with a new alternator, new coil and ballast resistor. I purchased a electronic distributor to get modern tech. The only old parts in the ignition system are the spark plugs and the spark plug wires. Could either the plugs or wires by the problem? Thanks Bob
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| supereal | -- 05-05-2014 @ 6:21 PM |
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Bob: we remove more electronic ignitions than we install for those reasons. Higher output often breaches old plug wires. With the hotter spark, carbon filament plug wires often improve performance. The stock for ignition in good shape is hard to beat. I'd run a dry/wet compression test to rule out leaking or sticky valves. If OK, put the stock distributor back on to see if the problem goes away.
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| 40 Coupe | -- 05-06-2014 @ 3:19 AM |
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You may have a sticking valve? Try adding some MMO to your engine oil and see if the condition improves. You can also put it in a squirt oil can and remove plugs and squirt it down the valve stems on open valves.
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| TomO | -- 05-06-2014 @ 5:58 AM |
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Bob, You have complicated the trouble shooting process by making major changes while you have a problem. The best bet is to start with some basic tests, compression and vacuum. These will give an idea of the mechanical condition of the engine and eliminate stuck valves and vacuum leaks as a source of your problem. Next check out the spark by using an adjustable gap spark tester. Hook it up to one plug and watch the spark as you increase the RPM. You should have the same intensity spark at all RPM ranges. If the previous tests have not pointed out your problem, start looking into the fuel delivery system. Disconnect the fuel line at the carburetor and with the ignition off, direct the output of the fuel pump into a 16 ounce or larger graduated container. Crank the engine long enough to get 2 ounces of gas in the container and then continue cranking for 15 more strokes of the pump. The pump should have delivered 6 more ounces of gas. Tom
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| avrotom | -- 05-06-2014 @ 9:39 PM |
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Ive run into similar symtoms, not on flatheads but on engines in general. A bad lobe on a camshaft will do this along with a bad, plugged exhaust system. Those two problems will not show up on a compression test however should show on vacuum test. Secondary ignition circuit leakage may show on acceloration or load but maybe not on just increased rpm. Just my thoughts.
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| Pauls39 | -- 05-07-2014 @ 6:06 AM |
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Amen to everything Super said! Sounds like you may have a cross fire on a couple of plugs or the advance is way off. Check your plug wires to be sure they are on the cap in the correct order, and on the plugs correctly. Some electronic distributors don't play nice with solid wires. What does the manufacturer recommend? Follow the instructions on setting the advance, if there are any. With a lot of aftermarket stuff you are on your own.
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