| planojc | -- 05-21-2010 @ 3:39 PM |
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New rebuilt engine in a 39 Ford has bad miss at idle. The hole car shakes. All new autolite plugs are fireing, Dist. was checked on a Sun Machine, new coil from Skip, Have tried 3 different rebuilt carburators and still have same problem. Compression check shows 82 to 92 range. This may be low but the motor has not been broken in. Vacuum gage bounces between 10 and 15 at idle but runs smooth between 18 and 25 at higher rpm. The plug wires are the repop origional looking wires. I'm running out of things to check or change. Any thoughts? Thanks in advance. John
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| 37RAGTOPMAN | -- 05-21-2010 @ 5:32 PM |
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recheck the ing wires to make sure they are installed correctly, check the intake manifold for vacuunm leaks, the ignition wires a real pain to install and not hard to make a mistake, and also spray the wires with water mist to check the ignition wires for shorting out,do this in a dark area,if the wire are bad you will see spark jumping, new does not mean good, I use the RHRODE ISLAND WIRES, have tried a few different ones and found these to be good, not cheap but do the job, carbs do not cause a miss , not unless they foul the spark plugs.,they would really have to be messed up, like a float that does not shut the fuel off, or overflowing problem, a bad needle and seat, hope this helps,37RAGTOPMAN, I assume you have the metal wire looms, lets hear how you made out.,!!!!!!!!!!!!
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| 37 Coupe | -- 05-21-2010 @ 5:38 PM |
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May be a stuck valve or two,to eliminate this as the problem get it running and remove air cleaner and drizzle some Marvel Mystery oil down both sides of the carb,lots of smoke but see if something this simple will clear up the rough running,it did for me. This message was edited by 37 Coupe on 5-21-10 @ 5:39 PM
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| Pauls39 | -- 05-21-2010 @ 6:06 PM |
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Assuming the plug wires are on in the correct order I would look for a valve problem. If you can drive it for a couple of hundred miles, the valves may seat and the shake will go away. However if it is really bad you may want to pull the intake and besure the horse shoe clips that hold the valve guides are in place properly. Were the guides and valve replaced during the rebuild? Did you use one piece guides? The old style spilt guides can be a source of many problem.
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| Stroker Coupe | -- 05-21-2010 @ 10:26 PM |
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I had a very similar miss in my newly installed flathead with all the same symptoms. The only difference is that mine did make a ticking noise like excessive valve clearance. I tore my hair out searching for the problem and eventually discovered that 3 valve guide horseshoe keepers had fallen out or were not installed properly. I re-installed them and the engine runs perfectly now. I was able to do this by just removing the intake manifold and not the heads. i hope this works for you. This message was edited by Stroker Coupe on 5-21-10 @ 10:32 PM
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| planojc | -- 05-22-2010 @ 5:57 AM |
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Thanks to all for your input. I do think it's a valve problem so I'm going to first try some snake oil down the carb and run it for a while to see if it will clear up. If not then remove the intake and check the valve guide keepers. Thanks John
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| 37 Coupe | -- 05-22-2010 @ 6:16 AM |
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I hope you get back to the forum and tell us what you find out and what the final diagnosis and cure was or will be. I thought mine was totally out of balance or valve timing was off but "snake oil" did correct and I put the recommended dosage of 4 oz. to ten gallons of fuel. I was lucky to learn this myself from old GM postings.
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| supereal | -- 05-22-2010 @ 7:58 AM |
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John: That vacuum pattern usually indicates a valve problem. Occasionally, we find that the head gasket is leaking between cylinders. Before you pull the intake manifold, remove the spark plug wires from the plug, one by one, to see if it affects the idle problem. If so, note which cylinders to see if it is limited to one or two, possibly adjacent cylinders, or is a random effect. Test each plug wire from end to end with an ohmmeter. They should all be withing the range of the others. If they are the carbon filament type, as many repros are, it is likely that one or more of the terminals on either end are not making contact. For a recent rebuild, the compression seems low, even with unseated rings, making me wonder if the valve clearances were properly set. Finally, check all connections to the intake manifold for a vacuum leak, such as a loose or cracked hose or vacuum line to the distributor. The sealing grommet on the back of the distributor should have been replaced when rebuilt.
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| planojc | -- 05-22-2010 @ 3:53 PM |
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Well I am now a happy camper. Two jugs of snake oil, Berrymans B12, down the carb. and she now idles and runs great. I never was a believer in additives like that, but am now. Thanks for everyones help. John
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