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Posted By Discussion Topic: engine backfire -- page: 1 2     39topless 02-21-2013 @ 12:23 PM reply profile send p.m. Member Posts: 77 Joined: Feb 2013 I am getting an occational( like every 10 seconds) backfire in the engine of my 239 '40 ford. Would this be a timing problem or something else? This message was edited by 39topless on 2-21-13 @ 12:34 PM supereal 02-21-2013 @ 12:32 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Is the backfire thru the exhaust or carb? Is it often, or occasional? Does it happen mostly or only on deceleration as you coast? Common exhaust backfire is often due to a vacuum leak. Check your vacuum hose to the wiper for cracks, and the line to the distributor, to be sure it is tight. We check for hard to find vacuum leaks by spraying some carb cleaner on the suspect places. That stuff is very flammable, so be careful. It can be, but rarely, due to a leaky intake manifold gasket, or faulty power valve, or its gasket, in the carb. If your plug wires are old, it can be crossfire, particularly in the plug wire confuits. Same is true of carbon paths inside the distributor caps. I wouldn't suspect the timing. 39topless 02-21-2013 @ 12:39 PM reply profile send p.m. Member Posts: 77 Joined: Feb 2013 backfire is through the carb. seems to change frequency everytime I run it. The wipers are not hooked up to the vacuum line. should I plug this line? Thanks alot. Great advice. supereal 02-21-2013 @ 4:07 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Yes, plug any unused vacuum lines. From your description, I would run a compression test, and hook up a vacuum gauge. If you need a diagnostic chart, I 'll post one. I suspect you may have a sticking or burned valve. alanwoodieman 02-21-2013 @ 6:27 PM reply profile send p.m. Senior Posts: 868 Joined: Oct 2009 look into the tail pipes-are they sooty? Pull the plugs and look for one that is a different color or look---sometimes an overly rich mixture can lead to what you are experiencing. Timing problem would most likely cause numerous back fireing, check you wiring- is on of the wires on the wrong plug? a loose wire in the inner cap can cause a backfire by "leaking" the coil charge to another plug. 39topless 02-22-2013 @ 8:50 AM reply profile send p.m. Member Posts: 77 Joined: Feb 2013 Great suggestions. I will get on this this weekend and post my results. Thanks so very much. oldford2 02-22-2013 @ 5:18 PM reply profile send p.m. Member Posts: 275 Joined: Oct 2009 If you have been getting backfires thru your carb your power valve may be blown too and leaking gas down the throat. Check it also. John 39topless 02-27-2013 @ 5:47 PM reply profile send p.m. Member Posts: 77 Joined: Feb 2013 Ok, figure this one out. I checked for vacuum leaks,none. I pulled all the plugs, 5 were very black, cleaned and replaced and did a compression check. All between 55-75. Started up the engine, NO backfire. I am guessing maybe a hanging valve decided to be good.??? Thanks for all your help. Phil supereal 02-27-2013 @ 6:51 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 A sticking valve wouldn't affect all five cylinders. Sooty plugs usually indicate an over rich fuel mixture. In the carb, the only part that would affect more than four cylinders is the power valve because each side of the carb feeds four cylinders only. It is probable that either the power valve is leaking, or its gasket is the source of excess fuel, and also causing the backfire. It can also be due to carb flooding caused by overfilling. In that case, suspect the float.or the float is hanging up. I'll bet your problem will return. It only takes one backfire thru the carb to blow out the diaphragm in the power valve. This message was edited by supereal on 3-1-13 @ 8:38 AM 37RAGTOPMAN 02-28-2013 @ 3:52 PM reply profile send p.m. Senior Posts: 1971 Joined: Oct 2009 39topless I had the same problem with a MODEL A, the plugs were dirty,it was poping though the carb, This was in a rebuilt engine,I think breaking it in, caused to it to soot up,maybe to much slow speeds.? and I disected the carb,points timing,etc, there is not alot to look for in a simple system like a MODEL A I found solution in a old time repair manual, make sure you have the correct plugs [heat range] in for your type of driving, I can tell you I had a problem with original CHAMPIONS, in my 37 ,they were very old,and one or 2 were burnt away,from many years of use, I tried a set of NGK, Let me tell you that my 37 runs very well with them it it, I was Amazed how much more power it has, and seems like it gets better MPG, My 3 cents 37RAGTOPMAN

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