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EFV-8 Club Forum / General Ford Discussion / Rough idle and back fires out of exhaust.

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Posted By Discussion Topic: Rough idle and back fires out of exhaust. -- page: 1 2     supereal 11-14-2019 @ 12:16 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Check the engine with a vacuum gauge. One possibility is that you have an exhaust restriction. This allows an engine to start and idle, then the vacuum drops as the car is run. It can be from a carbon filled muffler. If you tap the muffler with a hammer, and you get a dull thud, it is time to replace the muffler. I have seen them so filled that they were hard to lift! If you don't have a vacuum diagnosis chart, I can post one or email it if you leave a message in my box on the header of this site. The vacuum gauge is still a very valuable diagnosis tool, and we use it often at our shop. sarahcecelia 11-06-2019 @ 9:04 AM reply profile send p.m. Senior Posts: 1171 Joined: Mar 2013 Back firing out the exhaust can be retarded timing. We used to do that as kids to make them backfire like that! Regards, Steve Lee 40 Coupe 11-06-2019 @ 4:23 AM reply profile send p.m. Senior Posts: 1646 Joined: Oct 2009 The 33-34 engine block does not have a breather passage on the front of the engine block. The breather came into use after 34. Look at the bottom of the engine at the front, RH side of the oil pan and see if the small triangle shaped breather is there or if the block above this area has the breather passage. Maine 11-05-2019 @ 2:32 PM reply profile send p.m. Member Posts: 8 Joined: Aug 2018 During the time the engine was being rebuilt I went through the distributer . replaced the rotor (key was worn resulted in some drive play), one bushing on driveshaft had play so it was replaced, reset points (looked good ) replaced inner and outer caps and the spark plug wires. When the problem developed I checked the spark at each plug and it appeared ok but I did have a new condenser so I replaced it and still had the problem. At one of the members suggestion, I checked the voltage at the coil and it was low at 2.4 volts, so since I had a new resister I replaced it and got 3.3 volts but no change in problem. Just so nice having a great teem from the members working with you to solve a problem. Thanks for your input. flathead4rd 11-04-2019 @ 8:22 AM reply profile send p.m. New Member Posts: 169 Joined: Oct 2009 Sounds like you have solved your problem. I just thought I would add my own experience with the same exact problem for future reference. After checking all the possible problems I could think of including resetting the adjustable lifter clearances and still having the backfire out of the tail pipe, I decided the only place left to look was at the plug wires. Sure enough, #1 plug wire was breaking down and causing a weak spark. It would fire just enough to almost go unnoticed. Replaced it and problem solved. A lot of hours spent on such a simple solution. Maine 11-03-2019 @ 2:54 PM reply profile send p.m. Member Posts: 8 Joined: Aug 2018 At this time I believe I solved the problem by addressing the rich gas problem, rough running and backfiring at the exhaust. the combination of going through the carburetor, running Marvel Mystery oil in the fuel supply and then running the car on the open road at 50 mph and a total 15 miles. On the existing 97 Stromberg carburetor I installed new jets .044, emulsion tubes, a designated 97 model power jet, idle jets and idle screws, and the new Grose jet that allows higher inlet pressure. The accelerator pump looked new but I did replace the pump check valve. The existing main jets were marked .045 but one had orifice almost twice the size as the other. I also decided to install a new diaphragm in the pump as I had it on hand. So the 97 Carburetor is from a 1936, is there some way to identify the year of the engine? With winter weather on the horizon, I put the car away until spring. I learned a lot through this problem and appreciated all the suggestion I received. Next spring after some more road trips I'll check the spark plugs to see if the fuel mixture is ok. Thanks to all of you who gave me so much info. 40 Coupe 10-22-2019 @ 5:43 AM reply profile send p.m. Senior Posts: 1646 Joined: Oct 2009 The typical float setting for a Stromberg is 11/32" down on the free end from the top of the bowl. The standard factory jets are: Model 40 or 48= 0.048" Mains and #63 power valve Model 97=0.045" Mains and #65 power valve. They should all be marked. The original Carb for the 34 was the Stromberg Model 40 which is nearly identical to the Model 48 used in 1935. By 36 Ford changed to the Model 97 for better fuel economy. Ford Strombergs used an all metal input valve needle some aftermarket needles have a Vitron tip which is not stable with alcohol fuel. Not a good idea to run more that 2-1/2# of fuel pressure it can cause input valve to leak and excessive fuel in the float bowl. If your above this level I suggest removing the electric pump and have your original pump rebuilt by Charlie Schwindler. Excessive fuel tends to wash oil film from valve stems and rings 37RAGTOPMAN 10-21-2019 @ 3:09 PM reply profile send p.m. Senior Posts: 1940 Joined: Oct 2009 HI Maine did you try using MARVEL MYSTERY oil in the fuel, I think you have sticking valves, especially the exhaust valves this happens when the engine is not broken in and sits idle for a period of time, worth a try ,,,,, also with the engine running, use a light and a mirror and look down the carburetor and check to see what is happening, is gas flowing over ?maybe a bad float or needle valve, causing overflow down the throat of the carb ? causing running rich hope this helps 37RAGTOPMAN MAINE This message was edited by 37RAGTOPMAN on 10-22-19 @ 10:23 AM MG 10-21-2019 @ 12:28 PM reply profile send p.m. Senior Posts: 1248 Joined: Nov 2009 Is the mechanical fuel pump new? Some of the new fuel pumps (off shore) out there have excessive pressure. There's been a rash of reports of the symptoms you are experiencing caused by excessive fuel pump pressure. Ideally you want 2-1/2 lbs. pressure - no more.... Maine 10-21-2019 @ 11:57 AM reply profile send p.m. Member Posts: 8 Joined: Aug 2018 Talked with Jeff at the shop that rebuilt the engine. He can't come up with why the timing gears would fail so early, fiber gear is new and all press fitted tight. after further discussion on my activity he determined I should address the rich fuel problem. This was based on my the running of the engine right after recleaning the spark plugs. The engine ran fine for about 15 minutes smooth and the turned rough again and started to backfire at the exhaust when dropping back to an idle. I can't smell gas in the oil but it does blow black smoke when it runs rough. The carb is a Stromberg 97, and at this time, I don't know the jet size nor do I really know the vintage of the engine. the heads are 19 bolt cast iron. i

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