| Dustbowl | -- 03-17-2011 @ 4:54 PM |
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My 36 Flathead (one 97 carb) has dual exhausts and virtual straight through mufflers. When they are warm, I get a lot of sharp backfires at the exhaust when de-accelerating. I believe this is common. Is it primarily caused by too rich mix in carb, or something else?
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| shogun1940 | -- 03-17-2011 @ 7:50 PM |
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its unburned fuel, contact the EPA for catalytic converter, exhust scubbers and the 10,000 page booklet on why that is bad.
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| 37RAGTOPMAN | -- 03-18-2011 @ 4:37 AM |
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it might be air leaking into the exhaust system,this is just one of many things that make it backfire, take a rag and hold it over the exhaust pipe,if it if you have Dual EXHAUST have a friend help you,becareful NOT to get burnt, if it starts to slow down your exhaust is good, if you hear exhaust leaking out,you will have to seal those issues, without hearing how loud,,it is hard to figure out exactly what it is, when you have straight though exhaust, you might have to rejet the carb,when you do one thing,, it sometimes leads to another, do a few check and get back to us, Also are you using the original aircleaner,? try it without one,just for test purposes also check for intake manifold leaks, how does it idle, does it run smooth? I have duals on my 37 85 hp, with headers and one baffle in the mufflers, and have not noticed any backfiring,just a nice mellow sound, just my 3 cents 37RAGTOPMAN
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| supereal | -- 03-18-2011 @ 8:51 AM |
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A common cause of backfiring is badly worn throttle shaft bushings in the carb. This allows air to enter. Also, inspect the carb throat to see if the throttle plates close all the way around when released. You can test for vacuum leaks by spraying some carb cleaner on suspicious areas such as the carb base gasket. The last backfire we cured was caused by a cracked wiper hose. Be sure that the vacuum link to the distributor advance is not leaking, and that the intake manifold gasket is properly tightened.
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| Dustbowl | -- 03-21-2011 @ 1:32 PM |
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great and useful responses. gives me lots of things to check. Many thanks to all.
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| Stroker | -- 03-21-2011 @ 3:29 PM |
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Just goes to show....in the 50's, we called this "back-rap", and cultivated it. The cause is excess oxygen in the exhaust system on trailing throttle, and as has been suggested can have several sources. It's not all that bad, and won't occur if you ease off the throttle, or de-clutch.
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