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Backfire
Topic Started: Jan 15 2013, 07:58 PM (607 Views)
GunnersWillys
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'58 3B, runs and drives great. Starts right up. Idles fine. Accellerates fine. But I have a pop, pop, pop backfire during decelleration, when using the engine to brake, engine in gear, foot off gas. I've timed it to the best of my ability, but I suspect that may be the problem.

Any suggestions? It would be nice to be rid of it. Thanks!
58 CJ3B
Near Gainesville, Florida
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jeepdan
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Are you getting a black sooty film in the tail pipe?
Mine did, but the exhaust didn't smell that rich with fuel.
I didn't have the backfireing while descending a hill, or slowing down.
But mine would create a load embarassing backfire after turning the engine off :blink:
Increasing the timing helped, but it didn't go away until I replaced the carburetor.
I later found out that the float needle and seat was too large,.
Dan Walton Jr. Wheeling, WV

1964 U.S. Army CJ3B ( pride and joy)
1967 Kaiser Jeep M715 (my newest pride and joy)
2016 Jeep Wrangler JKU- Black Bear Edition (daily driver)
91 Grand Wagoneer (in storage)
Two 56 Willys pickups (one, restoration started, never finished)
1966 M416 1/4 Ton trailer
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Rus Curtis
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Gunners,
You say you've done your best on timing. Was it static or did you use a light?

This area is not anywhere close to my comfort zone, so I Googled some key words. What I saw as possibilities were timing too advanced, too lean, modified exhaust, leaky exhaust, idle too low, vacuum leak to name a few.

Sounds like a bit of troubleshooting is in order. If you have access to a timing light and meter to measure your rpm, you could begin to rule out some possibilities.
Rus Curtis
Alabama
'54 CJ-3B "Green Gruntt"
Bantam T3-C
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oldtime
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Too many variables to pinpoint the cause without much more input.
Could be anything from the carburetion to valve adjustment to valve condition or even the ignition timing.
You need to verify that those components are up to acceptable service standards before you can eliminate them as a possability.

We just don't know your engines history.
If engine needing a rebuild I might suspect bad valves to be the cause.

Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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GunnersWillys
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I kind of figured it wouldn't be easy. As to black, sooty exhaust, not really. I get a little blue smoke at start-up and after a long idle. Compression numbers are good so I lean toward that being valve related. I've adjusted my valves and they seem okay. I've rebuilt the carb with a kit from Kaiser Willys. It's working fine. And I adjusted the timing with a light, but I am not comfortable it is perfect. Kind of hard to read the marks.

It's the original engine, about 18,000 miles on it. I've no idea if it's ever had valve work, but I suspect that is something it could use. No vacuum leaks I can find. I'll start back through the list, starting with some subtle timing changes to see if it fixes it. Thanks.
58 CJ3B
Near Gainesville, Florida
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oldtime
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Bad valve condition should show up on W/O standard vacuum test.

Please read: http://z4.invisionfree.com/CJ3B_Bulletin_B...?showtopic=4640
Currently building my final F-134 powered 3B .
Rock Crawler using factory parts from the Willys Motors era (1953-1963)

http://s4.zetaboards.com/CJ3B_Bulletin_Board/topic/30228766/1/#new
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