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In Reply to: Backfire - Lean/Rich or timing? posted by Chris Peterson on March 05, 2000 at 15:58:16:
: Hey Group,
: She is alive again, but ornery!
: Car is a 76, stock cam & pistons but newly added 40 DCOE's that backfire like mad. Cam has been added to the wish list.
: I am running a 002 mechanical dist. and crane XR3000 ignition. I've timed to spec, no good. Timing (by ear) when running best causes most backfiring. I realize this is a compromise going with the mech. dist., but seems like eventually I can get close enough to be pleasant. What might work? The neighbor kids are running scared!
: I am also tinkering with the mixture. What causes least amount of backfire? Leaner or richer?
: Any thoughts?
: Thanks, Chris Peterson
: Las Vegas Driving Events Coordinator
: 76 02, fresh 205/50/15 Kumho V700's stuffed under the wells -- Talk about sticky! (H&R's and Bilstein Sports -- nice setup)
If it's backfiring through the carb and the timing is OK, the idle is too lean. Trouble is, turning the screws might not help. If these are "unknown" DCOE's, like maybe they were set up for an '02 with a performance cam, then try the next-size-up of idle jets. You see, the idle jet controls the mixture through both the idle ports (in conjunction wiht the screws) as well as the "transition" holes that are important at idle and at partly-cracked throttle. If it spits at idle and has a flat spot (especially with backfiring) at partly cracked throttle, get bigger idle jets. I've got the same problem with my 45DOCE's, stock cam and compression.
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