I've been putting some good miles on my 1966 200cid Mustang this summer and it's been a lot of fun. Carb was rebuilt (Carter YFA) along with some other tune-ups in the spring and it's been running smoothly and reliably. Recently though I've been getting backfires while downshifting (3 speed manual) from 3rd to 2nd and the idle feels a little rough/rich. If I sit at a light and then move, I get dirty exhaust come out for a couple seconds as I accelerate. New York metro area so temps have been 75-90 degrees at the hottest lately. I'm young and not incredibly experienced with carbureted engines so I'm curious to hear from folks more experienced what some initial things to check or adjust should be. I already replaced my plugs after this started. Should I check my distro cap/spark/cables? Is it a carb thing even though it was just rebuilt? Time to replace fuel pump/filter? Time to put on an electric choke?
All Small Six 1966 ford 200 Backfires on Downshift and Running Rich (?)
- Thread starter gavincorneliusedmonds
- Start date
This relates to all small sixes
Hmmm… That’s a tricky one to figure out remotely online. Backfiring on deceleration usually indicates a lean condition (not enough fuel when decelerating and the carb is closed). It can also be caused by air entering the exhaust system (bad exhaust manifold gasket or cracked pipe and igniting unburned fuel. It can also be caused by ignition timing being too retarded but it sounds like the engine is running well from your description.
Check your distributor and cables just to be sure and also make sure you don’t have any vacuum leaks on the intake or exhaust leaks.
Hi, my 66 Bronco would pop through the exhaust sometimes when I let off the gas, while I still had the original LOM-SCV ignition system. I admit it was fun. That all stopped when I installed the Holley 2 barrel and newer distributor. I think the cause was the ignition timing "catching" up to the engine. Good luck
That’s a thought. Maybe it is the ignition catching up and igniting unburned fuel on the way out. My old hot rod BMW 2002 used to pop on deceleration and it had a points ignition. To be honest, I was surprised that my mildly hyped up inline-6 doesn’t do that too but I’ve got an HEI electronic ignition on mine.
Check your choke to make sure it's open all the way after the engine is warm.
Offering as a thought - I was always taught not to downshift to slow down because it puts a strain on the driveline, especially if you don't do it correctly. Brakes are much easier and less expensive to replace than are clutches, transmissions and driveshafts.
Offering as a thought - I was always taught not to downshift to slow down because it puts a strain on the driveline, especially if you don't do it correctly. Brakes are much easier and less expensive to replace than are clutches, transmissions and driveshafts.