Deceleration backfiring

StarDiero75

StarDiero75

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Howdy Guys,

So its been a bit and I've done lots of work to the Ranch lately. i ended up having to re-ring it and did the rod bearings too. Also noticed my NEW valve seals were shot, lovely. The motor is broken in and running like a champ. i got the PCV working properly finally. Apparently you can't run the PCV on the front vacuum port on the 1980 heads.... the car always ran like trash when i did that. The AFR gauge would go nuts. I drilled a hole in my carb spacer, tapped, and put a fitting in there and it works perfectly. Anyhow....

I've noticed when I let off the gas it likes to backfire out the exhaust during deceleration. Especially when its a hard deceleration from like 3-4k RPMS. Initially the AFR gauge shows normal like around 14-15, then it'll lean out to around 17,18+. I'm not quite sure why its doing this. Before the rebuild it was doing this and before the PCV it was doing that. Before, my remedy was running a rich idle circuit (11.5-12 AFR), but thats not right. Now i have it properly set about 13ish. Any reason as to why it does this?

Thanks Guys,
Ryan
 
All emissions era cars ran leaner with lower compression ratio and more advance to increase heat. The solution for decleration lean outs was various systems...lift off delay by a dampend dash pot or electrical solenoid or Direct Current stepper motor or air fuel richening that was offset by adding or removing air to the throttle body.

For V8 and I6 2 bbl and 4 bbl carbs between 1968 to 1988 its primary solution was called a dashpot. The systems that do lift off throttke delay are variously called :-

VOTM = Vacuum Operated Throttle Modulator

TSP = Throttle Positioner Solenoid

TK = Throttle Kicker ( note...an Air Con device that can be repurposed)

ISC = Idle Steeper Control

IAC = Idle Air Control ( generally Port EFi, but can be operated as a Mixture Control Solenoid, and called an MCS when used in 1, 2 and 4 bbl carbs).

The carb position on direct mount Log head sixes prevents any of these Five (5) systems fitting on the carb easily, but there are work arounds.

Do a google images search

xctasy VOTM
xctasy TSP
xctasy TK
xctasy ISC
xctsay IAC

And youll most likely get these devices in their OEM Ford 3.8/4.2/5.0/5.8/6.6/370/429/460 habitat.

Then see if you can track down one with a bleed down rate which will help you delay the throttles return to curb idle by 6 to 14 seconds.
 
Hi, I know exactly what you are experiencing. It happens on my Bronco. It is common on circle track race cars going into a corner. Engine braking from high RPMs to low RPMs. We always felt that was the ignition timing retarding before the engine catches up. As mentioned, a dashpot could help. I don't think it is doing any harm, and besides, I kind of like it. Good luck
 
"...I've noticed when I let off the gas it likes to backfire out the exhaust during deceleration. ..."
what does that mean?
What is your system (exhaust)?
Any damage? (valves, exhaust, ego, neighbors)?
Sounds pretty normal to me ~
 
So I'm running a 1968 Autolite 2100 and my car is a 5 speed. I thought dashpots were for auto cars? I do have one that I can rig up. B/c i notice if I do let the gas out much slower I don't really have that prob.

Could I also try running the ignition vacuum to the intake? From what I've read is that the popping is caused by unburnt gas going out the exhuast and exploding there. If I run the timing from the intake, i believe the engine runs cooler and during that time of deceleration, the timing actually increases due to the high vacuum, which will burn the gas sooner so it won't boom in the pipe. Does that sound like good reasoning?

I like it a little sometimes but I'd much rather not hear it. I've heard it's not good for exhaust valves either which is the main reason I want it gone

Thanks guys keep it coming,
Ryan
 
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