Technical Flathead exhaust pop goes away with a little choke

my flathead Ford has been popping pretty good on deceleration through my glass pack dual exhaust. I thought it was running rich so i went to 43 main jets and 66 power valve on my stromberg 97. Didnt help. Found out that if i give it some choke the pops go away. Anyone have an idea why richening it up like that works?

 

Vacuum leak??
Paul in CT

 

Running a little lean and/or timing is off.

More choke means less air-to-fuel: otherwise known as enriching the mixture.

Look for any air leaks that would allow unregulated air into the intake tract, and check the timing.

Lean fuel mixtures burn more slowly than rich ones, so they require more advance. That is also why you may not have complete combustion by the time the exhaust valve opens.

The popping is not-yet-burned fuel hitting the hot exhaust, and burning off there.

A cheap hardware store infrared thermometer like this, or similar: https://www.homedepot.com/p/General...ximum-Temperature-608-Degree-IRT206/100651817

Will help diagnose and tune. Point it at the exhaust runners. Lean and late both make the exhaust hotter.

 

Hi, Paul. I may have wandered all the way to the other coast, but I am from Connecticut.

 

Lean pop. Fatten it up, and advance the timing.

 

It's an A/F ratio tuning issue. I've experienced 'popping' exhaust notes many times just from simple factors such as changing mufflers from chambered to straight through. I know it's "traditional" to sort out tuning issues by the seat of your pants and hashing it out with your buddies, but I've learned that sometimes you have to go over to the Darkside and actually use technology. If you can find a dyno jockey who can deal with carbs, he's sure to have a 'wideband' to dial in the size jets for your application. I know that's not always easy to find that guy because most of them are focused on fuel injected, 'tuner cars' but there are many others who don't have a dyno in their back pocket but they do have a wideband gauge in the toolbox that can be hooked up temporarily for a road test-n-tune.
I know, I speak blasphemy. But a little injection of tech (pun intended) wouldn't hurt any of us to learn.

 

Timing. Check your gap and make sure cap is seated properly. Mine was not and that was the issue

 

Different vehicles, but we encountered the popping on deacceleration and traced it to exhaust leaks between the head and muffler. Couldn’t heard the exhaust leak on acceleration , but it was there. Might be your problem, check your muffler connections.










Bones

 

Greetings to all....l joined to reply to the carb popping....ok this will be hard to believe but here it goes....your pop happened when the air speed inside your carb goes super sonic.....ok the sample fix is to get a #2 pencil and place between the air horn plate as a starting point....then open to open as needed and make all adjustments and road speed.

 

First, his carburetor is not popping. His exhaust is.

Second, what the heck are you talking about? At no time does the intake velocity reach 767.269 miles-per-hour, and especially not on a flathead.

Typical intake velocity is 350-400 feet-per-second, which is 238.636 to 272.727 miles-per-hour.

Force that velocity of air into any street engine, and you will scatter the internals in every direction.

 

Take note of......"that warm feeling of smoke being gently blown up our 'neather region'"!!
Very uncomfortable but still ellicits a smile.....strange indeed!
6sally6