Flathead back pressure

[47 dodge 1.5 ton]

As I have been playing around with my motor, added a few items and I’m not sure where I have made a mistake. Engine is a 237, w/factory dual intake /balance tube, b&b ETT1 carbs. I changed the factory exhaust manifolds for Langdon’s cast iron headers and have temporarily hooked up 2 1/4” pipe x 4 ft with glass packs on the end until I drive it to the exhaust shop. It seems very obnoxious, loud, rough idle IMO, and pops unburnt fuel when snapping the throttle. It breathes better than I thought possible and I was wondering if these flathead engines require some back pressure? Before I go with 2 1/4” exhaust and dynomax super turbo mufflers, thought I’d ask some opinions. Exhaust length will remain the same. Thanks, Kevin 

Edited September 20, 2021 by 47 dodge 1.5 ton

[chrysler1941]

Remove one carb and see if any change.

[47 dodge 1.5 ton]

Guess I need to add, installed this manifold on the 237 because the original intake had a crack. I have a 265 that I’m working on for this application but figured I’d give the manifold a swap to work out the bugs.

[Sniper]

There are exactly zero engines that need back pressure.

 

You carbs probably need tuning due to the improved airflow.

 

Gas burning in the exhaust comes from one thing, too much unburnt gas in the exhaust system.  Either a cylinder is misfiring or the carbs are too rich. 

 

 

Edited September 20, 2021 by Sniper

[47 dodge 1.5 ton]

Your first statement was what I wanted to confirm. I believe it’s tuning, possibly need to pull carbs apart and take a look. Seems very smooth throttling up and extremely responsive. After a few quick stokes, I’m getting a pop here and there. One item that I had uncertainty in—the gaskets under the carb. I could not find the exact thickness, so I made my own. Not sure I needed the notches and if they needed to be a certain depth. (I put notches in that may not be used for these carbs).That may explain the slightly rough idle. 

Edited September 20, 2021 by 47 dodge 1.5 ton

[47 dodge 1.5 ton]

Just wanted to reply that after pulling carbs down several times looking for issues in the idle delivery side and adjusting float level, I believe the root cause was too much fuel pressure. I started at 5 psi, have set at 3 PSI currently and am very pleased so far. I think 5 almost works but just a little too much for the needle valve on ethanol fuel. I currently have an electric pump with a regulator so the carbs saw 5 PSI at idle, not sure what a mechanical pump produced though. 
 

Again, this is just my thoughts currently and wanted relay what I have found. Thanks all, Kevin
 

  Ie… glass packs are Too loud!

Edited December 7, 2021 by 47 dodge 1.5 ton

[desoto1939]

the gasket under the carb base on the original carbs did use the four slots. When you took off the carb one of the slots lines up with a small home. If you are using a goenor on the truck then you do not use the four slotted gasket and use the full gasket instead.

 

The old carter rebuild kit insturction sheets informs you about these small points.

 

Rich HArtung

desoto1939@aol.com

[47 dodge 1.5 ton]

 Yes, only needed (1) slot to match carb base, so believe I am good. Not using a governor, my goal is more towards the other way of the spectrum “make it breath”.  Thanks  for the clarity on the gaskets, I was trying to determine why the (4) slots were necessary.