Thought that would get your attention. OK, here's a good one for you, I really did this (unwittingly). Would be interested in your analysis. Please bear with me. Background: 1971 Chrysler 440hp, been having an issue with surging/dying on letup from full throttle operation, noticed starting about a year ago. All indications are something to do with the air valve on the Holley 4bbl carb. Adjustment helped a little, but didn't cure.
You may already know 1971 was the year Chrysler began making their first feeble attempts at pollution control in the form of a .5 reduction in compression and the addition of a fuel vapor recovery system on most models. So looking at the mess of plumbing involved with the breather cap and that fuel revovery vent on the one valve cover the other day, I decide it needs a new breather (that is "just" a breather) and re-do the plumbing, eliminating the big wastedump hose going nowhere and the fuel vent tube. I cap the fuel vent tube with a filter and run a smaller section of tubing back out of sight under the firewall. The fuel tank must be vented, just happens to be this tube running up to the breather on the passenger side from the charcoal cannister. Prior years used a vented gas cap. Well wouldn't you know it, the air valve was also plumbed into that breather. So I fabbed up a fitting and ran it into the clean side of the air filter. This is when I suffered the sudden realization what had been happening and took a big suck on that gas vent tube. Yep you guessed it: Gasoline bubbling back through the charcoal cannister!
That vapor recovery canninster probably stopped functioning about 30 years ago, but the only symptom of what was happening was the full throttle letup when it pulls enough vacuum and simultaneously opens the air valve - Raw gas straight into the carb, at high speed no less, enough to bog the engine. Amazing it didn't hydrolock or literally blow up! I confirmed this when further testing proved the problem did indeed disappear immediately after finishing the repairs. I subjected the motor to this treatment probably more than dozen times over the period of the last year.
Oddly though, it seems to be running better than ever. Now I'm wondering if it is about to grenade from the abuse, or maybe just has really clean combustion chambers?
You may already know 1971 was the year Chrysler began making their first feeble attempts at pollution control in the form of a .5 reduction in compression and the addition of a fuel vapor recovery system on most models. So looking at the mess of plumbing involved with the breather cap and that fuel revovery vent on the one valve cover the other day, I decide it needs a new breather (that is "just" a breather) and re-do the plumbing, eliminating the big wastedump hose going nowhere and the fuel vent tube. I cap the fuel vent tube with a filter and run a smaller section of tubing back out of sight under the firewall. The fuel tank must be vented, just happens to be this tube running up to the breather on the passenger side from the charcoal cannister. Prior years used a vented gas cap. Well wouldn't you know it, the air valve was also plumbed into that breather. So I fabbed up a fitting and ran it into the clean side of the air filter. This is when I suffered the sudden realization what had been happening and took a big suck on that gas vent tube. Yep you guessed it: Gasoline bubbling back through the charcoal cannister!
That vapor recovery canninster probably stopped functioning about 30 years ago, but the only symptom of what was happening was the full throttle letup when it pulls enough vacuum and simultaneously opens the air valve - Raw gas straight into the carb, at high speed no less, enough to bog the engine. Amazing it didn't hydrolock or literally blow up! I confirmed this when further testing proved the problem did indeed disappear immediately after finishing the repairs. I subjected the motor to this treatment probably more than dozen times over the period of the last year.
Oddly though, it seems to be running better than ever. Now I'm wondering if it is about to grenade from the abuse, or maybe just has really clean combustion chambers?
