74 Dart EVAP canister purge is not working.
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KitCarlson
Well-Known Member
Adding pictures of canister, carb and hoses will help. Also is you have the hose routing diagram post that.
KitCarlson
Well-Known Member
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67Dart273
Well-Known Member
I thought there was more to it in the book. There's a little in the fuel system section, and this is from the emissions section.
I believe your car would have the vapor separator built into the tank, rather than the separate can above the tank. They do mention that the overfill valve MUST be vertical, and you might check that it is not plugged/ gummed/ rusted, etc. I'd forgotten, these were once replaceable as a "stub" line, you just cut them off and attached the new one.
According to the fuel system section, the pressure/ vacuum cap is supposed to be .9--1.25 psi pressure, and .1 -- .25 psi vacuum. This is specified in psi, NOT inches of Hg
Hope these are readable and hope they help
I believe your car would have the vapor separator built into the tank, rather than the separate can above the tank. They do mention that the overfill valve MUST be vertical, and you might check that it is not plugged/ gummed/ rusted, etc. I'd forgotten, these were once replaceable as a "stub" line, you just cut them off and attached the new one.
According to the fuel system section, the pressure/ vacuum cap is supposed to be .9--1.25 psi pressure, and .1 -- .25 psi vacuum. This is specified in psi, NOT inches of Hg
Hope these are readable and hope they help
67Dart273
Well-Known Member
Yeh, bear in mind that some amount of pressure can be expressed in many forms, psi, inches of mercury (Hg) or for smaller amounts, inches of water, which I used to routinely use in HVAC
So if the cap is supposed to release INTO the tank from .1--.25 pressure, that would convert to approx .2" Hg, and .25 psi would be about .5" Hg.
I'm surprised at how much positive psressure is allowed. 1 psi on a big tin tank is a LOT
KitCarlson
Well-Known Member
I think you stated that your carb does not have a bowl vent, so the system cannot recover the vapors after shut down there. In the information provided by 67Dart273 there is a note that only some models have the bowl vent.
I also noticed comparing 1972 evaporative controls to 1974 changes were made to eliminate the internal purge valve in the canister. This makes me think that the purge line on your carb is throttle ported, else purge could happen at idle. Later they moved back... It is my opinion, the mid 70's were not good years for emissions controls.
I recently had a significant bowl vent issue on an early Barracuda. I solved it by changing to a carb with bowl vent, added a tank vent line, and added a canister. Like you I rebuilt the original carb and that did not solve the problem. I paid close attention to float setting and even verified on the car following service manual procedures. I believe a 46 years of use, a porosity problem in the bowl casting, and volatility of modern gasoline are the root causes. By changing things I basically moved from 1966 to 1985. I am pleased with the results. Perhaps a solution is to locate a similar 1B carb in a later year, prior to feed-back (lean burn), with bowl vent, and change the carb and vapor recovery system.
I also noticed comparing 1972 evaporative controls to 1974 changes were made to eliminate the internal purge valve in the canister. This makes me think that the purge line on your carb is throttle ported, else purge could happen at idle. Later they moved back... It is my opinion, the mid 70's were not good years for emissions controls.
I recently had a significant bowl vent issue on an early Barracuda. I solved it by changing to a carb with bowl vent, added a tank vent line, and added a canister. Like you I rebuilt the original carb and that did not solve the problem. I paid close attention to float setting and even verified on the car following service manual procedures. I believe a 46 years of use, a porosity problem in the bowl casting, and volatility of modern gasoline are the root causes. By changing things I basically moved from 1966 to 1985. I am pleased with the results. Perhaps a solution is to locate a similar 1B carb in a later year, prior to feed-back (lean burn), with bowl vent, and change the carb and vapor recovery system.
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