So I was over in the Weber tune up thread and we were discussing the finer points of tuning a carb with the vapor canister attached. In my case, I was able to get the Weber tuned up as the OP described and all was well with 0" of vacuum at the S port. Than Matt drops the bomb, is your canister working???? So I went to the Sprynet Jeep Adventures Under the Hood site and checked out the vapor canister page. The test listed in that site was to pinch the main purge line and if the idle stumbles then the canister need to be replaced.
I little about my setup, I have the main purge hooked to the PCV valve and the Purge Signal runs off of the 5 port CTO that is tied to the S port of the Weber 38.
I completed the pinch test and the idle took a nose dive. SO it got me thinking, why does this happen??? What exactly is happening in the canister that causes the idle to dive when the main purge line is pinched. I opened up the 1983 FSM and read the following: From 1J-6
It would be different if the FSM did not state clearly that the canister is venting while running through manifold vacuum. Although it does not state it that clearly, one can infer that since it is hook to manifold vacuum then by default it is always "purging" and that when it is presented with the appropriate amount of ported vacuum that purge rate increases.
Using that reasoning, does it not render the pinch test invalid? Seems to me that it does but that is me using my walnut sized brain trying to wrap my head around exactly what happens in the canister. To me it is always drawing air through the canister because of the manifold vacuum.
Those of you that really understand this, please chime in and tell me what I am missing or I don't have laid out correctly above. I attached a snapshot of the FSM for review.
Gary
I little about my setup, I have the main purge hooked to the PCV valve and the Purge Signal runs off of the 5 port CTO that is tied to the S port of the Weber 38.
I completed the pinch test and the idle took a nose dive. SO it got me thinking, why does this happen??? What exactly is happening in the canister that causes the idle to dive when the main purge line is pinched. I opened up the 1983 FSM and read the following: From 1J-6
Seeing that the main purge line is hooked to a manifold vacuum source it is drawing in air through the canister from the moment the engine is started which is confirmed in the above listed paragraph (see emphasis). Would it not stand to reason that if it is supposed to be drawing in fresh air from the canister from the moment the engine is started that if you pinch the line it would be restricting airflow that it expects to be receiving causing the idle to fall.
It would be different if the FSM did not state clearly that the canister is venting while running through manifold vacuum. Although it does not state it that clearly, one can infer that since it is hook to manifold vacuum then by default it is always "purging" and that when it is presented with the appropriate amount of ported vacuum that purge rate increases.
Using that reasoning, does it not render the pinch test invalid? Seems to me that it does but that is me using my walnut sized brain trying to wrap my head around exactly what happens in the canister. To me it is always drawing air through the canister because of the manifold vacuum.
Those of you that really understand this, please chime in and tell me what I am missing or I don't have laid out correctly above. I attached a snapshot of the FSM for review.
Gary