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Sorry this is so long, but it's been an interesting adventure. Thanks again to everyone who replied to my thread yesterday on what I thought was a timing problem. Here's an update on what I found last night.
With the help of this vacuum diagram from OlJeeps site, I did some investigating and found some creative vacuum line work by the PO.
When the PO installed the Edelbrock Performer intake manifold and Holley carb, he left a lot of the vacuum hoses in place, but very few of them really went anywhere. I discovered that he used a non-egr intake manifold. So, there is no EGR valve to go bad. Next, I discovered that the HDC CTO was removed entirely. The Spark CTO was still there, but all of the hoses went directly to the non-linear valve. So, neither component was actually doing anything. And, since the CTO's were out of comission, the distributor vacuum advance was connected directly to a ported vacuum source on the carb.
Now for some cleanup. I removed the non-functioning non-linear valve and the hoses going to the non-functioning Spark CTO. This freed up a manifold vacuum source on the base of the carb. So, based upon several old threads that I found, I moved the dist. vacuum advance to this manifold vacuum port and capped the ported vacuum port. This made a significant improvement in idle quality and seems to have helped the detonation problem that I had. But, I'll have to test that more on a longer drive.
Now for today's mystery. When the PO did the carb/manifold upgrade, he removed the AIR pump and hoses. According to the above diagram, there is supposed to be an AIR hose from the charcoal canister to the carb bowl vent. Since the Holley carb doesn't have a bowl vent, the PO connected this line to a manifold vaccum port on the base of the carb. So, I basically have a "controlled" vacuum leak through the charcoal canister. I disconnected this hose and plugged both the vacuum port and the port on the canister and the engine ran very poorly. Rough idle and starting trouble. I reconnected the hose and all is well. So, what gives, why does this work? Hopefully someone with more vacuum knowledge can explain this mystery to me. Thanks.
John
With the help of this vacuum diagram from OlJeeps site, I did some investigating and found some creative vacuum line work by the PO.
When the PO installed the Edelbrock Performer intake manifold and Holley carb, he left a lot of the vacuum hoses in place, but very few of them really went anywhere. I discovered that he used a non-egr intake manifold. So, there is no EGR valve to go bad. Next, I discovered that the HDC CTO was removed entirely. The Spark CTO was still there, but all of the hoses went directly to the non-linear valve. So, neither component was actually doing anything. And, since the CTO's were out of comission, the distributor vacuum advance was connected directly to a ported vacuum source on the carb.
Now for some cleanup. I removed the non-functioning non-linear valve and the hoses going to the non-functioning Spark CTO. This freed up a manifold vacuum source on the base of the carb. So, based upon several old threads that I found, I moved the dist. vacuum advance to this manifold vacuum port and capped the ported vacuum port. This made a significant improvement in idle quality and seems to have helped the detonation problem that I had. But, I'll have to test that more on a longer drive.
Now for today's mystery. When the PO did the carb/manifold upgrade, he removed the AIR pump and hoses. According to the above diagram, there is supposed to be an AIR hose from the charcoal canister to the carb bowl vent. Since the Holley carb doesn't have a bowl vent, the PO connected this line to a manifold vaccum port on the base of the carb. So, I basically have a "controlled" vacuum leak through the charcoal canister. I disconnected this hose and plugged both the vacuum port and the port on the canister and the engine ran very poorly. Rough idle and starting trouble. I reconnected the hose and all is well. So, what gives, why does this work? Hopefully someone with more vacuum knowledge can explain this mystery to me. Thanks.
John
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