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| Hello from a new member https://slantsix.org/forum/viewtopic.php?t=52852 |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 10:58 am ] |
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I'm ready to move on! She is running nice, smooth and quiet. Any idea why the vacuum advance degrades the idle a wee bit? I was guessing maybe a leak or the pod. |
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| Author: | Reed [ Mon Aug 05, 2013 11:18 am ] |
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The vacuum advance should have no effect on the idle. The vacuum advance should be connected to a port on the carb that gets no vacuum at idle. It sounds like you are hooking the vacuum advance up to a port that sees manifold vacuum and sees vacuum at idle. Don't do that. |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 11:29 am ] |
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Thank you much Reed, it's connected to a port on the air cleaner. That port is connected to some vacuum device mounted on the air cleaner I need to look up. I'm on it! Heading out to look now. |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 11:39 am ] |
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Ok that device is labeled OSAC. The other end of the OSAC goes to the small vacuum port right beside the PCV port on the 1945 carb. That must be wrong? |
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| Author: | Reed [ Mon Aug 05, 2013 11:40 am ] |
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Sounds like you have attached the distributor vacuum advance hose to the heated air intake system thermostat. The device on the air cleaner should have two nipples. One attaches to a hose that goes to a source of constant vacuum on the carb, the other goes to the round can with a vacuum nipple on the top of the snorkel on the air cleaner. The hose for the vacuum advance pod should not connect to the air cleaner. The hose on the vacuum advance pod should connect directly to a port on the carburetor. Again, the vacuum advance pod port will have no vacuum at idle but full vacuum as soon as the throttle is opened. EDIT: Oh, you have an air cleaner mounted OSAC valve. OK. The OSAC valve was an early emissions device. It is the Orifice Spark Advance Control valve. You should bypass it. Take the hose that goes from the distributor to the OSAC valve and plug it into the port on the carb that is currently occupied by the hose from the OSAC to the carb. In other words, bypass the OSAC valve but hook to the same vacuum supply port on the carb. |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 11:43 am ] |
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Thanks again Reed, I'll post back when I gather more info. |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 11:48 am ] |
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Ok got your edit. But there is always vacuum at that carb port (I think, there would have to be right?). I've got the factory manual on CD and I'm looking through it right now. EDit: Geez, its near impossible from the factory diagram to tell what port on the carb is for the vacuum advance. Can anyone describe it or have a pic? In the meantime, I'm looking at carb diagrams. 
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| Author: | Reed [ Mon Aug 05, 2013 11:52 am ] |
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There should be no vacuum at the distributor vacuum advance port on the carb. What carburetor do you have? |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 11:54 am ] |
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Holley 1945 |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 11:58 am ] |
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I looked it up and the port is correct. Now I am thinking about what could cause vacuum all the time at that port. Wrong gasket when I rebuilt the carb? It came with two, maybe I got the wrong one. Idle is too high? Wild guesses. |
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| Author: | Reed [ Mon Aug 05, 2013 12:10 pm ] |
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Is the carb original to the engine? There were Holley 1945 cabs built in the 80s that were intended for use with the lean burn system that had no part time vacuum port for traditional distributor vacuum advance. Is it possible someone swapped one of those onto the truck? |
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| Author: | Reed [ Mon Aug 05, 2013 12:16 pm ] |
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THIS thread may help as well. |
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| Author: | Sean Mallory [ Mon Aug 05, 2013 12:22 pm ] |
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great info there, yes it is possible the carb is wrong I do have an automatic. I'll be checking that throttle plate tonite. |
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| Author: | Sean Mallory [ Tue Aug 06, 2013 7:03 am ] |
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Thanks for the replies and providing me with knowledge and a learning experience! I've been perusing the forum a lot and one thing I noticed is the engine building knowledge is sublime here. Ok, the throttle plate is closed entirely and I still get 12 in of vacuum at the port. This is the EXACT scenario in the link you posted Reed. And the idle was way low too. I don't have a tach yet so guessing around 400-500 rpm. I tweaked the timing a little back just a degree or so. Drove to work and she is running pretty nice. Idle isn't perfect but not bad at all. Looks like the vacuum at idle might be normal for my truck. I was thinking about adjusting the pod with the 3/32" Allen, but I think I'm just going to drive the thing for now. I've only got one more emission test to pass (ever) and then I'm going to get some advice here and try to bump up from the pathetic 100hp I got now. I guess I'll work on the inop fast idle solenoid so I can run the AC. It's removed for now. I printed the wiring diagrams and I'm going to bench check the solenoid. I looked at the appropriate underhood wiring and spotted a harness cluster* created by the PO.  So that's where I'll start. 
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