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PostPosted: Sun Feb 16, 2014 6:05 pm 
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Rogue

Joined: Tue Jul 02, 2013 7:19 am
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Location: Colorado
I would be hesitant to start limiting mechanical advance without knowing how much it is actually advancing the system. Vacuum advance is mostly just there to help with combustion at cruise (advancing the timing helps with burning lean mixtures that are present at light throttle cruise, especially when the EGR valve operates). I would take it for a spin with the vacuum advance disconnected to see how it operates without it. If it runs good with it disconnected, then I would check things in more detail before limiting the mech advance.


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PostPosted: Sun Feb 16, 2014 7:57 pm 
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Javelin
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Location: Royersford, PA
I may try that once, but I really want to avoid running it without vacuum advance. My drive up the mountain last week was a good example of what's happening. On a relatively steep incline, the car could barely maintain 35 mph with my foot nearly to the floor. Just before I reached the top, the car dropped to 25 mph with the pedal fully depressed and would have kept decreasing if I hadn't reached the top. Something is CLEARLY wrong here, and vacuum advance shouldn't be doing anything at WOT. Btw the mountain isn't extremely tall, right around 1500 ft, and shouldn't have had a significant effect on the carb operation.

It is on ported vacuum, which I should probably change back to manifold like I had it originally. The distributor was advertised as having an adjustable vac canister, so if I can't get it to adjust I need to contact Skip White. Oh, and my EGR valve is non-operational.

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PostPosted: Mon Feb 17, 2014 9:10 pm 
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Hornet
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The way most of these rigs were set from the factory was for the vac advance to work when cold then cut off when warmed up (CTO switch) What plugs are you running? I got rid of ping and my EGR by switching to NGK 2288 plugs.

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PostPosted: Mon Feb 17, 2014 10:40 pm 
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Javelin
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I believe I have the Bosch single platinums in right now, don't know the part number. I might even have a set of copper plugs that I could throw in.

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1982 AMC Eagle SX/4 Sport 4x4
-4.0l I6 Engine (circa 1996)
-GM Hydroboost Brakes
-TF998 Auto/NP129
-Carter BBD Carb
-MSD Streetfire Ignition/TFI
-Aluminum CJ Radiator
-205/75/R15 General Grabber A/T Tires


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PostPosted: Tue Feb 18, 2014 8:11 am 
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Rogue

Joined: Tue Jul 02, 2013 7:19 am
Posts: 73
Location: Colorado
carnuck wrote:
The way most of these rigs were set from the factory was for the vac advance to work when cold then cut off when warmed up (CTO switch) What plugs are you running? I got rid of ping and my EGR by switching to NGK 2288 plugs.


The CTO switch is closed when cold, and opens up when the engine is warmed up.


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PostPosted: Tue Feb 18, 2014 4:55 pm 
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Hornet
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It's closed cold and added as a tee to the advance line then opens when warmed up and allows the EGR to operate

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PostPosted: Tue Feb 18, 2014 5:45 pm 
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Javelin
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My CTO is not hooked up either anyway lol.

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1982 AMC Eagle SX/4 Sport 4x4
-4.0l I6 Engine (circa 1996)
-GM Hydroboost Brakes
-TF998 Auto/NP129
-Carter BBD Carb
-MSD Streetfire Ignition/TFI
-Aluminum CJ Radiator
-205/75/R15 General Grabber A/T Tires


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PostPosted: Wed Feb 19, 2014 5:48 am 
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Hornet
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Location: North Seattle sort of
The EGR valve's job is to cut ping.

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PostPosted: Wed Feb 19, 2014 8:23 am 
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Rogue

Joined: Tue Jul 02, 2013 7:19 am
Posts: 73
Location: Colorado
carnuck wrote:
The EGR valve's job is to cut ping.


To expand on this, the EGR valve opens up at high vacuum conditions (lower throttle cruise), recirculating exhaust back into the engine. This leans out the mixture in the engine. To compensate for this lean mixture, the high vacuum also actuates the vacuum advance, advancing the timing, giving more time for the combustion to burn. If you do not have an operational EGR valve, the vacuum advance may be advancing the timing too much for the mixture that you are trying to burn, causing ping.


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