I have made this modification to my distributor. The problem is that the VC1810 vacuum can from NAPA is made to 20* @ 10-11" hg., not 16* @ 8" hg. I have tried two of them and they are the same. This is causing dithering and the engine will die from lack of advance at 900 rpm. My engine idles fine if I keep the rpm up to get 11'' hg. I emailed Standard Motor Products to locate a source for their equivalent part number VC177 (which JohnZ gave me) and was told that Dana is the only manufacturer of that vacuum can anymore, no matter whose box it is in. The VC1810 from NAPA is identified with the number B28 (the Dana ID number) stamped on the flat, which mine have. Any suggestions? Does anyone have a good spare they are sure of? I think this is my last hurdle for tuning.:sad:
JohnZ vacuum advance modification
Gary L
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I have made this modification to my distributor. The problem is that the VC1810 vacuum can from NAPA is made to 20* @ 10-11" hg., not 16* @ 8" hg. I have tried two of them and they are the same. This is causing dithering and the engine will die from lack of advance at 900 rpm. My engine idles fine if I keep the rpm up to get 11'' hg. I emailed Standard Motor Products to locate a source for their equivalent part number VC177 (which JohnZ gave me) and was told that Dana is the only manufacturer of that vacuum can anymore, no matter whose box it is in. The VC1810 from NAPA is identified with the number B28 (the Dana ID number) stamped on the flat, which mine have. Any suggestions? Does anyone have a good spare they are sure of? I think this is my last hurdle for tuning.:sad:
Joined
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2,843 Posts
At 900 rpm, there shouldn't be much vacuum advance impacting idle,..certainly not enough to kill the engine.
If it is, I think I know how to fix it if you're running a Holley with some cam.
If your VA is impacting idle it's because your primaries are open too much at idle (usually because of a longer duration cam) and the carb thinks the engine is cruising and the VA is kicking in. Is your engine slow to return idle speed after you've stopped at a red light? That's another symptom.
Here's a trick to fix the prob. Open your secondaries a bit at idle,..there's a small stop-screw accessed from below the secondary throttle shaft on the passenger's side. Turn this screw using a very small flat-head screwdriver about a half turn clockwise (looking up). I'm able to do it with the carb on the car but you'll need a short small screwdriver,..maybe two inches or shorter.
By opening the secondaries a bit it will raise your idle a bit. Now you can adjust the idle screw to reduce the idle which will close the primaries and remove all or most the vacuum signal to your vacuum advance and give you a consistent idle speed.
Good luck!
If it is, I think I know how to fix it if you're running a Holley with some cam.
If your VA is impacting idle it's because your primaries are open too much at idle (usually because of a longer duration cam) and the carb thinks the engine is cruising and the VA is kicking in. Is your engine slow to return idle speed after you've stopped at a red light? That's another symptom.
Here's a trick to fix the prob. Open your secondaries a bit at idle,..there's a small stop-screw accessed from below the secondary throttle shaft on the passenger's side. Turn this screw using a very small flat-head screwdriver about a half turn clockwise (looking up). I'm able to do it with the carb on the car but you'll need a short small screwdriver,..maybe two inches or shorter.
By opening the secondaries a bit it will raise your idle a bit. Now you can adjust the idle screw to reduce the idle which will close the primaries and remove all or most the vacuum signal to your vacuum advance and give you a consistent idle speed.
Good luck!
Joined
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6,242 Posts
You can get adjustable VA cans and limiters from:
http://www.kendrick-auto.com
Check out the parts here:
http://www.kendrick-auto.com/ignition.htm
Having the vacuum connected to a manifold source will improve the combustion efficiency at idle and allow you to reduce the throttle opening and get off the transition slot. Just make sure the VA is all in at idle.
http://www.kendrick-auto.com
Check out the parts here:
http://www.kendrick-auto.com/ignition.htm
Having the vacuum connected to a manifold source will improve the combustion efficiency at idle and allow you to reduce the throttle opening and get off the transition slot. Just make sure the VA is all in at idle.
Gary;
What is your vacuum level at 900 rpm? I could only barely get eight. I bought my NAPA can a year ago and am sure with the mitivac its in maybe not all the way at 900. I didn't get any dither at idle but then again when I'm on the light it's with the vac can disconnected. Is that thing rock solid at idle no vac? I'd look again at your 900 rpm setting without vac to make sure its not moving, I know you had said you worked it on a distributor machine right?
Just throwing some possibilities at you.. Now you make me wonder where mines at. Might have to go throw a light on it this weekend.
Todd
What is your vacuum level at 900 rpm? I could only barely get eight. I bought my NAPA can a year ago and am sure with the mitivac its in maybe not all the way at 900. I didn't get any dither at idle but then again when I'm on the light it's with the vac can disconnected. Is that thing rock solid at idle no vac? I'd look again at your 900 rpm setting without vac to make sure its not moving, I know you had said you worked it on a distributor machine right?
Just throwing some possibilities at you.. Now you make me wonder where mines at. Might have to go throw a light on it this weekend.
Todd
The canister I have is niot fully deployed until 11" vaccum. I saw this on the Sun machine. Idle at 900 I get 9", but can vary by about 1". So I think that once the vacuum changes a small amount the vacuum advance changes by a couple of degrees and starts going lower as the engine looses rpm. If the cannister is holding tight at 8" the timing will not change.
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7,729 Posts
I've never used one of the adjustable vac advance cans - anyone know whether that adjustment increases spring tension on the diaphragm (delaying the beginning of deployment), or if it changes travel of the rod (changing maximum advance it provides)? Just curious. :thumbsup:
I talked to these guys today. They have someone that can rebuild them to spec. Tommy is the guy and will check to see what he has.onovakind67 said:
JohnZ, am I on the right track to think that full advance at 11" will cause dithering at 9" vacuum?
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