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| Engine won’t always return to set idle rpm. https://slantsix.org/forum/viewtopic.php?t=42019 |
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| Author: | wjajr [ Thu Sep 23, 2010 12:16 pm ] |
| Post subject: | Engine won’t always return to set idle rpm. |
Ted, At times my engine will want to idle higher than I have set it to after driving. It will jump from pre set 1000 rpm to 12-1300 rpm.. So I have been setting it lower so it will settle down, but than the idle in gear is too low, allowing low vacuum to start the power valve fluttering open & closed mudding the idle speed still more. Damned if I do, damned if I don’t… This up & down rpm at the whim of the “Idle†Gods has been bothering off an on for sometime, particularly since backing off valve lash to make more low rpm vacuum. Today I had had enough, and got out the timing light & vacuum gage, discovered that at about 1300 rpm the mechanical advance starts to creep in boosting the 1000 rpm advance of 10 degrees to 12 degrees, 14 degrees @ 1400 rpm, 15* - 16* @ 1500 rpm and than the vacuum advance kicks in for 5 to 6 more degrees of advance bringing the total above 20 degrees at say around 1600 rpm. In gear Idle is 600 to 800 rpm depending on the lope, it sort of runs up & down 200 rpm due to this cam. Vacuum almost follows rpm in that at 900 rpm vacuum = 9†HG ; 1200 rpm vacuum = 12†Hg ; 1500 rpm = 15â€Hg where it doesn’t increase until the low to mid 2000 rpm range an additional 2†Hg. This is a big improvement from before the slacking of the lash where 600 rpm was giving zero to 6 fluttering vacuum gage needle, and 1500 rpm about 9â€Hg. of Vacuum. I think I need to perform a slight re tune of my custom advance curve due to the increased vacuum, and that green spring not being able to pull the advance weights back in consistently each time the engine throttles back to idle. According to the chart accompanying the new spring kit, a black spring won’t allow advance until 1400 rpm, and only + 4 degrees at 1800 rpm, and +8 degrees at 2000 rpm.--- a slower advance curve that should sequester the weights well within my in “Park†idle which should end idle rpm creep. Additionally I may need to give the vacuum advance can a few turns to slow its contribution so it doesn’t kick in until past 1600 rpm. Dose this make sense? |
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| Author: | Aggressive Ted [ Fri Sep 24, 2010 4:26 pm ] |
| Post subject: | |
Bill, Quote:
Dose this make sense?
Yes, "this" makes sense. A couple of questions... 1. Did you try backing off (unscrewing the vacuum advance) more than 3 turns? say 4 or so turns to take it out of the equation? 2. Is this after soldering up the holes in the throttle plates? or are they still 3/32"? 3. What is your initial timing set at? 10 degrees? 4. I would change the primary spring as the last straw if 1 and 2 do not stabilize the idle. |
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| Author: | wjajr [ Fri Sep 24, 2010 5:45 pm ] |
| Post subject: | |
Ted, 1. According to notes the vacuum pod is out three turns. Once I locate a 3/32†wrench that isn’t housed with eight of its brothers I’ll give it a turn or two. When I re-checked the timing yesterday, I pulled the vacuum line to see just how much the mechanical advance there was. Also my notes state that an 11-R (VC-208) can is installed which, I think, gives advance between 10* @ 6â€Hg / 12* @ 9 “ Hg to 11†Hg. I’m wondering if a VC-185 that provides 7* @ 9†HG/ 10.5* @ 15.5â€Hg would be better now that my vacuum is stronger at idle? 2. Haven’t soldered up the 3/32†holes residing in the throttle plates. Haven’t located my soldering irons or solder & flux yet. They are in an unopened box somewhere in the basement perhaps marked “Glass Shopâ€. A lot of tools and parts are still packed from the move. We dragged the last trailer load of crap here from the old house last Sunday…I’ll go on a hunt this weekend for the stuff. 3. Yes, initial timing is set at 10 degrees. 4. Agreed, I don’t feel like cracking open the distributor if it is not necessary. Bill |
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| Author: | Aggressive Ted [ Fri Sep 24, 2010 7:25 pm ] |
| Post subject: | |
Bill, When you find the 3/32 just be sure that when you plug the vacuum line back in the timing doesn't change. |
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