Pulling V.A at idle

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Ironracer

Ironracer

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Hi Everyone, Hope All Y'all, Your Family's, Friends, and any one else are all Well! I have a quick (I hope) question.
Had a Distributor done. Finally had a Bro come by to watch the tach and run the mat pedal. Before he stopped in, I checked the idle airs... 3.5 turns out ( a buddy "helped" do that when i went to the store)
So, when I set the timing ( Vac Advance disconnected, plugged hose) it was close to where it was supposed to be...
BUT, plugs were ugly, pig rich, ( pulled em and posted em here, different post)
Anyway, when I hooked up the VA, the idle snapped back to "life"! Sounded Way Tight, like it should! Question is : Why am I pulling Vac advance off Ported Vac?
Thanks Everyone!
 
Ironracer said:
Hi Everyone, Hope All Y'all, Your Family's, Friends, and any one else are all Well! I have a quick (I hope) question.
Had a Distributor done. Finally had a Bro come by to watch the tach and run the mat pedal. Before he stopped in, I checked the idle airs... 3.5 turns out ( a buddy "helped" do that when i went to the store)
So, when I set the timing ( Vac Advance disconnected, plugged hose) it was close to where it was supposed to be...
BUT, plugs were ugly, pig rich, ( pulled em and posted em here, different post)
Anyway, when I hooked up the VA, the idle snapped back to "life"! Sounded Way Tight, like it should! Question is : Why am I pulling Vac advance off Ported Vac?
Thanks Everyone!
Click to expand...
Because it's not a ported vacuum inlet.
 
Ironracer said:
Well, it's a Holley 3310, 750 vac sec... port is on passenger side, high up, almost level to the Sight plug....
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Then somethin's "wrong". Where is your initial timing? If it's too low and you have the carburetor idled up to compensate, you may be pulling vacuum from that port when you're not supposed to be.
 
RustyRatRod said:
You 100% SURE?
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Well, I'm using a Matco dial back, I figuredit was a good light, traded a chainsaw fer it, got it from a mechanic pal o mine...Not 100% sure that my damper is "dead on" TDC.... been driving that mill for 12 years, some years daily.. Hmmm Rob, don't know if Ya remember, but remember the Detonation scare? Could the thing have spun, showing Less ?
 
Would it hurt to set the timing w/ a Vacuum GA? And run off that? Or could I pop her that way? I don't have another light to compare it to...
 
The t/blades are open too far at idle & you are accessing the ported VA port. Needs bypass air so that the blades can be reset, with about 0.020-0.040" of T slot showing at idle.
 
Bewy said:
The t/blades are open too far at idle & you are accessing the ported VA port. Needs bypass air so that the blades can be reset, with about 0.020-0.040" of T slot showing at idle.
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So pull the carb, flip er over, check the #'s, and drill some?
 
Ironracer said:
Well, I'm using a Matco dial back, I figuredit was a good light, traded a chainsaw fer it, got it from a mechanic pal o mine...Not 100% sure that my damper is "dead on" TDC.... been driving that mill for 12 years, some years daily.. Hmmm Rob, don't know if Ya remember, but remember the Detonation scare? Could the thing have spun, showing Less ?
Click to expand...
I do remember that. Have you ever verified TDC with a piston stop?
 
RustyRatRod said:
I do remember that. Have you ever verified TDC with a piston stop?
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No Sir, that I have not. Never thought I really needed to... but now... oh, and I found an old vid of the mill, in my old Sat ( w Princess too!) I'm going to try and dig it up... it's not detailed, at all, but, that sound, Man, I swear it was there! Lol
 
Arrgh, forgot how to get it on you tube, to share it. Y'all might find it funny.. what kills me, is She Sounds WAY tighter w/ points... strange..
 
I wanna say that was 12° BTC...w/ points. Point is, I think that sound is there back then....I was chasing a Ghost maybe... we ran her Mother's Day ( Peace to All Good Mothers) it didn't even seem to make the piston slap, way more quiet.. but 3rd Distributor since... anyways, Hope Y'all Have a Blessed Day! Gotta rest for work...
 
Timing jumping is probably the engine vacuum trying to pull in the VA plunger but vac is not high enough or stable enough.
So you need to check the T slot as per post #9. Too much T slot gives a rich idle, another one of your symptoms. What size engine, cam?
 
Bewy said:
Timing jumping is probably the engine vacuum trying to pull in the VA plunger but vac is not high enough or stable enough.
So you need to check the T slot as per post #9. Too much T slot gives a rich idle, another one of your symptoms. What size engine, cam?
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One Distributor had a soild line at 2500 or above. That Distributor was built wrong, and probably stiffer springs... mill is a 340, ported J heads, biggest valves you can shove in em, .484 MP cam, Strip Dom, 155 psi w/ forged stock bore TRWS...wanna say she's pulling 9hg. But, it's a xhina gauge
 
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I think I'd start at the top......Timings gotta' be right. I would confirm TDC before I went any further. JMHO:)
 
Ironracer said:
I wanna say that was 12° BTC...w/ points. Point is, I think that sound is there back then....I was chasing a Ghost maybe... we ran her Mother's Day ( Peace to All Good Mothers) it didn't even seem to make the piston slap, way more quiet.. but 3rd Distributor since... anyways, Hope Y'all Have a Blessed Day! Gotta rest for work...
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RPM idle? How nasty is your cam?
 
Ironracer said:
Do ya check that w/ a drill bit?
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Transfer slots? Yes.
Holley Jet size
Ironracer said:
I checked the idle airs... 3.5 turns out ( a buddy "helped" do that when i went to the store)
Click to expand...
3310 doesn't have adj idle air bleeds. Stick some wires in them. And I've had to do that with 3310 when adding bypass air - in my case by drilling the primary throttle plates.
Ironracer said:
So, when I set the timing ( Vac Advance disconnected, plugged hose) it was close to where it was supposed to be...
Click to expand...
????
Ironracer said:
BUT, plugs were ugly, pig rich, ( pulled em and posted em here, different post)
Click to expand...
Cant find but I'll take your word for it.
Ironracer said:
Anyway, when I hooked up the VA, the idle snapped back to "life"! Sounded Way Tight, like it should! Question is : Why am I pulling Vac advance off Ported Vac?
Click to expand...
Primary throttles are too far open.
See posts here. Holley Jet size
Ironracer said:
She's cranked up to 18° ....
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At what rpm????
Ironracer said:
I wanna say that was 12° BTC...w/ points.
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Again, at what rpm????
This is critical.
The mechanical advance can come in real fast on many factory distributors.

Ironracer said:
One Distributor had a soild line at 2500 or above... mill is a 340, ported J heads, biggest valves you can shove in em, .484 MP cam, Strip Dom, 155 psi w/ forged stock bore TRWS...wanna say she's pulling 9hg.
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I've run a similar 340.
9 in in neutral is weak but not surprising. You can get it a little better so it will be at least 9 in D when warmed up.
Its going to take some time and trials to tune it in.
Get the notebook and set the throttles. Set fuel level. Let in a little more air, You can crack the secondaries but take notes on how many turns on that little screw so you can go back to factory. Then start making changes - one at a time and readjust the mix screws. Test in gear. Idle in N is not important, In gear is what counts.

IMO it will want between 17-19* BTDC initial. The problem is you may not be able to measure true initial because at this stage in the tuning the slowest idle you may be able to get is 1000 rpm or so. If that's the case, then try 20 or 21* at 1000 rpm. Whatever timing change you make after that, always get a measurement at 1000 (or whatever your baseline was). That way you have at least one consistant reference rpm.
 
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I would pull the carb , flip it over and set the T-Slots first. Then set your initial timing to whatever brings the rpms to what you want (700 ish). Then reset your idle screws. If it still requires 3.5 turns out you may need to enlarge idle air bleeds.
 
12many said:
What’s this you say?
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Sounds like he's talking about idle mixture screws. 3 1/2 might be a bit rich but it shouldn't produce ported vacuum unless it's idling too fast.
 
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