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 Post Posted: Sun May 13, 2012 1:47 pm 
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Location: Greensburg, Pa
Today i went back to the .040 ij, .078iab, .025mab, and timing locked at 38. i got the best vacuum, 6 with the mixture screws 1 3/4 out while keeping the idle 950-1000.This puts the idle speed screws at 2 turns and that should have them just a hair from uncovering the t slot.Throttle respose seemed good but plugs still got black and dry and would blow some black smoke if you reved it up quick. starts bye just turning the key warm and drops 100-125 rpm going into gear.

Next i set timing at 20 and had to turn in speed screws just under half a turn to bring idle up to 950-1000 and should give me some t slot exposure. Seemed to still like the same turns on mixture screws and rpm drop was the same but it did seem to burn the eyes more which could be from being in the garage with doors open since it's raining.


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 Post Posted: Sun May 13, 2012 2:04 pm 
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Burning your eyes in an enclosed area is not surprising. With a non stock camshaft thats very possible.
Try turning your mixture screws in 1/8th a turn on all 4 at a time.

About the black smoke when you rev it. How big are the squirters?


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 Post Posted: Sun May 13, 2012 2:49 pm 
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I didn't measure them but it's stamped 35 primary, and 32 secondary. I will measure to make sure but thet were on it new and i havent molested them yet.


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 Post Posted: Sun May 13, 2012 2:53 pm 
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How is the throttle response?

You could go up .005 on the IAB and that will lean the Tslot some. You may have to open your Mixture screws 1/4 turn after the IAB change to get back to where you were.

BTW,
How much vacuum did you have?


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 Post Posted: Sun May 13, 2012 3:06 pm 
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Location: Greensburg, Pa
Vacuum was 6 @ 1000 rpm, i have a 3.5 pv but it's not a high flow. What do you recomend for idle rpm? I see some like under a 1000 and some like 1200.


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 Post Posted: Sun May 13, 2012 3:11 pm 
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6" of vacuum? What are the cam specs? Sorry if you already posted it.
Is the engine combo in here somewhere?

FYI I don't run a 3.5 PV in anything regardless of Vacuum. I would run a 4 min and more like a 6.

A 3.5 is so small it can close back up at wide open throttle and lean it out.


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 Post Posted: Sun May 13, 2012 3:14 pm 
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RPM depends on the combo. My SB2 idles at 1200 like a kitten.


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 Post Posted: Sun May 13, 2012 3:23 pm 
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I just put the 3.5 in so it didn't change anything today on the idle and not knowing how low the vacuum was. I have a standard 4.5, and 6.5.

The cam specs intake dur 252.2 lift .6804, exh dur 260.4 lift .68067. This is 502 with ported merlin iron heads, and a ported dart intake with 9.5 compression and 3.5 exhaust. I took it to the track last year to see what it would run and it went 10.43 @ 128 but only 1.5 60 ft so that's next on my list after the carb.


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 Post Posted: Sun May 13, 2012 6:31 pm 
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I also put my finger over 2 idle bleeds cold and it picked up rpm's, and warm it lost some rpms so this sounds close combined with the 100-125 rpm drop when going from neutral to in gear.

Should i be concerned that i don't have any t slot showing? The blade is right at the edge of the slot on both primary, and secondary.


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 Post Posted: Sun May 13, 2012 6:35 pm 
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Quote:
Should i be concerned that i don't have any t slot showing? The blade is right at the edge of the slot on both primary, and secondary.


As long as you don't have an off idle hesitation like just barely cracking the throttle in cruse your fine.


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 Post Posted: Sun May 13, 2012 6:43 pm 
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The power valve has nothing to do with the idle, ask Ken! =;

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 Post Posted: Sun May 13, 2012 7:27 pm 
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Slowpoke wrote:
The power valve has nothing to do with the idle, ask Ken! =;

I had a 6.5 in but changed it prior to tuning the idle, i was worried that it would open and screw up the idle. My vac at idle is 6, soo i will be fine wth a 6.5? Ken? Lol


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 Post Posted: Sun May 13, 2012 8:18 pm 
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The 9.5 compression is a major issue. With that camshaft there will be very low cranking compression and low compression on the idling engine. The cylinder will have considerable exhaust contamination, blackening the plugs. The low vacuum wont hold sufficient fractions of the fuel in vaporized state in the inlet manifold and it will be collecting fuel on the walls and floor and it will blow black smoke when you snap the throttle. The ported heads will have very slow air speed at idle combine that with the 6" vacuum and you will have poor running quality. The fuel will be collecting on the floor of the runners and when the air increases with the throttle snap it all goes into the cylinder.

The low vacuum is because the exhaust is filling the manifold via the overlap so you have to use lots of timing at idle to get it to burn in the contaminated environment. Exhaust contamination slows the burn necessitating more timing advance.
The low compression ratio simply isnt pumping the stuff out, there's too much volume at TDC. The earlier you open the intake the less vacuum you get and with the largeTDC volume you have a lot of material to discharge backwards into the intake runner.

You are changing tune settings too extreme, you need to make smaller steps of tuning changes. Going from IFR .040" to .035' is a huge change to this style of engine. Small steps will make more sense, adjust tiny bits of timing and jetting.
Good luck


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 Post Posted: Mon May 14, 2012 1:22 am 
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driftbuster wrote:
Slowpoke wrote:
The power valve has nothing to do with the idle, ask Ken! =;

I had a 6.5 in but changed it prior to tuning the idle, i was worried that it would open and screw up the idle. My vac at idle is 6, soo i will be fine wth a 6.5? Ken? Lol


Well, Ken proved that the MJ in or out made no difference in idle on a Dominator, which would be about the same as having the PV open at idle. What the question was then was whether idle would be affected by a jet change so I ran my engine and recorded a log of the AFRs at idle with my Gas 8896 Dominator I had just built. After that I took the jets completely out then ran it again at idle and there was NO change in AFRs from the original run with 87 jets in it. So from 87 jet to .200 diameter hole made no difference in idle AFRs. That also means that with a PV installed that was open wouldn't matter either.

There is a case where going to a larger jet, or with PV open might make a difference and that would be with a smaller 4150 type carb with the smaller jet orifice. The jet size that is used with a Dominator takes the jet out of the idle equation though.

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 Post Posted: Mon May 14, 2012 8:41 am 
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Shrinker that definately explains why the plugs are getting sooted up at idle and why it seems to like the timing locked at 38. The cam was supposedly for the low compression to try and build cylinder pressure.

Ken that's good info, looks like I will be getting a 6.5 high flow and plug for the front if I can get to the track for some main jet tuning. what kind a/f guages are good for tuning?


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