I have an SS-850, consists of the following:

Primary Main Jet: 80
Secondary Jet: 86
Idle Air Bleed: 70/70
Hi Speed Bleed: 28/28
Pri Nozzle: 35
Sec Nozzle: 35
Needle & Seat: 120
Power Valve: 3.5

So, i'm trying to fine tune my motor that I just put in:
10.4:1 compression 406, AFR 1054 heads, Victor Jr. Intake & Quickfuel SS-850 carb.

I started today with a vacuum reading while in "Park" at about 12 inches but I was running rich through-out the whole rpm band.

First & Foremost I got rid of my "All-in-one" $45 distributor & purchased an MSD Pro-Billet distributor and an MSD Blaster coil.

With that installed, we begin to adjust mixture screws and set the timing. The focus this time was not to obtain most vacuum, rather it was to obtain the proper A/F mixture. The AFR figures below are my readings and they reflect what a local speed shop told me is what I'm looking for. As far as my vacuum figures go, I'm not too sure:


AFR in park: 12.8 - 13.1
AFR in gear: 13.9 - 14.2
AFR at WOT: 12.9 - 13.1
Fuel Pressure: 5.0psi
Fuel bowl level: just below center site glass, as instructed on the Quick Fuel Carburetor manual
Vacuum in Park: 8in
Vacuum in Gear: 4in
Initial timing: 12
Total timing: 34
All mixture screws are turned out about 1 full turn.
Power Valve is 3.5

I haven't gotten it on dyno to see results but it feels minimally stronger. Though I still think it has more in it. Any other suggestions?

This is the camshaft I have (with 1.6 rockers)
http://www.skipwhiteperformance.com/...Item=180345-10


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ok to start, forget about afr in park. It is meaningless. Make all idle adjustments in gear with foot on brake.
Second forget about tuning idle with afr. With any decent size cam (like you have) you are going to get some exhaust dilution which will throw off the afr readings at idle. Use max vacuum and or by ear to set the idle afr screws. Give the engine what it wants to idle, not some number on an afr gauge.
Third put the black 18 degree bushing in the distributor. This will give you 4 more degrees at idle with 34 total. This will help idle quality among other things. I would even recommend getting a 10 degree bushing which you can find on ebay which will give you 24 at idle with 34 total and will make a huge difference in idle quality.
Also Change the springs to one light silver and light blue so all your timing is in before 3000 rpm.

 

Question: What do the advance bushings have to do with idle?
Do you mean to say reduce the amount of mechanical available (with bushings) and add the reduction to the initial timing, is that correct? (Just a question of wording I suppose but that one got me!)

 

I have the light silver & light blue springs, with blue 22 degree bushing. If I install the black 18 degree, then i would do 16 initial? thanks for that info, its a place to start.

 

If you set total to 34 and go from a 22 deg to a 18 degree you will now be at 30 total. Just reset the total to 34 and this will now give you 16 at idle.

The advance bushing controls the total amount of mechanical advance. So if you have the 22 deg bushing that comes stock with the dist and set total timing to 34 degrees you will wind up with 12 degrees at idle. Unless for some reason you put springs in it so light it is advancing at idle, which isn't usually a good idea.
Now you have a big cam and realize 12 is really low for a cammed engine so you notice that bumping up the timing to say 26 at idle really helps idle quality . But how do you get 26 at idle without having 48 total? There are a few ways but for the purpose of this thread it's with a 10 degree advance bushing.
Now you will have a smoother idle, more vacuum at idle among other things and it will allow you to back off the idle screw so that you are not idling on the mains instead of the idle circuit which causes a whole bunch of problems.

 

Reviving an old thread of mine.... I put a new exhaust on over the winter and it made a substantial power gain from last year. My Wideband O2 sensor is constantly reading 11's (under deceleration) and 12's cruising now. WOT is still 12.5 - 12.8 so there's nothing I want to change relevant to that.

My current set up is 70/78 primary/secondary jets. I moved up my idle air bleeds from 70 to 76, in intervals of 2 each time with hopes to lean out the cruising mixture. That had made such a minimal difference, it brought it up from the 11's to the 12's, but I would think 13's would be best?

My motor produces 7" of vacuum at idle (in gear) and increases under moderate acceleration. That being said, I know that's not opening my *3.5 Power Valve pouring more fuel in. I wonder if I should keep increasing my Idle Air bleeds or knock it down a jet size or two on the front. If I do that, would that affect my already dialed in WOT reading?

 

from the holley tuning sticky in this forum(you should probably check that out), think the quick fuel is the same as holley. to adjust cruising mix you play with the primaries. and wot is last and that is secondaries.

"Once you get it to do that, look at the primary side power valve. If it's stock, it's probably a 65. Stupid. Raise the value until the flat spot goes away when you're in high gear and driving along at about 35 mph (basically, as slow as you can possibly go in high gear), and you give it gas. It'll take a MUCH higher number power valve.... probably a 105 or a 125. If it starts giving you the burn-your-eyes idle, go back down one step."

 

Idle and light cruise doesn't run of the main jet (much). It runs off the idle circuit. You may need to restrict the IFR. Follow the tuning sticky and see where it gets you.

For the future...vacuum advance distributer is what you really need. MSD markets theirs without because it is cheaper to make (more profit for them) and people think it is the hot ticket! Your car probably needs something around 42 degrees at advacne and light throttle for best performance. This will allow you to close up the throttle blades and run of the idle circuit like the carb is designed to do.

 

Couple of questions and comments.
What idle speed speed do you target?
Do you know the position of the transfer slot on the primary and secondary bores?
Despite what the speed shop told you, idle speed is best set to the highest vacuum. There's no way of telling what the AFR might be because of the mixture dilution due to overlap. What's more the single plane intake can really mess up the mixtures of cylinders adjacent to each other in the firing order as is the case with 5 and 7. AFRs are somewhat meaningless at idle but should still fall into the 13-14:1 range for what you have. (Seeing that at one point you were producing 12" of vacuum.)
Did I see it mentioned that you're not running a vacuum advance? You'll suffer on many levels without one. Cruise AFRs included.
WOT is last on the list and is a function of the secondary jetting and the PVCRs.
Get your timing close (but less than optimal) for the mixture tuning. Set the idle mixture first. Make sure the accelerator pump is providing enough fuel so that when you snap open the throttles in park or neutral it revs instantly with no black smoke from the tailpipes. (the fine tuning of this circuit will come a little later). Take your vacuum gauge with you on your tuning tours and observe the levels at various cruise speeds. Once you're past the transition slots you'll be into the mains and can work your air bleeds as you've been doing but the idle mixture needs to be spot on first. It'll make a difference in the cruise AFR as you know.
After the mixtures have been set then it's time to dial in the precise timing curve needed. That's difficult to do if the AFRs are off as different mixtures will have react to timing differently. An example of the kind of timing an engine like yours might need is something along the lines of 25 degress at idle and 50 degrees at cruise. There's the benefit of the vacuum advance right there.

As for your question in your last post, 15:1 is a reasonably cruise AFR target. (I shoot for values approaching 16:1)
If at cruise (and by cruise I mean that the booster and primary jet are providing the engines fuel requirements) then the adjustment is made with the primary jet. If you find the AFR is satisfactory and low speed cruising but high speed cruising gets rich, then increase your HSAB. If the mixture becomes leaner at the higher speed, then decrease the size of the HSABs. You have to be certain that you into the main circuit while doing this (hiway speed) and the secondaries are not part of the equation.