First time Holley tuning help

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mechanic190

mechanic190

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What is the Proper way to adjust holleys and in what order? I have a 4160 converted to 4150 with vac secondaries. I am having an issue getting the off the line stumble out of her. Currently running 66 jets in primary and 70s in secondaries. Have played with the accelerator pump cams and have not found one that will take the stumble out. Engine is a 360 stock with a bigger cam and 2500 stall.

First of all I'm saying that she is rich because it doesn't seem to back fire and stutter but more of a lazy throttle.

Next my idle circuit and primaries look good for jetting but haven't been able to make enough passes to get a good reading on the secondary side.

Should the secondary jetting sizes be adjusted before pump cams and vac springs?

Tried pump cams all the way from the leanest pink to the rich blue but they all seem to have about the same effect just she takes off a little faster or slower.

When do you decide to play with vac secondary springs? Should I be playing with these the same time I change the pump cam to try to get the secondaries opening sooner if it's lean or later if it's rich?

Any more description on what I'm actually looking for when doing a launch to see if it's rich or lean. If it's lean will I be able to to hear it backfire at 3k rpm and open headers?

PS this is my first Holley
 
There are bonifide Holley videos on their web site that can explain it better than anyone on here can. They are very simple to follow. They show it step by step and in the proper order. Straight from the horse's mouth so there's no mistakes.
 
You need to know your vacuum at idle in gear (if auto) and what rating power valve you have installed. What list # Holley? How much of the transfer slots are exposed? Are you running a PCV? Jets are not an issue at this point. You will likely need to adjust the secondary stop screw to add idle air bypass so you can back off the primary idle stop screw to close up the transfer slots. This is common with bigger cams. You need a power valve rated at close to 2" below what idle vacuum is in gear usually a 4.5 will accomplish this.
 
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I haven't checked vac at idle in gear. In park it is 10-11 in hg. I have power valve plugs if that would make it easier to tune since it is a just going to be used at the track. Pvc is from rocker cover to intake manifold where the brake booster line normally goes. Current power valve is a 6.5 from a trick kit. Carb is an 1850-2
 
Have you sorted out the initial timing? If not that's first.

On a correctly tuned carb/enigne, the PV has no effect on idle quality. What exactly is a "bigger" cam?

I use PV plugs all the time to help set up carbs. Rarely run them in the primary side after getting the tune up correct.
 
Definitely want to have your timing up to snuff as mentioned above as this affects vacuum and throttle response a lot.


Power valve plugs open another can of worms with idle mixture and are more suited to tunnel ram appications or very radical cams. How far in do you have to run the idle mixture screws to get it to run decent? If they are just barely cracked open then you definitely need some idle air bypass by using the secondary stop screw or drilling the holes in the primary throttle plates. This allows you to close up the primaries some and cover the transfer slots and stop dumping in fuel at idle. You may also find a PCV valve that has more bypass which can help.
 
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Stock 360 with larger cam will definitely want lots of initial timing say 20 degrees or so which means time to shorten the advance curve. Do you have an FBO timing plate in your distributor?
fbo-mopar-distributor-limiter-plate-8.gif
 
Timing is 21 initial and 37 total I do not have that timing plate or anything done to the distributor still have vac advance to the vac port in front of the carb. 37 total without vac advance. Idle mixture screws are 2 1/4 out set off a vac gauge. Cam is comp 274deh. Converter foot brakes at 2500 rpm. Engine bogs at 3k for about 150 feet and after that it takes off and runs like a champ. I'm thinking of plugging the power valve tonight and going up 4 jet sizes in the secondaries make a test pass and see where it is. Before I got a flat tire last night I had the blue pump cam in it in hole 1 and it bogged. I was going to put the slowest opening spring in the vac secondary just to see what that did for it with plans if it took off smoother with less of a hesitation then I figure I need to lean it out
 
Did I miss it somewhere or did you tell us what size carb or list#?
 
Forget the vacuum advance until you sort out these issues. Adds another fly in the ointment.

You could wire the secondaries so they don't open at all. Then go hammer it. See if it still bogs. That's quicker than changing springs. If it doesn't, put a stiffer spring in it.

The rear metering plate, 134-9, that comes factory on those carbs is equivalent to a 64 jet. You got a BUNCH more rear jet in it at a 70.

Those universal 600 vacuum carbs are usually pretty solid out of the box.
 
66s and a PV plug?
That's your problem right there!
I have a bit of a cam in my 360 too. It likes 72s and a PV on top of that!I think the front PV is marked 10.5
I think I have 80s in the back, with no PV (it's a DP) back there.

With your tuning skill level, I would back up the bus, a long long way.
That means defeat the Vacuum advance. Defeat the secondaries.Get the T-port synced up (see below). Leave the PV plug in the front, but put at least 70s in there.Put the acc pump back to stock; that is one of the last things to mess with. Put a vacuum gauge on it with a hose long enough so as you can EASILY see it from the driver's seat.This is how I do it.
Take it for a short ride on a deserted road. Get it into second gear and up to 30 mph minimum, and over 1800 rpm. Then gently roll into the throttle, and watch the gauge.As soon as the engine complains that it's not getting enough gas, note the vacuum. Repeat this at least a dozen times until you get the hang of it.That vacuum reading is where the PV needs to be already delivering some fuel. So start with a PV that is marked for that vacuum. Make sure it is not open at your idle vacuum.How will you know? Cuz the engine will be slowly flooding itself to a stall, or you will need to keep blipping it to clear it out.
Now here's something I have discovered; the numbers on the PV may not behave as you might expect them to. I bought a really nice PV tester, and tested my collection of PVs;some new/some used. They were all over the place. So I just numbered them from earliest opening to latest opening, and started road testing.
For a streeter you can balance an early opening PV against a small MJ, to get better gas mileage.Or a slightly later opening PV against a slightly larger MJ, for a bit of snap when off the PV. If the AFR gets too lean as the PV comes on line, you will feel the car slow down during the transition. Too fat is really hard to feel, so I work from the sag to just getting it gone.
What you are striving for is a linear power delivery below about 3000rpm, with no lean surging, and no fat mushy low speed driving and no tendency towards stalling at idle.
After this you can start feeding more and more pedal and higher and higher rpms until you get the primary MJ dialed in.I would quit testing when it takes full throttle to 5000 without going lean.Yes the primaries will go to 5000, if the fueling is adequate. They will go as far as the valve springs go, with the right fueling.Yes you can try 68s; but then you may have to try a different PV timing.
Ok so that will keep you busy until next week.
That's how I do it.Yes it's time consuming and a PITA. But it's one change atta time and that makes it hard to get lost, and you won't end up stuck saying What do I do now. You will be either backing up one step, or moving ahead one step.
Remember, at this time we still have no Vcan hooked up and no secondaries yet either.And the #1 thing was the T-port sync/timing..
If it ever detonates, you have to back off immediately and revisit your timing before moving ahead.
Or you could just go to the Holley sight, as mentioned.
 
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So tonight I left the blue cam in it. Blocked the power valve upped the jets in the primaries to 75s (might be overkill) 74s in the secondaries and had the black spring in it. No stumble but definite delay in the secondaries coming in. Ran pretty good other than that. Switched to the white spring to see what it would do and it stumbles. Obviously I still need fine tuning and gonna go to the long yellow spring or purple first thing but my front tire tube valve stem went to leaking so testing ended. Haven't pulled a plug yet to see how far jetting is off. But I feel like it's definitely on the right track. Only have till Saturday to get her tuned in
 
I give up. I mean seriously.
 
Check the other thread with the Auction. There are two Holley tuning books up for bid.
 
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