need help tuning my 750 vac sec holley its still bone stock carb where should i start ? setup in sig

 

How does it run?

 

it runs good just want it to run great

 

With the engine warmed up, check the manifold vacuum at idle. The power valve should be a number 1/2 of the idle vacuum. If it's 16" Hg, for instance, 1/2 = 8, pick the next number down which is 7.5.

Take it for a cruise, try to shut the engine off w/o idling, pull over and pull a plug. Jet the primaries based on the plug color.

From low speed, when you floor it, can you feel the secondaries open? If so, you're "bogging", meaning the secondaries are opening too quickly. Put in a stronger secondary diaphragm spring.

 

it dont have a bogg at all just smooth taking off. I will take it for a cruise and do that and take a pic and post it.

 

i've been messing around with my 4160 holley 600cfm vac sec. carb. when reading the spark plug black is rich, lean in white. what are you shooting for a nice gray color???

 

Ignore the spark plugs, if it's a street car. They are worthless because whatever they did LAST, if that was let's say mosey down your street and schlep up your driveway, is what you'll see when you "read" the plugs.

On a Holley, 1 jet size is an imperceptibly small step. 2 jet sizes is a tiny but noticeable step. 3 jet sizes is a standard adjustment. 4-5 jet sizes is a big step.

Look at your primary jets. Whatever size they are, buy some that are 2 sizes, 4 sizes, 5 sizes, and 6 sizes smaller; and 2 sizes larger. You'll be needing them.

First, set the fuel level. If it has sight plugs, set the primary one to where gas dribbles out while the engine is idling, when you just bump the fender; and set the sec one to where you have to jiggle the car pretty good to get it to come out.

Lean the primary jets (using the "step size" description above) until the car just barely starts to surge while cruising (55-60 mph) at a steady speed on a level highway and it starts going up a hill. Ignore all other misbehavior of any kind for the time being. Once you find that point, go back up 2 jet sizes.

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.

When you get that right, set the idle speed right (800 RPM out of gear, say); then get the idle mixture right by turning each pimary idle screw in until the RPM drops, then back it back out 1/8 turn. Shut the motor off, and average the 2 screws (like, if one is 5/8 turn out, and one is 7/8 turn out, set them both to 3/4 turn out), and restart the motor, and check them again. Repeat until they're equal, or until you have determined that they absolutely CANNOT be made equal. In no case should they be more than 1/8 turn different.

Take the carb off, flip it over, and look at the transition slot. You want less than .050" of it exposed below the pri throtle blades. If more of it is exposed than that (it will be), open the sec throttles with their idle screw, 1/8 turn; put the carb back on; re-set the idle speed and mixture; then pop the carb back off and look at it. Repeat until you have between .030" and .050" of the transition slot showing.

At this point, the thing should run like a bat outta hell, on the primaries. The secondaries could be just about anywhere. Put a 65 power valve in them, if they don't already have that; and select jets for max ¼ mile mph.

At that point, you'll have your Holley set up better than about 95% of all other Holley owners. You'll be getting nearly the same gas mileage as you would with a Q-jet, and you'll be making 20% more power than most cars with the same cam & heads, and FI.

 

SRY I don't want to hijack this but I need to ask.

What are sight plugs?

My idle screws are all the way in, If I move them out the idle drops and the car wants to stall also it makes taking off from idle very hard without stalling.

 

Sight plugs - removable brass plug on the side of dual inlet Holley carb fuel bowls, used to set the float level. Demons use a sight window, those you set at the midpoint of the window.

Very few Holleys have secondary PVs these day. Would be unusual indeed.

 

so how is it done on a basic vac secondary holley?

 

Wow, you sure got all those other steps where I said "ignore all other misbehavior of any kind" completed really quick!!!

How did all of those other things work for you? How's your fuel level?

 

That is what I was asking earler, How do I check with a old Holley 600 (Vac Sec).

 

If it's the dual feed, center-hung float type bowl, by using the sight plug.

If it's the single feed, side-hung float type, by setting the float height with the bowl off the carb.

 

yeah but how do you know where it should be?

 

I think sofakingdom covered that already.

 

Which type does your carb have?

 

If it doesn't have sight plugs, you have to follow the instructions inthe carb kit. Which you'll need anyway if you're going to change the float level, because you'll almost certainly damage the gaskets.

Go get a carb kit and go for it.

 

my carb is a holley 4160 600CFM (vac sec) I was told it was off a old camaro but dont know if it was a factory carb or not.

 

i believe i have the same carb. are there brass flat head plugs/screws on the passenger(right) side of the fuel bowl?

 

Yeah a brass screw/plug, LOL didn't evan realise it was there till you just described it.

 

Clear back on Post #9. . .

 

lol I feel like an idiot but I got a 14x3" drop base air filter and it hides 80% of my carb so i didn't remember seeing the plug but I looked at some photos of it after Justin mentioned it and spoted the plug.

 

So if my idle vacuum is between 14-15 hg, then is the stock 6.5 power valve ok? Keep in mind I'm running a 650 Speed Demon on a 305 right now.

 

Probably not.

More likely, your car will work better with the jets leaned down, just like the Holley procedure above; and the PV number raised to where you don't have to floor it to get it to open.

The "half of idle vacuum" recommendation usually results in jets that are too large and a PV that's too low of a number. That's a leftover from the days of super-cheap gas and ancient design cams that are too big for the motor they're in.

However, the vacuum number that you should be using, isn't necessarily "idle vacuum"; it may be that, it may be "idle in gear vacuum", it may be "cruising at 35 mph in high gear vacuum", etc. The proper PV sizing number is THE LOWEST VACUUM OBSERVED DURING NON-POWER NORMAL OPERATION. Whatever that is.

 

the way i myself do that is run what seems like a mile long hose from the manifold though the cowl to a hand held vacuum gauge inside the car. just get enough hose. thats what works for me. then just take a cruise around town and watch the gauge

 

That's almost WORK!!!!

The way I do it is to run a short piece of hose out the back of the hood and duct-tape the gauge to the windshield.

I HATE work.

 

Could you explain this a bit better? ie: In lamest terms.

Basically, not sure what you mean by "surge", and "transition slot"

 

Surge = that feeling that you get where the engine feels almost like a cyl is intermittently dropping out and returning; a sign of being too lean

Transition slot = a little slot (duh) in the throttle bore that is right near where the throttle blades are when at idle. It's "vertical" in the bore, maybe 1/32" wide and 1/4" tall. Most of it should be ABOVE the blade, which means it's at atmospheric pressure (no vacuum), when the blade is at idle. It leads to a passage that holds a small amount of fuel during idle, and feeds as the throttle blades sweep past it. The general situation is, when at idle, a small amount of it is exposed to vacuum; that pulls a bit of fuel into it; but there's not so much of it exposed to vacuum that the motor draws it down. But then, as the throttle blades are moved off idle, more and more of it gets uncovered BELOW the blades, i.e. exposed to vacuum, so that little stash of fuel contributes to the fuel feed. Kind of like a mini automatic accelerator pump. If the idle screw is set such that too much of it is exposed to vacuum, then it doesn't do its job because the vacuum contnuously empties it, and instead you get this funky flat spot off idle; most of the brouhaha about accelerator pump tuning is a DIRECT RESULT of having this set incorrectly. Set it correctly, and you almost don't need an accelerator pump at all. The way to set it correctly is to set the "curb idle speed" screw to put the pri throttles where they belong in relation to that slot, and then tune the idle speed with the sec throttle stop screw (which you have to take the carb off to get to). Why Holley made their carbs so that you have to disrupt that critical relationship in order to set the idle, I'll never know; seems kind of stupid to me. But that doesn't change the fact that that's the way it needs to be done.

 

well said. whatever works works, as long as the end result isnt jimmy rigged

 

i believe this is my problem. very well described and i did find that when i took my carb off that most of the transfer slot was being exposed to vacuum. so the secondary throttle stop will do exactly what and where is it exactly. i have the carb off the intake and i don't see a screw anywhere that looks like it would do anything with the idle. or one that only accessible with the carb off. i have a 4160 holley with vacuum secondaries. thanks for the help, justin

 

wow, definitely one of the most in-depth carb tuning instructions i've read! bookmarking this one for when i get my holley (long way down the road... still have to rebuild the engine!)

 

I'm glad it at least appears useful!! Hopefully when the moment of truth arrives, it will live up to expecations.It is a small screw, looks like a set screw, in the throttle plate of the carb, near the secondary throttle shaft. It's either a small flat-head or an Allen-head screw. It's just the stop the sec throttle comes to rest against, just an idle speed adjustment so to speak.

Just adjust it such that with the pri throttles in the position as described, the idle speed is about right. Might take a couple of tries of taking it off, adjusting it, and putting it back on. Oh well. There's no short cuts to perfection. Sorry.

Incidentally, make sure your ignition timing is correct before doing any of this; regardless of what your "light" and "mark" tell you, unless you KNOW FOR ABSOLUTELY CERTAIN BY CHECKING YOUR MARK WITH A DIAL INDICATOR OR PISTON STOP, advance it until it starts to ping, then back it back off until it quits. That may or may not be "right", but it sure beats the hell out of fussing endlessly over some "number" obtained by looking with a "light" at some "mark" that in fact is only randomly correlated with piston location. Inadequate advance will lower the idle speed, which in turn will require opening the throttles more, which in turn will expose the transfer slot, which will add to the whole "flat spot" and "unresponsive" character that inadequate advance already creates. If you KNOW FOR ABOSLUTELY CERTAIN that your timing mark is accurate - and when I say KNOW FOR CERTAIN, I mean that you have PHYSICALLY VERIFIED it with a piston stop or a dial indicator, and you're NOT just "assuming" that some damper you happen to have just happens to coincide with some timing mark you happen to have - then set your ignition timing for about 36° of advance at 3500 RPM with the vacuum advance disconnected, and the centrifugal advance set up to give about 16° of advance from "static" to "total".

 

Ok I have no idear here but can you explain the "ping" noise?
Im still learning when it comes to ignition/timing systems

 

Sounds like marbles rattling around in your motor when you give it gas

 

ok thanks i actually found it before reading your post but that just verifies what i found. i guess i wasnt looking hard enough. i can see what you mean by it taking a couple of trys. i did'nt know that tuning a holley was this in depth but at least i'm learning new things. thanks and i'll post about how i'm doing with the 4160

 

my cars got that sound on the drivers side near the back of the engine, i thought it was a dud lifter....

 

it still could be a bad lifter. try retarding your timing and see if it goes away

 

I will give it a go, hopefully it fixes it.

 

Ever wonder why it is, that some people can take THE SAME PARTS and bolt them together, and just always seem to go faster with them than everybody else?

This is one reason why.

Now YOU have the chance to be one of THOSE people, instead of the ones that no matter what they build are always asking questions like "I went to the track and I thought it would be faster" or "why does the guy with less motor make more power" or "my car gets gallons per mile instead of miles per gallon" or "my car stumbles/idles funny/bogs when the secondaries open/etc. etc.".

Next lesson to learn in tuning would be on how to set up a distributor. Being able to tweeek a carb and dial in a distributor will allow you to get every bit of what an engine can do out of it.

Enjoy!!!

 

What does 65 and 105 and 125 mean? Just part numbers? Im used to seeing lik 6.5" HG or 10 HG of vacuum for ratings.

So where exactly is idle? I like to idle it at 1000 rpm, because i need a new tranny and torque converter. I have a fairly big cam, so when i pop it into gear, it still drops to about 400-500 rpm. Which is why i idle it so high. The 900rpm stall doesnt help, and just strains everything when i hold the brakes.

SO!!! That being said, at warm idle, i get 17-19" HG vacuum (at 1000-1100rpm). Does this mean that i should go with a 9 or 8.5 power valve? .......

I have a motor with 69 heads on it. Im assuming its ancient block as well. During normal driving, in ANY condition, my vacuum never drops below 9.5-10ish. SO should i use this as my PV, or something a bit smaller?

its a 355, with a 284H cam from crane cams i beleive. It either has a 110 or a 112 LSA, and a 228 lift at 0.050 tappet lift. They are TRW 11:1 forged pistons, on 72cc heads i beleive. Used to be a dual quad 600cfm setup on a tunnel ram. Later downgraded to stock manifold with a CC Q-jet. Was too rich before, now its fuel starved.

Im going to a 750 cfm mech secondaries holley, that i bought from Kevin on this board. (firebird383). He said it has 71 jets all around, not sure about the rest, but ill check it out. And this is gonna sit on a RPM Airgap intake manifold.

Im gonna see if i can get a better advance curve kit from crane, for my HEI ignition with ACCEL super coil.

But which power valve do you guys figure i need? Should i go off of Five7kid's description or sofakings?
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I have never heard detonation, i dont have an ear for it. People always say it sounds like a "ping". SO what am i listening for?

Is it a steady high pitched noise like PIIIIIIIIIIIIIIIIIIIIIIIIIIIING......
or is it intermittent? PING PING PING PING PING PING?
or does it sound like a knock? close to an exhaust leak? "CLICK CLICK CLICK CLICK????

Also, im running 92ish octane, will it ping if i just advance the distributor?

 

Sorry i just found this. Anyone have a video of it? Like tuning the distributor and all of a sudden it starts to ping?

 

Both.

A 65 opens at vacuum below 6.5"; a 105 opens at vacuum below 10.5"; etc.

This is not rocket science here, it's just a car. Some amazingly stupid and some other amazingly uneducated people, and some who are both, can master it. EVEN I can figure some of it out; so it can't be that hard.

Incidentally, five7 is quoting the Holley book. But what Holley doesn't tell you, is that the "½ of idle vacuum", means vacuum OUT OF GEAR; and furthermore, as detailed above, is based on an expectation that the user will have a combo of too much carb, too much cam, too much intake, not enough head, not enough compression, too much weight, and not enough gear. In other words, that the least amount of load on the engine, makes the vacuum drop into the basement. But for a well-set-up car, it's not right.

Idle for any street car should be no higher than 850 or so out of gear, and should not drop more than 250 RPM in gear. If it does, it indicates a need for carb tuning. Start at the top of this post, with setting your fuel level; proceed to the discussion about jet size; once you get your jets right, pick a PV (sounds like, in your case with that super-mild cam, you'll want a 105 PV or maybe higher); THEN AND ONLY THEN, you'll be able to set the idle up correctly. Most likely, once you get it tuned right, you won't have to set the idle up into the stratosphere any more, because the carb's idle circuits will feed fuel properly and the car won't starve for fuel and die the way it's doing now.

Keep in mind, a Q-Jet works COMPLETELY DIFFERENTLY from how a Holley does. They have similar systems that perform the same basic functions (measure air, meter in an appropriate amount of fuel), but their fundamental assumptions and purposes are polar opposites. The procedures for optimizing them are quite different therefore. Just because your Q-Jet requires the idle to be at 1000 so that it won't die when you put it in gear, doesn't mean that the Holley will be the same way. It could even be WORSE, right out of the box. But it shouldn't be hard to get it much better.

"Ping" is another name for "spark knock". Sounds like marbles rattling around in your motor when you give it gas. It's bad, you don't want it; but it tells you what THE ENGINE thinks about the timing. Which is what really matters, not some blinky light. It's how THE ENGINE says "back it off a little bit or give me better fuel". Learn to speak, or at least understand, the language your engine talks in.

 

Gotcha.

1) The number you were mentioning 65, 125 etc... i couldnt find power valves on summit that went higher than 10.5, hence the question.

2) Im pretty good at getting the q-jet in tune, but i have my holley 750 on the side ready to go on, so why bother swapping metering rods and jet sizes and the works. Im just gonna throw the holley on there and work from that. The car has only been driven 2 weeks. I definately have a knock, not all the time, just when its not getting enough fuel around 3000 rpm. SO ive kept it in high gear and low revs, and as of last week, stopped driving it!

3) Thanks for the power valve clarification. Ill start with a 9.5 and adjust it if needed.

 

to retard timing...rotate the distributor clockwise?

 

Yes.


The rotor spins clockwise. So if you turn it the same direction, all the points will come in contact LATER in the cycle. IF you go against the cycle, they will come in contact sooner.

 

i leaned my jets on the holley 3310 and redid the idle...actually to max. idle vacuum,,,the motor now idles so smoothly..but now when i give it more gas while driving, i get a bog where i didn't have one before. i hope it's not the secondary housing spring! it's such a bitch to change. could it be the accel pump? i know it's one of those.........

 

Raise your PV a number or 2.

 

thanks again, sofaking.....

 

i had the same problem i had to set the transition slot on the primary barrels by opening the rear blades more. you want the slot to show about .030 -.050 at idle speed so set your idle then take off the carb. if the slot is open alot more then crack the rears and then you can drop the front. i there is more on this earlier in this thread