Carb is running too rich!

[DarkoNova]

Hey guys, I'm trying to tune a QuickFuel 750 with vacuum secondaries.

I have an O2 sensor and with the previous Edelbrock, I had it idling at 14.7.

I can't for the life of me get anything better than 9.9 with the QuickFuel.

Adjusting the idle mixture screws doesn't do anything, and all the way in doesn't kill the engine. In fact, all the way in is where I get 9.9. if I turn it counter clockwise at all it just gets richer.

The first thing I did was pull the carb and check the transfer slots. The secondary slots were completely covered. The primary slots were something like 1/4" to 5/16" long. So I backed off the idle screw to get a nice little square and adjusted the secondaries to have a nice little square.

Then I checked the jets.

I remember watching a video from Jegs stating that an engine between 350-400 cubic inches should have 64/70 jets for a good starting point.

This thing had 72/82!

Supposedly the guy never ran it, he just put it on the engine and decided to go fuel injection. But I jetted it down to 68/72 because I have a somewhat healthy build.

Now I think I'm at about 2 and a quarter turns out on the idle screws, but it still hovers around 9.9 and smells pig rich.

I have a jet kit but the smallest jets are 64's. I'm probably going to swap those in tonight after work and see if that helps at all.

Any other advice?

I don't know what my vacuum is, I can't find the gauge. I'm going to dig through my stuff and see if I can find it.

Oh yeah, and after idling for maybe 20-30 minutes, when I shut it off, there was like a vapor/mist coming out of the carb. Not sure what that means, but I'm guessing that's a sign that it's way too rich, lol.

[ilikeike]

Turning idle mixture screws all the way in/lean and it’s still running still seem like your throttle plates are open too far and your running off the main circuit.
You might need to adjust idle or hi speed air bleeds and or the idle feed restrictor jets.

You never know what you’re going to get or what the last guy screwed up when you buy a used carb.

Familiarize yourself with the Holley, this book will help.
Good luck.

https://www.amazon.com/Vizards-Modify-Holley-Carburetors-Performance/dp/1934709654/ref=asc_df_1934709654/?tag=hyprod-20&linkCode=df0&hvadid=312031082787&hvpos=1o1&hvnetw=g&hvrand=8989732815098262742&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9032287&hvtargid=pla-489446084288&psc=1

[DarkoNova]

Yeah he said he never ran it but I don't know if it was set up for a bigger engine or something.

I did some googling and I remember reading something about the primaries being open .020" to have a nice square shaped transfer slot at idle. I wasn't sure where to measure so I just set it up to get a small square exposed.

That's why I'm thinking the main jets are still too big.

Hopefully jetting down to 64 is all I need.

I'll order that book and see if it can help me figure it out.

[btmatt]

Is the float level too high? Do you see fuel dripping from the boosters at idle?

[eville]

+1 check the float levels

[BonzoHansen]

We've been working on my qft 780 VS all season. We chased some tuning issues until we found the base plate was not flat. Once we fixed that and reset the primary and secondary transfer slots it started getting better. We did find it a bit sensitive to float level at idle. Got idle around 14.5:1. Ended up changing accelerator pump cam to a smaller one, and smaller squirters. Really woke it up. It's pretty good now. We just have some start up idle issues to beat, hot and cold. we may tinker with air bleeds and jetting. It still has the factory 72/83 jets.

Oh, is your power valve ok?

This carb has also proven to be more heat sensitive than ones I've used in the past.

[DarkoNova]

It has the clear sight glass covers for the floats, and they're all set to the middle of the glass. I thought that was right, but I could try lowering it.

Fuel pressure is rock solid at 6psi.

I can spray some carb cleaner around the base of the carb, but I don't think the base isn't flat. I can check that, though.

Looks like I've got a list of things to check after work.

Thanks guys!

[eville]

Fuel should be just below the sight plug hole. Sounds like they need to be lowered.

[OLDFLM]

Fuel should be just below the sight plug hole. Sounds like they need to be lowered.

Below the sight plug "hole" = yes! With "sight glass" they need to be set to the bottom 1/3rd of the glass... not half way, that's too high.

[DarkoNova]

So after work (I work nights, so I can work on the engine at around 6am) I checked it with a coworker. Before the engine was started, both primary and secondary sight glasses were at the middle of the sight glass.

Once the engine was running, the secondary sight glass was basically full. Primary was at about 75%.

So we adjusted both of them to the middle of the sight glass since the instructions said that's where they should be. There's even little marks on each side of all the sight glasses right at the middle of them, which we assumed meant that's where the fuel should be.

You know what they say about assuming....

But now there's no vapor/mist coming out of the carb when the engine is shut off, now.

The problem is it still won't go past 9.9.

Choke is off, engine is idling at 190°, unsure on vacuum or initial timing. I want to say timing is 18°. I'm going to dig through everything and see if I can find my vacuum gauge. If not, I'll buy one tonight before work.

Turning the idle screws all the way in still doesn't kill the engine. In fact, turning them all the way in gives the highest idle rpm, so I'm probably going to pull the carb and recheck the transfer slots.

My friend said maybe the spark plugs were too fouled to give a good reading, or the O2 sensor was too fouled to give an accurate reading. But the tank was pretty low and the car actually ran out of gas idling, lol.

Fuel filter and bowls were empty, and when it died, it went from 9.9 to 12.0 to 14.0 and maxed out at 16.0), so I think it's safe to say the sensor still works.

So, I'm going to pull the carb, recheck transfer slots, and maybe drop to 64 primaries. I sprayed carb cleaner all around the carb and intake and the rpms never changed, so no vacuum leak.

I'll update tonight with more info.

[eville]

Get a timing light on it.
What's the idle RPM?
If you can run the idle mix screws in and it still runs, it must be idling on the primary circuit.

[DarkoNova]

I try to get the idle at around 800-900. I can't remember the specs on the cam, it was a custom grind, but that's about as low as I want it because I have an electric fan that draws a huge amount of amps when it kicks on. So the rpms dip when it comes on and the idle drops even lower.

I'll check timing and vacuum tonight, and see if I can find the cam card.

[BonzoHansen]

Qft does say mid sight glass. i run my primary at half but the secondary at the bottom of the sight trying to combat a stalling issue when i hit the brakes hard at the end of an autocross

[DarkoNova]

Updates.

So I can't find the cam card. I don't know if the specs are necessary, but with the Edelbrock 650 I at least had it idling at around 800 and had no surges or hiccups in the powerband.

So today after work, I dropped the primaries down to 64.

Still couldn't get the gauge past 9.9 fully warmed up.

But the carb backfired so I shut it off. I have a feeling that the O2 sensor isn't accurate anymore, since a backfire through the carb means it's too lean, right?

Anyway, after the backfire, it wasn't idling right. It was idling at 850-ish, but it just didn't sound right. It kind of sounded like an old diesel idling. I might have blown the power valve, is my guess.

After that, I checked timing. With the vacuum disconnected, I had 17° initial. I've read that for a healthy small block, 16-18 is a good initial. But I backed it down to 14° just to be safe.

Still couldn't find the vacuum gauge. I know as soon as I buy one I'll find the other one, but at this point I need one.

And then the neighbor came over and said every morning there's a ton of noise and fumes and she asked if we could not mess with the car so early in the morning. Sucks because this is basically the only time I have because I work nights, but I'm not gonna be rude and disturb the neighbors. So I'm going to have to find a new time to mess with the car.

Does anyone know what a blown power valve looks like? Is it obvious when it's blown?

I can't start the car but I'm going to at least buy a vacuum gauge and pull the power valve to make sure it's not dead.

EDIT: Nevermind, I just googled, and Holley says carbs made after 1992 have built in power valve protection. The way to test it is to turn the idle mixture screws all the way in. If the engine dies, the valve is good.

And I turned both screws all the way in and it died, so I don't know why it's running weird now. Maybe it's just super lean and the gauge is wrong.

Thoughts? Opinions?

[eville]

If it’s idling rich for so long maybe check the plugs. At this point I’d put a rebuild kit in that carb.
Also, how good is your timing mark?

[WallaceMFG]

I ran into some of the issues you're having with the Demon (Holley) on my car. I was the same spot, idling about 10:1 at 1100 rpm with 12 degrees initial. If I went lower than that with idle it would stumble and become nearly undriveable. Idle adjust screws seemed to do nothing except if they were turned in too much it had a bad off idle lean spot. I threw a rebuild kit at it because the carb had sat and I figured it was plugged up. It ran a little better, but not much.

It honestly took me giving in and having my dad help me with the tuning. It only took him about 10 minutes of fiddling with it and we had it idling at 13.6:1 at 800 rpm with 12 degrees. I hooked up the vacuum advance and readjusted, 14.2:1 at 800rpm. The car ran perfect, and is getting way better fuel mileage than it did before. Also, no more stink! I used to reek like gas when I would drive the car. Now it smells no worse than any other old car with no cats.

The adjustment screws on these carbs are very sensitive, 1/16th of a turn can be enough to make a change. Only go that much at a time, keeping all four even. 2+ turns out seems like a lot, I would run them in to 1 turn out and start from there. Make sure you are adjusting the idle as you are messing with the screws. As you run them in, it will get lean and raise the idle, which needs dropped back down to get an accurate reading. You can try closing up the secondaries too, they don't really need to be open at all at idle. That could be where the extra fuel is coming from. I also second the suggestion about plugs, mine were all nasty from running so rich. i cleaned them and it helped, still need to put a fresh set in.

[DarkoNova]

Timing mark was solid at 14°.

I thought about the plugs, too. They're almost guaranteed to be super fouled by now.

I'm for sure going to buy a vacuum gauge today and I guess pull the plugs to see how they look.

I also thought about closing the secondaries up as well.

[eville]

14* doesn't mean anything if the balancer and pointer aren't correct.
I always think timing when it backfires through the carb.

[OLDFLM]

14* doesn't mean anything if the balancer and pointer aren't correct.
I always think timing when it backfires through the carb.

Good point! Verify TDC and mark the balancer at the TRUE TDC (zero degrees) and go from there... new plugs, and jump on YouTube for Holley tuning videos... there's a bunch that say the same thing and have the same steps to follow.

But you'll need that new vacuum gauge! Keep tuning and let us know how it goes! Good Luck!

[DarkoNova]

Well when we put a new cam in it earlier this year we degreed the cam and put timing tape on the balancer. So I'm 99% sure the timing mark is accurate.

Today I had a little spare time before going to work early so we put new plugs in it and put the 68 primaries back in and readjusted the transfer slots so there's a nice little square on the primaries and secondaries.

Once it warmed up we checked timing, and it was at 9°, which explains why it was backfiring through the carb.

Bumped it up to 15° and started messing with the mixture screws.

I got the AFR to 11.9 at idle, and vacuum was about 15", but the idle speed screw was backed out completely and it was idling at 1400 rpms. Ran out of time to do anything else before heading to work, so tonight we're gonna pull the carb and close the secondaries so I can have more adjustment on the primary transfer slot. Maybe put a bit more timing in it.

[OLDFLM]

Start with all four idle/air screws 1 turn out... set your idle to 1000rpms. Verify TDC... did I mention "verify TDC"? I know you put the timing tap on their but it doesn't take long to verify TDC.

How much mechanical/vacuum advance do you have in the distributor? If's it's 12-14* set your initial timing to 18* for 30-32* total... you can verify total by holding the rpms at 3000rpm and checking your timing. It should be "all in" by then.

You'll need to know how much advance you have it you want it to run well down the road... you may have to start by verifying total timing... then check your initial so you know what your mechanical/vacuum advance is.

What type of distributor do you have btw?

Back to the carb:

Adjust your idle screws... check the vacuum gauge... adjust the idle back to 1000rpms... adjust idle screws... check the vacuum gauge... adjust the idle back to 1000rpms... repeat as necessary.

Shoot for an AFR of 13.2 in park should get you to 14.0 when driving.

[DarkoNova]

What's an easy way to verify tdc without a piston stop? I guess I could pull the belts and crank pulley and put the degree wheel back on and use my dial indicator on a valve.

It's just that I did all that when we installed the cam so I don't really want to do it again. If there's an easier way, I can do it.

Initial timing was only 9°. With vacuum advance connected to full manifold vacuum, it went up to 19° at idle. So my distributor only gives 10° with vacuum.

Distributor is an MSD pro billet.

I bumped the timing up to 16° initial, I forget what the total was at 3000. I knew I should have written it down.

I have an adjustable vacuum canister, I just didn't want to install it right now because I'm already having such a hard time getting the carb dialed in. I didn't want to add more stuff to mess with.

So far at 900 rpms I have 13" of vacuum.

I'm pretty sure the O2 sensor is useless at this point. I took it for a few test drives and the first two with the low initial timing, it just showed 9.0. After bumping up the timing, it maxed out at 10.7.

We pulled a plug and it looked almost perfect. The threads were black but the porcelain was a dark tan color. Darker than ideal, but nowhere near as bad as the old plugs.

I'm probably going to get a new O2 sensor just to rule that out.

[eville]

You set initial with vacuum disconnected and plugged. Mechanical advance also with vacuum disconnected and is checked at 3000 rpm. The mechanical advance is controlled by weights and bushings in the distributor. When it’s “all in” is controlled by the springs in the distributor.

Measure initial and total timing then report back.

[OLDFLM]

TDC = pull the #1 spark plug and put a rubber cork in the hole... rotate the engine under the cork shoots across the garage! LOL

Also check to make sure the rotor in your distributor is pointing directly at the #1 spark plug wire/terminal in the distributor cap.

You HAVE TO make sure your timing is right or you're just chasing your tail... Watch these videos if you haven't already:

https://www.youtube.com/watch?v=FHX1yXVyIMg = Finding TDC with your thumb over the hole

https://www.youtube.com/watch?v=UYGU7mTwsZc = Setting timing and total timing to 35*

I'd run the light blue/light silver spring combination with the black bushing in the MSD Pro Billet distributor.

It'll bring total timing "all in" by 3000rpm and then set your total time to around 35*. HTH

[DarkoNova]

Yeah we checked total but I forgot what it was. I thought I'd remember but I didn't. I'll have to check again.

I thought putting your finger on the spark plug hole was just a rough estimate?

I thought you guys wanted me to like get a degree wheel and go clockwise/counterclockwise to make sure the balancer's zero mark was actually TDC.

I coulda done the finger thing if I knew that's what you were talking about, lol.

I'll see if I can make time to do some tinkering tomorrow and check timing again.

[eville]

Check it with the vacuum advance disconnected and plugged.

[DarkoNova]

Been a while, but I finally got a chance to take the car to work so I got a good 25 Mile drive to see how it's running.

At idle and cruising on the freeway when it's flat, it's running at 13.7-14.0:1.

But if I try to give it a little more throttle, like say 50%, or there's an incline, it goes up. Getting on the freeway it hit mid 15's and peaked at 16:1, and then further on the freeway when I hit an incline it peaked at 18:1!

Since the idle is almost perfect, I'm going to assume it's a secondary issue.

I don't remember what secondary jets are in it, but I'm going to bump them up a decent amount. I'd rather make a bigger change and just have it run richer but still be able to accelerate than still be lean and risk damaging anything.

Right now I can't even accelerate hard because it's so lean that the engine just sputters and runs like crap.

[WallaceMFG]

Yes, go with a couple sizes bigger on the secondaries. Mine ran about 14:1 cruising, 14.5:1-15:1 if I tried to accelerate, and at WOT would spike up to about 16:1. I went a size or two bigger on the secondary jets. Find a carb guy to pick the jets for you. I went into a speed shop and the guy helped me out, the jets I thought I needed were completely wrong because of how Holley jets are labeled apparently.

[TheJDMan]

I got so tired of messing with Holley carb tuning. You really need to take a serious look at an EFI system like FiTech. These EFI systems have come down in price to the point that anyone can afford to make the switch these days. Everyone who makes the switch to EFI says they wish they had done it sooner.

[BonzoHansen]

Been a while, but I finally got a chance to take the car to work so I got a good 25 Mile drive to see how it's running.

At idle and cruising on the freeway when it's flat, it's running at 13.7-14.0:1.

But if I try to give it a little more throttle, like say 50%, or there's an incline, it goes up. Getting on the freeway it hit mid 15's and peaked at 16:1, and then further on the freeway when I hit an incline it peaked at 18:1!

Since the idle is almost perfect, I'm going to assume it's a secondary issue.

I don't remember what secondary jets are in it, but I'm going to bump them up a decent amount. I'd rather make a bigger change and just have it run richer but still be able to accelerate than still be lean and risk damaging anything.

Right now I can't even accelerate hard because it's so lean that the engine just sputters and runs like crap.

I would be looking at squirters, accelerator pump cam, and if it’s a vacuum secondary the spring before i messed with jets.

[DarkoNova]

I went back to the stock 82 secondaries, didn't make a bit of difference.

I tried messing with the secondary opening rate, QuickFuel uses a screw instead of springs for the vacuum secondaries. I forget which way we tried turning it but it didn't help.

We watched an episode of Roadkill Garage where they were tuning a carb with a wideband and they said the power valve is supposed to help with part throttle transitioning/load.

So I bought a new power valve with a higher number. If I'm understanding it right, the higher number will open sooner, so it should help richen it up when I need it to.

I'm going to install it today after work so we'll see.

[DenRS]

Take your highest vacuum reading and divide by two. This is generally what size power valve you should run. Before you go crazy playing around with everything, write down your settings and the changes you made so if they don't work you can go back to the way it was.

[DarkoNova]

The bigger power valve didn't really do anything either.

Not sure what else to do.

It's weird because if I punch it, it goes super lean at around 2400rpm and sputters and falls on it's face. But if I keep the pedal to the floor, it will eventually work through it.

But it honestly feels like a spark issue when it happens. That doesn't make sense, though, because if any plugs weren't firing, it should read richer when it happens.

I don't know. I haven't had time to work on it since my last post since I'm working 12 hour days and 6-7 days a week. I'm almost at the point of just taking it to a shop, but the shop I used to use doesn't tune carbs anymore. They only work on carbs if it's a smog era vehicle and it came from the factory with a carburetor.

[David Pozzi]

The bigger power valve didn't really do anything either.

Not sure what else to do.

It's weird because if I punch it, it goes super lean at around 2400rpm and sputters and falls on it's face. But if I keep the pedal to the floor, it will eventually work through it.

But it honestly feels like a spark issue when it happens. That doesn't make sense, though, because if any plugs weren't firing, it should read richer when it happens.

I don't know. I haven't had time to work on it since my last post since I'm working 12 hour days and 6-7 days a week. I'm almost at the point of just taking it to a shop, but the shop I used to use doesn't tune carbs anymore. They only work on carbs if it's a smog era vehicle and it came from the factory with a carburetor.

O2 sensors only react to Oxygen. A misfire will not burn Oxygen, so it will be read by the sensor as lean. You should take it to a dyno tune shop. We gained over 50 hp on a dyno tune so it's well worth it.