Carb running rich

[69clone]

ok I’m running out of ideas. I really don’t know my way around a carb especially one like my quickfuel 880 with 4 corner idle and stuff. So I’m hoping one of y’all can help guide me in the right direction otherwise only other option I can think of is taking it to the dyno shop and paying them 400+ 150 an hour to tune the carb...
I know it’s running rich when I pull the plugs they’re soaked and black. There’s a lot a ton of soot under the car (open headers). I have an o2 gauge that works when I test it using brake cleaner but goes max rich as soon as it starts. I tried doing minor adjusting to the entire carb and even put all new gaskets and diaphragm. All I can think of right now is the butterfly is open too much and it’s not running on the idle bleed? I have the floats set to the very bottom of the sight glasses and it starves for fuel now when I give it gas. Fuel pressure is set at 6lb.
I don’t know if it’s related but ever since I tinkered with the carb and put new gaskets it randomly back fires through the carb.

 

[65-440]

Adjust your float levels back up some ... check your power valve, that would be my first guess if your running rich enough to soak the plugs. Where are are idle mixture screws set at ? Those are very simple carbs, just be patient ...

 

[Scatpack]

To get a better idea of what’s going on, how big is the motor? Or how much HP?

 

[69clone]

Adjust your float levels back up some ... check your power valve, that would be my first guess if your running rich enough to soak the plugs. Where are are idle mixture screws set at ? Those are very simple carbs, just be patient ...

I appreciate it. I’ll bring the floats back up, Yes it soaks the plugs. I also forgot to mention I am getting fuel in the oil. I am hoping it’s due to it running so rich. I’ll have to double check the idle screws but I believe I have them set back to stock 1-1/8 turn out? I’d have to double check though. The power valve is 6.5lb if iirc from when I had it tore apart.

To get a better idea of what’s going on, how big is the motor? Or how much HP?

It’s on a 440 stroker somewhere in the 6-650 range.

 

[Scatpack]

Ok so that carb isn’t to big for that hp range. Set the floats so the fuel level is half way in the sight glass or little below. I would set the idle screws in all the way and turn them out 1 1/4-1 1/2 turns out. After the car has run for a while and you turn it off, is it hard to start again because it feels like it’s flooded? I had a carb that would dump fuel hard core, the floats were set right and idle screws where set 1 1/2 turns out. I ended up just rebuilding the carb, the kit is 45 bucks and that cured the problem. Look down in the carb while it’s running (make sure you have timing right so it doesn’t back fire, haha) watch how much fuel getting dumped

 

[Paul_G]

Getting a Holley carb to run right is half science half art. They have many adjustments on them, each effects a small part of the performance and manners of the engine. On a 600 HP engine there is no carb that will run the best out of the box. It is going to need a good tune.

Is the carb brand new? Has it been tuned to run on a different engine before? Has it ever back fired up through the carb? What idle speed should the engine be running at?

All new Holleys have power valve blow out protection. But it still may have blown out the power valve if it has back fired with enough force. At 600 horse power your engine has enough force.

To test the power valve, the engine must be idling at a low rpm, one at a time turn the idle mixture screws all the way in, the engine should stumble and die. If it does not die, you are getting fuel from some place other than the idle circuit. There are some things to check before you replace the PV. It could be idling in the transition circuit which means the throttle blades are open to far. the secondary throttle plate could be open too much, or lastly the power valve is blown out. If the carb is new it is unlikely that the secondary throttle is incorrectly adjusted.

You say the you "tinkered" with the carb. Now you have issues. Are the transitions slots back to square? View them from the underside of the carb.

 

[Paul_G]

One more thing. Most carb problems are ignition related. Make sure the ignition system is set up corectly. How much base timing are you running?

 

[69clone]

Hey I appreciate the suggestions I haven’t had a chance to work on the car til today first thing I noticed is my butterfly are open a lot more than the picture above. (Transfer slots aren’t squared) Does that mean it’s idling off the primary?




Okay I closed the transfer slots to small squares exactly like pictured in Paul_G post above. In order to do that I had to turn the choke and and rpm screw? To get the butterfly’s to close enough. I started it up and it runs fairly smooth, idle is low due to me having to turn the screw out in order to get the butterfly to close enough to create a square. According to my wide band gauge it’s still off the chart on the rich side at idle and leans out to 11-13.2 at WOT
I raised the floats to half the sight glass. I also raised the fuel pressure to 5.5
I took a video but need to figure out the best way to post it.

 

[Paul_G]

Those throttle plates are open pretty far and likely idling in transition. Adjust the throttle plates closed a little until the slots look square. Primary and secondary slots should all appear to be square. Thats the starting point. Adjust all four mixture screws in until lightly seated, then back out 1 1/2 turns. The engine should start and idle now, check float levels and adjust if needed. Lots of videos on youtube for adjusting holley floats. Adjust the idle speed to what you would like the engine to run at, how is 700 RPM to start with? Engine should be idling fairly well at this point.

If the engine needs some fine adjustment, start adjusting the primary side mixture screws first, 1 mixture screw at a time, turn it in 1/4 turn, then try out 1/4 turn, whichever is better (smoother more stable and/or highest idle) leave it there and move on. Go to the other primary screw and do the same, then do the secondary screws. Repeat the process with smaller adjustment, like 1/8th turn until you have the best idle. You can also use a vacuum gauge doing this adjustment, trying for the highest vacuum with the smoothest idle, needle on the gauge holding steadiest. You may need to bring the idle speed back down if the RPM has increased substantially.

This works well unless there other things going on.

 

[68 HEMI GTS]

Fairly large cam im guessing, you may need to add some holes in the butterflies so you can close up the throttle plates. That’s providing the carb and distributor are not all out of wack. What are the cam specs ?

I had to put transfer slot restrictions In my qf 1050/4150 main body to lean out the cruise. It also took some air bleed changes, and I reduced the emulsion. Similiar power range 511. Great carb once I got it dialed. Chances are if you take it to a dyno shop you’ll be disappointed. Not that many guys that really know how to tune carbs anymore. I just went through a QFT 1050 dominator that was “dyno tuned” on a similiar type motor. I did a lot of work to straighten that one out also.

 

[69clone]

Thanks guys, I don't know if you seen where I edited my last post below the pictures to include more info. I did square up the transfer slots. But in order to do that the I had to adjust the idle screw and now idle is low (was idling around 900-1k now its sitting at 500rpm). I did reset all 4 mixture screws, lightly turned in til felt resistance then turned them all out 1 1/8 turns. (If I'm not mistaken to check if its running off the idle slot if I turn all 4 mixture screws in it should die right?)
The cam specs Comp Cam: Duration 294/306, Lift .519/.524.
Here is a link to a video I took http://vod-share.com/video/carb-rich/4329.html

 

[Paul_G]

While idling at 550 like it is, turn in all 4 screws and yes it should die. Then you can raise the idle speed up to say 800 RPM if thats what the engine likes. Then turn the mixture screws in again and see if dies as well. When the idle is up to a point you like, re adjust the mixture screws again.

 

[Paul_G]

Holleys like fuel pressure around 6 to 7 psi. Float levels look good. A/F ratio will change when idle speeds change. When the idle is raised more transfer slot comes in to play, which is not easily tunable. The more of the slot that shows, the less effect the mixture screws have. Try to find a happy area in the middle if possible.

 

[Paul_G]

Your A/F gauge is reading out of range, thats what the dashes mean. How old is the sensor? Does the exhaust smell rich and burn your eyes?

 

[69clone]

Thanks Paul_G, I’ll give it a shot. The A/F gauge/sensor is only 6 months old and when it goes to dashes I assumed it was too rich because as you can see if I give it gas it leans out and starts reading. It does not burn my eyes or smell that bad but the entire underside is covered in a thick layer of soot. So what would drilling holes in the butterfly do? Would that help raise rpm while keeping it running off the idle portion?

 

[68 HEMI GTS]

Just FYI your A/f gauge probably isn't even close to giving a proper reading with open headers unless you have some extensions or somethin on it. Your trying to idle it to low. That cam is probably gonna be happier around 900-1000 rpm idle. If it's to far into the transfer slots to make it idle the holes provide bypass air. Allows you to keep the plates where the cab stays on the idle circuit. Cam is not super big, could probably go either way. 5.5 is fine for he fuel pressure. That's all holleys need. Initial timing is also Going to be important to getting it to idle.

 

[Paul_G]

Open headers? Is there an exhaust system on the car right now? How much vacuum is it pulling at idle? Makes a huge difference in the power valve sizing.

Drilling the throttle plates is a last ditch effort. Only recommended when all else fails. If it doesnt work, meaning something else is the problem, you trashed the carb. Throttle plates are not easily replaced.

Big cam big power engines are not easy to tune. There is lots of info on Holleys website on how to tune a carb. Low vacuum signals really mess with the carb and make it tougher to tune.

 

[69 GTX]

What is your base timing & all in timing. Helping my friend tune his 6pack with a cam similar his timing was all out of wack. We re did the base and timing curve and it fixed 50% of his problem. I'm guessing you probably need 16 degrees base and 32-36 all in at about 2400-27000. But that's just a guess on my part.

 

[68 HEMI GTS]

Open headers? Is there an exhaust system on the car right now? How much vacuum is it pulling at idle? Makes a huge difference in the power valve sizing.

Drilling the throttle plates is a last ditch effort. Only recommended when all else fails. If it doesnt work, meaning something else is the problem, you trashed the carb. Throttle plates are not easily replaced.

Trashed the carb? Man I love the Internet. That’s why I stay away from these threads. And the power valve has no effect on the idle unless it’s leaking or blown.

 

[Paul_G]

Trashed the carb? Man I love the Internet. That’s why I stay away from these threads. And the power valve has no effect on the idle unless it’s leaking or blown.

Have you been following this thread? The complaint is the car is sooted up and running rich. That doesnt happen at idle. If the engine vacuum is low the power valve is opening too soon creating a rich condition at cruise. Not an idle problem. The power valve needs to be sized for the amount of vacuum the engine is pulling. Go do some reading on Holleys site. Lots of info there.

The OP has not finished testing yet. He has the engine idling down, but has not reported on what happens when he screws the idle mixture screws in. Still waiting for that information.