Carb running rich

[69clone]

Thanks for the response guys I want to at least turn the idle screws down and make sure it’s running off the idle circuit. I’ll test everything when I get off work later

I’m not sure on the timing I’d have to double check it. My harmonic balancer is rusty/dirty so it’s hard to see but I wanna say it was close to 20 at idle when I tried checking before.

I did not know that about the a/f sensor yes it’s open headers and the sensor is about 4” from the tip.

What’s the best way to check the vacuum? Off the carb vacuum port?

 

[threewood]

Thanks for the response guys I want to at least turn the idle screws down and make sure it’s running off the idle circuit. I’ll test everything when I get off work later

I’m not sure on the timing I’d have to double check it. My harmonic balancer is rusty/dirty so it’s hard to see but I wanna say it was close to 20 at idle when I tried checking before.

I did not know that about the a/f sensor yes it’s open headers and the sensor is about 4” from the tip.

What’s the best way to check the vacuum? Off the carb vacuum port?

Check the engine vacuum off manifold vacuum or the lowest port on the carb.

Depending on where you are initially, after you square the ports and with the mix screws out about 1-1/2 turns, you can advance the timing to increase your idle RPMs to where you need them for your cam to idle well. But doing this will also require you to check the total advance and possibly make adjustments there as well. Every adjustment has an effect on other adjustments so it will require some back and forth.

 

[68 HEMI GTS]

Thanks for the response guys I want to at least turn the idle screws down and make sure it’s running off the idle circuit. I’ll test everything when I get off work later

I’m not sure on the timing I’d have to double check it. My harmonic balancer is rusty/dirty so it’s hard to see but I wanna say it was close to 20 at idle when I tried checking before.

I did not know that about the a/f sensor yes it’s open headers and the sensor is about 4” from the tip.

What’s the best way to check the vacuum? Off the carb vacuum port?

You need to get full manifold vacuum. Most people just pull it off the intake. The carb should have at least one port on the front that’s full manifold vacuum. I don’t expect the idle vacuum to be all that high given the cam specs. Under cruise though it’ll have plenty. Like already said, if the distributor isn’t set up right you’re chasing your tail.

Ignore your A/F gauge untill you get some pipes on it.

 

[68 HEMI GTS]

That carb has the IFR’s up high. They idle better when moved to the lower location. Unfortunately it takes a few special items that probably are not in your tool box. That’s usually the first mod I do to one.

It hasn’t been mentioned yet either but a good fuel filter is an absolute must. Holley type carbs absolutely hate debris. It’s always worth mentioning.

 

[69clone]

Thanks yeah I’d have to take vacuum reading off the carb because the Indy intake doesn’t have anywhere to hook up. IFR location?
I have decent filter I forget the micron rating though.

So what should my next step be? Check the idle screws to confirm it’s running off the idle circuit. Get a vacuum reading and figure out the initial timing then go from there?

 

[69clone]

Well I accomplished two things,
1 it must be idling off the idle circuit because when I got to the 2nd to last screw it died. It appears to me we aren’t running as rich anymore at least not enough to cause soot because I placed my hand near the exhaust (it was fairly warm, lol) but no soot nor did my hand smell like gas. Now when I hit the gas I am still seeing a black cloud out back/out of the pipes.

2: I also was able to take just alittle timing out to bring the rpm up to 8-900 idle in park. It also seemed to start easier, usually I had to pump the gas once before turning the key but I am now able to just turn the key and it fires right up.

As for vacuum I thought I had a gauge to test it but I can’t find it so I’m going to get ahold of one tomorrow.

I also tried cleaning up my harmonic balancer so I could read the numbers with my timing light. I just having a difficult time figuring out what the number says when it flashes..

 

[69clone]

Alright so apparently I was wrong about it idling good. I stood about 10ft behind the car while it was idling and my eyes were burning. So I turned the screws in alittle, roughly 1 turn out from snug on all 4 corners. Walked back and it seemed slightly better but still burned pretty bad when I got to the bumper. I am assuming I have a problem else where because the idle screws shouldn’t have to be turned in further??? I’m also noticing a hint of gas smell in the oil again so it’s definitely pouring fuel and cloud of black smoke behind the carb when I give it gas.
Next I was able to check vacuum off the carb port. I got 6-7 kinda bounces around.
Any suggestions on what to do now?

 

[Paul_G]

What jets are in it and what size power valve? Still need to know how much vacuum it's drawing at idle to get the PV sized right.

You really cant tune the carb running open headers either. There should not be any black smoke out the exhaust regardless. You may want to take the carb apart again and make sure you have everything together right, no ripped or torn gaskets, jets in and tight, PV in and tight etc.

 

[69clone]

What jets are in it and what size power valve? Still need to know how much vacuum it's drawing at idle to get the PV sized right.

You really cant tune the carb running open headers either. There should not be any black smoke out the exhaust regardless. You may want to take the carb apart again and make sure you have everything together right, no ripped or torn gaskets, jets in and tight, PV in and tight etc.

Yes sadly it smokes worst then my cummins... Thats not a bad idea I'll see if I can tear it apart tomorrow I've already got it off the intake.
Like I mentioned earlier my vacuum appears to be 6-7 psi at idle in park. As soon as I start giving it gas it starts to drop I'd say it is at 0 by 2000rpm.

According to the spec sheet that came with the carb it has: PV 6.5, Primary Main Jet 80, Secondary 86, Idle Air bleed 70/70, Hi Speed Bleed 28/28, Pri Nozzle 35, Needle and seat 120
I will have to pay attention when I tear it apart again and verify that the above info maxes whats actually on the carb.

This is all new to me I've really never done any of this before so I apologize if I am missing something obvious.

 

[Paul_G]

That explains a lot. With idle vacuum at 6 to 7" vacuum, and 6.5 PV. The PV is dumping fuel as soon as you open the throttle and probably dribbling a little even at idle. The PV number determines at what amount of vacuum it opens. A 6.5 PV will open when engine vacuum drops to 6.5" of vacuum. You need to try a smaller number PV.

I wouldnt even mess with jetting till you get the exhaust on the car and A/F gauge is working correctly.

I would get a 35 PV and start there. Holley states that the PV size should be 1/2 the amount of idle vacuum. So if an engine is making 13" inches of vacuum or more, a 6.5 PV should be used. If your engine is making around 7" vacuum I would try a 35 PV first. Power valves are sized by the amount of vacuum drop they open at. Any amount of vacuum higher than the rating on the PV and it stays closed. Holley disregards the decimal point. a 6.5 PV is marked 65. The marking is on the PV.

BTW, once you get the engine running again set the mixture adjustment again. Then you can adjust idle speed with the idle speed screw. You have the throttle blades set correctly when they are squared up on the transition slots. Fine adjustment can be made with the idle speed screw as long as it is not opening the throttle blades so much that they are idling on the transition slot.

I would suspect that engine would like 16 to 18 degrees base timing, with no more the 36 total.

 

[beanhead]

Timing first...always. Depending on your compression ratio that cam may like around 20+deg. at idle. With your transfer slots squared bump up the idle timing for the highest vacuum. Then move to mixture screws, at each corner, gently, giving 20 or 30 seconds for the carb to adjust...my 850 demon responds to 1/16th turn increments. Best vacuum reading during mixture adjustment is what you want. If at this point, the idle speed needs to change then you can slightly adjust the idle speed screws(butterfly position). Drilling the plates is a last resort if nothing else gets you where you want. Keep in mind, this is a starting point as every combo has different requirements so you have to keep adjusting until it's happy. --For example, for warm weather driving 8 months of the year here, my aluminum head 440 with a milder cam than yours and 9.5 compression behaves best at 22/38 degrees advance, idles right along at 700 with only the primary butterflies exposing the slots. Secondaries closed (barry grant recommended secondary slots exposed only for engines idling at 1000rpm or higher, yours may want the higher idle?) When I had pri and sec slots exposed it idled piggly-rich even at the same idle speed. My mixture screws are 3/4 to 7/8 out from closed. 1 turn or more causes loading up at idle. Some may say these settings are wonky but the combo absolutely loves it. My vacuum is 13-ish idling in gear. Very strong runner! Holley-design carbs have lots of things to tweak and when you get it dialed in you'll love it...

 

[68 HEMI GTS]

That explains a lot. With idle vacuum at 6 to 7" vacuum, and 6.5 PV. The PV is dumping fuel as soon as you open the throttle and probably dribbling a little even at idle. The PV number determines at what amount of vacuum it opens. A 6.5 PV will open when engine vacuum drops to 6.5" of vacuum. You need to try a smaller number PV.

I wouldnt even mess with jetting till you get the exhaust on the car and A/F gauge is working correctly.

I would get a 35 PV and start there. Holley states that the PV size should be 1/2 the amount of idle vacuum. So if an engine is making 13" inches of vacuum or more, a 6.5 PV should be used. If your engine is making around 7" vacuum I would try a 35 PV first. Power valves are sized by the amount of vacuum drop they open at. Any amount of vacuum higher than the rating on the PV and it stays closed. Holley disregards the decimal point. a 6.5 PV is marked 65. The marking is on the PV.

BTW, once you get the engine running again set the mixture adjustment again. Then you can adjust idle speed with the idle speed screw. You have the throttle blades set correctly when they are squared up on the transition slots. Fine adjustment can be made with the idle speed screw as long as it is not opening the throttle blades so much that they are idling on the transition slot.

I would suspect that engine would like 16 to 18 degrees base timing, with no more the 36 total.

You should really understand how the power valve enrichment works before you post advice.

 

[Paul_G]

You should really understand how the power valve enrichment works before you post advice.

I guess Holley must have it wrong. Or do you have a better understanding?

https://www.holley.com/blog/post/holley_power_valve_tuning/

1) Hook a vacuum gauge to an intake manifold vacuum port.


2) Warm up the engine and note the vacuum reading at idle. Automatic transmission vehicles need to be in the Drive position, while manual transmission vehicles can be in Neutral.

3) Divide the vacuum reading in half. The number will determine the correct power valve.


Each power valve is stamped with a number that indicates the correct vacuum opening point. For example a power valve with the number #65 stamped on it, will open at 6.5 inches of engine vacuum. As an example, a vacuum reading at idle of 13-inches, is divided by two and results in a 6.5 inches of vacuum. Therefore, you should have a #65 Holley Power Valve installed in the carburetor.

 

[68 HEMI GTS]

I guess Holley must have it wrong. Or do you have a better understanding?

https://www.holley.com/blog/post/holley_power_valve_tuning/

1) Hook a vacuum gauge to an intake manifold vacuum port.


2) Warm up the engine and note the vacuum reading at idle. Automatic transmission vehicles need to be in the Drive position, while manual transmission vehicles can be in Neutral.

3) Divide the vacuum reading in half. The number will determine the correct power valve.


Each power valve is stamped with a number that indicates the correct vacuum opening point. For example a power valve with the number #65 stamped on it, will open at 6.5 inches of engine vacuum. As an example, a vacuum reading at idle of 13-inches, is divided by two and results in a 6.5 inches of vacuum. Therefore, you should have a #65 Holley Power Valve installed in the carburetor.

Please explain how a 6.5 power valve enriches the idle circuit (or as you put it dribbles fuel). Let’s say on an engine that only does have 5.5” of idle vacuum. I’m not talking about reading from a website that is providing guidelines on choosing a power valve. Explain how the fuel from the PV is enriching the idle circuit? I can explain why it’s not but this seems like more fun.

 

[Paul_G]

Sure. If the engine is idling at 6 to 7" vacuum with a power valve rated to open at 6.5" vacuum, what do you think is going to happen? As soon as the throttle is opened the power valve is getting the vacuum drop and opening. You do understand that engine vacuum can fluctuate right? Can you guarantee 6.5 PV is staying closed at 6 to 7" vacuum at idle? With the PV right on the edge it is wise to put a smaller number PV. Would you not agree?

 

[68 HEMI GTS]

Ok, so the powervalve is open. I agree with that. Now, how does it enrichen the idle circuit?

I’ll give you a hint. Go take a look at a primary metering block. See where those PVC restrictions lead too.

 

[Paul_G]

Really? What happens when you remove the power valve and leave the open hole?

 

[beanhead]

Power valve works through your main discharge circuit, not the idle circuit. If it's too large (or blown) you'll definitely be over-rich just not at idle specifically. (The little holes and passages don't connect the power valve to the idle circuit in other words)

 

[beanhead]

Oops all these new posts hit while I was still typing...sorry to butt in to your fun!

 

[68 HEMI GTS]

Really? What happens when you remove the power valve and leave the open hole?

Study a power valve, it does not allow fuel into the vacuum chamber. That’s the situation you would have if you removed it. The float bowl would empty into the vacuum chamber and into the engine