[Ivo]

Hello, I Need some recommendations About my Idle/Mixture.
My set Up:
Camschaft Roller Lunati 20510712, Duration 231/239 on 0,50lift, Roller Morell lifters, 1,5 Scorpions, 87cc E Heads.
Carb. Holley 950 Street HP, 84/84 jets, 31/31 nozzle, 6,5 PV. Rear Butterflays 0,020 open.
Ignition Initial 16 / 19 advanced ( MSD Distributor, Heavy/ Light Silver Spring, Purple bushing, 34° all in 3200rpm
Dizzy is on Ported Vacum. I have try also with full manifold but i have to much RPM Drop, About 400 rpm. I have posted two Videos of my current Set up on Ported Vacum and Rpm drop is About 200 rpm
https://www.youtube.com/watch?v=03Tb...ature=youtu.be
https://www.youtube.com/watch?v=n5ag...ature=youtu.be
and that is the best what I can adjust. I know Maybe is 6.5 PV to big for 11 vacum but I have not overriching under acceleration./ WOT.
On first Video My dual Spals coming on.
You can see Idle rpm ( 1000) and idle (800)in gear, vacum idle ( 14-15 ) and vacum in Gear ( 10-11 )
On second Video ( Little longer )you can see crusing conditions and acceleration mixture / vacum.
I Need some recomendation, I Think the Engine is Little rich on idle.
Can you see anything wrong with my Setup because off my mixture / airfuel ratio, Vacum,high and Idle rpm
How dramaticly can Ported / Manifold Vacum Change idle Temp.
Thanks Ivo

[Cliff R]

What CID is the engine?

What is the compression ratio?

What is the vacuum reading at 750-800rpms with 16 degrees initial timing?

[PDC]

Ive got a pair of 73s. One was running a Holley 750 HP and I really liked the way it ran. So I put a Holley 750 ‘Street’ HP on the other car - thinking the specs would be the same. I could never get the idle clean on the ‘Street’ HP equipped car no matter what I did. It was fouling plugs left and right. After doing some digging, I later found that the ‘Street’ HP carbs are jetted significantly fatter than their Original HP counter parts and use different Power Valve values. I ended up selling the Street HP and bought an Original HP and the car ran like it had fuel injection outta the box. Again, I was running the 750. I’ll bet the 950 Street HP is jetted really rich. I wonder if your combo would like the original series 850 HP? Pull up the spec sheets on the Holley website and compare the jets and PV values between comparable cfm HP and ‘Street’ HP carbs.

[Ivo]

Originally Posted by Cliff R

What CID is the engine?

What is the compression ratio?

What is the vacuum reading at 750-800rpms with 16 degrees initial timing?

Cliff CID is 469, compression 10:1 and it Run very rough lower then 950 rpm

[Cliff R]

It should not have a "really rough idle" below 950 RPM's with 16 degrees initial timing in it.

That cam isn't really very big for 469CID and 10 to 1 static compression.

The 110LSA isn't helping but with a 231 @ .050" camshaft (assuming it's installed correctly) vacuum production at idle should be good and idling nicely around 750-800 rpms making at least 12" vacuum with a nice "lope" in the exhaust note. It should actually do that down around 10-12 degrees initial timing and not want or need any additional timing from the vacuum advance.

A while back we did a 455 Super Duty engine with about 8.8 to 1 compression and installed a 281/287 @ .006" roller cam in it, 230/236 @ .050" on a 112 LSA. It idle dead smooth clear down to 600rpms with only 12 degrees initial timing in it. It was making over 13" vacuum at 700rpm's.

Your larger CID engine with more compression shouldn't need 16 degrees initial, nor should it be unhappy idling below 950rpm's.

Not really sure how to help at this point, but if it's really unhappy and you can't tune it out with timing and idle fuel I'd look at fundamental stuff like cam timing and valve events.

I'd also be interested in what it shows on a cranking compression test?.......Cliff

[TCSGTO]

Originally Posted by Ivo

Hello, I Need some recommendations About my Idle/Mixture.
My set Up:
Rear Butterflays 0,020

Are you saying .020” of the secondary transfer slots are exposed? If so adjust the front transfer slots to .020” and use the secondary plates to set idle speed. It shouldn’t need more than 1/2 turn from full closed and you shouldn’t see any of the secondary slot under the throttle plates.
Check that the distributor isn’t adding a few degrees of timing at 1000rpm that get pulled out when you put it in gear and cause that big drop in idle speed. As little as 2 or 3 degrees creeping in can make a difference.

[shaker455]

Originally Posted by Ivo

Hello, I Need some recommendations About my Idle/Mixture.
My set Up:
Camschaft Roller Lunati 20510712, Duration 231/239 on 0,50lift, Roller Morell lifters, 1,5 Scorpions, 87cc E Heads.
Carb. Holley 950 Street HP, 84/84 jets, 31/31 nozzle, 6,5 PV. Rear Butterflays 0,020 open.
Ignition Initial 16 / 19 advanced ( MSD Distributor, Heavy/ Light Silver Spring, Purple bushing, 34° all in 3200rpm
Dizzy is on Ported Vacum. I have try also with full manifold but i have to much RPM Drop, About 400 rpm. I have posted two Videos of my current Set up on Ported Vacum and Rpm drop is About 200 rpm
https://www.youtube.com/watch?v=03Tb...ature=youtu.be
https://www.youtube.com/watch?v=n5ag...ature=youtu.be
and that is the best what I can adjust. I know Maybe is 6.5 PV to big for 11 vacum but I have not overriching under acceleration./ WOT.
On first Video My dual Spals coming on.
You can see Idle rpm ( 1000) and idle (800)in gear, vacum idle ( 14-15 ) and vacum in Gear ( 10-11 )
On second Video ( Little longer )you can see crusing conditions and acceleration mixture / vacum.
I Need some recomendation, I Think the Engine is Little rich on idle.
Can you see anything wrong with my Setup because off my mixture / airfuel ratio, Vacum,high and Idle rpm
How dramaticly can Ported / Manifold Vacum Change idle Temp.
Thanks Ivo

Adjust all your mixture screws evenly to achieve 13.2 to 13.5 AFR in park

[Formulajones]

Agree, You can adjust your mixture screws and slightly lean out the AFR but there are other things to consider that will likely happen.

Sometimes leaning the idle AFR will decrease your vacuum readings and idle rougher. Some engines respond well and some don't.

I'm going to assume you ended up in the mid 12's for idle AFR because that's where you found your best vacuum readings and best idle quality.

Some engines, with tight LSA's, not enough compression for the cam, air gap intakes with no heat cross overs etc.... Generally want to idle with slightly richer AFR's to be happy. Not saying that's the case here but it's not an unusual scenario.

Since the rest of your AFR's look fine, I'd try what Shaker said and make an attempt to lean the idle AFR slightly, which will lean the entire fuel curve slightly as well. You may find your idle quality suffers and idle vacuum drops in which case it's telling you the engine just likes to idle a little on the fat side with your current setup.

Nothing wrong with idling AFR's in the mid 12's. I have one car here that likes to idle in the mid to upper 12's on the gauge, and the plugs actually stay clean despite what the gauge says. With todays ethanol pump fuels being a little richer is a good thing anyway.
I tend to tune for best drivability and idle quality and then look at the gauge for reference. Sometimes trying to shoot for specific AFR's doesn't always give the best drivability on some engines.

[shaker455]

Also, you can test to see if you need to add a bit of bypass air to the carb.
While fully up to temp with timing light digital tach unplug the small full vacuum source in front base of carb and record how much your RPM's increase.

Also the newer Holley's like what you have sometimes feature a high location idle feed restriction (IFR) in the metering block.
This is above the float level and a side effect of this is it can create a rough or uneven idle cause it above liquid fuel.
This is why I relocate them to a position below float level.

[antique69lemans]

Originally Posted by shaker455

Also, you can test to see if you need to add a bit of bypass air to the carb.
While fully up to temp with timing light digital tach unplug the small full vacuum source in front base of carb and record how much your RPM's increase.

Also the newer Holley's like what you have sometimes feature a high location idle feed restriction (IFR) in the metering block.
This is above the float level and a side effect of this is it can create a rough or uneven idle cause it above liquid fuel.
This is why I relocate them to a position below float level.

I would advise this along with transfer slot inspection. You might be in a dead zone between idle and main circuit. If you can get a needle valve plugged into pcv or booster port and dial in some bypass air, then back of idle speed screw and see if it straightens out. Once you get close it should accept tip in and park to drive transition. Surging idle also plays havoc with vacuum advance.

[wbnapier]

Ivo,

In my opinion,

In your first video, your idle in park AFR was in the high 12's. It is OK.

In the second video, your AFR seems to be OK under cruise / heavy acceleration.

I have a 455 with a tri-power, and my AFR is similar to yours under all conditions.

After installing my wide-band O2 sensor, I thought I was too rich and I spent hours playing around with the carb, but more experienced people on this forum cautioned me not to be obsessed with the AFR readings.

If the throttle is responsive, it idles OK, and has good vacuum, you are already winning. I think your engine qualifies as a winner.

And, your GTO is beautiful. Get on the German roads and enjoy it!

[Ivo]

Originally Posted by shaker455

Adjust all your mixture screws evenly to achieve 13.2 to 13.5 AFR in park

Today Late afternoon second test drive, it was very hot, air temp about 98f Transmission temp. 180F idle Vacum 11, AFR 12.6. .
I think AFR in idle is to Low. Cruise 13,4 .
Cliff crank compression all around 172-175 PSI.
I will tray next week to retard my initial from 16 to 14 but I think my Problem is idle circuit.. I have secondary butterflys open 1/2 Turn,the Transnition Slot is 0.020 visible with feeler gauge (below the carb). Now at 98f Outdoor temp, I noticed that my idle at this evening, without anything to do jumped from 800rpm (in the morning adjusted) to 950 rpm now in drive Position. In the morning we have an Outdoor temp about 73f. That iritates me That the idle is raised about 150rpm now. Tomorrow i will Check my plugs, but I think i will do some Experiment with the air Bleeds.
I dont know where to start, with idle airbleeds or jetts are to big

[Cliff R]

With 172 psi cranking pressure idle quality should be decent, and it should settle down nicely about 750-800 rpms without much trouble.

Changes in idle RPM are typically caused by the timing moving around some below apprx 900 rpms, it must be ROCK SOLID at idle speed cold, warm or hot engine. It could also be caused by the idle mixture being too lean so it idles much faster once the engine is fully warmed up and intake well heat soaked.......Cliff

[Formulajones]

Originally Posted by wbnapier

Ivo,

In my opinion,

In your first video, your idle in park AFR was in the high 12's. It is OK.

In the second video, your AFR seems to be OK under cruise / heavy acceleration.

I have a 455 with a tri-power, and my AFR is similar to yours under all conditions.

After installing my wide-band O2 sensor, I thought I was too rich and I spent hours playing around with the carb, but more experienced people on this forum cautioned me not to be obsessed with the AFR readings.

If the throttle is responsive, it idles OK, and has good vacuum, you are already winning. I think your engine qualifies as a winner.

And, your GTO is beautiful. Get on the German roads and enjoy it!

My thoughts exactly and what I eluded to.

[Tom Vaught]

Originally Posted by shaker455

Also, you can test to see if you need to add a bit of bypass air to the carb.
While fully up to temp with timing light digital tach unplug the small full vacuum source in front base of carb and record how much your RPM's increase.

Also the newer Holley's like what you have sometimes feature a high location idle feed restriction (IFR) in the metering block.
This is above the float level and a side effect of this is it can create a rough or uneven idle cause it above liquid fuel.
This is why I relocate them to a position below float level.

I was also going to post "MOVE THE IFRS BACK TO THE LOWER POSITION" BUT SHAKER455 TREED ME.

Tom V.