Dual Quad 428 CJ

[Khobra]

Hey all, I'm new to Club Cobra and just recently discovered this forum. Really enjoy the read.
Was wondering if someone could help me with this combination. The intake is a C7ZX off a 67 Mustang Shelby GT 500 428. The carbs I'm running are Ford P/N 5752426, which are 600 CFM units, basically 1850s. I'm running #60 jets on all corners and it works great. My problem is a rich idle. Running in my garage it burns my eyes. I've tried everything I know but can't seem to lean it out enough.
Power valves are 6.5

Additional info is as follows:

Cam - Comp Cams, Roller, 282/288 adv duration, 521/532 lift.
@ 0.050" 230/236 deg duration
Lobe sep is 110 deg.

Anyone have any ideas?

[Jerry Clayton]

Check vacume at idle and change power valves to 2 numbers less than vacume guage reading

[Khobra]

Thanks Jerry,
Vacuum at idle is just under 12. If I change to lets say 9, would the PV not open even sooner then 6.5? I feel that the PV is within range.

[DanEC]

Jerry's advise is generally the text book guide to selecting power valves. Not sure what happens if a lower range one is used than needed - possibly a rich condition.

Are you carbs sensitive to idle mixture adjustments and the primary throttle blades resting around the middle area of the little idle transition slots in the bores? Or are they resting at the top of the slots at idle?

And I assume you are tuning the idle mixture and speed on both carbs equally?

Normally I would think you are just fighting the characteristics of a fairly big cam if those duration figures are at .050 inches lift, but if you can pull 12 inches of vacuum at idle I think you should be able to get an outcome that isn't obviously rich. But even my 231/236 @ .050 cam with my dual quads is not something I let idle inside my garage for long.

[undy]

My dual quads (twin QickFuel 750s) idle at 14.5 to 1 AFR, perfect not a hint of gasolene odor inside or out. There can be sooooo many problems here;

1) incorrect fuel bowl levels
2) excessive fuel pressure (blowing by bowl inlet needle valves)
3) air bleeds need "correct" sizing
4) power valve section wrong
5) (as stated) transition slots uncovered on one or both carbs
6) linkage mis-adjusted

[Khobra]

Originally Posted by DanEC

Jerry's advise is generally the text book guide to selecting power valves. Not sure what happens if a lower range one is used than needed - possibly a rich condition.

Are you carbs sensitive to idle mixture adjustments and the primary throttle blades resting around the middle area of the little idle transition slots in the bores? Or are they resting at the top of the slots at idle?

And I assume you are tuning the idle mixture and speed on both carbs equally?

Normally I would think you are just fighting the characteristics of a fairly big cam if those duration figures are at .050 inches lift, but if you can pull 12 inches of vacuum at idle I think you should be able to get an outcome that isn't obviously rich. But even my 231/236 @ .050 cam with my dual quads is not something I let idle inside my garage for long.

Dan and Undy,
Thanks for your input. Yes, idle mixture screws are somewhat sensitive but not like they should be. The throttle plates are nearly closed and yes, both carbs adjusted equally. Spoke with a very knowledgeable individual at the race track today and I think he is on the right track. I need to increase the size of the idle air bleed restrictions. This will be my next step. I will drill out the current restriction and tap and install a screw in type.

Undy, did you have to play with this on your carbs?

My linkages are bang on, the power valves are 6.5. In the past, on other applications, I have drilled small holes in the primary throttle plates which did help a huge amount but I don't want to go that direction in this case if I don't have to. I would rather take the air bleed restriction route.
Hopefully I can do this sometime this coming week.
Will keep you posted.
BTW undy, what is your initial and total advance that you're running on your engine? I'm at 16 initial and 36 deg. total.

[Khobra]

Originally Posted by undy

My dual quads (twin QickFuel 750s) idle at 14.5 to 1 AFR, perfect not a hint of gasolene odor inside or out. There can be sooooo many problems here;

1) incorrect fuel bowl levels
2) excessive fuel pressure (blowing by bowl inlet needle valves)
3) air bleeds need "correct" sizing
4) power valve section wrong
5) (as stated) transition slots uncovered on one or both carbs
6) linkage mis-adjusted

undy,

Out of the six points you mention, the only one that makes any sense is number 3, which I will address next. The other points have been addressed.

[DanEC]

Originally Posted by Khobra

Dan and Undy,
Thanks for your input. Yes, idle mixture screws are somewhat sensitive but not like they should be. The throttle plates are nearly closed and yes, both carbs adjusted equally.

I have drilled small holes in the primary throttle plates which did help a huge amount but I don't want to go that direction in this case if I don't have to. I would rather take the air bleed restriction route.

The following may be a wild goose hunt as possibly I'm taking your comment out of context, but if your throttle plates are nearly closed you don't need to drill holes in your primary plates. Usually that was done on engines with a big cam and low vacuum because the primary throttle plate had to be opened excessively to get the engine to idle and they end up above the idle transfer slots in the bores - basically taking the idle mixture adjustment circuit out of commission.

You seem to have the opposite condition for some reason (throttle plate possible closed too far). Also, although I have drilled the throttle plate on one Holley before - it was before I discovered that most if not all 4-bbl Holleys have an adjustment screw on the secondary throttle plates. You have to pretty much remove the carb to access it because it's on the underside of the base plate. It's there for two reasons - first, to slightly crack the throttle blades open so they don't become wedged in the bores and won't open, and two, on engines with big cams and low vacuum the secondary throttle plates can be opened slightly more to pass more air at idle, allowing the primary throttle blades to be closed to where they rest in the middle of the idle transfer slots and the idle mixture screws will again function.

If you have a pretty healthy cam and your primary plates in the carbs are excessively closed you might experiment with increasing your idle speed or pulling the carbs and see if the rear secondary plates need to be closed slightly.

[olddog]

Originally Posted by Khobra

My problem is a rich idle. Running in my garage it burns my eyes. I've tried everything I know but can't seem to lean it out enough.

Anyone have any ideas?

I suggest you have it checked with a wide band O2 sensor and find out for sure what the AFR is. Burning too lean can cause NOX which burns the eyes, too. Too lean can be mistaken for too rich.

[undy]

Originally Posted by Khobra

Dan and Undy,
Thanks for your input. Yes, idle mixture screws are somewhat sensitive but not like they should be. The throttle plates are nearly closed and yes, both carbs adjusted equally. Spoke with a very knowledgeable individual at the race track today and I think he is on the right track. I need to increase the size of the idle air bleed restrictions. This will be my next step. I will drill out the current restriction and tap and install a screw in type.

Undy, did you have to play with this on your carbs?

My linkages are bang on, the power valves are 6.5. In the past, on other applications, I have drilled small holes in the primary throttle plates which did help a huge amount but I don't want to go that direction in this case if I don't have to. I would rather take the air bleed restriction route.
Hopefully I can do this sometime this coming week.
Will keep you posted.
BTW undy, what is your initial and total advance that you're running on your engine? I'm at 16 initial and 36 deg. total.

No, I gave QuickFuel all my engine specs; max RPM, displacement, cam profile and target HP. They custom built the pair. They were perfect as delivered.

16 degrees initial with 38 total.

[Khobra]

Originally Posted by olddog

I suggest you have it checked with a wide band O2 sensor and find out for sure what the AFR is. Burning too lean can cause NOX which burns the eyes, too. Too lean can be mistaken for too rich.

Thanks muchly for your input Olddog. I am also an old dog :-). This is definitely a rich condition. Will go back to square one and figure it out. When I do I will post how I went about this. You guys have been great with your ideas. Will continue to read this forum.

[Khobra]

Originally Posted by DanEC

The following may be a wild goose hunt as possibly I'm taking your comment out of context, but if your throttle plates are nearly closed you don't need to drill holes in your primary plates. Usually that was done on engines with a big cam and low vacuum because the primary throttle plate had to be opened excessively to get the engine to idle and they end up above the idle transfer slots in the bores - basically taking the idle mixture adjustment circuit out of commission.

You seem to have the opposite condition for some reason (throttle plate possible closed too far). Also, although I have drilled the throttle plate on one Holley before - it was before I discovered that most if not all 4-bbl Holleys have an adjustment screw on the secondary throttle plates. You have to pretty much remove the carb to access it because it's on the underside of the base plate. It's there for two reasons - first, to slightly crack the throttle blades open so they don't become wedged in the bores and won't open, and two, on engines with big cams and low vacuum the secondary throttle plates can be opened slightly more to pass more air at idle, allowing the primary throttle blades to be closed to where they rest in the middle of the idle transfer slots and the idle mixture screws will again function.

If you have a pretty healthy cam and your primary plates in the carbs are excessively closed you might experiment with increasing your idle speed or pulling the carbs and see if the rear secondary plates need to be closed slightly.

Dan,

I will start from scatch to make sure that all your points have been addressed. I may have made some mistakes. Will update you when I have conclusive results'

[Khobra]

So, after much digging I found that I had more issues then I thought. Long story short, had way too much oil to the top end. Was literally emptying the oil pan and loosing oil pressure. All the oil was at the top end in the valve covers.
Between my engine builder and myself we decided to go with the T&D rocker arm system and push rod oiling at build. This was my engine builders first use of said rocker system on FE engines. He called T&D for advise and got very poor directions. He decided that .125" restrictions were required for the rockers at the head oil ports.
After an accidental find that there was way too much oil to the top end I called T&D myself and was told that I need to plug the head oil port completely because we had decided on push rod oiling. Can't have both.
This issue has now been resolve and after some more fine tuning I have also eliminated the issue of rich idle by playing with timing. I was running 32 degrees total timing. I increased total to 37 degrees which made a big difference. Now runs much cleaner at idle. Didn't check initial, so don't even know what it is.
All is now good.

[undy]

Originally Posted by Khobra

So, after much digging I found that I had more issues then I thought. Long story short, had way too much oil to the top end. Was literally emptying the oil pan and loosing oil pressure. All the oil was at the top end in the valve covers.
Between my engine builder and myself we decided to go with the T&D rocker arm system and push rod oiling at build. This was my engine builders first use of said rocker system on FE engines. He called T&D for advise and got very poor directions. He decided that .125" restrictions were required for the rockers at the head oil ports.
After an accidental find that there was way too much oil to the top end I called T&D myself and was told that I need to plug the head oil port completely because we had decided on push rod oiling. Can't have both.
This issue has now been resolve and after some more fine tuning I have also eliminated the issue of rich idle by playing with timing. I was running 32 degrees total timing. I increased total to 37 degrees which made a big difference. Now runs much cleaner at idle. Didn't check initial, so don't even know what it is.
All is now good.

I'm running 0.060". The oil quantity is sufficient for my Ersons and there's no oil ponding.

It's always a plus to have a builder that's REALLY knowledgeable on FEs.
Right sized FE head oil restrictors is sort of "FE 101". O.125'" from jump street is waaay oversized, IMHO. Especially true if using a high volume/pressure oil pump.

[Khobra]

Originally Posted by undy

I'm running 0.060". The oil quantity is sufficient for my Ersons and there's no oil ponding.

It's always a plus to have a builder that's REALLY knowledgeable on FEs.
Right sized FE head oil restrictors is sort of "FE 101". O.125'" from jump street is waaay oversized, IMHO. Especially true if using a high volume/pressure oil pump.

Are you running push rod oiling as well?

[patrickt]

Originally Posted by Khobra

This issue has now been resolve and after some more fine tuning I have also eliminated the issue of rich idle by playing with timing. I was running 32 degrees total timing. I increased total to 37 degrees which made a big difference. Now runs much cleaner at idle. Didn't check initial, so don't even know what it is.
All is now good.

OK, you know, "eye burning" in the garage is a sign of too lean a mixture, not too rich. In a lean idle condition you do not get a complete burn and raw gas heads out the exhaust. That's why your eyes burn. Just thought I'd pass that along....

[Khobra]

Originally Posted by patrickt

OK, you know, "eye burning" in the garage is a sign of too lean a mixture, not too rich. In a lean idle condition you do not get a complete burn and raw gas heads out the exhaust. That's why your eyes burn. Just thought I'd pass that along....

Thanks Patrick,

By advancing the time there is more time to burn the fuel. Hence, a cleaner, sweeter smell. Assuming that the condition was rich, would you not agree?
Much has been written and posted about throttle plates exposing too much transfer port thereby causing a rich idle. The solution has always been to close the throttle plates a bit to limit fuel flow from the transfer ports at idle.
By advancing the timing I was able to close the throttle plates at bit and achieving my desired idle speed of approx 950 RPM in neutral and also giving the fuel more time to burn.

[DanEC]

Originally Posted by Khobra

Thanks Patrick,

By advancing the time there is more time to burn the fuel. Hence, a cleaner, sweeter smell. Assuming that the condition was rich, would you not agree?
Much has been written and posted about throttle plates exposing too much transfer port thereby causing a rich idle. The solution has always been to close the throttle plates a bit to limit fuel flow from the transfer ports at idle.
By advancing the timing I was able to close the throttle plates at bit and achieving my desired idle speed of approx 950 RPM in neutral and also giving the fuel more time to burn.

That sounds like a reasonable, thought-out approach to me. I've probably never had a car with a carburetor that idled lean so I wouldn't know if burning eyes is a sign of that or not. If it worked, it worked.

[patrickt]

Sounds good to me. After 40 years of adjusting carbs every which way you could think of, two years ago I tried a method recommended by an 80 year old ex-Ford mechanic and had used this method on my exact carb and my exact cam back in the early/mid 60's. The method sounds so goofy that I won't even bother to recite it here, but it absolutely worked better than my vacuum gauge or the "just guessing" method by backing the screws out the same amount.

[Khobra]

Originally Posted by patrickt

Sounds good to me. After 40 years of adjusting carbs every which way you could think of, two years ago I tried a method recommended by an 80 year old ex-Ford mechanic and had used this method on my exact carb and my exact cam back in the early/mid 60's. The method sounds so goofy that I won't even bother to recite it here, but it absolutely worked better than my vacuum gauge or the "just guessing" method by backing the screws out the same amount.

Patrick, I would love to hear about this method you speak of. Would you take the time to post please.