Tuning help please

[midnightrider1818]

Ok 73 charger 440, late model rv engine so not much compression, mild cam with a edelbrock performer rpm intake, holley 850 double pumper on top, around 36 degrees of timing in her, 3.23 gears or lower gears in her, I can get my idle air mixture at about 13.5 but at 60 mph I am extremely lean, 14.5 to 15 on afr, I feel like I am running off the idle circuit still as my throttle pedal is barely pushed down, if I crack the throttle a little more my afr will go down to 13.5, I also have a 750 vaccum secondary I was running on it before the adr but had a miss about 3 grand, once I put the 850 on that went away so im sure that miss was in that carb but could put it back on if that would be a better choice, not sure how to go about this, its a 850 holley double pumper 4 corner Idle, any help is appreciated, 60 mph with barely any throttle im very lean

 

[Geoff 2]

I would try this: screw in & seat the mixture screws in the secondaries. Then, re-adjust the mixture screws on the primaries & test drive.

 

[71Beeper]

Check the power valve rating - you may need to go to a higher rated one to have it kick in sooner.

 

[AR67GTX]

So as I understand your concern, it’s is the lean AFR at a 60 mph cruise. At 60 mph with a 3.23 rear I would think you have to be into the main fuel circuit even if you don’t think the throttle is depressed much. I don’t have any double pumper Holleys and I suppose that since you are cruising on all 4 barrels the throttle blades don’t have to open as much and you might still be on the transition fuel flow circuit. If so I think going back to a vacuum secondary carb might work best. Sounds like you could try increasing the jetting size in all 4 bores since it’s a mechanical secondary carb and see if that does the trick. Is this an auto or stick?

My 2 cents.

 

[bigbluedodge]

The 850 is a lot of carburetor for what's in your engine. What size are the primary main jets? At 60 mph you probably are in the transition between the idle circuit and the mains. Seems like either the idle mixture or the mains should be slightly richer.

 

[Rebelrouser]

Ok 73 charger 440, late model rv engine so not much compression, mild cam with a edelbrock performer rpm intake, holley 850 double pumper on top, around 36 degrees of timing in her, 3.23 gears or lower gears in her, I can get my idle air mixture at about 13.5 but at 60 mph I am extremely lean, 14.5 to 15 on afr, I feel like I am running off the idle circuit still as my throttle pedal is barely pushed down, if I crack the throttle a little more my afr will go down to 13.5, I also have a 750 vaccum secondary I was running on it before the adr but had a miss about 3 grand, once I put the 850 on that went away so im sure that miss was in that carb but could put it back on if that would be a better choice, not sure how to go about this, its a 850 holley double pumper 4 corner Idle, any help is appreciated, 60 mph with barely any throttle im very lean

View attachment 1938464

Even with a mild cam you may have too much overlap killing cylinder pressure. Run a cranking compression test, if it is below 130 lbs average for all the cylinders cam is too big. Next for best tuning on a Holley you need one that has replaceable air bleeds or maybe go to the trouble of drilling and tapping a cheaper Holley for air bleeds. I have had luck in reducing the idle air bleed diameter a few thousandths to help with problems like you describe. I don't like to mess with high speed air bleeds unless the engine is on a dyno, but it can be done as well if you use an air fuel meter which from your post you have.
So if you decide to buy a different carb get one with replaceable air bleeds, I would stick to around 700 cfm

 

[Bird 426]

Power valves probably have something to do with it. Double Pumper, 2 PV's? This sounds dumb, but my Sixpack richens up by going from a 160 summer thermostat to a 195 for fall and spring. I probably wouldn't go drilling out air bleeds unless you are that kinda guy. If you were good at all that, you would not be asking here.

 

[RemCharger]

850 carbs came stock even on the lowest of po 440s.

 

[midnightrider1818]

So as I understand your concern, it’s is the lean AFR at a 60 mph cruise. At 60 mph with a 3.23 rear I would think you have to be into the main fuel circuit even if you don’t think the throttle is depressed much. I don’t have any double pumper Holleys and I suppose that since you are cruising on all 4 barrels the throttle blades don’t have to open as much and you might still be on the transition fuel flow circuit. If so I think going back to a vacuum secondary carb might work best. Sounds like you could try increasing the jetting size in all 4 bores since it’s a mechanical secondary carb and see if that does the trick. Is this an auto or stick?

My 2 cents.

Yes, 60 mph she is lean. Throttle blades are barely open, it may even be a lower gear then that, im stock right now on the carburetor, 80 mains front and rear with 6.5 power valves front and rear, trying one step at a time to get it dialed in

 

[midnightrider1818]

Even with a mild cam you may have too much overlap killing cylinder pressure. Run a cranking compression test, if it is below 130 lbs average for all the cylinders cam is too big. Next for best tuning on a Holley you need one that has replaceable air bleeds or maybe go to the trouble of drilling and tapping a cheaper Holley for air bleeds. I have had luck in reducing the idle air bleed diameter a few thousandths to help with problems like you describe. I don't like to mess with high speed air bleeds unless the engine is on a dyno, but it can be done as well if you use an air fuel meter which from your post you have.
So if you decide to buy a different carb get one with replaceable air bleeds, I would stick to around 700 cfm

Cam specs

 

[BSB67]

14.5 is not way lean. Many folks target 14.5 for no load cruise.

Is there a problematic symptom that you are trying to fix? If so, maybe describe it.

And, you are not cruising on all four barrels like someone posted. It cruises no differently than a VS carb.

 

[Bird 426]

Any idea what your fuel pressure is?

 

[AR67GTX]

14.5 is not way lean. Many folks target 14.5 for no load cruise.

Is there a problematic symptom that you are trying to fix? If so, maybe describe it.

And, you are not cruising on all four barrels like someone posted. It cruises no differently than a VS carb.

Like I said I don’t own any dual pumper, mechanical linkage Holleys. How are they linked? Is it a progressive mechanical linkage such that the rear plates open later than the front and open faster so all reach full open at the same time? A 1:1 linkage was all I could come up with to imagine the car running on the transfer slot (minimum throttle) at 60mph.

6.5 power valves are not your problem with that cam if you are running at 12-13 inches vacuum. You don’t want them open at a highway cruise speed condition.