Tuning help please

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

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

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

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.

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.

midnightrider1818 said:

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

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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

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.

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

AR67GTX said:

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.

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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

Rebelrouser said:

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

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Cam specs

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.

Any idea what your fuel pressure is?

BSB67 said:

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.

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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.

Well I have a update, i put the 750 vaccum secondary on and im now running on the main circuit at cruise, looked at the 850 double pumper and there is alot more room from the idle hole to the transition slots, not sure how you would go about fixing that, i believe at cruise i was still running off the idle circuit if that is possible, ok on my 750 now that annoying pop thru the exhaust at about 3000 is back though. Afr looking good with about 12.5 afr, that pop went away with the 850, thinking it might be in my secondarys maybe, any help is appreciated
,

Popping through the exhaust is often a lean condition and sometimes caused by an exhaust leak at the manifold of head pipe allowing air to enter.

Looking at the bottom of your carb with the throttle seated on the idle stop, you want to see just enough of the transfer slot below the blades, to form a square. If too much is showing there is a set screw that adjust the secondary throttle plate opening. To reduce the transfer slot exposure, open the secondaries up the same amount you want the primaries to close, but don’t let any of the secondary transfer slot show below the blades.

I wish I knew more about double pumpers. I know they have 4-corner idle circuits and accelerator pumps. So you have 4 mixture screws to adjust. Same principle would apply to the amount of transfer slot appearing below the blades. It kind of makes sense the slot might be lower on the double pumper so that the blades can be closed more since you have 4 full idle circuits on it. The vacuum secondary carbs contribute a little fuel to the idle but mostly just to keep fuel moving through the bowl and not getting stagnant. Most of the idle fuel is coming from the primaries.

Just my thoughts. Lots of good Holley tuning info out there in the public.

Ok, I went back to the 850 double pumper, afr installed, timing backed down to 6 degrees and 34 degrees all in, afr about 13.5 to 14 at idle, problem is I would like to get my idle down some more but when I do there is such a gap from the idle circuit to the transition she runs lean at cruise speed, it has very low gears so barely off idle at 60 mph, how could I fix this, if I open the throttle blades a little more at idle she runs around 13.5 to 14 at cruise, I feel like the transition slots need to be a little longer or something, I have it where I can atleast drive it now but be nice to get my idle down, I feel like a little higher gear would cure the problem but dont want to go there yet

The only other thing that comes to mind is a vacuum leak pulling air into the engine at high vacuum causeing a high idle. Do you have PBs? If so I would temporarily plug it and check. Tighten the intake manifold bolts and make sure the carb mounting bolts are snug. Use an unlit propane or map gas torch around the carb base and the intake gasket edges to see if the engine picks up rpm anywhere. Check any vacuum hoses for split ends or cracking. Also double check your carb accelerator cable has enough play to allow the carb to close - although it seems you have verified it’s closed down at idle.

Going to 6* init timing is about the worst thing you could do. Low comp engine needs more initial timing, maybe 15-25* depending on the cam. Using 6* init timing makes the engine very inefficient & requires more throttle opening. You are probably running out of transfer slot for cruising because of the low timing.
Try 18-20* initial timing [ reset idle speed & mixture ] & test drive just for cruise. You will notice a BIG improvement.

The secondary butterflies on that 850 have an adjustment screw. It's located on the underside of the baseplate on the passenger side of that carb.
Lower the secondary butterflies to lower the idle without touching the primary idle screw.

You're getting some great advice and questions where it would be good to see your thoughts on. I think the main question is what @BSB67 (#11) was getting to... what is the issue you're experiencing at cruise that gives you the impression you're lean? I know the AFR says 14+, but some engines like 14, esp. at cruse. If you didn't have the AFR, would it be performing in such a way that would concern you?... And if so... share that here with this group. These guys are gurus... but they need info.

My $0.02... That's a really, really mild/small cam (213 @50) with very little overlap (LSA 111*), so you're probably pulling a lot of vac, especially at cruse. Depending on how you've set your idle circuit, that can be leaning you out. Check out @Geoff 2 post #2. I would also backup @Geoff 2 in post #18... you have way too little initial timing... I'd set at 22-25. As far as all in... you haven't (or I missed it) said the RPM at cruise. Based on how your describing, my gut says at 60mph you're around 1800-2000? IF so, I very much doubt your timing has come all the way in from 6* to 34*... so your base is 6* and 2000 at cruse, assume 25*? At that point your vac is high and you're basically pushing a portion of the combustion into the header, which will overheat and can cause lean read condition. Moreover, the slightest exhaust leak will let O2 in and cause popping as RPM increases.

If I was there standing in front of your car... I would tighten up the idle mix, put a more initial timing in, do a sweep check for total timing to 37*, check for vac leaks, check for exhaust leaks, and then test drive... repeat.

As far as jets, airbleeds, pumps, squirters, cams, etc. I try to look at a carb through 5 lenses... Idle, cruise, tip-in, 50%-75%, and full. Different circuits will come into play more than others in each "phase". The way you're describing here... I wouldn't even be bothering with the secondaries at this point the process. One last thing.. I would pick one of the carbs and stick with it through the process. Going back and forth between the 850 and 750... is causing more bad than good. Based on that cam and RV compression ratio, I would think the 750 would be a good place to start, but that's a total guess... pick the one that is in better shape! Worry about too little or too much CFM later.