Hello all I need your wisdom. I would like to install this carb on my blown french flathead so I started to take it apart for cleaning. Maybe someone could identify the carb and tell me on what engine sizes it was used. This will give me an idea if it could work as is or if I need different jetting etc... Any advice is welcome, I never played with this sort of carb but know my 97 Strombergs quite well. Thanks!
Google https://www.carburetion.com/CarbNumber.asp?Number=R6979 https://minuit10.net/EngineCode/holley/holleyCasting4.html '73-'74 motorhome 600, I saw a thread that said they have dual powervalves, looks like it in the schematic. Mike
Yeah...pretty simple...Google is your friend !! The answer is right there on the choke horn. Right there in plane view, 4th page in the Holley list number chart. Mike
The secondary metering plate shows that it is a 4160 with only one power valve. 4150’s had secondary metering blocks with some having power valves, some not.
Pic shows a dual-stage power valve, typically used on large trucks, buses, motorhomes. Not dual power valves.....dual stage means they have a stepped opening point and smaller than normal power valve fuel openings so the valve itself can act as a restrictor at mild throttle, like climbing a small hill where it only needs mild enrichment, without having the power valve go full open like a normal single stage valve and being badly over-rich as a result. Trying to use old OEM carbs as a performance carb usually doesn't end well, especially with these large ch***is type OEM Holley'. Air bleeds, idle feed restrictions, jetting and power valving orifices will all need changing/modifying...get your small drill index ready #61-80 sizes. You'd be better off to just buy a actual performance model carb, especially on a blower application. This OEM carb is going to give you fits unless you are very well versed in exactly how each fuel circuit in a Holley carb is configured and timed to the other circuits.
Thank you Eric, just what I need to know. I will probably sell the thing and get a better carb. What will you all suggest? I could fit my two 97 Strombergs and go from there. To adjust those could be easy as I have made several jets and have an AFR meter.
Holley carbs are the easiest ****in carb in the world to calibrate. The hardest thing about Holleys? Cleaning the old gasket off. 2 97s are good for what, 350 CFM? Now you have a huffer at the party trying to jam more displacement into the engine. Considering displacement is the prime measure of CFM requirement this little pre-calibrated 600 might serve you well. I'd leave the OEM block in place for primary and fiddle-**** the secondary side and power valve for full tilt boogie needs. New Holley carbs look like *** on old engines. That's just my opinion. Don't forget to rub some Chapstick lip balm on the gasket surfaces before you re***emble. Stops the need for s****ing and new gaskets when you tune. Show of hands, who else knew the Chapstick trick?
I like the ChapStick trick. I will put a tube of it in my toolbox. I recently went through an intense round of carb tuning and quickly went through several base gaskets. I started rubbing grease into the gasket on both sides. Worked great. But I like the ChapStick idea better. Do you use it on the blue gaskets., too?
I just routinely coat all carb gasket surfaces with it. I used the same carb gaskets for 2 seasons in my bracket racer. Then I learned to leave it alone, ET and MPH didn't matter as much as consistency and white shoe polish (non-bracket racers scratching their heads now, "WTF does shoe polish have to do with it?").
I am this many years old of learning the Chapstik trick. Lord knows I have a bunch of them around....
The twins would be happy! lol. Or was it Suzy? Anyways, never heard of that before. Good info on the chapstick edit: the twins were double mint gum I think. Oh well…
Knew of chapstick in the 80s. Holleys are easy if you have cut your teeth on them and hopefully started with a HP version that has all the stuff replaceable. Just like the guys that say Early Bosch FI is simple, but forget the cold enrichment, special tools and how a little dirt in the wrong place messes with things.
I always preferred a Holley over anything else. If I had a problem at the track, the pit-supply truck would have what I needed and it took minutes to change whatever it was. They were easy to drop the float bowls and clean the crud out of them.
Forgive me - this is the first Holley that I work on but I am not getting anywhere. I am in the process of tuning this carb but there must be something wrong and I could not find it: I set the floats to have gas just bellow the checking hole thread, it sloshes out when I move the carb. Fuel pump is putting out enough pressure, the float valves shut off precisely. The idle air bleeds are around 0,05". I have adjusted the ****erfly to just have a square end of that slot visible. The secondarys are adjusted the same. When I start the engine from cold I have to work the throttle until it fires. That ****erfly adjustment does not work at all, I have to adjust the throttlestop much further in before it will somewhat idle. It runs very rich the first few seconds but gets lean within the first 30 seconds or with choke fully open. If I cover most of the airhorn I can hold it running but roughly. As soon as I remove the cover it backfires and stumbles and dies. So I looked for a solution to richen the idle up as it is not reacting to the mixture screws. I found a hint somewhere that inserting wire into the idle air bores will rich it. I inserted 3 wires each, thereby reducing the bore. No difference so I added 2 wires more. The bore area was now reduced to around 60%. It did not help much in my case. What else can I do to richen the idle to make it adjustable and stable? Ignition is set at 4 degr btdc fully retarded. No vaccuum connected. When engine is blipped the acceleratorpump is quite rich, AFR goes down to under 10 - but once throttle is closed and gas is used up the AFR is fast approaching the other end of scale at 20 and engine dies after a couple seconds.
The way I do it is as follows. First, get it running and warmed up. You can't set up the cold enrichment (choke) first, it must be set up after warm idle is set up. Make sure the engine is running properly. Firing on all cylinders, good, steady vacuum, no vacuum leaks and no other issues. A good carb on a bad engine won't adjust the problems away! Once warm, set idle speed as close to desired as possible while still running smoothly. Check timing if you are close to desired idle, this will affect idle speed. Adjust as needed. Now, adjust idle mixture. Most of the time, this should be roughly 1-2 turns out from lightly seated. This may require adjusting speed, then mixture, then speed again. Always end with mixture. A typical speed is 700-900 unless you have a big cam, which will require a higher idle. If you are running an automatic, check idle in Park and Drive. Most tend to drop 100-200 RPM in Drive. The engine torque and the torque converter affects this amount. A stock powerglide behind a 283 can drop 300 RPM, a high stall converter behind a torquey big block might only drop 75 RPM. Once you have the engine idling at the desired RPM and it is smooth, recheck timing. Make sure the carb mixture is adjusted, the transfer slots are not pulling fuel and there is no dripping from the boosters. If it is content to idle (both Park and Drive if auto), shut if off and try restarting without touching the accelerator. It should fire off easily 30 seconds after and 5 minutes after. Keep adjusting until this is achieved. Now that it runs well warm, you can set up the choke to enrich the cold start operation. While still warm, you can set fast idle by lifting the fast idle cam and setting the idle speed on the cam to 1500-1800 RPM warm. Some may be as high as 2200 RPM on the top step of the ramp. NOTE: this following part may need to be repeated a few times, which means another overnight cool off. In the morning after it's cold soaked overnight, open the accelerator fully, watching for accelerator pump squirt. The choke should close with spring tension, but at full throttle, open up slightly. This is Clear Flood, meaning that when starting cold, if it has got too much fuel, opening the throttle fully adds more air. This also should cause the choke linkage to pull up the fast idle cam, increasing the idle speed when cold. Now try starting. It should start with one or two tries. Most have a choke pull off that once the engine starts opens the choke. This has a measurement spec in the rebuild kit or book. You can use a small ruler or drill bits to measure this gap. This can be adjusted by bending the linkage between the vacuum pot and the choke linkage. This must be set! The choke should be adjusted to rich or lean to current temps. Idle speed cold will be lower than the fast idle speed set before when warm. You can adjust this to the user's style so it doesn't die. Some want to take off as soon as the oil light turns off! Others will wait a few minutes to drop it into gear and ease away. Note that there is a ramp for first start (choke fully closed) and once the car starts and the pull off is opening the choke, the next step down on the ramp (lower idle) is used. Watch the choke open as the engine warms up at the choke spring relaxes. It should be fully open in 3-8 minutes unless it's very cold. I had one customer who had a mid 70s smogger engine and wanted to be able to get in, hit the gas once, fire it up and roar away. He had his reasons and was understanding that this would require a lot of fiddling. He left he car for a month in the shop. When he came back it did what he wanted and he was thrilled. It took a week's worth of trying to get it good, and another couple days to confirm it. Each morning, it was the first thing touched for a good 15 minutes. Someone who would allow for a longer warm up and maybe a couple starts and stalls would be adjusted first time. You mention A/F ratios, so I'd guess you have access to a gas ****yzer or a wide band (???). I would use this to get the warm idle mix right, but never use it to check cold start. That would just clog up the filters on a ****yzer and a wide band isn't up to operating temps at first. The mixture also changes a bunch during those first few minutes.
I’ll throw this out there FWIW, that List Number, 6979 caught my eye right away. Holley had an “emissions” carb, number 6919, that had reverse idle mixture screws and I wonder if your 6979 might also have used the reverse idle circuit. The fuel orifice was fixed, only the amount of air could be adjusted and you turned the mixture screws the opposite way from a standard Holley to adjust the mixture. Turning the screws in will richen the mixture. You might try removing the wire restriction you added and try adjusting the mixture screws again, this time starting rich with the screws all the way in and backing them out for the lean, best idle and highest vacuum reading. In looking around on the ‘net today I found a mention that the idle screws in the 6919 had a different appearance (I think they are referring to a different taper) so that may help to determine if your carb is reverse idle. I may be way off the mark here but it won’t cost anything to check the idle mixture for reverse adjustment. Conventional mixture screw from an 1850 Holley-
Interesting observation: I tried the two 97 Strombergs and could not even start the engine as they were way too lean. I had to close the chokes completely and put several squirts in before I got a cough. Once started I had to cover up both carbs 3/4 to keep the engine running at all, no idle possible. Yet they work perfect on my unblown engine which is the same engine. Only change is on this engine the exact same cam but with 0,04" more lift so almost no timing change but a bit accelerating of the valves. Rodsrace: Thanks for the reply - here is further food for thoughts: the AFR meters are in each exhaustpipe about 20 " away from the block. They are heated so I don´t need to wait for a warm-up. I don´t need the AFR meters as I would see black smoke exiting the headers once the adjustment allows to go rich. As long as the airhorn is almost covered, I can make it smoke black and run too rich. The AFR meters show this as the dial finger reads around 10. Once the covering is removed, the AFR meters show that it goes lean, the right side fluctuating more than the left side. I don´t know why the dial fingers move around between 15 and 20. This might indicate a dirt particle blocking and freeing a p***age? I had the carb apart several times but did not find anything. Had it running again for a short time and looked into the airhorn and noticed the squirter area was dropping fuel into the throat on both sides - almost very regular - this can´t be normal? I guess this kept the engine running.... Fordors: my mixture screws look a little bit different, I will take a pic tomorrow. But the engine does not respond in any way when turning the screws in or out. Next I will try to raise the fuel level. This carb does not have a conventional power valve but a springloaded ball valve that could be adjusted. When I open up the throttle, the squirters shoot a (too) large amount into the throats, the engine revs instantly and blows black smoke. So I guess I could use this thing once the overly lean idle is solved. Keep your ideas coming, would love to get this puzzle solved as the hight of this carb would allow me to keep the blower and carb, airfilter under the hood. Cannot do this with the Strombergs as I would need to cut the hood etc which will need a lot of explaining to the german authorities...
As said, the tailpipe monitors will not be happy with choke or heavy rich or bad misfire! You are going to plug up the inlet filter. Don't use that until the engine is warm and running on all cylinders fairly happy. I did testing for 15 years, so this isn't a backyard opinion. A lean misfire will make the AF meters move a lot. CO is going to be hit and miss when misfires happen, HCs are going to be through the roof. Sounds like the carb is not happy at all right now. Will it run okay at around 2k RPM warm (main circuit)? If so, it's idle circuit or a leak somewhere leaning out the mix. If it still runs poorly, that carb needs to be gone through or replaced, whichever is easier for you, and still check for any vacuum leaks. EDIT: The height of this carb will be the same as ANY 4160 Holley with a choke. That isn't a factor to keep this one. Also, another poster mentioned this is not a great start for a performance setup. Saying it's going on top of a blower doubles that sentiment! 4160s fit better when paired due to a metering plate rather than a secondary metering block and also the float bowl inlets on center hung bowls. Are you using a pair? Only a single 600 CFM stocker setup on a blown motor? What is the engine combo? Also remember, this carb is a mid 70s motorhome application, so it's expecting a mild cam with a fairly strong vacuum signal. Is that rear base screw (top of picture) fully seated? Does that PCV vacuum p***age at the rear of the base get sealed by the gasket and manifold and capped if not connected?
RodStRace: First of all, the thing almost idles now reliably. I have the carb into pieces again to find out a bit more about the idle circuit. I checked the metering block but all p***ages are clear. Then I looked at the ****erfly plate to see how far open the ****erflys are when the engine is idling. Don´t think that the blower below needs a much bigger opening of the ****erflys to keep the engine idling than a normally aspirated engine but if so, so be it. Maybe this is the reason for the weak signal on the idle? I found the carb might be missing a hole for the idle gas? Have a look at the picture with the arrows - there you see the missing hole. I might drill it to give that ****erfly a gas feed as well. I could also drill the ****erflys with a small hole to be able to close the ****erflys a bit. What do you wise men think? Picture of mixture screw shows what is fitted in my carb. The screw is connected to the barrel inside the carb so it adds air when opening it. Thus it will be rich when screw is seated.
I don't have enough experience with Holleys to diagnose a particular example pictured. Before drilling holes, work with what you have. That jet in the center isn't something I remember. Can't spot it in the drawing posted earlier, either. https://www.carburetion.com/CarbNumber.asp?Number=R6979 I think of blowers as just like another belt driven accessory at idle. It's going to take some power to spin so it drags the RPM down a bit, but won't cause a huge difference in airflow (and fuel) demand at idle. Kind of like an auto in gear, you don't need a full turn of the idle screw to keep up. It's not pumping 2X the air for the same RPM at idle unless the blower is REALLY tight, like getting hot tight.
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