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what course of action is indicated? |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6761 |
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Here is a link to an older article:
This has the holes drilled into the Primary butterfly's that I did not recommend doing. PHAT69AMX has more information on specific carburetors, but the basics of setting idle are in the article. Setting the Primary butterflies is crucial to have your idle circuit working properly. As the article also states you should be running your Primary circuit rich, especially on that massive intake. All the Mopar's were set quite rich on the primaries and idle circuits. After reading the reply above, the newer carburetor may not be an option of cracking open the Secondary's without having fuel flow. Don't know about these. I like the idea of running without the Secondary's to do an initial tuning, but the Primary butterflies and idle circuit have to be set up before adjusting your Primary jetting. At least on the older 4160's.
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bikerfox
Moderator Group Joined: Aug/02/2009 Location: USA Status: Offline Points: 4418 |
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Thanks for your insights, Phat. Yes, they are 9776s--right on with that! Interesting info with the "...very small secondary Main Air Bleeds..." A buddy who's familiar with the carb issues wants to take off the secondary plates and etc...and blow air through the secondary bleeds to see if the air is getting through the passages of the carb w/o any blockages...but maybe we're just seeing as you mentioned, "small bleeds." I had a thought to use the correct sized drill just to simply push it through the bleeds to make sure there's no blockage as well. Oh, and I just have to bring up... has any adjustment at all been done to the Secondary Idle Speed Screw adjustment ?... Not to my knowledge, as they didn't remove the carbs. There's a lot to it... sounds to me like I would not let those guys tune my Holley carbs at all. imho I can tell from what's already posted they don't know what to do with those Holley carbs. You need to find some older well experienced person with Holley carbs that actually knows what they're doing. Funny you say this as this place is a nationally known dyno shop that dynos a substantial number of engines (and chassis dyno) for big name guys and tv productions. Disconnect / removed the simple small primary to secondary linkage interlink rod on the drivers side of both carbs. Then do a pull running only the Primary side of both carbs and see what the mixture does. I'm unclear as to what the outcome would be and what I would do with that info.
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6761 |
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Disconnect / removed the simple small primary to secondary linkage interlink rod on the drivers side of both carbs. Then do a pull running only the Primary side of both carbs and see what the mixture does. I'm unclear as to what the outcome would be and what I would do with that info. What he is trying to do is get the engine to run properly with 2x 2 barrel carburetors. If you can get the engine to run with reasonable idle and good acceleration on the Primary's, then the Secondary's are the bonus that should be relatively easy to jet. You don't really care about the AFR, 3600 to 4000 RPM as long as it's rich and runs well on this intake. Once the Secondary's kick in the engine will go to it's maximum efficiency and start to lean out, and that's exactly what it's supposed to do. The dyno shows a short rich to lean curve on the Primary's and also it's stated the Primary jetting was used to fix a rich idle. That indicates the Primary butterfly's are too far open at idle. This is not the way to set these carburetors. It also shows Secondary's not leaning out as RPM increases. Well not the older 4160's at least and certainly not the way we used to set up Mopar's with similar intakes. The subtilty of changing air bleeds for fine tuning, I've never play with.
Edited by Trader - Apr/06/2021 at 8:14pm |
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5904 |
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To back up... it is going rich at rpm, correct ?...
Edited by PHAT69AMX - Apr/11/2021 at 12:56pm |
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67 Marlin
AMC Addicted Joined: Feb/21/2015 Location: Minnesota Status: Offline Points: 876 |
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If you want to dyno tune for max power based on AFR, a simple way is to square the jets and put a blank power valve in. That's your high speed circuit, and since it's WOT, all barrels are open with equal jets, so less tinkering. Find best power at say 4000-5000rpm or whatever your top-end WOT is. If smaller jets make less power, then go the other way. Then, if richer or leaner on one end of the WOT range, you can play with the air bleeds and see if that flattens it out or even bumps power along the whole range. I learned smaller or bigger bleeds don't always have the intended effects, so experimentation. The bleeds are for fine-tuning the curve, but it's the least tedious thing because you don't take the carb apart, and they screw right in. You can go up a size at a time or swing for the fences with 5 or 7 sizes to see what end of the curve they effect.
You'll need to drop the primary jets after, say 8 sizes and reinstall the power valve. Ideally the combo of the primary jet size and power valve channel restrictor will be equal to the AFR of the squared jets at WOT. That means more dyno testing, or buy an AFR gauge if you haven't already. Possible to maximize fuel efficiency while cruising and WOT power. After you know your max power with squared jets, if you don't have an AFR gauge, you could do timed runs with the stopwatch from say 3500 to 5500. Find the smallest primary jet with big enough PVCR to match the squared performance and it should consume less gas while cruising. I think idle and especially transition tuning is way more tedious than WOT tuning, and not nearly as fun.
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PHAT69AMX
AMC Addicted Joined: Jul/07/2007 Location: West Virginia Status: Offline Points: 5904 |
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In the 1989 edition of the Holley Illustrated Parts & Specs book for List 9776 it says :
"465 CFM Universal Off-Road Carburetor".
Edited by PHAT69AMX - Apr/10/2021 at 10:52pm |
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Boris Badanov
AMC Addicted Joined: Dec/14/2013 Location: NH USA Status: Offline Points: 4209 |
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What model number Holleys are you using? |
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Gremlin Dreams
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bikerfox
Moderator Group Joined: Aug/02/2009 Location: USA Status: Offline Points: 4418 |
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It's just like Phat's post above yours: 4160/9776
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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Boris Badanov
AMC Addicted Joined: Dec/14/2013 Location: NH USA Status: Offline Points: 4209 |
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Ok, here's my spin on the issue.
I still feel that unless you are running at high engine speeds all the time, just drive it and enjoy it. I suggest the issue has to do with that huge plenum and the poor intake "signal" that comes with it. Very poor at low engine speeds. Jetted to be correct at lower engine speeds as engine speeds increase the signal becomes strong and it goes rich. I do not have a clue how to tune that issue out. But I can tell you that having seen hundreds of Harley and Harley Davidson based engines on the dyno that power does not really go away till you get to 10:1 fuel air. They smoke a bit and 13:1~ typically makes the best power. Pushing the compression up in the 14:1 range makes an engine more sensitive to being overly rich. I could say that I am a confirmed Holley hater and toss a pair of 600 Carters on it, but as I see it your rig is making EXCELLENT power and the issue is well out of the normal driving engine speeds. As a comparison in big radial airplane engines fuel air ratios are in "auto rich" settings and are typically in the 10:1 range for take off. Best max power is in the 12:1 range. As I see it you have no problem here unless it is running like pooh. |
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Gremlin Dreams
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bikerfox
Moderator Group Joined: Aug/02/2009 Location: USA Status: Offline Points: 4418 |
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Thanks, Boris, for your feedback.
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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