74monacoHT
Member
Interesting. How badly would it run if it jumped a tooth? Seems like the kind of thing that would make it run *really* bad or fail altogether.
Hesitation when first putting foot on gas.
- Thread starter 74monacoHT
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jimmyessbee
Member
This makes me think of a '66 imperial I bought when I was 15 -- 1989 or so. Drug it home and put a battery in it. New gas. Had spark. Thing just wouldn't fire. Finally checked compression and it had 0. On all cylinders. Pulled a valve cover and the valves were moving. Pulled the timing cover and the timing chain had jumped just the right amount. Had no money so put it back how it should be and buttoned her up. Fired right up. And ran for a few minutes.
You increased timing to 25 BTDC??? If it is the warping airhorn problem, a carburetor kit regular rebuild will not solve the problem.
Usually, it takes about 9"Hg to activate the vac advance. The ported vac port should have a good bit less than that. Idle speed should be closer to 700rpm. Check the emissions specs decal under the hood.
When the air horn warps, fuel economy will drop significantly. Very similar in amount to if the vac advance isn't working . . . whether driving in town or on the highway. The choke plate should hang a bit on the air horn as it closes, which will leave a shiny spot on the air horn. No measurements are known to exist, but using a straight edge to look for warpage is all that's needed. You can use two air horn gaskets rather than one, as the one in the TSB kit was thicker and softer than the orig gasket supplied in the carb kits back then. Best to look for clues that it IS warped before disassembly.
When the air horn warps, fuel economy will drop significantly. Very similar in amount to if the vac advance isn't working . . . whether driving in town or on the highway. The choke plate should hang a bit on the air horn as it closes, which will leave a shiny spot on the air horn. No measurements are known to exist, but using a straight edge to look for warpage is all that's needed. You can use two air horn gaskets rather than one, as the one in the TSB kit was thicker and softer than the orig gasket supplied in the carb kits back then. Best to look for clues that it IS warped before disassembly.
Loadrunner
Active Member
Hesitation = lean.
To me this particular Holley is an abomination, I've switched one out for the older 383 Carter 2V with great results. The Carter is a fine carb, the Holley should be permanently disabled with at least a 10lb sledgehammer.
74monacoHT
Member
Update: It appears the vac advance is bad. No effect when I connect to constant vacuum.
The advance is probably not actually 25, so I guess something has moved. I usually tune timing by ear anyway. No pinging when you step on it. Cold start was perfect this morning. Didn't yet drive to check for hesitation.
74monacoHT
Member
I'm guessing this gap here is from warping. Does the carb need to come out or can I just remove horn (2 barrel). It looks like several Philips head screws holt horn on. I have a new gasket and will un-warp. Screw hole in middle of horn seems to be stripped as well. I assume a previous owner attempted to fix it by tightening...
Looking at it, I don't think this is all the fault of owners overtightening. The air filter housing is heavy and has a LOT of leverage on that attachment point while it vibrates or wobbles as you drive. Bad design as others have said.
Looking at it, I don't think this is all the fault of owners overtightening. The air filter housing is heavy and has a LOT of leverage on that attachment point while it vibrates or wobbles as you drive. Bad design as others have said.
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Triple Pickle
Senior Member
That’s it.
74monacoHT
Member
As a few of you suspected, there it is. So I have two or three issues. Warp, bad vac advance, and my timing mark is out of whack. No big deal on the third. I'll get to work on the other two. Thanks all for the replies!!
Loadrunner
Active Member
12 pounder is perfect.
Having spent a fair amount of time in my permanent assignment as an engineer in Chrysler's fuel systems lab in Highland Park, Michigan, I had the opportunity to evaluate especially the Carter and Holley brands of carburetors and knew both of the reps from those companies stationed directly in our lab on a full time basis. The Carter rep was Jim Pettis and the Holley one was Gary Congden who were both good friends of mine and I went out to lunch with both of them on a regular basis.
From my perspective and experience with both of those manufacturers, it was clear to me that at least when new, Holley carburetors just had more quick and uniform throttle response than the Carters, especially off the line and part throttle that gave a better performance feel overall. The Holley 4 bbls in the early 70s were especially excellent performers when new.
Their Achilles Heel though was that they were much more complex than the Carter 4 bbls for example with some intricate metering blocks in the center of the carburetors and they were also especially heavy units in comparison to the Carter AFB, AVS, etc models and therefore were more expensive to manufacture. So given the need to compete with the more simple and lighter Carter carburetors, Holley resorted to using casting materials that were not durable over time and more easily warped, both the 2 bbls and the 4 bbls. I was a student engineer in 1969 and 1970 and as such was able to afford getting a newer vehicle finally in 1972 and found my avatar car 1970 Chrysler 300 coupe as pictured at left on a Birmingham Chrysler-Plymouth used car lot and bought it on the spot - I just loved the colors on that car. Having only 29K miles on it, I was able to enjoy that car a lot but never used it in the snow back there and drove a beater 4 door 1966 Plymouth Fury sedan as my "salt car".
Anyway, after accumulating some 50K miles on the 300, my Holley 4 bbl started giving me problems so I tore it down and rebuilt it with a new carburetor kit, but that didn't help at all. So I asked Gary about it and he immediately told me to sit down and wait a minute and he brought out of the storeroom a brand new one (a 4160 model I believe it is). He said "here is your only real solution". He well knew the issue and I expect that is why the company no longer used that 4 bbl more than another year as I recall and then the Carter 4 bbls were the only 4 bbl. option on the V8s (the Carter Thermoquad 4bbls with their plastic fuel bowls also created some problems though).
My avatar car now has 205K miles on it and the drivetrain was pretty much rebuilt not too long ago - it is my favorite car of all time, although the 71s are just as desirable to me with a little better interiors in them. I mention this because Gary's assigned car that he got to select was a 1971 Chrysler 300 coupe in Tahitian Walnut and we went to lunch in it regularly that year - that car to me was just perfect in every way, both styling and engineering and that is why I have so many of them now - crazy
From my perspective and experience with both of those manufacturers, it was clear to me that at least when new, Holley carburetors just had more quick and uniform throttle response than the Carters, especially off the line and part throttle that gave a better performance feel overall. The Holley 4 bbls in the early 70s were especially excellent performers when new.
Their Achilles Heel though was that they were much more complex than the Carter 4 bbls for example with some intricate metering blocks in the center of the carburetors and they were also especially heavy units in comparison to the Carter AFB, AVS, etc models and therefore were more expensive to manufacture. So given the need to compete with the more simple and lighter Carter carburetors, Holley resorted to using casting materials that were not durable over time and more easily warped, both the 2 bbls and the 4 bbls. I was a student engineer in 1969 and 1970 and as such was able to afford getting a newer vehicle finally in 1972 and found my avatar car 1970 Chrysler 300 coupe as pictured at left on a Birmingham Chrysler-Plymouth used car lot and bought it on the spot - I just loved the colors on that car. Having only 29K miles on it, I was able to enjoy that car a lot but never used it in the snow back there and drove a beater 4 door 1966 Plymouth Fury sedan as my "salt car".
Anyway, after accumulating some 50K miles on the 300, my Holley 4 bbl started giving me problems so I tore it down and rebuilt it with a new carburetor kit, but that didn't help at all. So I asked Gary about it and he immediately told me to sit down and wait a minute and he brought out of the storeroom a brand new one (a 4160 model I believe it is). He said "here is your only real solution". He well knew the issue and I expect that is why the company no longer used that 4 bbl more than another year as I recall and then the Carter 4 bbls were the only 4 bbl. option on the V8s (the Carter Thermoquad 4bbls with their plastic fuel bowls also created some problems though).
My avatar car now has 205K miles on it and the drivetrain was pretty much rebuilt not too long ago - it is my favorite car of all time, although the 71s are just as desirable to me with a little better interiors in them. I mention this because Gary's assigned car that he got to select was a 1971 Chrysler 300 coupe in Tahitian Walnut and we went to lunch in it regularly that year - that car to me was just perfect in every way, both styling and engineering and that is why I have so many of them now - crazy
Justin Plant
Well-Known Member
I currently work with a 73 yr old, who worked at Fulton Motors in Roanoke starting in High school, until 1977. With a brief stint in Germany via the draft in the middle. I asked him about this particular carb, because it's the one that came on my 75. He said, "if there's no bridge on top of the carb, you're going to have problems with it." He was correct. I also asked why in the hell are all the adjustments squeeze this wire, and straighten that one? He told me he spoke with a Holley rep, back in the day. He said "we build these the way Chrysler wants them". Makes sense to me, a Motorcraft\Holley two bbl on any Ford of the same era isn't built this way at all. Either way I'm sure when it was new half a century ago, it probably worked fine.
74monacoHT
Member
So it's driving great but the alternator (or regulator) quit on me halfway to my destination tonight... fortunately my friends have a charger so I should be able to get home later. It's much too cold to troubleshoot.
74monacoHT
Member
Just an update to close this little saga. Changed alternator (unrelated to hesitation). Changed vacuum advance on distrib. This explains why I had 20+ advance at idle bexause the vac advance was completely stuck. And I fixed the horn, but would like to add a bridge.
Runs like a dream now!
Happy new year everyone
Runs like a dream now!
Happy new year everyone
Loadrunner
Active Member
MoParing into 2023 ;]
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