Tuning Holley 4160 Accelerator Pump?
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Mountain Pass
Joined: Apr 2020
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Tuning Holley 4160 Accelerator Pump?
Finally finished up my intake manifold upgrade to go with my EFI exhaust manifolds. The engine is stock. I managed to get an offenhauser C intake and 600 cfm Holley 4160 for a good price. The carter YFA and log manifold are no more.
It's idling and accelerating great, but has a lot of off-idle stumble I'm struggling with. I changed the original nozzle from a 31 to a 37 and from the orange pump cam to the blue. It's much better, but still struggles and I have to feather the throttle until the venturis overcome the idle circuit and accelerator pump issues.
I'm used to a carter AFB, a little easier to tune. Anyone have luck addressing this sort of issue?
It's idling and accelerating great, but has a lot of off-idle stumble I'm struggling with. I changed the original nozzle from a 31 to a 37 and from the orange pump cam to the blue. It's much better, but still struggles and I have to feather the throttle until the venturis overcome the idle circuit and accelerator pump issues.
I'm used to a carter AFB, a little easier to tune. Anyone have luck addressing this sort of issue?
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
One I think the 600 CFM carb is to big as some have issues tuning 390 CFM carbs.
Are you using a vacuum gauge and a air fuel ratio gauge to dial in the carb and if not what are you using?
What jets dose it have?
What power valve dose it have?
What is the vacuum at idle and at cruise speed (vacuum gauge)?
What is timing set to?
Mechanical advance timing?
Vacuum advance timing?
I am going to guess that you are making it richer and has helped but still running lean and with no way to know ( with out the gauges) its just a guess.
I have something I think may work but need the other information first.
Dave ----
Are you using a vacuum gauge and a air fuel ratio gauge to dial in the carb and if not what are you using?
What jets dose it have?
What power valve dose it have?
What is the vacuum at idle and at cruise speed (vacuum gauge)?
What is timing set to?
Mechanical advance timing?
Vacuum advance timing?
I am going to guess that you are making it richer and has helped but still running lean and with no way to know ( with out the gauges) its just a guess.
I have something I think may work but need the other information first.
Dave ----
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Mountain Pass
Joined: Apr 2020
Posts: 144
Likes: 0
I have a vacuum gauge only, and I've only used it to check @ idle - 20"
Come to think of it, I haven't messed with the idle mixture screws yet...other info you requested:
Jets - 66
Pump Nozzle - 37 (was 31)
Pump Cam - Blue (was Orange)
Power Valve - 65
Secondary Spring - "Plain"
Timing - 10* base, 23* mechanical (fully in by 3000rpm), 11* vacuum
Come to think of it, I haven't messed with the idle mixture screws yet...other info you requested:
Jets - 66
Pump Nozzle - 37 (was 31)
Pump Cam - Blue (was Orange)
Power Valve - 65
Secondary Spring - "Plain"
Timing - 10* base, 23* mechanical (fully in by 3000rpm), 11* vacuum
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
I have a vacuum gauge only, and I've only used it to check @ idle - 20"
Come to think of it, I haven't messed with the idle mixture screws yet...other info you requested:
Jets - 66
Pump Nozzle - 37 (was 31)
Pump Cam - Blue (was Orange)
Power Valve - 65
Secondary Spring - "Plain"
Timing - 10* base, 23* mechanical (fully in by 3000rpm), 11* vacuum
Come to think of it, I haven't messed with the idle mixture screws yet...other info you requested:
Jets - 66
Pump Nozzle - 37 (was 31)
Pump Cam - Blue (was Orange)
Power Valve - 65
Secondary Spring - "Plain"
Timing - 10* base, 23* mechanical (fully in by 3000rpm), 11* vacuum
Rule of thumb is start at half of idle vacuum so you have 20" you will want a 10" PV
Now before you go buying a 10" PV also check what our vacuum is at cruise and get a PV in that size also.
You may also need to adjust up / down from there but you need to start somewhere so get the PV's.
And yes try and adjust the idle mix screws using the vacuum gauge to get the highest reading when doing so.
Dave ----
Cargo Master
Joined: Nov 2009
Posts: 2,190
Likes: 620
You can make a 600cfm carb work on a mostly stock 300, but it really is too big, and isn't ever really going to run *well*.
I highly recommend finding a Holley 0-8007 (390 cfm, and almost the perfect carb for this engine if you want to run a 4bbl), Another option is finding something with an FE (352, 360, 390) with a factory 4bbl, they were mostly 425cfm Holleys. The other decent option would be a Holley 0-90470, which is 470cfm, and has a bunch of modification for offroad use.
I don't *think* anybody is building an AFB Pattern carburetor, in anything smaller than 500cfm anymore. (I could absolutely be wrong about this, I just haven't seen them), but there are a number of them out there on the used market, from past years.
The other *good* option is to find a small venturi (1.08) Motorcraft 4100, the flow just under 500cfm, and you can basically rebuild and tune them with a dime and a rock. These are just getting hard to find, for whatever reason (I mean, they've been out of production for years, so that's not helping)
I highly recommend finding a Holley 0-8007 (390 cfm, and almost the perfect carb for this engine if you want to run a 4bbl), Another option is finding something with an FE (352, 360, 390) with a factory 4bbl, they were mostly 425cfm Holleys. The other decent option would be a Holley 0-90470, which is 470cfm, and has a bunch of modification for offroad use.
I don't *think* anybody is building an AFB Pattern carburetor, in anything smaller than 500cfm anymore. (I could absolutely be wrong about this, I just haven't seen them), but there are a number of them out there on the used market, from past years.
The other *good* option is to find a small venturi (1.08) Motorcraft 4100, the flow just under 500cfm, and you can basically rebuild and tune them with a dime and a rock. These are just getting hard to find, for whatever reason (I mean, they've been out of production for years, so that's not helping)
Fleet Mechanic
Joined: Jul 2013
Posts: 1,997
Likes: 237
From: NE Ohio
Ignore the pv completely, not your issue with off idle stumble. It doesnt even come into play.
until you get into it hard and vacuum drops.
2nd the pv is always half of idle vacuum, never base it off cruise... there are other things to look at first. 3rd, double/ triple check advice given here.
the accelerator pump is set at 15 thousands of an inch. It may or may not be the source of your problem though. A missed vacuum leak can be the cause, over exposed transfer slots etc..
I dont know much but I do my best to give backed up advice.
until you get into it hard and vacuum drops.
2nd the pv is always half of idle vacuum, never base it off cruise... there are other things to look at first. 3rd, double/ triple check advice given here.
the accelerator pump is set at 15 thousands of an inch. It may or may not be the source of your problem though. A missed vacuum leak can be the cause, over exposed transfer slots etc..
I dont know much but I do my best to give backed up advice.
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