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Re: 140 carburetor jetting suggestion needed
Posted by:
brentc
()
Date: March 10, 2023 02:42PM
Generally a good starting point is disconnect the secondaries and figure out what really is best running just on the primaries. Then jet the secondaries three sizes leaner. Often this means you can use the former primary jets in the secondaries.
The Power Enrichment system in 1965-67 engines is seldom activated in 140 engines so you can err a little heavy for fuel.
Most 140 secondaries except very late engines have provision for accelerator pumps. On Powerglide cars I prefer all four carbs to have pumps, and deactivation of the lockouts for the secondaries if it's not a concours vehicle. Set the primary choke unloader to half an inch. This permits full throttle on a cold engine if neccesary without stumbling. Normally you don't need this but if a big truck is about to hit you, you want it to GO when you stomp the gas.
The lockouts were primarily to make the air injection reactor system work smoothly.
Altitude matters. At sea level around a 53 primary is right, at 5000 feet perhaps a 51. Generally about three jets richer than stock is good. Lean jetting tends to contribute to ping etc and doesn't save fuel as the timing advance must be restricted.
The secondaries need to be three leaner than optimum primary jets are. This permits even mixtures in situations where the secondaries are partly open such as long hills at heavy throttle or very fast cruising. 140 secondaries should not give a sensation of "kicking in" like a V8. It should feel like one big one barrel carburetor, very smooth progression.
Lots of good advice from others too, make sure you have the correct distributor as well!
Brent
Edited 1 time(s). Last edit at 03/10/2023 02:49PM by brentc.
The Power Enrichment system in 1965-67 engines is seldom activated in 140 engines so you can err a little heavy for fuel.
Most 140 secondaries except very late engines have provision for accelerator pumps. On Powerglide cars I prefer all four carbs to have pumps, and deactivation of the lockouts for the secondaries if it's not a concours vehicle. Set the primary choke unloader to half an inch. This permits full throttle on a cold engine if neccesary without stumbling. Normally you don't need this but if a big truck is about to hit you, you want it to GO when you stomp the gas.
The lockouts were primarily to make the air injection reactor system work smoothly.
Altitude matters. At sea level around a 53 primary is right, at 5000 feet perhaps a 51. Generally about three jets richer than stock is good. Lean jetting tends to contribute to ping etc and doesn't save fuel as the timing advance must be restricted.
The secondaries need to be three leaner than optimum primary jets are. This permits even mixtures in situations where the secondaries are partly open such as long hills at heavy throttle or very fast cruising. 140 secondaries should not give a sensation of "kicking in" like a V8. It should feel like one big one barrel carburetor, very smooth progression.
Lots of good advice from others too, make sure you have the correct distributor as well!
Brent
Edited 1 time(s). Last edit at 03/10/2023 02:49PM by brentc.
Re: 140 carburetor jetting suggestion needed
Posted by:
RobertC
()
Date: March 10, 2023 02:59PM
brentc Wrote:
-------------------------------------------------------
> 140 secondaries should not give a sensation of "kicking in" like a V8.
>
Not true with the early 1965 140 linkage.
To me, the linkage works like a mechanical secondary on a 4bbl.
And, you do feel the "kick in" - if the secondaries open...
-------------------------------------------------------
> 140 secondaries should not give a sensation of "kicking in" like a V8.
>
Not true with the early 1965 140 linkage.
To me, the linkage works like a mechanical secondary on a 4bbl.
And, you do feel the "kick in" - if the secondaries open...
Re: 140 carburetor jetting suggestion needed
Posted by:
gerg
()
Date: March 10, 2023 03:30PM
I am using that early 140 '65 linkage 
gerg
Monroe, LA
Current cars and other fun stuff -> [gregblakeney.smugmug.com]
gerg
Monroe, LA
Current cars and other fun stuff -> [gregblakeney.smugmug.com]
Re: 140 carburetor jetting suggestion needed
Posted by:
gerg
()
Date: March 10, 2023 03:37PM
Great info Brent.
I had pump cups in my secondaries till I realized the passages were not drilled for use. Took them out last night.
Definitely have the correct 140/PG distributor & correct vacuum pot.
gerg
Monroe, LA
Current cars and other fun stuff -> [gregblakeney.smugmug.com]
I had pump cups in my secondaries till I realized the passages were not drilled for use. Took them out last night.
Definitely have the correct 140/PG distributor & correct vacuum pot.
gerg
Monroe, LA
Current cars and other fun stuff -> [gregblakeney.smugmug.com]
Re: 140 carburetor jetting suggestion needed
Posted by:
gerg
()
Date: March 10, 2023 03:41PM
So the only other thing nagging me (hehe) . . . .
With the contribution of the idle circuit on the late secondaries, does that not lend reason for the main mixture screws to be somewhat leaner than on a early 140 or any other 2 carb engine?
gerg
Monroe, LA
Current cars and other fun stuff -> [gregblakeney.smugmug.com]
With the contribution of the idle circuit on the late secondaries, does that not lend reason for the main mixture screws to be somewhat leaner than on a early 140 or any other 2 carb engine?
gerg
Monroe, LA
Current cars and other fun stuff -> [gregblakeney.smugmug.com]
Re: 140 carburetor jetting suggestion needed
Posted by:
RexJohnson
()
Date: March 10, 2023 06:19PM
The idle circuits in the secondaries are to help eliminate lean miss fires in cyl 1 and 6. With the earlier 140's you had to richen the mixture to keep them from miss firing and then the other cyls. would be rich so yes the idle could be leaner with the secondary idle carbs. The secondary lock out was to keep it from going lean with a cold engine which would make for a big stumble. A warm engine can handle the opening/lean condition much better than a cold one. The high speed enrichment of the 65-7 carbs came in at a fairly low speed. Years ago at the Fan Belt Toss Bob Ballow? (RIP) had 2 carbs hooked together one on top of the other with different jets plugged between the 2 carbs. He would switch to a carb with the main jet plugged at a slow engine speed to show how it was running off of the high speed enrichment.
RJ tools
Salem,Oregon
RJ tools
Salem,Oregon
Re: 140 carburetor jetting suggestion needed
Posted by:
RobertC
()
Date: March 11, 2023 02:40AM
brentc Wrote:
-------------------------------------------------------
>
> The Power Enrichment system in 1965-67 engines is seldom activated in 140 engines so you can err a little heavy for fuel.
>
Do not know how carbs really work, but I disagree with this statement - as Rex's post above also notes.
People who relocate jets on 65 - 67 PEV carbs (removing the PEV valve) know (or should) that you have to run larger (richer) jets to compensate.
Been running 4 primaries (65 PEV primaries with jets relocated (PEV removed)) on my 140 for decades - using 55 jets.
-------------------------------------------------------
>
> The Power Enrichment system in 1965-67 engines is seldom activated in 140 engines so you can err a little heavy for fuel.
>
Do not know how carbs really work, but I disagree with this statement - as Rex's post above also notes.
People who relocate jets on 65 - 67 PEV carbs (removing the PEV valve) know (or should) that you have to run larger (richer) jets to compensate.
Been running 4 primaries (65 PEV primaries with jets relocated (PEV removed)) on my 140 for decades - using 55 jets.
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