hi guys gary here long time no say,been sick had two knee replacements but well on the mend.
ok i have some questions,
1/ the 65 carb has the power enrichment circuit which is zoned to come in at @ 60 mph only under acceleraton and stayes in from @80 mph on wards.
2/ the 66 std non air carbs also have the pev but have been re calibrated to come in on demand from the bottom up the range to high speed.the way i understand it is this is so you could run a leaner jet and get good gas milage but stil have a rich mixture when you excellerate.all this info i got from reading Bob Helts carb book.
3/ the 66-67 carbs both std and air also recieved the pev, according to Bob Helt the chevy engineers recalibrated the 66-67 carbs so that the pev valve would come in on demand,my question is what did they do to accomplish this.was the valve weight less ,was it the hidden jet size , or was there other channels drilled,
4/ my next question is the air circuit that is installed in the 66-67 carbs,if you wanted to make these carbs like the std 66-67 eg non air, could you not just turn the screw in till it seats to block off that factory set channel and then it would be the same as the std 66-67 carbs?
all answers will be greatly appreciated
thanks Gary.
65-66 carbs
Re: 65-66 carbs
Bob Helt's Rochester book, that I have, mentions different PES (power enrichment system) jet sizes depending on the carburetor number in a chart on pg. 48 (2008 publication).
In 66 there were TWO different primary carburetors. One was mostly used in Calif. to meet emissions. The other was used in the majority of cars sold outside Calif. (there are statements that a few counties in eastern states required emissions controls in 1966). The emissions control carburetors had a bulge on the outside near and above the idle mixture screw. This revised casting was to accommodate an Off Idle Air-bleed valve. When you look down the carburetor throat you see what looks like a sloted screw head (changed in 67). The standard 66 cars did not have this - HOWEVER later replacement carburetors that were NOT emissions control carburetors had the casting bulge, just no internal machining. So you can't tell by just looking at the outside of the carburetor base. I have one!!
ALL 66 model year primaries had a revised idle mixture circuit. If you look in the base throat at the idle transition slot (above idle mixture port) there is a hole above the idle transition slot. This was done to improve the off idle mixture and allow for a leaner idle mixture. When new this feature worked well, but it relies on internal passages from the cluster to the idle mixture screw chamber being smooth. I've had a few of these carburetors with passages that had become rough due to corrosion and when this happens it is IMPOSSIBLE to get the carburetors to idle smoothly. Basically they go in the trash. There is no "practical" fix since the passages must be both smooth and a specific diameter so you can't just bore them out to make them smooth.
The 1965 carburetors DO NOT have the additional idle air bleed hole above the transition slot and this makes the idle mixture circuit less sensitive to variations or roughness in the idle circuit passages.
Hope this helps.
In 66 there were TWO different primary carburetors. One was mostly used in Calif. to meet emissions. The other was used in the majority of cars sold outside Calif. (there are statements that a few counties in eastern states required emissions controls in 1966). The emissions control carburetors had a bulge on the outside near and above the idle mixture screw. This revised casting was to accommodate an Off Idle Air-bleed valve. When you look down the carburetor throat you see what looks like a sloted screw head (changed in 67). The standard 66 cars did not have this - HOWEVER later replacement carburetors that were NOT emissions control carburetors had the casting bulge, just no internal machining. So you can't tell by just looking at the outside of the carburetor base. I have one!!
ALL 66 model year primaries had a revised idle mixture circuit. If you look in the base throat at the idle transition slot (above idle mixture port) there is a hole above the idle transition slot. This was done to improve the off idle mixture and allow for a leaner idle mixture. When new this feature worked well, but it relies on internal passages from the cluster to the idle mixture screw chamber being smooth. I've had a few of these carburetors with passages that had become rough due to corrosion and when this happens it is IMPOSSIBLE to get the carburetors to idle smoothly. Basically they go in the trash. There is no "practical" fix since the passages must be both smooth and a specific diameter so you can't just bore them out to make them smooth.
The 1965 carburetors DO NOT have the additional idle air bleed hole above the transition slot and this makes the idle mixture circuit less sensitive to variations or roughness in the idle circuit passages.
Hope this helps.
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