Hello folks, need help from the carb experts: Its been a long time since I posted but I am trying to get back into this :-) When I recently went to drive my driver 67 Vert 327 300(partial 350)hp car I had idle issues. FYI, my Holley is actually a List 3806, which is a 67 carb used on other 327 Chevy's (Chevelle I think and others) with L79, and my understanding was that it is the same as the 3810 except it came from factory with the secondary metering block vs plate. I've been running it for 25 years without many issues, except that I would generally seem to be a bit rich at idle and off idle, with mixture screws usually about 3/4 to 1 turn out max. Sometimes closer to a half turn. But, all ran well so I didn't see a need to mess with it. I looked a buying a 3810 years ago when Holley was remaking them I wish I had, but didn't since my 3806 seemed just fine. Both my 3806 main body and both metering blocks are stamped 3806 by the way. Fast forward to today....
Now, something happened and in a recent drive I had bad whistling at idle. Determined that my primary throttle shaft might have excessive wear and leaking, so I ordered and installed brass bushings on the primary. That seems fine now. But after reassembly I still have rich condition and idle screws need to be almost all the way in to idle decently. Not sure what changed, but as mentioned my carb has always seemed to be a bit rich at idle and lacked full screw mixture control and has smelled gassy.
I've took the carb apart and recleaned and all passages are clean, good seals, no obvious problems. PV good etc, and have several PVs that I experiment with occasionally. Didn't see any of the classic causes of the rich condition or why it is recently worsened.
However, this time since I have been focusing idle circuits, and especially the Idle Feed Restrictors, I see that maybe the 3806 metering block has some differences that I didn't know ab out before. I started in investigate this further. I believe the 3806 was used ONLY on L79 engines which have less vacuum at idle and a more aggressive cam than my 300 cam. The 3810 was used on both 300hp and 350hp L79 in vettes. My car has probably stock type 300 hp cam, since it produces about 18-20 inches vacuum at idle.
See attached photo of my primary metering block. Best I can tell I don't see ANY Idle Feed Restrictors (IFRs) in place at all. The lower location where I "think" would be the normal 3810 location has no brass inserts and seems to be drilled large probably in the .080 range, certainly not the .031 size that has been mentioned in archived older posts for the 3810. The top of the idle feed location also has no inserts. None of these locations appear to have been redrilled by owners, but seem to be made that way from Holley.
Comments from the forum? Do ya'll think this could be why I idle rich and lack mixture control? And if so, what and where should I consider adding restrictors? Seems like the 3810 had .031 restrictors, but at what location and were they brass inserts? It looks like adding a restrictor at the top location would be easier. I haven't confirmed what the idle AIR bleeds (in main body) are at in the primary, but I assume I need to see if they are at the roughly .070 size that has been mentioned? They may be a bit larger than .070, more in the .085 range but I need to verify that. Any input would be appreciated.
One question, is there a resource to find out all these orifice parameters from the factory for various list number Holley carbs? I would like to find out what the list 3806 was from the factory, but haven't seen anything from google searches yet.
Thanks all!
3806 Main block.jpg
Now, something happened and in a recent drive I had bad whistling at idle. Determined that my primary throttle shaft might have excessive wear and leaking, so I ordered and installed brass bushings on the primary. That seems fine now. But after reassembly I still have rich condition and idle screws need to be almost all the way in to idle decently. Not sure what changed, but as mentioned my carb has always seemed to be a bit rich at idle and lacked full screw mixture control and has smelled gassy.
I've took the carb apart and recleaned and all passages are clean, good seals, no obvious problems. PV good etc, and have several PVs that I experiment with occasionally. Didn't see any of the classic causes of the rich condition or why it is recently worsened.
However, this time since I have been focusing idle circuits, and especially the Idle Feed Restrictors, I see that maybe the 3806 metering block has some differences that I didn't know ab out before. I started in investigate this further. I believe the 3806 was used ONLY on L79 engines which have less vacuum at idle and a more aggressive cam than my 300 cam. The 3810 was used on both 300hp and 350hp L79 in vettes. My car has probably stock type 300 hp cam, since it produces about 18-20 inches vacuum at idle.
See attached photo of my primary metering block. Best I can tell I don't see ANY Idle Feed Restrictors (IFRs) in place at all. The lower location where I "think" would be the normal 3810 location has no brass inserts and seems to be drilled large probably in the .080 range, certainly not the .031 size that has been mentioned in archived older posts for the 3810. The top of the idle feed location also has no inserts. None of these locations appear to have been redrilled by owners, but seem to be made that way from Holley.
Comments from the forum? Do ya'll think this could be why I idle rich and lack mixture control? And if so, what and where should I consider adding restrictors? Seems like the 3810 had .031 restrictors, but at what location and were they brass inserts? It looks like adding a restrictor at the top location would be easier. I haven't confirmed what the idle AIR bleeds (in main body) are at in the primary, but I assume I need to see if they are at the roughly .070 size that has been mentioned? They may be a bit larger than .070, more in the .085 range but I need to verify that. Any input would be appreciated.
One question, is there a resource to find out all these orifice parameters from the factory for various list number Holley carbs? I would like to find out what the list 3806 was from the factory, but haven't seen anything from google searches yet.
Thanks all!
3806 Main block.jpg
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