Actually there's two holes, one in each barrel where the throttle blade sits on a Rochester 2g carburetor. Found them while rebuilding one for a tripower setup. Of the thirteen carbs I have collected five base plates have these holes. Why are they there? Seems like an unfiltered air leak but they must serve some purpose?
Well let's just come out of the gate sprinting! Scotto- Any ID of the year of plates? If the carbs were complete, an ID should be obtainable (yr), and that should tell the tale as to your Q........ I had to jump around with words with my reply!
Pretty sure it's some sort of 'hot start' fix. I've also seen vented gaskets used between the base plate and carb body that may serve the same purpose.
I can't really get an ID on them, I've just collected these because I knew they'd be useful eventually in a multi carb set up. I figure they range from the mid 50s and 60s, I'm pretty sure two are from a '57 and one from a '67. The rest are questionable. One even came from an engine next to a dumpster.
I have one like that. I read somewhere what it was for, but can't remember. The hot start or vent sounds familiar.
Why wouldn't the air wouldn't be filtered? I mean... Talk about planned obsolescence! I'd be interested to hear the actual reason they are there from a carb expert. They're right at the throttle blade so I'd think they'd be at a point of high vacuum and probably cause a lean condition.
Only if they were located below the throttle plates would they ever be exposed to high vacuum. The engineers put it there for a good reason, run it and don't worry.
This is why we need an index. The HAMB is the best website there is but its difficult to find information
Here's a couple of threads where carbking explains the purpose of the vented gaskets used between the baseplate and carb body on some Rochester 2-barrel carbs. I would ***ume that the holes drilled in the base plate just above the throttle blades (again, not exposed to vacuum) serve the same purpose: http://forums.maxperformanceinc.com/forums/showthread.php?t=438508 http://forums.maxperformanceinc.com/forums/showthread.php?t=444149
They are something meant to let excess gas boiled out of bowl when parked to evaporate, I believe. At any rate, they are fully explained in Doug Roe's ABSOLUTELY NECESSARY Rochester carb book. Unfortunately, you MUST get the early book published around 1973 and NOT the one from the '80's that is easy to find...the first has EXCELLENT coverage of 1 and 2 barrels, the later one is useless except for Quadrajet. On the air leak...I would suspect that the rush of air past the plates might well block off ingress of air through tiny holes in the wall.
Well, I really thank everyone for the help. I just can't get around that thinking that unfiltered air shouldn't be let into in an engine....
It's doubtful that any significant amount of air if any at all goes in through those holes during operation, they're just there to vent after shutdown. The carburetor engineers wouldn't have put them there if they would **** in a lot of dirt.
Those are controlled vacuum leaks for sure, maybe to set idle speed? Any chance these came from the same person? Like maybe they were circletrack carbs and there's usually an extra hole or two in them. Most often those holes are in the throttle blades, I've even put them in the spacers below the carbs where the holes are drilled and tapped to use a holley jet so you can use them to 'tune' the engine and you'd put a pieces of scotchbrite for a filter and the tech guy would 'miss' seeing it. I've got a mess of those carbs and none have that set of holes.
These all have independent sources. I noticed one base only had one hole last night, some have two, one in each barrel, and most don't have any. It seems like a terrible fix for a 'hot start' problem.
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