I have a stock Holley 4160/3811 on my '67' 427/390. Several years ago the front bowl developed a crack and had to be replaced. Luckily I found a used replacement bowl in a junk pile at a local Corvette supplier. So its now several years later and its warped, but not leaking, so I decided to get a new one which I saw on Holleys web site. Well they have been back ordered for several months and unavailable so I found one at Summit. Great I figured, got one. Same p/n and from Holley. Well, received it and found it to be identical, EXCEPT that it dosen't have a hole for a vent on top of the bowl like my original. Anybody that has one of these knows what I'm talking about. Its a vent rod and spring assy. with a rubber seal that covers/uncovers the vent as you actuate the throttle. I've searched different web sites but cannot find any info or part numbers on this particular bowl. They call it a Marine float bowl, Holley p/n 34R10918AQ. This is a Holley p/n but it doesn't say vented or not. Nothing else to go on.
So I'm kind of frustrated. So many variations to this carb. I was hoping I could get some info from the forum here on where the hell I could find one of these float bowls that is vented or maybe its an updated bowl and dosen't need to be vented anymore, who knows. Any info from you guys would help. Thanks.

Desert Nomad,

 

Have you contacted any of the many carb restores and see if they have any correct bowls for sale.

 

No not yet. I did e-mail Holley Tech services tonight to see what they have to say but probably won't get an answer till Monday. I guess the next move will be to contact one of the premiere carb restorers. Lets see what Holley says. I did manage to go back in the forum archives and found a thread that "Rat Dog" was involved in a few years ago and the vent question about the front bowl came up. Actually, nobody had an answer to why the bowl was vented as its vented thru the stack tube anyway. Even John Z wasn't sure of why the bowl vent was there. We'll see. Hopefully others will chime in.

 

The vapor vent on top of the primary float bowl is there to vent fuel vapors to atmosphere at hot idle conditions so the engine does not load up and stall.

I do not think it's necessary to have the vent as the bowl is also vented to the vent stack inside the air horn. Keep in mind vapors vented inside the air horn will make a rich running idle and possibly stall.

The other purpose of the bowl vent is to stink your garage up. :-)

 

I know it must have had a purpose like you said for venting because it definatley stinks up the garage. My thinking also, that it may not even be necessary and that's why they don't make em that way anymore, but who knows. We'll see what Holley's answer is. Hopefully I'll hear from them this week.

 

Isn't the bowl vent supposed to be closed off by the spring loaded linkage and rubber cap when the throttle is shut or do I have it backwards? Been a long time since I worked on one.

Does the bowl you bought have an embossment you can drill a hole in and use it as original?

 

Mike, at idle or in the off position the vent is open. As you increase throttle, the vent closes. The enbossment would need to be machined down and then the proper size hole drilled. Also, a hole would have to be drilled and tapped for the retaining screw that holds this linkage assy. to the bowl. This did cross my mind when I first looked at it. Probably a job for a machine shop.

 

Let me try to upload a pic of these bowls:

 

With the proper size end mill, it would be easy to machine the bowl to match the old one. The seat surface looks like it's slightly convex shaped. That would be harder to duplicate. Also would be bright aluminum, not anodized like the rest of the bowl.

 

With the right size ball end mill it won’t be a problem

 

Believe me, that thought was rolling around in my brain. Rather than try it myself though, I would probably try to find a good machinist shop. Not that its that hard, but I don't have the proper tooling to attempt it. Personally I can't see that this vent is really necessary as most 4160's and 4150's that I have seen don't have it as they vent thru that stack tube. Anyways, I'm waiting to see what Holley says, hopefully in a few days. Thanks for the responses.

 

Unless you are going for the gold and want it to look original, I wouldn't drill the vent. It is a fire hazard if the float sticks or the needle sticks and gas pours out and floods the top of the engine.
I taped the hole and put a threaded plug in the vent on the 3367 on R66. There is a thread in here showing how I did it to somewhat look like it was still functional. R66 is a driver so I am more concerned about safety.

Don't really know the function of the vent, but I have not experienced any bad effects at hot idle or other throttle positions from plugging it. Also, how many new Hollys do you see with this vent??

 

I don't drive more than once a month and the fuel in the bowl is gone from evaporation through this vent. To save battery and starter life, I've begun filling the bowl through the sight hole before starting, usually about 4 oz. Now a single crank fires it up whereas before it took three or four tries. A bit of nuisance but saves the life of my original starter.

 

Good point on the float sticking. That would not make my day if that happened. I'm a thinking that I'll probably use the new bowl as is a see how it goes. Still waiting for a response from Holley.

 

How hard would it be to fix the warped one?


Gerry

 

Think of it as a hot idle compensator, just keep one thing in mind when considering the float bowl vent and today's fuel. Ethonal will turn to vapor at approx 170* so on a hot day (without the vent) the engine idle can become rich and possibly stall.

The reason the rubber valve closes when the throttle blades open is because the primary vent stack in the air horn keeps the same pressure in the float bowl as in the air horn so pressure moves fuel into the main well.

I don't know why some carburetors had the vent and some did not maybe it has something to do with the hot slot under the primary float bowl.

 

Allstate Carburetor, located out of the east coast would be whom I would call.

Pat

 

Well, I thought about it but was afraid it would crack. Looks like cast aluminum.

 

My thinking also, why some have it and others (4160's & 4150's) don't have this vent. If plugging the hot slot would make this bowl usable, I'd do it. Still waiting for an answer from Holley.

 

I would just do it. What do you have to lose if you have to undo it?

Those external float bowl vents go back to the beginnings of that carburetor design. The external vents also disappeared due to emmisions rules which conincided with elimination of heat on the carb base.