Converting Holley 4160 short bowl carbs to true dual feed for 2X4 setup ?

[427LX]

 Anyone running the 4160 style carbs on the 2X4 intake convert the secondary bowl to a standard fuel inlet for a true dual feed.   I had a transfer tube O ring just suddenly give up causing a nice leak. Luckily this happened in my garage and not on the road!  Had done a jet change on Saturday and everything ran fine all day. Next morning try to go for a drive and O ring failed on startup.
First time that has happened in 10 years running my carbs and now I just don't trust the O rings!!  I have modified an extra bowl I have and it is simple enough to do. Set it up in my mill and machine off the spun over material. Take a center drill and when it gets a bite the steel plug with O ring spins right out. The inlet bore diameter is same as the primary bowl so I tapped it for 9/16-24 thread like the other for screw in Holley type hose barb. Now sealing up that transfer port you have some options. I am trying the tap it with 1/8-27 pipe/plug tap and will use brass Allen socket plug with generous amount of Permatex Aviation sealant.   
Any of you race guys do this mod? Will test one carb out and see if the plugs stay leak free.

[mike7570]

I ran dual 660 on my 427 engine for many years. This was an engine used in 2 of my race cars that saw frequent jet changes. I kept a good supply of new O rings available as the frequent removal of the transfer tubes seemed to cause failure. Make sure your tubes are in good shape, they seem to be made out of cheap metal that becomes rough and pitted over the years.
With good clean tubes and new O rings I didn’t have any leaks.

[427LX]

Tubes were clean and I always lube up the O rings been doing it for the 10 years I have had this setup but why not move up to something better? Can't figure why one decided to leak the next day? Who knows what the new O rings are made off and from where these days. I remember15 years ago I had a friend who was running a pair of 4160 carbs on his 70 Hemi Challenger and he always had some trouble with them and I think those were the "better" boot design. I never could get those to work well and went back to the old O ring.
Anyway I will be testing out my new setup on the bench and if the pipe plug stays leak free....good to go and NEVER worry again when doing jet changes!

[GerryP]

I use Viton o-rings for the needle and seat assembly.  I got a bag of fifty for very cheap.  You should be able to find Viton seals for the transfer tube.  Sort of one of those reinventing the wheel deals.  Surely your effort is a unique solution but might not be very necessary.

[6667fan]

Many racers have got it done with transfer tubes. However, to rule out any possible fuel supply worries I fed each bowl. Used braided steel lined hose with AN fittings. Quick Fuel carbs with transfer tube left in place so fighting with O rings can still manifest.  I would share images but they are jpeg and I cannot execute the attachment.

[475fetoploader]

I’ve done this, when I get home from work, I’ll try to post some images.

[e philpott]

I use this with a new style tube and works great
https://www.jegs.com/i/Holley/510/26-115/10002/-1

[427LX]

My dual feed setup works great and no leak issues! I use the Gates EFI type rubber hose as it has a better liner for E10 and higher fuels.

[cleandan]

There are a few possible things happening with the transfer tube and associated parts. This assumes the parts are correctly sized, and without physical faults in the first place.
1) The tube is not smooth, straight, round, so it can't seat against the O-rings, or the rubber fitting of the other type.
2) The internal passage for the transfer tube on the float bowl body has something going on that is causing things not to seal. Scratch, delaminating finish, old gunk, been cleaned out with abrasive methods thus making the hole bigger than it should be... something could be there so look carefully.
3) The tube end lip is a little sharp, or has a burr of some type, causing issues with the seals... I chamfer the outer edge of every tube ever so slightly to ensure they won't cause issues. I also deburr the inner edge just to make certain there is no foreign material that will come loose and get in my needle and seat and give me that super fun fountain of gas all Holley owners know and love.
4) The O-rings or end gaskets were not fully seated when installing the tubes... easy to do especially with the O-rings.
I like the little special tube end gaskets better than the O-rings.
I check each gasket carefully for any imperfections and remedy those before installing... they are usually good out of the box, but sometimes there is casting flashing or nibs that must be dealt with.
I lube every rubber end gasket with Vaseline, or silicone grease, before installation (very lightly, almost like you are trying to wipe it off rather than put it on)

O-Rings, I like to double up and stack tightly against each other, and I start them about 1/8" from the end of the tube.
The end gaskets I place over the end of the tube and stuff in the hole while working the tube ever so slightly to ensure they insert fully and smooth... You can push the end out of those if you just shove them in and things are not perfect.
I finish with the end gaskets by using a tool I made to push the gasket into the hole after both float bowls have been installed, and the tube has been centered by hand (mark the tube beforehand so you can see center). A tiny scribe mark is all you need.
Push the end gaskets in so they are fully inside the tube hole chamfer on the float bowl receiving end and be sure to push them in evenly around the circumference.

Doing these things will greatly improve your sealing situation, and it sounds like a lot, but once you have it down it adds about one minute to a full carb rebuild.