holley 4 barrel question

[rebars1]

I received my replacement Holley carb (600cfm four barrel) today and am getting ready to install it. On my old one (holley four barrel 450cfm) there is a rubber hose running from a connection on the starboard side of the base up to a pipe into the top of the carb. The new one has the connection at the bottom, but nothing to connect to at the top. In my manuals (Merc, Seloc), I see the connection at the bottom in the pictures, but neither describe what it is or to what it should connect. It is next to the electric choke, but lower. <br /><br />Can someone please help me figure this out? <br /><br />It is some sort of vent or vacuum advance? Should the new one connect to the flame arrestor?

 

[rebars1]

Re: holley 4 barrel question

Sorry, I forgot to mention the boat is a 1974 IMP 255s, Ford 302, Mercruiser R drive.

 

[Boomyal]

Re: holley 4 barrel question

rebars, can ya post any pictures of the two? Holleys have a lot of variations on vacuum ports for different applications. Sometimes you just have to plug some of them. A marine carb should never have had a vacumm port for a vacumm advance distrib 'cause all marine distribs are centrifugal advance.<br /> <br />Also, why did you switch from a 450 cfm to a 600 cfm?? Were/are they both marine carbs?

 

[rebars1]

Re: holley 4 barrel question

Boomyal, I've been in the process of restoring this boat. The carb that came with it was starting to leak at the throttle shafts and turned out not to be a marine carb anyway. I found a reman carb shop online in calif., and the 600cfm marine carb was what they had listed for the Ford 302.<br /><br />I'll get some pictures on for you to see.

 

[Boomyal]

Re: holley 4 barrel question

Ah yes. That is one of the differences between marine carbs and auto carb. The throttle shaft bushings are tougher and made not to leak. <br /><br />I'll look for the pictures.

 

[rodbolt]

Re: holley 4 barrel question

actually if the throttle shaft busings leak you have other issues as gasoline never is supposed to stand on the shft. the shaft does not pass through any fuel sourcesand is rarely sealed and is just a plain sleeve bushing or steel on steel or steel on aluminium.<br /><br /> occasionally certain carbs will have a seal but its to seal contaminants out not gasoline in.<br /> not supposed to be liqued fuel on the shaft to start with.<br /> as the throttles only meter air and not fuel, fuel leakage is not a shafting problem.<br />if the fuel circuits are leaking raw fuel can and does run out the throttle shaft of some carbs but thats not a shaft issue its a fuel control/circuit issue.<br /> some holley 600 uneversal marine carbs have various vacum ports to fit a wide varity of engines, thats why they are cheap. some engines in marine use actually run a PCV valve for some reason most dont, that universal carb will cover both. most marine universal carbs also have a nipple for the fuel pump diaphram vent connection to allow any fuel from a broken diaphram to enter the carb rather than squirt all over the engine box, some older engines dont have carb vented mechanical pumps. and occasionally it left the marinizer with a carb vented pump and some master technician installed a autozone cheapie automotive pump cause he knows more than any marine engineer and its the same pump only cheaper it just did not have that nipple thingy.<br /> so I really cant help ya without a picture of the universal mess thats been created and even then it may be limited help.<br /> my experience with universal fit crap is its universally gararunteed not to fit a dang thing out of the box.

 

[mkast]

Re: holley 4 barrel question

You said the original carb had a hose running from the base of the carb to the top of the carb.<br />For what?<br />Without seeing this installation, I'll guess. Someone tied the vacuum port at the base of the carb to the fuel pump port at the choke housing.<br />If I remember right, a 1974 used a fuel pump with a clear bowl, no hose to the carb. If your fuel pump is like that, plug the port on the base. The port at the choke housing is for the fuel pump (ruptured diagram), it doesn't matter if plugged or not. After engine start, after inspection for fuel leaks, and engine is stable, check for any vacuum leaks. By the way, no gasket between the spark arrestor and the top of the carb.

 

[rebars1]

Re: holley 4 barrel question

Here are some photos of both carbs side by side. With all the discussion about Auto v. Marine carbs, I thought a side-by-side look would help. <br /><br />Both side by side:<br /> http://i23.photobucket.com/albums/b365/rebars1/3367170-R1-006-1A.jpg <br /><br />Here's the one that came with the boat: (note rubber hose to top of carb)<br /> http://i23.photobucket.com/albums/b365/rebars1/3367170-R1-008-2A.jpg <br /><br />Here is the new one: (connection point at base)<br /> http://i23.photobucket.com/albums/b365/rebars1/3367170-R1-010-3A.jpg <br /><br />Carb with vent hole at top at end of hose:<br /> http://i23.photobucket.com/albums/b365/rebars1/3367170-R1-030-13A.jpg <br /><br />Marine carb (no vent hole at top:<br /> http://i23.photobucket.com/albums/b365/rebars1/3367170-R1-032-14A.jpg <br /><br />Again, what do I do with the connection point at the bottom of the new (black) carb?

 

[Reel Poor]

Re: holley 4 barrel question

The carb on the right is not a marine carb, and the hose has been improperly installed, it does nothing. Had it been hooked up properly the lower port would have been pluged off and the fuel pump diaphram hose would have been attached to the top port. If it has a glass bowl type pump without a vent tube, then the top port should also be pluged .<br /><br />If you need the upper port for fuel pump vent you could drill the new carb like the old one is at the top, remove the tube from the origional carb and install it in the new carb, then plug the lower port.

 

[rebars1]

Re: holley 4 barrel question

Thanks for the input.<br /><br />I have the glass bowl type without a vent tube. So I guess I should just plus off the lower connection point on the carb.<br /><br />In a car, what is the connection used for?

 

[Boomyal]

Re: holley 4 barrel question

I think you will find that this connection is blocked. I don't think you need to do anything with it. You can unscrew the nut and check.<br /><br />Here is the new one: (connection point at base)<br /> http://i23.photobucket.com/albums/b365/rebars1/3367170-R1-010-3A.jpg

 

[rebars1]

Re: holley 4 barrel question

It looks like it goes into the choke body. I'll replace the nut with a cap plug.<br /><br />Do I need to put anything on the threads to help seal the plug or to the fuel line connection point (brass)?

 

[Reel Poor]

Re: holley 4 barrel question

It wouldn't hurt to put some teflon paste on the vaccum port, the fuel inlet should be a flair fitting, no sealer is necessary or recommended.

 

[jimmbo]

Re: holley 4 barrel question

That black hose does have purpose. It provides fitered air to the choke pull off mechanism. The marine carb has the same choke pull off but no hose attached since there isn't too much dust in a bilge. Pluging it off will affect how the choke opens during warmup.

 

[superpop]

Re: holley 4 barrel question

That is nothing more than a vent for the choke. Do not plug or block it. If you remove the brass nut there should be a piece of screen in the hole. This is to vent the choke.

 

[rebars1]

Re: holley 4 barrel question

There was no screen in the nut, so I cut a piece of super-fine screen to fit and reinstalled it. So that hole is there just for the choke to breathe? I did not see any definition for it in the carb diagrams.<br /><br />Thanks again.

 

[Reel Poor]

Re: holley 4 barrel question

My understanding is that the lower vaccum port is for an integral hot air choke, and pluging the hole would not affect the choke pull-off. The ckoke pull-off on the holly carb is operated by a piston and not a diaphram. This piston loosely fits the bore it is in. Vaccum bypassing the piston is the source of the vaccum that would be produced at that port. I'll also say that a leak there should not cause a problem as long as it does not suck in moisture. If it takes in moisture there it could cause a corrosion issue. Hence the rubber hose going into the venture (filtered air) on the origional carb. NOW....With all of that said, it may be possiable they are using that open port to reduce the amount of heat build-up in the choke housing, created by the electric choke stove. IF this is so, it should be left open. <br /><br />Opened or pluged would not affect the choke pull-off.