5.7 Venturi Cluster

[Mcguiver]

I bought carburetor for a 5.7 vortec engine, part number 861245A1, which had the correct venturi cluster in it, part number 802745T. I'm not sure if the aspirater nozzle for one side is suppose to have more holes in it than the other side. Could anyone tell me if this is supposed to be like that or send a picture of what the holes look like from both sides. My old venturi for my 5.0 vortec engine has symmetrical holes on both sides.

 

[alldodge]

On a Merc carb or Rochester 2GC I'm not seeing an aspirator. Some do have main jet with aspirator, just not seeing one on these carbs.

That said, there are no new carbs, only rebuilt ones. They would normally be the same, and if not then the rebuilder didn't have the parts to rebuild correctly.

 

[Scott06]

Which carb did you buy specifically from whom, I think Sierra does make a merc a knock off that is new, likely other sources are remanufactured carbs that may have a mix of parts if some one made a mistake during rebuild

 

[Mcguiver]

I purchased a used mercarb on ebay (part numbers for carburetor and venturi cluster are listed above). It's in great shape, the screws aren't worn out as though someone has had it opened numerous times so I assumed there would not have been a need for modifications. The guy sold it because it was running extremely rich but when I opened it the float arm was getting metal bound and could apply full force to the spring loaded needle. The venturi cluster number matches what the service manual calls for.

The larger brass tubes are what I'm calling aspirator nozzles or at least that was the proper terminology on some carburetors. Just about every photo I've seen has the same number of holes but there is normally 1 less hole on the opposite side of the same tube (see photo on left). I haven't come across any having a difference from one half or the other. I was hoping someone could post photos of a mercarb 475 venturi cluster or knows for a fact what the hole pattern is so I'd know mine are correct as is or I need to solder it shut.

 

[Scott06]

ok now I see what you mean. I don’t have a mercarb handy but does seem really odd.if you can’t find one there are a number of YouTube vids rebuilding these carbs or call a carb shop like mikes carb parts and ask.
I would not Think you would want to solder it shut as it looks unmolsted , you could run it as is and check you plugs Color. The different bores feed two sets of cylinders , every other one on each bank so you can see if there is a bore to bore difference.
if the carb hadn’t been apart likely that’s the way it came from merc.

 

[Lou C]

If it’s a 2bbl Mercarb I think that it’s a modified Rochester 2BBL carb. You might ask this question on Cliffs High Performance Quadrajets forum someone may know.

 

[alldodge]

Your probably correct but I have always called them emulsion tubes.
I'll go back to my first comment. A remanufacture or someone had replaced one of the tubes during a rebuild, most likely from finding one damaged.

I would say they need to be the same so each side gets the same amount of fuel. Found a NOS one on ebay with a good pic



They are pressed in but maybe instead of soldering one up, drill the other out. Can always solder up both if need be

 

[Mcguiver]

Thanks all, drilling another hole was also option I was thinking about but concerned it may lean out or bog down under certain load condition because it isn't getting enough fuel. I agree a rebuilder involvement could certainly be possible. I reached out to the seller of the carburetor who told me he bought the boat, a 96' model, from the original owner and they had a 5.0L that blew up under warranty and was replaced it with a 5.7 in 2000' before he bought it.

I'm extremely familiar with rebuilding carburetors but don't have access to reference material anymore since changing careers decades ago. I never came across a non-symmetrical venturi before but that doesn't mean they don't exist. I was hoping by posting I'd find someone who had an identical cluster number to confirm the pattern or access to that kind of documentation.

 

[Scott Danforth]

i would drill out the other emulsion tube with the additional holes.

 

[Mcguiver]

Update on project. Looks like there's more to it than just having one hole difference. I checked the hole size diameter between the two and the hole sizes differ as well. Decided to harvest the tubes from an old 5.0 cluster since they were the same size as the one with one less hole. Running it in driveway it ran smooth throughout 650-2000 RPM but would backfire under rapid acceleration. That didn't happen when I had my old 5.0 carburetor on it. Swapped float needle to a solid and most of the backfire went away but now I'm wondering if it should have had the tube with more/larger holes. Wasted $$ on what I thought was a rebuild able used carburetor, not imagining someone could mess up something to that extreme and no morals to put it up for sale. Still too stubborn to give up if anyone has photos or specifications they'd like to share.

 

[Lou C]

As I said before, even though its not a Quadrajet, post this up on Cliff's Quadrajet site, someone there may know.

 

[alldodge]

There is a different float setting for a solid and spring loaded needle valve