So I'm trying *ahem* trying to run two U&J carburetors on my 4 valve Rajo speedster. However, she's acting like she's not running on all cylinders. I thought at first it was an ignition problem, but I have good compression and spark everywhere.
After much fussing I have determined that the U&Js are the same model, but one is very early and the other very late. The early one has a brass venturi with a simple cross section, like it was made from a flat piece of sheet metal punched with a cone. The other, newer model has an aluminum venturi and it has sort of a tear-drop cross section, like it was cast. See photo below.
The end result is that the two cylinders mainly feeding from the brass venturi are getting way better flow than the two feeding from the aluminum venturi. I even swapped the lower half of both carbs and tried it again and sure enough cylinders 3 and 4 had all the bang instead.
At the moment I haven't figured out how to remove the aluminum venturi, it's a bit stuck down in there. But my next step is to swap just the venturis and make sure it isn't something crazy like the float levels being different or a tiny passageway isn't cleaned out.
Does anyone have a U&J that they could look at and maybe swap venturis with me? I think either one would work fine, I just need them to be the same. I sent Uncle Stan an email. Hopefully someone will trade with me instead of me having to buy a whole other U&J just to try and get two that balance right.
(Message edited for horrible spelling)
(Message edited by Wreckrod9 on April 07, 2017)
Are you running a inlet manifold equalizer tube as well?
Yeah, the same intake ran great on two Zenith S4BFs.
U & J's were made for a variety of makes of engines. They were popular on Model T, Overland and others. That's why they have different venturi's as far as I know.
That makes sense Stan. I just need to swap one of mine with someone so I can have two of the same kind.