the "miracle" venturi

[Horst]

Some time ago I bought for an insane amount of money the modified venturi for the Zenith carburetor (mil-plus). This is how it looks like:


Now I tried it out in an average to good running take-out carb. What I got after the modification is an average to good running Zenith carburetor. I am not really sure if something improved considerably. Anybody tried that conversion? I had read, also on this board, that some people had bought the complete carbs from mil-plus. Would be interested what they say about before and after.

[svramselaar]

hello
horst

my opinion on the modification is
the airflow in the venturi is a litle restrickted by the pipe
therefore the air is going faster trow the venturi (the engine wil have the same amound of air )
than you gets a higher sucktion on the main jet (more petrol )
thads wat i think thad is happening
i maybe am wrong on this
were is the pipe air in the inside carb come against

george

[rickf]

I just can't see any advantage there. As George said, where does the emulsion come in? A venturi has to be concentric to work efficiently, That is far from concentric! They did not even clean up the weld.
Rick

[halftracknut]

Hey Rick, My Dad was a mechanic all his life and every time I tied something custom on a car or engine he always said: " son if the factory had wanted like that they would have made it that way"...... ....... Cessna had an AD afew years ago on the 2 piece venturi, FAA said take it out and replace with 1 piece (engine never did run as well) if they were worried about it failing and being sucked into engine, i for sure would not use a welded one.....good luck with that....

[Floyd]

Horst: You're a pilot! You can see the answer to that one.

Floyd

[Horst]

This is how it looks installed. That picture is taken in the polished carb I tried last year, but for some reason it would not even start with this one. As I could not figure out why, I used another take-out, late model (emission-type) carb. Still shows the location of that second tube.

Adding to the comments above I would say that any stock, high volume production part is a compromise between performance and cost. And I think I know how carburetors work, but you never stop learning something new. That's why I tried this one. I think most will agree that the Zenith is doing it's job ok, but it is not the best carburetor design and you can feel that there is more potential in the engine but both the intake and exhaust designs are everything but good flowing.

[rickf]

I can't see that being anything more than a restriction. It is not near the emulsion tube or idle circuit. It is not taperd. What would it's purpose be? The intake is not a bad design, if you don't count the mounting. The exhaust manifold is a joke!
Rick

[halftracknut]

Rick, I saw a picture somewhere of an exhaust header on a 151 head. Have you seen this? The guy milled the head and built a custom header, I think it was on the mutt motor pool site...check it out...HTN...

[raymond]

I always thought it might be interesting to add a second outlet to a standard exhaust manifold. Probably not as good as a header, but a much easier modification.

[svramselaar]

hello

for the exhuost manifold look at the m151 site from ron rietfors
google for it

greetings george