Which zenith?

[Flyguyeddy]

I have two zenith carburetors for use on a potential 45 horse power build. The larger one is 14998 And the smaller one is an L 63. With the bigger one be OK with the 45 hp? I have read that the zenith is not a good match for the 45, but maybe the bigger zenith would be better off

[Flyguyeddy]

Nobody has an opinion on this? 

[BobSeverance]

I'd use Mikuni's...28mm to 30mm

[CHARLES DEBOER]

I have a 45 hp built by S. Casler and it came with dual Mukuni 28mm.

[Flyguyeddy]

Cmon guys im talkin about zenith here

[CHARLES DEBOER]

Go to the search button, click it and you will find 66 messages referencing the word zenith.  The people who started those messages may or may not reply to PM.

[leshoman]

FYI
When i changed from a single Zenith Carb to two Mikuni carbs picked up 7 hp measuring with wood bar dyno.

[Flyguyeddy]

Yes but was that the model 68 zenith or the bigger model 267?

[leshoman]

That was several years ago and ibwill have to see if i can find the order form.  Do not remember of top of head

[Flyguyeddy]

Was it the carb feom the yellow plane?   If so that was one of the bigger zeniths (the one you have listed in the for sale, section) Unless i am mistaken.

[leshoman]

It was

[Flyguyeddy]

Weird.  Thats the same one they use on the full size vw engines

[BobSeverance]

Think about it.. there is only one cylinder at a time sucking fuel/air through it at a time

[Flyguyeddy]

How does the 267 fuel a 2300 revmaster just fine but not a 1200 half vw?   I can only assume the 1200 turns faster revs than the 2300

[stevejahr]

You are barking up the wrong tree...

From a power perspective it is not so much the carb size that matters as it is the design of the entire intake.  The more air you can get into the engine (the more fuel you can add) the more power you can make.  Air does not like sharp corners or other direction changes.  It slows things down and creates turbulence which is not good over your wings and even worse in your intake.

The carb needs to accomplish two things: A) it needs to feed the right metered amount of fuel into the intake air stream and B) it needs to convert liquid fuel that does not burn well to "atomized" fuel that does burn well.  Honestly both of these things favor using a smaller carb throat diameter to maintain higher velocity of the air flow through the carb.  Go too big and you lose vacuum signal to pull fuel from the float bowl and, because pressure transitions help break up the fuel droplets, you also lose fuel atomization.

Length of intake has some impact as well with longer intakes providing potential improvement in intake tuning (just like exhaust headers) at the expense of fuel condensing on the intake and not making it to the cylinder.

Hanging a Mikuni off the cylinder head is crude but works because it provides a very clear straight in air flow to the engine.  There is also some increase in vacuum pulses with the short distance from individual carb to intake valve.

Many typical carb/intake designs involve a sharp 90 degree turn right at the carb.  These are horrible air paths and kill power.

So focus on the intake design and pick a carb that works with that.