Purpose and Principle of Carb Rotators?

[cvair4life]

Ok so I'm trying to understand what it is that the carb rotator kit does?

I understand that adding a second primary adds the enrichment circuit back in??

How does it help prevent corner flooding?

[Trip]

First you need to understand what the cornering problem with Corvair carbs is: If you look at your carbs you will note a vent hole to the float bowl on each side of the carb (2 per carb). In hard cornering the fuel in the float bowl sloshes over to one side, and sometimes even up and out the vent hole on the outside of the turn.

If you rotate the carbs 90 degrees the float bowl is now longer from front to rear and narrower from side to side... so you get less sloshing effect. In addition the vent holes are now located at the front and rear of the carb rather than the left and right so the fuel can not easily exit the float bowl through one of them while cornering hard.

The other solution to this problem is to install "vent tubes" into your carb vents.. this is the more common method. You put a tube into each vent hole and curve it slightly to the middle of the carb... they should stick up 2 inches or so above the top of the carb. These make the fuel have to travel much higher (slosh a lot further) before it can exit the float bowl.

[cvair4life]

Hey Ray - That was my basic understanding of how the rotator idea worked. So just to check you are referring to the vent holes in the top inside of the throats?

[cvair4life]

Ok so what are the implications of using 4 primary carbs on the 140 setup?

[Trip]

Zach, yes those are the holes to which I am referring =)

I have four primary carbs on my 66' Corsa 140 coupe. It really doesn't make much difference... here are the couple things that do figure into it.

1) Primary carbs have a choke, secondaries do not. That being the case you have to eliminate the choke and seal off the holes if you are using primaries as secondaries.

2) Primary carbs have an idle circuit where secondaries do not. This makes tuning trickier because you have to balance two carbs. Some people just turn the idle mixture screws all the way in but this may not be a great idea because the primary carb type does let some air through with the throttle plate closed (because it is intended to provide idle) and therefore may cause lean idle mixture issues on the cylinders nearest the carb throats with the idle needles turned all the way in.

I have observed that it can be difficult to get my idle as low as I'd like because I run out of adjustment at the bottom end... if I turn them out far enough to get the idle where I'd like it I might not have enough room to adjust for balance in some of the idle stop screws. This has been a minor irritation and I have not yet heard others complain of this so it might be specific to my car for whatever reason.

3) Original secondaries have a "lock out" that prevents them from opening up (even under full throttle) until the chokes on the primary carbs are fully off. When using primary carbs as secondaries you will not have this lock out and the secondaries will come in even at full choke. This "could" lead to the mixture leaning out enough for the engine to act up or even quit if you go to near full throttle while the engine is still cold and needing choke.

In practice I have never found this to be a problem at all.... I've never missed the lockout a bit but I doubt GM would have gone to the expense of building the lock-out system if it was totally unnecessary. Perhaps in very cold weather it might make a difference? Or maybe I just have the good sense to not go to wide open throttle in the first two minutes the engine is running... I don't know why for sure but it has never given me a single hiccup.

4) I'm pretty sure that factory secondaries do not have an accelerator pump, if that is the case you "might" get snappier throttle response with four accelerator pumps, but more likely you will create a momentary rich condition and burn some extra gas. I think I've got all four accelerator pumps working in my 66' and I think it does run a bit rich.

Disabling the two extra accelerator pumps would be EXTREMELY simple to accomplish. I'm pretty sure you could just leave the accelerator pump pistons out completely without any ill effect.



I hope this helps! As far as I know there is no real advantage to using four primaries, other than the fact that the "correct" secondary carbs are semi-rare and therefore more expensive to obtain.

Ray "recently became intimately familiar with Corvair Rochesters" Rodriguez III

[Gregory_Miller]

You can't leave the accelerator pump pistons out of the secondaries whether they are primaries converted or not... the pump return spring is what snaps the throttle plate closed after you open them up. You can however leasve the pump cups out and achieve the same effect, no accel pump squirt.

[mart]

Ive bought a set to go on my 110 (a long way off yet) and have a pair of wolf enterprise modified primaries to use as secondaries, keeping the stock primaries for low throttle use. Will this work ok or will I over richen on heavy acceleration?Would I be better using them the other way round? My main aim is for economy, but with an extra boost when needed. Would I need to set mixture on all 4 carbs or just the primaries as it is only a 110 with single inlet per head?

[martyscarr]

You can get the same results of using the carb rotators by installing vent tubes and relocating your jets. When the jet is relocated it is no longer as affected by cornering forces, as it's in the X axis instead of the Y axis of the car. Makes autocross SOOOOO much more fun!

relocated jet

vent tube extension inside velocity stack

Marty Scarr